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

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

There's a good discussion here (which is where I borrowed RG's comment from):
http://www.diystompboxes.com/smfforum/index.php?topic=60143.0
culturejam wrote: We are equal opportunity exposure artists.

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tschrama (27 Oct 2011, 12:51)

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

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?

Thanks.
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

tschrama wrote:Hi all,

I think you are all right to some degree but the in the first three big muff gain stages has two feedback mechanisms
1] the emitor resistor, 2] the input series resistor and collector bias resistor.

Without Collector feedback, you are right that the Rc/Re would determine this stage gain in a c. This is only thrue as long as 1/Re is much smaller than the BJT transductance. In a typical BMP, Re = 100R and Rc is 10-to-22K. Gain would then be 100 to 220. The gain of a BMP is about 30-to-35, so obviously somethin else is going on:

The Collector feedback resistor is typically 470K, input series resistor is typically 8k2. If the Vac at the base is small, we can state that Vin/8K2 = -Vout/470K, That leads to Vin-/Vout is equal to 8K2/470K, which is about 57.

Yet the gain stage is neither 100x to 220x, nor is is 57x is it about 30x to 35x. So both assumption associated with both these simplified gain calculations do not apply and transductance and Hfe of the BJT does is significant for the real realized gain.

PS
don't mean to hijack this topic; Mods: maybe we can move this discussion to a seperate thread?

PPS
Pspice is dead on near perfect for these simple, low freq, AC and DC calculations.

PPS
3dB is significant, unless so think that turning gain pot back to to 70%to80% is not significant. It has nothing to do with the fact that the signal might clip.

PPS, Hfe of 120 would lead to 6dB gain reduction in a typical BMP. Thats halve of your gain.

Plus, you have to remember that the max gain for a single transistor (and a resisitve load) is limited by the voltage supply and "transconductance".
Randall Aïken said :
Q: Is there any advantage to using solder with a 2% silver content?
A: Yes. Silver solder keeps werewolves away from your amp.

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

I just built this pedal and the sound is great.
thanks
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Sorry for digging up an old thread, but I'm curious about something.

Dirk, when you were degooping and tracing this pedal, did you happen to note the brand/type of coaxial cable used?
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Nope. Sorry.
Other than that, while re-reading the last pages of this thread, I have never had the feeling that at any point real effort was put in component selection. All seemed "oft-the-shelf" stuff form the first available supplier.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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PokeyPete (16 Apr 2012, 07:13)

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Dirk, thanks for that super fast reply! I remember reading that Pete C. had said that he tested numerous
cables before he found the perfect one (my phrasing). I was looking at cables today for a project and this
came to mind. I'm not mojo minded, but I was curious to know what cable that was, so that was the
reason for my asking. Thanks again.

PP
“No man is so foolish but he may sometimes give another
good counsel, and no man so wise that he may not easily err
if he takes no other counsel than his own. He that is taught
only by himself has a fool for a master.”
–Hunter S. Thompson
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

thanks it's great job!!!!!
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

thanks!
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

I bet Kitrae could solve diodes mystery by degooping Toptone DG-2 or at least just little part with diodes and post some high-res pictures. What you say, Kitrae?
Cheers

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

For fuck sake, anyone with a pair of ears and half of brain could do better than Mr.Cornish as we already learned - nothing groundbraking, just well know circuits with double input buffers

I already started a tread with some suspicions based on Cornish description, scraps of info and what Gilmour was using, with hope we can figured things together, but you bitches are sadly to lazy
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Unfortunately in Poland nobodys interested in Meatheads ;|
I would contribute, but at this moment I'm busy tracing and looking for right components of headphone amp.
edit: okay, got it, but nothing revolutionary there.

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

edit: okay, got it, but nothing revolutionary there.

Like I said - Pair of ears and half of brain is minimum to figure it out
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Like I said - Pair of ears and half of brain is minimum to figure it out

Maybe that's why nobody hasn't found a solution yet

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Again, because you guys are lazy bastards.

I'm no brainiac in "EE" world, but Im not as blind to still believe in "magical diodes". There is at least three other spots in BMP schematic you can bright up the circuit, and having Kit's website you mentioned, with semi complex BMP technology page I can't believe my eyes you still seeking for solution around the diodes.

Dude, you're AGH student, you can do better than this
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Can someone please explain the function of C3, the 1nF capacitor in the input buffer? And would lowering it to 100pF make it brighter?

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

silverface wrote:Can someone please explain the function of C3, the 1nF capacitor in the input buffer? And would lowering it to 100pF make it brighter?

Yeah, it's low pass filter after all
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Look at this, can give you even more ideas

http://www.kitrae.net/music/BIG%20MUFF% ... 0GUIDE.jpg
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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Sinner, you're saying DH's trace is wrong? Like couple of mistaken values?
Can anyone check combination of 2x1n4148 at first stage and 2xoa47 at second?

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Re: Cornish G2 - Guts, Schematic, Layout (from Tracer's Fund

Never said that, perhaps Cornish did what we see on Dirks schematic, but we also hear a lot of opinions that the circuit is to dull for there likening. If it's really, then you have THE ears - now just half of brain and start twicking - BMP is not an rocket ship
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