Pete Cornish - G2 Guts, Schematic, Layout (from Tracer's Fund)  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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mictester
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Post by mictester »

Dirk_Hendrik wrote:
mictester wrote:
soulsonic wrote: A simple opamp buffer would have better performance.
A simple op-amp buffer would have much better performance!
True.
But that density of PCB layouting, combined with the high level of the technology used in an opamp, might be too much for mr Cornish.

bear in mind the PCB layouts from the G2 are routed in a style I do know only from early 1970's elektor magazine. Some here call that style artwork by the way. I prefer to call it lack of progress. Thank the programmers for CAD. (not to be mixed with autorouting!)
Dirk - I did some of the designs of the early Elektor PCBs! There was a definitive "house" style that had to be followed. Somewhere here, I have the original design briefs for board layouts. One thing that Elektor demanded was a PCB layout for every published circuit They banned Veroboard even before the first issue!
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Post by Dirk_Hendrik »

mictester wrote: Dirk - I did some of the designs of the early Elektor PCBs! There was a definitive "house" style that had to be followed. Somewhere here, I have the original design briefs for board layouts. One thing that Elektor demanded was a PCB layout for every published circuit They banned Veroboard even before the first issue!
Fine and no problem. The question is what you did after that. Do you, close to 40 years later, still design PCB layouts by hand using black tape for pads and traces??
Sorry. Plain out of planes.

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Post by prnet »

I just finished to build... First impression is a nice gilmourish sound... (oh.. my dr504) I tried different clipping modes..
first: all 1n4148/1n914 which make the sound very loud and fuzzy...
second: I used 1n34a for the first clipping stage, then it sounded much more smoothed, as expected.. But a bit darked and less gain.
third: all 1n34a... sounds very smooth and dark.. I think the sound has a very good response in dynamic... but.. very dark.. and the sound seems to go in the OD zone.

I think that switching diodes is a must for me..
Nice pedal, but I still don't understand if the buffer eats signal in someway.. I don't have a looper at home now..

THANK YOU ALL

(p.s. the led is reversed in the layout)

Paolo

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Post by silverface »

The forward voltage of the diodes is important. Some have used diodes in the 180-200mV range, others tried diodes around 270mV. It probably depends on the exact type of diode used. I have some 1N34A's that measure about 400mV, and I'm not sure how those will sound. You'll have to try different germaniums in there to get the right sound! The G-2 seems to be built by mr. Cornish with readily available and common parts, so the actual diodes should not be anything funky or NOS.

And by the way, do not expect this thing to sound as gainy or boomy as a normal big muff. It's much more overdrive-like.

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Post by prnet »

silverface wrote:And by the way, do not expect this thing to sound as gainy or boomy as a normal big muff. It's much more overdrive-like.
Of course.. with germanium.. I think the sound is similar to tscreamer, but more warm, and darker..
silicon diodes instead bring it to muff zone...

I used a switch to select between germanium and silicon in the first clipping stage.
In the second stage, only germanium.

here the pics of my build :D http://www.thepiper.eu/?page_id=180

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Post by darkglass »

Dirk_Hendrik wrote:
mictester wrote: Dirk - I did some of the designs of the early Elektor PCBs! There was a definitive "house" style that had to be followed. Somewhere here, I have the original design briefs for board layouts. One thing that Elektor demanded was a PCB layout for every published circuit They banned Veroboard even before the first issue!
Fine and no problem. The question is what you did after that. Do you, close to 40 years later, still design PCB layouts by hand using black tape for pads and traces??
In the Mesa Boogie factory tour they claim that Randall Smith uses that method! Which giving the size and complexity of some of their Amps (I owned a Bass Walkabout) is either bullsh*t or freakin' impressive... anyways, I agree with you guys, despite the romance for the old school stuff, IMO any CAD program will provide the designer much better routing options (don't mean autoroute either).
But that's just my opinion.

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Post by RnFR »

Dirk_Hendrik wrote: Some here call that style artwork by the way. I prefer to call it lack of progress.
:lol: just because i find it aesthetically pleasing doesn't mean i'm about to shut down the mac and pull out the tape! what can i say, i just think it's a rather nice looking piece of abstract art. but for the record, i hereby fully endorse the CAD way of life, even if i have to defend it to my girl. she somehow thinks it's "cheating"! :slap:


and yeah- autoroute's for pussies!
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Post by Jarno »

mictester wrote: Dirk - I did some of the designs of the early Elektor PCBs! There was a definitive "house" style that had to be followed. Somewhere here, I have the original design briefs for board layouts. One thing that Elektor demanded was a PCB layout for every published circuit They banned Veroboard even before the first issue!
And the designs should use obscure parts, that you couldn't get anywhere even when they weren't obsolete, and part substitutions weren't given.

As someone who's only just beginning to route his own PCB's, does anyone know of a concise strategy to do this? I know I should snake the ground around, any other tips?
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Post by mictester »

Dirk_Hendrik wrote: Fine and no problem. The question is what you did after that. Do you, close to 40 years later, still design PCB layouts by hand using black tape for pads and traces??
I actually did my first computer-based PCB design on a Northstar Horizon machine (and a few of the boards were for Elektor), but the early software wasn't much better than crepe tape on acetate on a light box - often the older way was quicker! That was about 36 years ago. Things have got a bit better, but I still lay out microwave and UHF circuits by hand.

Moving on - I'm firmly of the opinion that all those old effect circuits -

the ones that relied on the faulty characteristics of the devices used,
the ones that were seriously noisy because the designer hadn't got a clue about low noise circuitry,
the ones that didn't work into some loads,
the ones that relied on a dying battery to get just that sound,
and the ones that claimed that they require bizarre, unobtainable, ancient components

should all be buried as the dinosaurs they are!

It's fun to abuse a germanium transistor occasionally - my update on the Burns is a case in point. I admit that getting just the same sound with silicon would be more difficult, but certainly worth doing. We might learn some new methods from it!

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Post by silverface »

You may have been looking at an older version of the schematic. That one has a 470k sustain pot and indeed no 100k to ground.

This is the right and latest one:
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Cornish_G2.pdf
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Post by marwatt »

is the sustain pot 47K or 470K...????

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Post by MWichni »

marwatt wrote:is the sustain pot 47K or 470K...????
47K!!!!!!!!!!!!! :wink:

Regards,
Mariusz.

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Post by Dirk_Hendrik »

marwatt wrote:is the sustain pot 47K or 470K...????
preps read the whole thread? :roll:
Sorry. Plain out of planes.

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Post by darkglass »

mictester wrote:
JOHNO wrote:Do you guys know what brand of caps are used in this circuit?
It doesn't matter what kind of caps are used - as long as you have the same value, you'll get the same sound. Remember - all you read on TGP is complete bullsh*t - they wouldn't be able to distinguish one effect from another if they couldn't see the boxes they're built into.

We recently had an "overdrive shootout" at a local studio. We had a genuine TS9, one of my homebrew jobs, and a $500 Boutique thing that was horrible inside. I spent twenty minutes tweaking the three controls on each pedal until they were as similar as I could get them, then asked the players to try each one - blind - and rate them. Nobody was able to distinguish one from another. The only way that mine distinguished itself from the others is that I had slightly more gain available, and a greater range of drive and tone setting. This goes to show that the "diodes in the feedback loop of an mid-humped op-amp with a simple tone control after it" topology sounds pretty much the same whoever makes it, and at whatever price. The only advantage of one over another is a greater (or different) range of control and different noise levels.

I'm getting more and more cynical with every "new" Boutique effect I see....
I once built 6 of my bass overdrives (same layout) 2 with Wimas, 2 with multilayer ceramics, and 2 with non-boxed polyester... and they all sounded different. All the other components were exactly the same, resistors, pots, switches, jacks, opamps, etc.
I eliminiated any psycoacoustic bias by doing blindfold tests with 4 friends in a geek meeting, they all recognized the differences the different caps (they couldn't find any difference when the 2 pedals using the same caps were in A/B)! Ceramics were really darker and "warmer" I suspect at least -6dB of treble content (over 3.5kHz probably) and the wimas and polyester were almost the same, Wimas had more treble though... in a clean preamp, this shouldn't matter so much, nor in a fuzz (where you basically saturate the whole spectrum of the input signal)... but in any Overdrive changing the frequency response before the clipping may dramaticly change the compression and texture.
2 of my friends where no musicians, and they all could notice the differences (without knowing if they were listening of two of the same caps, or different).
So the differences were quite noticeable. I may need to clarify that there is heavy filtering in my Overdrive (the version without EQ has over 70 components, 30 caps aprox!) so maybe changing the types in one or 2 caps may sound quite the same, but changing 30...!
Since then I only use Wimas... despite what everyone says, I did my experiments, and made my own conlusions. I encourage you to try this!

Best Regards

Douglas.

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Post by phibes »

darkglass wrote:
mictester wrote:
JOHNO wrote:Do you guys know what brand of caps are used in this circuit?
It doesn't matter what kind of caps are used - as long as you have the same value, you'll get the same sound. Remember - all you read on TGP is complete bullsh*t - they wouldn't be able to distinguish one effect from another if they couldn't see the boxes they're built into.

We recently had an "overdrive shootout" at a local studio. We had a genuine TS9, one of my homebrew jobs, and a $500 Boutique thing that was horrible inside. I spent twenty minutes tweaking the three controls on each pedal until they were as similar as I could get them, then asked the players to try each one - blind - and rate them. Nobody was able to distinguish one from another. The only way that mine distinguished itself from the others is that I had slightly more gain available, and a greater range of drive and tone setting. This goes to show that the "diodes in the feedback loop of an mid-humped op-amp with a simple tone control after it" topology sounds pretty much the same whoever makes it, and at whatever price. The only advantage of one over another is a greater (or different) range of control and different noise levels.

I'm getting more and more cynical with every "new" Boutique effect I see....
I once built 6 of my bass overdrives (same layout) 2 with Wimas, 2 with multilayer ceramics, and 2 with non-boxed polyester... and they all sounded different. All the other components were exactly the same, resistors, pots, switches, jacks, opamps, etc.
I eliminiated any psycoacoustic bias by doing blindfold tests with 4 friends in a geek meeting, they all recognized the differences the different caps (they couldn't find any difference when the 2 pedals using the same caps were in A/B)! Ceramics were really darker and "warmer" I suspect at least -6dB of treble content (over 3.5kHz probably) and the wimas and polyester were almost the same, Wimas had more treble though... in a clean preamp, this shouldn't matter so much, nor in a fuzz (where you basically saturate the whole spectrum of the input signal)... but in any Overdrive changing the frequency response before the clipping may dramaticly change the compression and texture.
2 of my friends where no musicians, and they all could notice the differences (without knowing if they were listening of two of the same caps, or different).
So the differences were quite noticeable. I may need to clarify that there is heavy filtering in my Overdrive (the version without EQ has over 70 components, 30 caps aprox!) so maybe changing the types in one or 2 caps may sound quite the same, but changing 30...!
Since then I only use Wimas... despite what everyone says, I did my experiments, and made my own conlusions. I encourage you to try this!

Best Regards

Douglas.
Did you take the tolerances of the different capacitors into effect before conducting the study? That's probably what you were hearing more so than the material. WIMA's have shitty tolerances from what I can remember so those babies could be all over the place value wise. Especially with a 30 cap count! :shock:
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Post by Amstel »

Are better Wima MKS2 or FKP2? :hmmm:

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Post by darkglass »

I thought if tolerances, but if were that the case, then all of the 6 should have sounded different.
And as far as we could tell, both made with ceramics sounded quite alike (at least I couldn't find any difference) I had done about 20 before the experiment with those yellow box film caps from mouser, and all ten of them sounded the same. Then made 10 with ceramics (ran out of film) and those ten sounded the same with each others, but really different compared with the film version (had to re design one lpf at the output version for compesing the lack of lo end) and after tha I made the experiment.
I know is probably not a strong argument, but if they all sounded the same, I guess RG Keen would use cheap ceramics instead of film box in Visual Sound pedals (hopefuly we'd hear his opinion on the matter). And remember as well that there are some film caps in the Tech21 Character series (why would Andrew go through all the trouble using 2 different sized, and pricier caps than the rest?. Not trying to argue with anyone... just telling my humble experience using different types of caps... at the end, I still use some ceramics (for values below 1n).
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Post by mictester »

phibes wrote:
Did you take the tolerances of the different capacitors into effect before conducting the study? That's probably what you were hearing more so than the material. WIMA's have shitty tolerances from what I can remember so those babies could be all over the place value wise. Especially with a 30 cap count! :shock:
EXACTLY! Also, if you're insisting on using NOS rubbish (for some kind of bogus mojo factor), those capacitors will have random amounts of leakage, wildly different values and all sorts of chemical nastiness going on in the dielectrics.

Build your circuits using modern components, not some old crap found in a wet cardboard box in the mould-infested depths of some Far Eastern warehouse. The "mojo" associated with old components is simply specious nonsense promoted by unscrupulous (or more usually, clueless) Boutique Boobs in an effort to try to justify their silly prices.

If a circuit is going to sound good, it'll sound good no matter what capacitors and resistors you use. There's little change in sound between transistors with the same gain characteristic, though a change in op-amp (usually just a change in slew rate) can have an effect. You can also get tiny changes in tone by using differing elements for clippers - germanium diodes, silicon diodes, bipolar transistors, FETs, LEDs, Schottky diodes, zener diodes all sound slightly different, but you'll get much more change going from symmetrical to asymmetrical clipping!

The mojo really is a lie!!!
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Post by darkglass »

Well, another thing is that my Bass Overdrive is a "cascaded stage" circuit, I have 3 gain stages (Jfets, then Opamps, then Cmos) so filtering between stages is quite critical in the sound... that´s why I think my circuit could be more sensitive to caps type than a clipping diodes one, where all the clipping is produced at one stage (therefore the filtering giving the overdrievs "texture" is basically shaped in only one stage)... but well, that´s just another theory.

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Post by darkglass »

mictester wrote:
phibes wrote:
Did you take the tolerances of the different capacitors into effect before conducting the study? That's probably what you were hearing more so than the material. WIMA's have shitty tolerances from what I can remember so those babies could be all over the place value wise. Especially with a 30 cap count! :shock:
EXACTLY! Also, if you're insisting on using NOS rubbish (for some kind of bogus mojo factor), those capacitors will have random amounts of leakage, wildly different values and all sorts of chemical nastiness going on in the dielectrics.

Build your circuits using modern components, not some old crap found in a wet cardboard box in the mould-infested depths of some Far Eastern warehouse. The "mojo" associated with old components is simply specious nonsense promoted by unscrupulous (or more usually, clueless) Boutique Boobs in an effort to try to justify their silly prices.

If a circuit is going to sound good, it'll sound good no matter what capacitors and resistors you use. There's little change in sound between transistors with the same gain characteristic, though a change in op-amp (usually just a change in slew rate) can have an effect. You can also get tiny changes in tone by using differing elements for clippers - germanium diodes, silicon diodes, bipolar transistors, FETs, LEDs, Schottky diodes, zener diodes all sound slightly different, but you'll get much more change going from symmetrical to asymmetrical clipping!

The mojo really is a lie!!!
Mojo is a lie, I know! I have actually never even seen a colorfish cap with my own eyes. I have always only used brand new components, they are cheaper and easier to find.... one more time I have been missunderstood!
I'm not talking about ocus pocus carbon comp resistors, or oil can caps... just metalfilm resistors, right angle mounted alpha pots, and different types of BRAND NEW CAPS. All these experiments, and manufacuring processes have been done within last and these year. And all the components have been either bought in Mouser, or in Partco (a Farnell distributor here in Finland)

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