The "SRV Special" Story
Original Mods
JC Maillet (c) '97/'08
 |
Somewhere around '97 a couple of Nashville producers asked me to collate some home-reversed schematics, original circuits, musings and ideas in roughly bookish format ... it was called "Rainbow of Sound" and I sold about 20 copies by word of mouth - mainly to studio engineers and producers ... it was a rough fake-type of affair that included some theory on the Univibe, the TS808, the MutronIII, lots of mods to well-known pedals (much of which is now on this site) and a bunch of other stuff for filler ... one or two members on Aron's DIY Stompbox forum got a copy of the book in the spring of '98 - not surprisingly some of the info ended up plagiarised ... below are the three pages from "Rainbow of Sound" which details the analysis and mods for the Tube Screamer circuit ...
At some point I became acquainted with the parasitic nature and modeling of general circuit elements and realised that it wasn't always possible to do "well" within the confines and limitations of their effects on otherwise normal circuit behavior ... one of the first things that I could equate that kind of technical artifact to my parallel music/gear life was the tone sucking aspect of jFET "passing" of audio signals which was routinely used by Asian guitar effect makers. The ripping out and bypassing of the parasitic jFET switching circuitry by a physical (non-parasitic) DPDT foot-switch was one of the first hi-fi mods I ever came up with ... It was in the early 90's I was looking at this stuff, and when the internet came up I started chatting about these things on the rec.effects newsgroup, the idea caught on with many people and the Direct Bypass switch transplant became a staple mod with many OD pedals ... now, I'm not discounting the benefits of buffering in "long-distance" stage conditions - two seperate problems here ...
The target with this later TS808 mod was to elliminate some of the muddyness that still remained after converting to Direct Bypass and my theory at the time was that it could be made clearer (transient wise) by removing what I had come to consider to be redundant caps in the signal path ... the mod also explored the idea if using a different input coupling cap (10uF instead of the stock 0.02uF) as well as using a 2meg gain pot (upping the gain range) ...
The Tube Screamer was the first place I explored the idea of running a "signal path" on a lesser (total) number of (series) caps... in this mod I call these "un-essential" signal caps; I call them so because for one there is no real need to isolate DC between the stages they couple (I provided DC offset analysis for this) and also because they also don't produce any essential tone shapping other than what the input and output coupling caps already provide ... everything else stays the same except for the cap on the op-amp which seem to produce high-frequency ringing and provide no significant benefit to the operation of the circuit in either modes (clean/dirty) ... between the removable of un-essential caps and the replacing of the FET switching by a physical switch things seem to sound quite a bit better without changing the whole deal ... for some reason, I was satisfied with that and played the circuit for a couple of years before friends started asking me for clones ...
Cloning Around
 |
The result became the "SRV Special" overdrive, of which I sold about 30 units between '98 and '05 - mostly to finnicky old tone purists ... many of them where done in plain Hammond boxes, some where handsomely finished ... the picture below from '97 shows my original re-boxed TS-5 with the mods (far Right) and the two first clones I ever made - the first one (middle) was done for guitar wiz' Tim Butler in Winnipeg ... some pedals had a "fat-input" cap (10uF) while most had a stock value (0.02uF) ... eventually, I got to build some multi-function stage units. The one pictured below was built for guitar hot-shot Todd Taylor in Vancouver, it features switche-able Gain and switche-able Volume controls - both using pop-less/optical switching circuits ...
 |
Land of the Rising Tone
 |
It would appear that one of my "10uF" clones made its way to Japan and some pedal junky named Matsumin reversed it ... from this schematic some DIY layouts started creeping out ... then, somebody in the forums suggested that my TS-808 circuit mods had made their way to the inside of the current Maxon TS-808 pedal (with the 10uF input cap) ...
 |
 |
 |
 |
Permission to repost provided by Ulysses (thx!)
 |
Permission to repost NOT provided by MarkM (can't find email)
epilogue ... You know how things get with words, all twisted and #$%@ ... some people actually think my circuit tweaks, and therefore the Maxon TS-808, will make you sound like Stevie-Ray Vaughn - it's not meant to, it's only a clearer sounding version of the original TS-808 circuit ... with extra available gain if you include the 2meg gain pot swap ...
the moral of the story: with signal caps, less is more ...
viva Analog /// jc CHEZ lynx.net