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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Greg
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Post by Greg »

mojah63 wrote:
StratWiz wrote:DH, you are correct, you are rude!
Don't try to patronize anyone just because you did some nice tracing work, and don't try to block people from making constructive progress beyond your capabilities.
Unlike you, I was able to actually build a great G2, in spite of the lack of information, and I also helped other people to make progress. Here's a little proof:

We share different views on Mr. Cornish's skills, on how critical are these diodes to the overall sound, and on how to find great sounding diodes. That's OK.
But, if you feel offended by that then perhaps you should consider getting yourself a shrink.
StratWiz
Post ur diodes or shut the F**ck Up already! We've been waiting since 2011...
^^^^^^^
THIS.
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Post by andymanicy »

Come on guys - this has gotten really ugly now.

Let's keep it friendly, be grateful for the info we did get, and move on to something new:)

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Post by monkeyxx »

I settled on some 1N695 NOS diodes in my G-2 build. Same as "Harmonic Percolator" apparently. Sounds really nice, and better than some other options I tried.

forward voltage is a little higher, maybe .0268V or something. So I guess that's a tiny bit more gain, and maybe a tiny less treble. That's fine with me. Just turn up the tone knob and down the sustain knob if you want. All the knobs have a good range and the pedal is widely useful.

I really like the SS-2 as well. Really turned ON by these cornish drives right now.

:horsey:

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Post by monkeyxx »

Sorry I put an extra zero in there. Diodes vary, but my 1N695 measure around .27 to .29 V on the diode tester on my multimeter.

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Post by stojanos »

Did anyone get this working with a decent volume level knowing that low forward voltage of germanium diode will clip the signal at much lower voltage than silicon diodes ? I have build this (without buffer though) and volume is too low and hardly clipping (used 1N60 diodes with the decent Vf of 0.35V). Somebody recommended changing the config around second transistor (transistor in front of clipping stages) replacing emitter resistor with 100R instead of 680R and collector resistor with 18K instead of 15K but my logic is that clipping after that will still tame it. Apparently TopTone DG2 is a very good G2 clone. Does anyone know if diodes that TopTone DG2 is using are solely GE diodes or they combine it with silicon one? Would there be a benefit of germanium soft clipping and silicone high Vf if we use two GE diodes in series bringing Ge Vf to silicon level ? Sorry for too many questions but any view on these questions would be appreciated.

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Post by stojanos »

By the way, I have recreated schematics and PCB layout in KiCad. If anyone is interested it send me a message.

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Post by monkeyxx »

I wrote a post about my findings with the DIY G2 circuit. In my opinion there are a number of common problems.

Rather than re-type I will just link to it here:

http://dantonewac.blogspot.com/2018/02/ ... uilds.html

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Post by modman »

There is a thread about the tracing in a folder reserved for contributors to the Tracer's Fund. Maybe I should make it public to dispell all rumors.

There is a mistake in the DH schematic, but this was pointed out in the thread:
Dirk_Hendrik wrote:
MWichni wrote:Hi guys, the correct value of the sustain pot is 47kA. Dirk's schematic has there an error. He changed that in another pdf but I don't know why it isn't uploaded in this thread. If you want to build one you can use madbean document which is 100% correct.
47k indeed. Thanks Mariusz
Cornish G2 schematic Dirk Hendrik detail
Cornish G2 schematic Dirk Hendrik detail

1nF capacitors must be correct, because
C2, C6, C8, C9, C11, C12, C13, C16, C20: WIMA MKS
1nF is the smallest value for these type of capacitors:
WIMA MKS
WIMA MKS
Reading this thread you will also find comments like:
rgm wrote:No wonder it sounds dark. That "tone" control is in fact a reverse wired treble cut, you would need to put it almost at 10 to get a balanced response.
engineelite wrote:So I built a G-2 clone and it sounds excellent but a tad dark in "bypass" and "active" modes. Does anyone have any recommended value changes in the buffer to make it a little brighter?
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Post by monkeyxx »

There's just no way those caps could be right in my build. The pedal sounded broken. I am using the correct pot values.

Even 20 minutes on YouTube looking at real G2 will show you they don't sound like "that."

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Post by Greg »

I can only say that I've built a G2 in the past using Dirk's schematic, and it sounded excellent and right to me.
It's hard to compare a pedal to YouTube clips.. along with the compression and degradation of the recording from the format and computer speakers, there's the effect of the guitar used and the amp plus amp settings.

If you've made mods to the circuit and it sounds better to you then all is good. It's what this hobby is about.
Enjoy :)
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Post by modman »

monkeyxx wrote:There's just no way those caps could be right in my build. The pedal sounded broken. I am using the correct pot values.
Did you omit the buffer? like JAVICAP?
Screenshot from 2018-06-10 11-21-42.png
Screenshot from 2018-06-10 11-21-42.png (43.79 KiB) Viewed 2114 times
Screenshot from 2018-06-10 11-22-21.png
Please buy a G2, ungoop it and show us the proof. The unit that was traced on the forum years ago does have the MKS caps, which are at least 1000pF aka 1nF
Or spend 30 seconds looking at this picture and please point out those ceramic coupling caps.
Cornish G2 component side.
Cornish G2 component side.
Even 20 minutes on YouTube looking at real G2 will show you they don't sound like "that."
Tracing a pedal is not done by listening to youtube clips... this is not TGP.
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Post by monkeyxx »

Mine has the buffer.

The pedal is un-usable if built to the suggested "trace."

We can argue about it all day but it simply doesn't sound right. In fact, very wrong.

I was getting ready to throw it in the trash before I decided to tweak the caps. Now it sounds great.

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Post by monkeyxx »

Here's one of many links selling a 500 pF Wima

https://pt.aliexpress.com/item/2015-Sal ... 78306.html

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Post by modman »

You cannot prove a trace is wrong just because your build doesn't sound right and needs this mod -- according to your ears, with your amp and guitar...
monkeyxx wrote:Here's one of many links selling a 500 pF Wima
https://pt.aliexpress.com/item/2015-Sal ... 78306.html
that's a MKP, probably even Chinese knockoff
Any quick listen to a decent G-2 demo of a Cornish pedal on YouTube will show you how far off it is. The video where Shnobel compares it to the Vick Audio pedal (probably built to this wrong schematic) is a good real world demonstration of how far off these builds can be.
this one? don't hear a problem... other than that Schnabbel apparently does not know how to dial in a good sound
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Post by Intripped »

well, there is something here
...even if the caps we are talking about are the fatter ones in the pic - see attachment.

These caps seem to have 5mm spaced legs, or PCM 5mm, and they could be of the FKP2 series.
https://www.wima.de/en/our-product-rang ... ors/fkp-2/

...so their value can be so low as 100pF, if we just look at their dimensions.
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Post by modman »

Intripped wrote:...so their value can be so low as 100pF, if we just look at their dimensions.
This unit was not traced from pictures, so you are saying DH misread both the value and capacitor type?
You could have chipped in $10 or so and witnessed the tracing first hand at the time...

Of course basic Muff has 470pF in this position... it will not sound bad. I really wonder if you could hear the difference.

Spend the bucks on a unit, degoop it yourself, come back with pictures, then we will talk.
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Post by Intripped »

i'm just following the discussion that is happening now,
and if you say that those caps can not be lower than 1nF because of the dimensions, well, that's not true.
it would be nice if DH said something about it and cleared all doubts.

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Post by juice2 »

Guys, if you like a sound of 470p-560p more than 1n in this circuit, it's ok, nobody forces you to use 1n.

When I breadboarded mine pedal I also messed with different resistor and cap values and found that 470p sounds a bit better to me, it just added a bit more clarity and air. Though difference in tone wasn't significant at all.
Making stages less gainy (by increasing emitter resistors to 680r) and using GE diodes is much more important for the tone of this pedal.

Also keep in mind that Cornish suggests G2 to be used in a clean, full frequency response amp. Thereby I have no doubts that Dirk traced schematics correctly and we should thank him for all his work on this pedal.

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Post by stojanos »

I had a problem with my build due to wrong wiring of, you would not believe, battery. :slap: I did not realize this immediately because somehow this schematics will still produce sound and work like a booster when battery polarity is switched. Unbelievable.

Now when it is fixed I believe that schematics are right. I have built it from scratch using my PCB layout that resembles as much as possible original. I played with different capacitors but put back original values. For example, putting ~500pF instead of 1n will give a more headroom for room level playing but it will not work that great on loud tube amp. I can also confirm that buffer is mandatory.

For me different diodes have more influence than capacitors. This schematics are designed for germanium diodes which typically have low Vf. Dirk said that Vf is ~0.22mV. I could not find diodes with such a low Vf but 1N43 and 1N914 are close (~0.25mV). 1N60 Vf of ~0.35mV is too high to produce acceptable clipping.

I have build few different big muffs and tube drive pedals but I was not able to get acceptable overdrive/fuzz sound from my strat single coil CS69 pickups. This pedal finally gave me thick (not screaming) high notes and dynamic and rich fuzz on low strings. For example it was difficult for me to get rich sound from D string on 12 frets and above without overdriving it too much (adding more gain) which consequently add more high string screaming and dynamics loss (no noticeable sound separation between strings when played together). Now the sound produced from different neck positions is much more balanced. Beautiful.

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Post by Dirk_Hendrik »

Intripped wrote: it would be nice if DH said something about it and cleared all doubts.
True. That would be very nice!
However, that trace was quite a while ago and the material I have left is the material you have. Even if there was, for some obscure reason, another error found, there would be another legion of corksniffers and keyboard warriors posting youtube vids and stating the trace is still not right. Why bother?

Other than that the tracing was not only about the components (It's a Big Muff guys) but also about the way Cornish builds his pedals. I think it to be 70's technology and style but hell, it is sturdy). Way sturdier than about all of the "clones" that came after it.

So, As Modman says,
Buy one, trace it, post the result. If you find any errors I'm the first to state Mea Culpa.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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