Shaun Allen of the group http://www.harpoonistaxemurderer.com/ asked to have his 2012 Fender Exelcior modded so that it would breakup earlier (at lower volume) and see if I could do anything with his problems with his amp feeding back all the time … as those of you who know this amp is very bright sounding, equipped with a limited Bright switch, and no other eq’ing options … not a great situation for a Harpoonist
I gave the output section a four position attenuation/dirt-enhancer switch option // where the user can go from stock/full output to increasing the tradeoff between natural output stage dirt and power reduction … again, works like a charm on the last setting // producing super creamy delight at much lower volumes using a standard Shure bullet mic … on top of this, I’m providing Shaun’s amp with a 12-position rotary control switch and depth control that allows a mid-scoop to be dialed in a 12 different frequencies, and with a variable scoop depth of around 15dB … this wide range eq. mod give a total re-voice of the amp’s response // making it sound like “many” different amplifiers in one …
lastly, I included a treble cut control that at the latest point possible in the preamp … not only can it be used to give the amp a darker sound and help avoid his mic from feeding back but it also kills accumulated noise in the preamp leading up to that point … making the amp appear quieter noise-wire // great for recording, etc …
this has now become a standard mod that I do to vintage and modern re-issue Fender Champs, VOX AC4-TV and other small amplifiers … I also perform this work on not-so-small amplifiers like the ones displayed elsewhere on this page
wow // strangest grounding I’ve ever seen maybe … main filter cap GND is going to tube rectifier socket, from there to power tube socket to provide GND for grid bias resistor and one side of filament circuit, thru filament leg to 12ax7 socket and to signal GND line to input jack ring lug and finally grounded THERE to the chassis … (LOL, re-did the whole scheme) … great sound going into my ’68 4×12 cab with 25w greenies // minimal hum …
Over the past few weeks I’ve been conversing with Don Julien, a programmer who dedicates himself to updating the open-source program ‘pdf2gerb’ // … pdf2gerb is a text based ‘PERL’ instruction set that’s meant for converting PDF vector graphics language files to Gerber “Numerical Drilling” (CNC driver) ones // the brainchild of Matthew Swann … (!)
“… in essence, the instructions that are meant to drive a printer are similar in nature to those used for driving an automated CNC machine” …
makes sense to me ! … and as I had sudden access to a friend’s CNC machine myself, I wanted to see if the PDF output generated by expressPCB in tandem with a print-2-PDF application like PDFcreator could produce constantly reliable file sets ‘as is’ // … ie., with no edits, and running on the more common ‘XP’ platform (I think Mathew is a Mac dude) …
Don was able to detect a coding snag that prevented things from working perfectly with my examples // … two revs later the code is now able to select between 2.3 and 2.4 (0.1 thou) Gerber drill formats … to me this is a useful feature to add as not all CNC machine owners have upgraded their machine’s coding to the latest format … (like ours was …)
three PDF “layer” files are print-created from within expressPCB // this produces true (simple) vector files … I combine top and bottom layers into a top.pdf file, in order to produce copper text in the end, then the bottom.pdf only (without text, logos, etc .) and then the silk.pdf layer … the program code and three object files are piped to a compiler to produce seven Gerber output files … from here a visual confirmation of translation accuracy to the new format can be made using a Gerber file viewer such as “viewPlot” …
the files are then sent away for “mecanofacturing” // … (*!*)
>> that’s it !! well done guys … and amazing //
three finalized newborns on the bench tonight // two full days of assembly time, including a couple hours of testing fun … (!)
the tru-Comp mode is a real trip to handle as it hisses and spits between notes if you let it // breathes like you’ve never heard a compressor do it before … under the right conditions it gives infinity violin-like sustain; at times it sounds like backwards guitar … ok, that’s in the special effects dept. // in Limiter mode (what pretty much all comp pedals are) it can go from spanky to “is it ON or wut ?” …
an LED indicator provides a visual gain-redux indicator, even when you can’t tell if its doing anything there’s a visual clue // it’s THAT imperceptible at times … there is also provision for side-chain processing, as inserting an EQ., for tailoring the envelope response to signal frequency … headroom wise, it can take any kind of signal (active Bass, keyboards, line level signals, etc ….) as it has an internal signal headroom of at least 12volts pk-pk … the capacitor-less signal path ensures low phase distortion between DC and its roll-off frequency, and also avoids cap-based transient distortion artifacts …
this bute came in with “scratchy” volume, MV and tone controls … measurements revealed output DC offsets between 30mV and 137mV on most of the LF353 op-amps … replacing these by 8-pin sockets and inserting an OPA2134 in the front and TI-NE5532′s all the way to the back brought the preamp’s noise floor down quite dramatically; and offsets to negligible levels …
the next round of mods involved cutting the lines leading to each input of the 300w and 100w power amps … a 1/4″ shorting jack is used to open the 300w line as it is perfect for slaving other preamps, like my 360+ preamp (Lite version shown) // when there is nothing plugged into the jack the switching function ties the input of the 300w amplifier to the 300w MV pot (stock mode) … the switch next to the slave input jack either ties the 100w amplifier input to what the 300w input sees, or to the 100w MV pot (stock mode) …
when an external preamp is plugged into the slave input the 300w MV control has no longer any effect, nor does the jFET boost stage (hence the reason for doing all this) as it is avoiding all that … the 100w amplifier can now be used to feed another speaker // in one case feeding the same signal that is sent to the input of the 300w amp, and in the other from the GK preamp … so, with this head alone, you could conceivably have one player pumping bass through a preamp into the 300w side and another instrument plugged into the front of the GK and driving its own speaker with the 100w amplifier … independently …
well known locally for offering the best in music instructors and providing first class luthier services; Richard Leighton, owner of Arbutus Music in Nanaimo BC, asked me about giving DIY pedal building seminars at his store … and so, in 2013 we plan on providing an innovative in-store approach to doing DIY electronics // the goal is to get builders to pull off some of my pro-quality viva Analog pedal designs … and later branch out into the pro-audio realm, all done DIY
A common bench gig for me is performing total Black-face conversions on CBS-made Silver-face Fender tube amplifiers // of course, this includes restoring the Bias circuit to full variability and properly biasing-in the power tubes … my thing is to go further and add a couple of subtle touches in key areas …
over the years I’ve figured out how to go beyond the straight conversion and give these babes near zero-hum capability, zero pop-corn noise at full volume (when needed), slightly enhanced bottom-end tightness // same as I do on vintage Black-face amps … all this is done without touching the signal path structure or altering gain-scheduling … the end result brings the original designs up to their full maximum potential without “changing” the tonal/gain character in any sort of way // it’s my approach to doing Leo Fender’s legacy full justice …
A step in the right direction perhaps, this time using a soft switching approach to opto-controling the gain level in my original (non-linear) “triode emulating” booster design // unlike previous true-bypass builds
The switcher allows going between unity gain and variable output, capable of delivering considerable boost levels (x11 or more), with added pick “edge” sharpness and squeaks … Rory woulda dug this I believe & much less noise than a Rangemaster // … a special design for Arbutus Music in Nanaimo, BC
having found a work-around to a blown reverb pan on a recent GA-1RVT resurrection job, I decided to apply the idea to my JTM45-Reverb modded ’69 Fender Super Reverb amplifier to see how it would work there … doing the same thing, applying a terminating resistor on the output of the reverb driver tranny and switching the leads so the signal is not out-of-phase with the signal path I got a killer response while using a Zoom G1 69-bit-depth DSP processor for adding verb and delay to an already great tone … some players old enough to remember will think “Ice Cube”, that plugin thing that went on the jacks of a Fender Reverb amp // it’s a similar idea except that in that case you couldn’t reverse the phase of the signal plugging that gizmo alone as far as straight-drive goes … in my case I can adapt an effector of any kind (pref. reverb/delay) in the circuit and totally expand on the possibilities the amplifier has to offer – namely giving it a more modern feel in the gain and effect department
hadn’t seen one of these before, the Dual-Showman Reverb ones a few times but not a tube rectified Bandmaster Reverb … the owner had won a Mercury Magnetics OPT/Choke combo in a giveaway contest and had installed the F050BM-16 OPT with the output leads flying outside the chassis to a plate carrying three speaker jacks – one for each tap … he had changed every resistor and almost every cap inside the chassis and was complaining of circuit instabilities … when I got the amp it was quite hummy as well …
after checking the whole circuit for cold solders and the like, I then proceeded to : (i) change the passives on the power tube sockets, (ii) fix some serious lead-dress issues inside the chassis (noisy PSU lines traveling too close to signal lines, etc…), (iii) re-biased the gorgeous set of NOS GE-KT66′s that was already in there (and running way too hot) and (iv) installed a Lorlin rotary switch to provide impedance selection on the fly … the darn thing was hard to give back once the work was completed; it had fantastic breakup on 10 and a very sweet top end // quite an awesome sounding piece … now, virtually hum-less and solid as a rock!
I dig a good challenge // reverb and tremolo were DOA, more surprises waiting within … here’s a quick rundown of what I found …
(i) the PSU and overall wiring … everything looked and measured pretty ok considering age and corroded state of the chassis // that is, except for a filament voltage that laid at 5.8vac instead of the customary 6.3vac (right on the edge of no-go) … (ii) turns out the reverb pan guts were destroyed // three of the four ferrite beads that drive the coupling transformers inside the can were totally stretched out and beyond repair (weird) … I wired in a fresh pair of wires with RCA plug ends and tried a few pans I have handy here and none were giving a strong enough response … I then tried hooking up a Zoom G1 effects box and got great verb/delays and an interesting signal boost option … the owner could try his luck at finding a suitable reverb pan that will couple (quite unlikely considering the low-gain natuere of the drive and recovery circuits) … the external effector approach is very cool IMO and opens up a host of potential applications that goes well beyond what the basic design could do // keeping the original signal path and Tremolo circuit intact … to make this work I loaded down the reverb transformer output with a resistor to keep the signal from getting too massive there (the Zoom G1 has a high Zin so we can’t rely on that to keep the signal tame) … with a properly chosen load value this would not interfere with a reverb pan if we decided to use one, that option remains open // best of both worlds … (iii) the Trem, turns out there was a cold solder in the circuit, and in addition the shorting switch on the back of the Speed pot was no longer working // doubly dead … what I decided to do was to use the Reverb kill pedal and wire it to the Trem pot switch terminals … we now have a perfectly functioning and foot defeat-able tremolo … and with the reverb, now potentially an external unit, can be foot defeated as well // this made most sense … (iV) other things … I found the 620ohm Cathode bias resistor on the power tube to measure around 880ohms … I inserted a 5watt 600ohm resistor that actually measures 612ohms cold // Cathode bias voltage went form 30vdc to 18.5vdc, schematic shows 20vdc … the gain of the amp has gone up as a result, reaching max (stock) power … I did not tweak or alter any other part of the signal path // it could be modded for more gain, but I didn’t touch it … also, to try to remove some hum form the circuit I lifted the grounded side of the filament circuit and applied two 100 ohm resistors to balance the filament circuit w.r.t. ground … didn’t notice a huge change, but I left it balanced/modded
I tested the amp using the speaker in my Champ; that is, a Celestion Super8 // indeed, I was getting great sounds using the Zoom G1 in the reverb’s Send/Return circuit … killer actually
update:
after a first round of mods I was still annoyed about the amount of hum, even with the volume controls set to zero, the amplifier had // of course, this is very common with single-ended (SE) amps … after taking a closer look at the grounding scheme I noticed that the whole amp was grounded to the chassis via the input jacks … the only other time I’ve seen this was in an 90′s re-issue AC30, which was also noisy (in that case beyond repair) …
all I did in this case was re-route the two main current absorbers in the PSU circuit by giving them their own seperate attachment points in the chassis // as far as possible from the input jacks at the same time … this, in tandem with the balancing of the filament circuit, gave the amp a virtually hum-free performance … as it lies now, this is definitely an impeccable “recording ready” guitar/harp tube amplifier, with a natural tone that compresses naturally … amazing little amp // apparently Gibson shipped 232 of these in total between 1962 and 1963
Here’s a great example of what my in-a-pedal clone kit for the famous “Acoustic 360 Preamp” can look like once completed … this economic project allows you to build a circuit that will give you that classic Jaco, J-P Jones, Whallers (etc.) vintage Bass sound … construction details and modification options can be found at my private work forum which are included with the purchase of a kit … special thanks to Domdec in Florida for sending in this picture
A continuation in my evolving exploration of the low-power/high-dirt mod. This involves the addition of power resistors with the speaker load of a vacuum tube amplifier … a request by players who want to hear a mojo’ized tube amp sound at lower volumes …
so far I’ve done a ’79 Champ (1x 6v6, 8 ohm load), a VOX AC4TV (1xEL84, 8 ohm load), recently a Peavey Delta-Blues (4xEL84, 16 ohm load) … and lately, seen below, on a Fender Hot-Rod DeVille (2x6L6GC, 8 ohm load) …
In all cases the results are similar, the resistance provides added high end sparkle in addition to the increased distortion produced at the expense of power … I’m hearing really great rock and blues tones here // looking forward to trying this out on an EL34 based amp !!
gain figures are now lining up with my original ’94 Quadra640-Intusoft derived results … as an example, we can compare the AC simulation output of a typical Common-Cathode gain stage produced by using my updated RCA12ax7 Spice model against Randall Aiken‘s run-through of the corresponding “incremental” algebra using idealized terms :
we find that his math derives a un-bypass’ed cathode (ie., absence of cap-to-ground on the Cathode) AC voltage gain of 30dB, and a cathode-bypassed voltage gain of 35dB for a “typically” biased 12ax7 Common-Cathode gain stage // … of course, good modeling should corroborate such known results, and right on the money mostly …
as with any kind of non-linear network/device transfer modeling this form of AC-response comparison does not validate the large-signal aspects of the model … but it is a first step heading in that direction // … thank-you Randall !
here’s my RCA12ax7 model adapted to TINA-TI’s Spice syntax rules:
this turned out to be a cool job, coulda been a nightmare (had I tried taking another typical route) … owner wanted what many guitarists want // full-on output stage dirt at low volumes … well, I had done it on Champs and AC4TV’s but never on a push-pull amplifier … after tinkering to find the right value resistance to stick in line with the speaker load (a pair of 8 ohm drivers) the appropriate value this 4xEL84 beastie needed to get it sounding right …
I wasn’t too crazy about the attack qualities of the amp in “stock” mode, even after installing a fresh set of high-grade Czech power tubes, but in low power mode both Normal and High-Gain channels give a squeaky higher-gain edge on transients that is (IMO) more musical than stock … a very recordable sound if I may say (getting nice rich volume swells from a Zoom G1 in the effects loop !!) …
this low-gain behemoth, and its associated 10″/15″ crossover-ed cab, came lumbering in after being worked on previously … Trem circuit didn’t work, amp had no goose, and showed no balls … after studying the schematic provided by this generous chap : http://www.backfromthesixties.co.uk/Pages/Gibson_Mercury_II.aspx I went to work … turns out this is another tube amplifier with the choke in the wrong place (same as some Fender E-series tweed models) … also, there was NO main cap in what normally is the main B+ node in the PSU … no wonder !
so, I inserted a main B+ cap (47uF/500v) and wired the choke right // inserting a proper variable bias circuit … as for the rest of the circuit, I replaced the wimpy low-gain PI circuit by that of the classic VOX AC-50 (as it also has no NFB coming off the speaker as well) // and also inserted 22uF caps in the cathode circuits of both 6EU7 preamp gain stages … finally, biased in JJ 6L6GC tubes (around 28mA with B+ @ 480 vdc) now and the amp exhibited the normal “humph” of a 6L6 duet amplifier
next came the Trem circuit … as it normally worked on a minute filament tungsten bulb I replaced the whole affair with an Silonex NSL-32 opto-coupler // in an almost identical way as my original Univibe “LED-mod” … the result was an extremely wide ranging Trem circuit, going easily from nice-round shapes to ultra-choppy
pleased to see my original Generalized Algebraic Triode models converging in TINA-TI’s mixed-mode circuit simulator // … adding to a list of recent number crunching tests and design tweaks using this newly discovered piece of software
TINA-TI offers a very impressive list of device models, but its ease in allowing the creation of custom models via import of Pspice-style .subckt text files is perhaps what matters most to me … TINA-TI seems to support the typical set of functional control source equations as Pspice does // and thus paves the way for mathematically characterized (purely empirical) modeling and simulation, as I’ve done with my Triode modeling work … I’m pretty sure ICAP/4, LTspice and AIM-spice all support general forms of algebraic modeling, but it’s on TINA-TI that my models finally seem to be working without a hitch (more to come on this …)
to confirm Tina could handle hefty circuits, I was recently able to simulate an entire Acoustic 361 power amplifier circuit by importing modern power device models (MJE340, MJE350, MJL21194) // … better yet, this week I got Tina to reproduce the original Triode simulation results I first saw in ’95 on a Macintosh Quadra640 running Intusoft’s Pspice5.0 and Matlab …
Here’s Tina in action displaying the classic DC-Transfer characteristics of my data-derived RCA 12AX7 vacuum tube Triode model :
… Tina in action displaying the classic DC-Transfer characteristics of a Common-Cathode gain stage running on my data-derived GE 12AX7 Triode model :
… Tina displaying typical “class-A” TRANsient (real time) overload characteristics of a Common-Cathode gain // with Capacitive bypass @ 5.2v pk-pk input sine-wave :
… Tina displaying typical “class-A” TRANsient (real time) overload characteristics of a Common-Cathode gain // without Capacitive bypass @ 9v pk-pk input sine-wave :
-> a recent milestone in my exploration of non-linear booster topologies … // in this case a single Triode-emulating stage which comes with a modest gain factor of around 14db (~ x5) … most importantly, the super flat tonal response and harmonic enhancing dynamics are some of the best so far on guitar, and the noise addition is extremely low //
I think I’ve figured out on exactly what basis a Triode Emulating circuit should best be defined, and also realize (taking into account many papers and patents written on the subject) that there are two main approaches to emulating the large-signal Transfer profile of Triode circuits ..
one way involves reactive (often Capacitive) elements present as part of their basic implementation, where the emulation is based on AC response of signals // while the other sees a non-linear operator occurring in the DC realm ALSO, just as a Triode circuit does // … in principle, the later case produces the desired effect without introducing extra capacitor-borne artifacts
fine-tweaking a late 60′s Garnet PRO tube amplifier … the problem was that the user couldn’t up the gain on the Stinger circuit and have the straight channel running (to provide heavy bottom) without the amp going into massive fits of squealing … this was fixed by doubling the .005uF Treble cut cap in the Colour circuit // which gave that control more spread in its range and provided the needed stability … unbelievable tone out of one box // no exterior Fuzz or Booster needed with this gem of an amplifier // a mighty 10 !!
This evening I chanced to discover a new (?) method for extracting the jFET modeling parameters: Idss and Vp … this was done with emphasis on low Vp valued devices (2n5484, J201, …) operating in a 9 volt environment …
the method is intuitive as it involves visually estimating when a “proper” transfer profile has been achieved, with values taken directly off the scope // … accuracy in aesthetics !!
the above shows what it’s like to “tune in” the proper amount of back-biasing on the jFET’s Gate in order to get a Parabola-like response on the output current … once the output waveform is set to a near-quadratic profile (ie., no flat part or point at the intersection) the results are read off the scope directly: for this particular 2n5484 device I show Idss = 2.95 mA and Vp = -1.34 volt (@ Vdc = 9vdc) … otoh, Idss measured with a DMM (without correcting for voltage drop in current mirror) gave 2.85 mA …
A very simple method paves the way for reliably extracting jFET device characterization parameters and allows for accurate specification matching, useful in balanced circuits …
A final round of repairs on this unit saw a change of power tube sockets // I would say this is mandatory for these old amps regardless of behavior … remove the sockets and clean both sides of the board around there with iso99 // if necessary dig out arc-burns with Dremmel // replace with new gold plated sockets … these are fantastic builds // thanks to Bob Pletka at Eurotubes for treating my customer with aplomb
I came up with the idea in 2008 // it’s a non-linear wave-bending amplifier design that runs on 9v and it replicates (i) the small-signal, (ii) large-signal and (iii) both extreme transfer limits (soft clipping and hard saturation) exhibited by Vacuum Tube Common-Cathode Triode Gain stages
ie., the “stuff” that’s behind the so-called “tube sound” …
I’ll be candid and admit it’s something I once thought couldn’t be done … now revamped with analog LED “elongation” monitoring //
A streamlined version of my modded Acoustic 260/360 fuzz clone with new graphics and PCB design … the BLEND (dry volume) circuit provides about 20db of clean boost over bypass/unity … hand selected vintage Ge and Si transistors are chosen to get the breakup just like the originals had // with the dry signal added to fuzz to produce a crazy kind of monstro bottom
Fall time is when I pause to reflect on where I am, where I’ve been and where I think I might be going … it’s hard to describe the feeling of randomly trecking up the steep backs of a river in search of the beautiful Chanterelle mushroom // the Queen of wild edible mushrooms (Morels are King !) … the rainforest setting where they fruit is of the most peaceful sort, and even though the hunt requires effort, sweat, and caution there is no more pleasurable surprise than to land on a small patch of beauties lying in the most unsuspecting of places // under a fallen log or stump, under a density of Salal bushes, or out in an open bed of fir needles … and that’s just the hunting part !!
this new “end-design” prototype is finally completed, glad how it turned out // sounds wicked … switched LED indicator follows envelopes when engaged // jacks on top are an effort to keep footprint on pedal board to a MINIMUM … using matched opto-couplers in the filter section and custom ordered hardware from Smallbear Electronics
For many years the Major Scale bugged me // fer sure, I could intuitively noodle using what I thought was the Blues Scale and such non-sense… but when it came to noodling over pure (boring) Major tonality, as in the ii-V-I jazz cadence or just pedaling over I maj, I felt dead in the water // as what I was playing possessed no real motion … I knew I was missing something important, that feeling became especially strong when comparing what I was doing to masters like Vince Guaraldi and Sonny Greenwich, who always play beautifully and purposefully over I maj …
I’m the kind of person that has this habit of keeping a blank notepad around and drawing things down whenever I feel like it, and pondering whatever comes up (whether it be Math, Electronics or Linguistic relations, etc …) … one day the sky split open for me when I discovered that the Major Scale could be “regarded” as the union of three Pentatonic scales // something I had never seen in any music book (turns out the Beatle’s song “Dig A Pony” uses this concept in the riff portion of the song) …
Pentatonic scales are interesting critters in themselves actually … when I was a young lad in Montreal I took 5~6 lessons with Jazz great Mike Gauthier // I didn’t know much about scales or even notes at the time, but I distinctly remember Mike saying that, as a rule, “we (in Jazz) can add the 9th and 13th to any chord and not change its essence or function” … even tho I didn’t understand it at the time, it’s something I never forgot … many years later I saw that we can conceive of a Pentatonic scale simply as a Major Triad embellished by these two neutral sounding notes // this intrigued me greatly as it seem to supply some basis for application of Logic in an otherwise emotional field …
more recently, I was scribbling stuff down in my note pad when I decided to draw the Venn Diagram (where the basic Logical operation of AND and OR can be visually represented) of the Major scale in terms of the union of the three pentatonic scales contained therein … there are several ways of looking at the outcome of this exercise, one is to see the three Major triads (the ones built on I, IV, and V) as all/each having such possible embellishments … if we draw these Pentatonics in Venn form the Major scale looks like this:
this may seem like a trivial exercise but it says something important about the notes in the scale as far as them belonging (or pointing at) the associated sub-Pentatonics … for example, both 4 and 7 are on the outside, in the sense that they belong to one (separate) sub-Pentatonic scale each, and only one … also, interestingly, there are three “universal” notes which belong to all three sub-Pentatonics // they are 5, 2 and 6
food for thought when improvising in the Ionian mode …
my first attempt at cloning/modernizing the Acoustic 361, companion power amplifier to the Acoustic 360 pre-amplifier (head part) … initial bench results show the circuit able to drive 167 wRMS into a 4 ohm load // that’s on a fully loaded rail voltage (80.1 vdc at onset of clipping) … built using a beefed-up transistor set and a Roly Roper inspired heat-sensing fan circuit, the unit can now be expanded in power using this adaptive arrangement … above all, I plugged my mexi-Tele into the 360+/361+ combo and for the first time was blown away by the response of a fully SS system
this re-build involved the following changes : replacing two electrolytic caps by modern equivalents or larger (100uF same, 330uF -> 470uF), replacing all 0.68uF film caps by 1uF Panasonic ECQ-C film, replacing the BC148 oscillator device by a 2n5210, and the missing jFET by a 2n5457, and also receiving a new dual-100k anti-log pot …
the first 2n5457 I picked had no trouble biasing from the (stock) 6.4vdc zener and trimmer // circuit differing against … the noiseless signal path is quite spectacular if I may say (and obviously a basis for other noise-less effector circuits) // almost reminds me of this paper by Mieda
Just released is a “parts” kit that allows you to build the very same original (extended performance) Univibe+ I’ve been making for pro players since ’94 // that is, either in boxed format or in a Dunlop Wah-Shell (the original Wah-Vibe PCB kit !) … the official ’96 signed PCB boards are stable design and haven’t changed since and can be used to embody ALL of my original mods … builders get access to my forum, where supporting documentation and mod options are provided//
$130US air-shipped to US/Canada
(does not include box/shell, AC adapter or opto-Speed controller add-on circuit/parts)
[note: for a limited time only the kit will be shipped with a matched quad of vintage CdSe photo-cells]
spent the day with ex-NY producer buddy doing a full restoration on his 22-09-71 Marshall SL100 // B+ = 530vdc (plexi volts!) … I wired three-way Lorlin rotary switch for Ohms select on a copper plate mounted to cover previously discarded original line-voltage and ohm-speaker select switches … corrected some poor PSU mods, replaced missing signal caps in preamp with NOS Mullard’s from same era … one of the best sounding Marshalls I’ve ever played // 11 on scale of 1 to 10
The revival and update of an original 2005 circuit, the viva Analog “Uni-Trem” is one part opto-controlled Univibe oscillator (stable 2008 version) and one part jFET emulation of the Fender Vibro-Champ tremolo topology. Providing classic sine-wave Tremolo (extending into chop territory) along with the response of a class-A signal path. Two LED’s for Depth and Speed status indication : Green “on” / Red “off”
I de-modded and re-modded this baby into a ’64 BlackFace Bassman // both channels deliver different and very versatile tones … I replaced all resistors on the main board, and missing signal caps with original ones from similar “era” Fender amps … the usual power tube “passives” upgrade, and a re-adjustment of the PSU circuit to make the ’64 circuit run correctly
the Cino KT66′s that were in the amp before still biased “ok” (28.1mA vs 22.5mA) and respond well to loud dynamics … the “Normal” channel sounds amazing for a blues/rock sound with a full range of “tasty” dynamics // ie., it sounds great on 2, 4, 7 … and 10 … the “Deep” channel is quite aggressive and stunning as well // a total tone monster
This mid-80′s Tube Amp came into my shop for a re-tube and motor-boating issues. Turns out the “Hi” sensitivity jack doesn’t short out the input of the front boost stage when nothing’s plugged in there // a design flaw according to the schematic. A simple re-wiring of that jack cures the problem.
After spending too many years playing Russian Roulette with Sovtek, Svetlana and Winged-C tubes (and their many re-brands) I’m pleased to announce that I now deal exclusively with Bob Pletka at Eurotubes. Over the last few years I have requested that my customers purchase tubes from Bob when bringing me an amplifier for repair or maintenance
You may ask why ?
First, because he does proper testing of their tubes, the way I would do it : in “all” modes. I grilled him extensively about this many years ago // proof that he knows what he’s doing shows on the bench when I do my in-amp testing over the course of a few hard-driving days. Yes, I beat the living daylight out of new power tubes (… and re-test for any sign of drift) before returning an amplifier
Second, I have not yet once seen an amplifier come back to me because a JJ tube suddenly crapped out or drifted radically out of spec, which is not something I can say about the other stuff. In private conversation with Eric Barbour he agreed that the JJ KT77 (with hand-aligned Screen Grid) and JJ E34L, are likely the most reliable EL34′s on the market today
this clip, taken from Roosevelt Radio’s first album, features a custom one-off pedal I designed and built for Adrian McCullough … the Bleeding Aliaser can be heard during the intro, as the circuit transforms his Bass signal into a Synth waveform … the actual effect is produced (Chris Wonzer) by engineering the “tails” through fader use, going from dry to wet
Some players will ask for a high headroom version of the 360+ circuit, producing less growl per pound of signal … in this case high-end film caps are used, yielding a slightly brighter response overall
This is my adaptation of the famous EMS VCS3 noise circuit (Dr. Who, Pink Floyd, etc …) // a very listenable noise as far as noise sources go … the circuit is tweaked to run on two 9volt batteries and can be successfully built using the most common parts available. The sudden on-off response of the tone control should remind you of some of the noise events heard on “Welcome to the Machine”
My book “Inside Fender and Marshall Tube Amps” ISBN 0-968849-1-3 is now available in PDF format. The first 80 pages covers foundational Triode Circuit analysis based on accurate wide-range Spice modeling and simulation, an approach which eventually produces both a qualitative and quantitative picture of how the “non-linear Transfer” characteristics of gain stages play a direct part in establishing such aspects as the compressive and distortive nature of the so-called Tube response
Many of the results presented in the first part play a key role in helping understand why and how guitar tube amps are designed and to what extent they can be modified for tailored response, which is covered in the Mods section
In for an overhaul, these 6550 based super rare birds came from Pete Burns’ studio in Montreal via his son who’s avid tube amp collector himself. I’m told these power amplifiers were used during the mixing of some Harmonium stuff including “Les Cinq Saisons” // something Pete apparently never got credit for.
I remember seeing Tim for the first time in a small bar in Winnipeg in ’87, the same night the Fab T-Birds with Jimmy Vaughn were playing there … the second time was in this “chique” Gas-town bar in Vancouver in ’96 blasting away on an old Marshall 100watter …
Recently uploaded on his youtube channel features a vid showing off a “super parametric” Vibe I built for him in ’98 (on Slow Blues) … as well of a killer jam (I Feel Good) playing alongside Tony Springer, the fantastic blues-man from Toronto // aka “Wild T”. If you meet Tim ask him about the Silverface Twin I modded for him …
Here’s an original instrumental called “Haida Brave” taken from Tim’s self-titled album. One of my favorites of his that we’ve jammed over the phone a few times with …
My 2nd Edition Silverface/Blackface Fender Champ/vibro-Champ mods (gain unleashing, bottom flab curb, total PSU hum removal, 3am-dirt, mid-scoop, hum-less DI, etc.) are now available in pdf format
A buddy just told me to check out this interesting (but poorly chaired) interview with Frank Marino – his candid impressions of DSP-based amp modeling caught my attention.
IMO part of the misconception about Vacuum Tubes in Audio Functions comes from the habit we’ve taught ourselves, namely of ubiquitously using the word Tone as reference to sound “generation” quality. In reality (EE/Math-world) the Tonal side only represents one aspect of the overall response – upon where DSP limits itself “mostly” in its imitative efforts.
In fact, the dichotomy between the two main forms of analysis in Spice/EEngineering, and an allusion to Causality, IMO is enough to form a Theorem that answers why/how DSP cannot duplicate certain classes of non-linear analogue circuit responses as we see in Tube amps.
A new set of SE class-A tube amplifier output stage mods: hum-less variable DI, spkr kill (useful in DI mode), attenuation/dirt combo switch … this time applied to a current production (medium-gain) Fender Champion 600.
The variable output can be used to send the reflected “load” signal to : a PA, pedal chain (eg. delays), or a bigger tube amplifier yielding old-school “Boogie” tones … check out as061 app. note at Jensen for a version using a high quality shielded coil.
To be clear, the “3am” switch is used to produce higher distortion levels at whisper quiet volume settings // requested by obsessive players who stay up late and want real tube MOJO without waking anybody up. It’s a cheap way to achieve relatively good power soaking and dynamic wave-shaping enhancement combinations.
The latest 360+ Bass preamp Kit boards are in. The PCB/documentation Kit includes a membership to the VA-works forum where all circuit extensions and mods live. $55CDN
Joy! a brand new lot of custom-wound 1.5Hy inductors for my 360+ Bass preamps and other eq. projects. Yackin’ with Cinemag’s head honcho, Tom Reichenbach, is always a hoot. Turns out he was an engineering at Acoustic Control when the 360 was making its rounds, and has a great story of Jaco’s un-announced crashing of NAMM in ’69 … thx Tom!
(ed. I’ve since learned of Tom’s passing // my condolences to Tom’s family and friends … RIP friend)
The characteristic “ghosting” when driving old AC30′s hard is present in this unit (a common thing it seems) – the Silver Dogs are in great shape. Interestingly, signal caps are WIMA foil throughout – as opposed to Mullard films as we see in the ’62-’63 “Copper Top” AC30′s. A tube amp that sounds superb when dime’d (drool …)
Over the last 6~7 years I have built many circuits to this fantastic piece of high-improv music that my friend Miguel Barella (guitarist) made and sent me. He is strongly involved in the “experimental” scene, both in his home country of Brazil, and also abroad …
I recently asked Miguel for permission to post some audio here, says he: “… it is ok to copy for non-commercial use” … a big thank-you and congrats on creating/sharing these great musical moments! You guys make the North-American music scene look a thing of the past (LOL)
The second piece comes from the other CD project he sent me, entitled “Slow Link”, and it features Celio Barros on Bass and Kuki on Percussion. My jaw dropped the first time I heard it!
Winter’s obviously a good time to work on tube amps // during the testing phase I leave them on a little extra longer than I really need. This Hiwatt 50 tube amplifier had a badly corroded impedance selector switch. Otherwise, circuit is still original and in top shape.
The circuit that became a Maxon classic, it features my “capacitor lean” (hi-fi’d) mods to the “Tube Screamer” Over-driver, along with the extra (x2 increase) Gain range and matched components in the clipping sections. This pedal yields squeaky pick attacks and penetrating OD transients. With my choice of components it blows away any other TS circuit I’ve ever played.
Here’s a trick you can play to get modern Metheny-esque verb/delay textures using a single 2-channel (reverb shut-off or non-existent) Tube Amp while retaining a good “straight in” response:
go straight into input “1″ of either channel (your preference)
then, go from the “2″ input of that same channel -> to the DSP box’s input … then from output of DSP box to the “1″ input of the other channel …
set the volume on the DSP box so that overall volume doesn’t change when bypassing verb/delay … EQ both channels to taste
this way you get a straight in the amp “fidelity” response plus the reverb/delay effect instead of going through a DSP unit and relying on the internal wet/dry mixer before going to the amplifier … all other effects, Wah/OD etc. are in line with guitar before the amplifier
cheap DSP option would be the Zoom G1 with its 24bit/26kHz front end and 69bit processing depth, it does ok fake/imitations of the long-tail verb/delay
Sean has shared the stage with the likes of Betty Carter, Mike Stern, every of the Marsalis brothers, and he also leads his own Jaco tribute band in Victoria BC. He recently sent me some righteous sounding recordings of his band along with the following performance notes:
I’m playing a JV Squire Jazz Bass (frets pulled and Maple Strips done by Mike Hortie) through your 360+ Pro preamp through a 361 cab. The musicians are: Sean Drabitt – bass, Brent Jarvis (producer/engineer) – rhodes and synth, Josh Dixon – drums, Roy Styffe – saxophones, Leone Torres – conga and percussion
Brent’s list of gear:
Bass – Audio Technica AT4033, Seventh Circle N72, RME Fireface 400
Sax – royer mod large diaphram – seventh circle N72 preamp
Rhodes – ART tube d.i.
Synth – ART tube d.i.
Congas- royer mod small diaphram stereo pair – RME preamps on the interface
Drum overhead – Spieden SF-12 stereo ribbon mic – seventh circle C84 preamps
Snare Drum – Shure sm57 – Aphex preamp
Bass Drum – royer mod large diaphram – Aphex preamp
My third attempt at carving a dynamic-fidelity (Push-Pull) stereo tube amplifier on a custom-made chassis. Built around 60′s Eico ST70 transformers, this Standard Pentode design tests exceptionally well on a pair of Tannoy 3828′s.
Now in its third year, the 5.2b version of the 360+ Bass Preamp kit is starting to evolve into a “Dlx” version … this month at the forum we’re exploring what it takes to add optical based Dynamic Limiter functionality to the existing output drive/amplifier
aside from being super quiet (by not incurring extra gain stages to the signal path) the limiter circuit comes equipped with continuous Threshold and Ratio controls … most importantly, this envelope-servo circuit doesn’t suffer gain trailing effects like many old-school comp/limiters do, providing near invisible “leveler” response when set right
This original design uses common off the shelf components, including a 5-volt Panasonic relay (so it’s cheap and a snap to assemble) and requires no programing. The novelty for me lies in its topological similarity to a push-pull tube amplifier.
This multi-purpose circuit can be used to provide soft heel-switching of WAH and WAH-VIBE pedals, for example, all the way up to complex foot-switch based routers and remote stage controllers.
The hunt is on for low draw op-amps that will work here, as it stands the 5532 draws 6mA while the logic circuit only draws 2mA.
I once heard Nicholas Slonimsky say that he admired how Frank found ways of using simple means for deriving complex sounding harmonies – I think this applies to this chord
It’s formed by superposing a minor third (bottom) pair by a major triad (top) whose root lies a whole tone below the root of the bottom minor pair … in terms of my crude understanding of harmony these could be the i and bVII triads in the Dorian mode – the cluster is equivalent to a minor-11th but Frank spelled in his specific ways
In “Yo Mama” it appears as G/Am : A, C (piano left hand) G, B, D (right hand) in order from low note to high … if we arpeggiate these notes up and down we get the introductory motive behind “Yo Mama” – the same chord is used as solo substrate for the later “atmospheric” section in that piece … the guitar rendition can be played like this:
In the song “How Could I Have Been Such a Fool” it appears in the dark-sounding bridge section as a D/Em – the piano voicing used there is interleaved as E, F#, G, A, D
After building some WAH-shell Vibe clones in ’95 (including one for Keith Scott of Bryan Adam’s band) I posted my recipe on the internet and distributed the plans around ’98 … these early (de-coupled supply/ground + regulated audio) plans were copied by others shortly after
I recently started a private forum board dedicated to explaining the fine tuning techniques I used back then to get the best UNIVIBE sound possible … you can become a member by purchasing one of my Univibe+ PCB’s
Enter Mr. Dave Foreman, a dedicated Vibe enthusiast from Ohio … Sometime around July he contacted me about helping him tweak some of his DIY circuits … in my work forum he started off by posting the following:
… about a year ago I built up a Nxxvibe .. And I don’t think the throb is quite right.. Just haven’t been pleased with it.. So it’s been dormant until recently I decided to try to make it sound better.
here’s what Dave had to say recently:
Anyway, I’ll get to the present here, the first thing I did to the Nxx was replace the cells again, this time, pointing the cells towards the bulb, and i think since I destroyed the 25ma bulb, it got replaced with the 12v, 40ma bi-pin from smallbear, (I liked the way it looked,:P).. Bingo!…. Swirl was happening, I was happy, yay!!! But I was deluding myself, I STILL couldn’t get the throb I wanted, although I tried to convince myself I did… Now by this time this poor board turned into a Frankenstein board, pads and traces starting to peel, a few buss wire repairs required, etc..
Now enter, the bias offset mod, NOW we’re even closer… But STILL not quite.. Enter 24v supply.. Houston, we have success!!
JC had always said the the LFO and audio circuitry run better at a 24v, and as much as I didn’t realize the original ran at about that!! The moral here, 15V does not cut it, IMHO!!! Running at 24 seems to have opened up everything, INCLUDING what the Bias Offset does for the circuit!!
The recording here was made with my usual amp setup, my Si FF, (he definitely used an FF at Woodstock, not Axis circuit IMO).. So I’m very happy to say.. THIS is what i wanted.
All Vibe PCB boards, whether mine or other copies, can be tweaked, or in some cases modded, to get the ultimate level of VIBE performance … details posted at the forum
A local producer asked me to design and build him a “re-Amp” box which takes a line level signal from the console and turns it into a guitar signal so that it can be sent to a real amp (or pedal) and processed …
well, there’s an extra step that needs to occur in the console first, but the idea is to produce an equivalent circuit whereby the coupling of all three circuits (console, box, amp) will “act” like a guitar PU going through a cable and unto the input of a tube amp … a variable capacitor switch is used to mimic the effect of varying cable runs, and a volume pot is included
This amp came in after it started to smoke – both Screen blockers where fried right open … power tubes toast
A new set of GT-6L6GE’s, new PSU filter caps, new power socket resistors, and a re-biasing later and she was good to go. Probably my fave for tone in the Black Face line, the AA864 Bassman sounds especially killer with KT66′s // but that’s another story!
PCB amp, component side flipped upside down in the chassis = impossible to work on “visually” while plugged in … almost all resistors are 1/4w – pretty chancy stuff … with ridiculously narrow traces in some areas on the PCB … and that’s just for starters // the rat’s nest around the PT is quite a sight … perfectly accurate schematics for this beast are not available, let alone a layout diagram (C11 as drawn in the one I have is not present in the chassis)
for starters, the input pin (5) on one power tube socket was lying at +325v instead of -v bias voltage … the pcb short was eliminated by wiring in grid bias resistors, signal caps from PI circuit, and grid blockers “flying” over the pcb board in pt-pt fashion
At first the main B+ voltage was lying at +515vdc, filaments at 6.7vac and Bias feed tap was too low to provide appropriate voltage to bias tubes below 60mA (each) … way too high for 6L6′s / not to mention providing very short filament life
obviously, the primary winding on PT had shorted windings – so voltages had to be brought down to sane levels by introducing a power resistor in series with Prim winding … B+ thus brought down to 483vdc, filaments to 6.1vac, new bias circuit introduced wider range voltage source // set to -49v (with room to spare), power tubes were biased at 27mA/30mA …
then, a leaky signal cap in the preamp section was replaced to removed DC which made vol/tone controls inoperative … channels C & B then worked ok / high gain channel A was still dead – and would require much more work to suss out … luv that switching system, a total circus !
tone of first two channels is good and worth the work … as much to expect from such an unfriendly design … if you own such an amp and it has worked flawlessly consider yourself fortunate
Always wondered how Frank built up this beautiful piece of music … here in its entirety is a bootleg recording of the Osaka ’76 performance, one of the most beautiful rock guitar solos ever recorded … interesting to see where Frank made his tape splices
The latest viva Analog 360+ Lite preamp – done in “Nuclear Winter”
Like my Pro units, these are built around Amplifier Grade 24mm Alpha pots and also use a custom wound Cinemag inductor for the Variamp section … this smooth sounding circuit provides replica tone and dynamics of the famous Acoustic 360 Bass preamp in a modernized package – but, unlike the Pro units, comes without the Fuzz effect … the foot-switch toggles an opto-MUTE function allowing for quiet, safe and convenient swapping of instruments
owner picked up this pre master-voloume SF Twin for a fair bit of coin, complained of poor tone, etc … was supposed to be Blackfaced but wasn’t / plus there was orange drops throughout – and circuit was very hummy
further inspection revealed a Bias circuit that was badly modded and way out of range / leaving the power tubes super cold at full rotation … vintage Fender Blue Foil caps were inserted in the Reverb channel signal path and tone circuits along with a NOS 0.001u/400v Mullard cap going into the PI circuit for a characteristic vintage feel
the rest of the circuit had a lead-dress hair-cut along with moving the trem-defeat line to reduce hum down to nil … a proper Bias circuit later and the amp was purring as it shoulda in the first place … sounding very AB763
Developed for Adrian McCullough, Bass player for Roosevelt Radio.
Adrian’s original request was to make his Bass sound like a saw-tooth synth tone. The only circuit I knew that could come anywhere close to doing that is my original Nyquist Aliaser (c) 2005 audio-rate sampler. The specific thing I like about Aliasing is its ability to leave the bottom end of the spectrum unaltered, making it more musical than a Ring Modulator.
My original design was modified so total clock nulling could be achieved and the effect made recordable. I made a short bench video to demonstrate the noise-less capabilities of the new “tunable” circuit
Adrian’s Bass/Aliaser application can be heard in the intro of the Roosevelt Radio song “Order in the Chaos” (produced by Chris Wonzer)
A buddy of mine recently bought a ’62 non-TB AC30 head … after playing it for a while he noticed strong “ghosting” on single notes when using a ToneBender or Fuzz pedal …
the filter caps were indeed leaking out … I thought that new caps would fix the ghosting problem but it only made the amp a little tighter – as expected … but after playing another ’62 and a ’64, and checking carefully for this, I started to realize that’s just how “wild” these amps are // somebody tell me there ain’t no ghost in that machine
Hooked up with guitar great Todd Taylor at Vancouver’s Comox Hotel Pub playing with power-house drummer Ron Briggs. I really wanted to lay my new Octave Amp on him and see what he would do with it.
Here he can be heard playing through a ’69 Silver-Face Twin Reverb modded by Dave Vidal, and amongst other toys a “SRV Special Overdriver” I built for him in ’97 … never a disappointment seeing Todd mangle a guitar
Satisfying die-hard Vibe fans many years later: the original (c)1996 “split-rail/regulated-audio” Univibe cloning kit // Copied by others but unsurpassed in performance thanks to an original Bulb-Bias Offset Mod. The PCB Kit includes a membership to the VA-works forum where all circuit extensions, including a new controller board, and mods live. $30CDN
Inspired by the underlying mathematics behind the operation of the Danelectro “Green Ringer” and Roger Mayer “Octavio” built for Jimi Hendrix, this circuit takes the frequency doubling experience to new depths … It features a high-voltage circuit capable of producing highly symmetric Full-Wave rectification
This circuit tests out what happens when the two lobes that form a double frequency waveform bend are perfectly matched … unlike single-ended PI circuits and transformer based FW rectifiers this one produces ultra high octave-to-fundamental ratios … to the point where the characteristic “ring” that one gets when playing double-stops (try a tri-tone!) goes beyond any other analogue circuit … this is for guitar players seeking a new version of the well-known effect, on bass it gives a very unique ringy fuzz which retains more bottom than your typical fuzz box, on Fender Rhodes it’s insane …
the switching circuit also features a new version of my constant-current LED switching circuit, providing (i) zero switch pop and (ii) adjustable bypass LED brightness (anything from off, low or full on) …
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Throughout the recording of Roosevelt Radio producer Chris Wonzer applied the Octave Amp to Joel Line’s guitar hooks to give them an understated edgy character ~ interesting use of the circuit
Here’s another great example of a PCB based tube amp that shouldn’t be … for starters the head of one of the screws that holds the PCB down overlaps against the “Screen” voltage rail … a little too much torque on the screw and guess what ?!
another thing, the PSU grounding is done through the potentiometer housings – one of the strangest thing I’ve ever seen in a tube amp !! … it baffles me that a corporation trusted some “designer” to do that
last thing, the profile shot above shows how pressure from the tube retainer has pushed the board out of shape in time – total silliness
Phill sent me what he said was a rough demo of his main gig “The Mother Tongue Band” after building him a 360+ Lite unit … chopped up a few sections of his killer sounding Live CD and collaged shots of 360 clones I’ve built over the last 15 years
