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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silverface
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Post by silverface »

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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Post by sinner »

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 :thumbsup

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Post by sinner »

Look at this, can give you even more ideas

http://www.kitrae.net/music/BIG%20MUFF% ... 0GUIDE.jpg

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Post by fakcior »

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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Post by sinner »

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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Post by sinner »

sinner wrote:
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 :thumbsup

My bad, I have just looked at Dirk's schematic. C3 is not an low pass filter, C9 is. And this is where I would start. Cornish said his buffers are unity gain, and add no coloration to the sound AFAIR, so BMP circuit it self is where the "problem" can be unsolved

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Post by Dirk_Hendrik »

All values in the schem are wrong. I did that on purpose. Before I posted photo's of the boards I painted new resistor color codes on the resistors. Then I replaced all UO-diodes with Ge and SI diodes......

gawd :roll:
That circuit was examined by hundreds. Don't you think that real errors would have shown by now? No. Decreasing that cap's value will not make it brighter.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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Post by sinner »

Dirk_Hendrik wrote:All values in the schem are wrong. I did that on purpose. Before I posted photo's of the boards I painted new resistor color codes on the resistors. Then I replaced all UO-diodes with Ge and SI diodes......

gawd :roll:
That circuit was examined by hundreds. Don't you think that real errors would have shown by now? No. Decreasing that cap's value will not make it brighter.

I don't know to who you addressing your answer to, but if it's me then, then chill. As I said, I never was thinking you fuck it up, and definitely never said that.

The problem is me - I still believe FSB is about learning. Twicking is a part of it - matching to your likening. This tread shows that I'm in fact an lunatic

Good day

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Post by fakcior »

Sorry, Dirk
I didn't mean to offend you. I don't know how the process of tracing was leaded, because I haven't been here then.
But now PCB pictures don't work.
So I can assume it's all about diodes?
Again try 2x 1n4148 + 2x OA47.

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Post by MWichni »

All four diodes in the clipping section was germanium. Unfortunately Dirk was unable to determine the brand/model of the diodes because of the paint...

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Post by fakcior »

But in TopTone DG-2 is combination of Si/Ge and sounds pretty the same.

OA47s could do the job since they have lowest Vf of germanium diodes:
http://baec.tripod.com/articles/crystal.htm

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Post by silverface »

Btw I was not implying the trace is wrong, just that guitar->amp sounds 'different´ than with the buffer inbetween. Without the buffer circuit I feel it sounds a tad fuller or snappier for lack of better words. Though one might suspect just the opposite. In AG's trace of the Guild Brian May booster (http://analogguru.an.ohost.de/193/schem ... MayBox.gif), which is basically a Cornish derivative, the cap between the transistor's B and E is 100pF. I'm only searching for clues :)

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Post by MWichni »

fakcior wrote:But in TopTone DG-2 is combination of Si/Ge and sounds pretty the same.

OA47s could do the job since they have lowest Vf of germanium diodes:
http://baec.tripod.com/articles/crystal.htm
Yes, but they probably use 2xBAT48 and 2xGermaniums.

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Post by silverface »

I tried some different values for the 1nF cap, and it does make a noticable difference. A higher value mostly smoothes out the highs, and lessens the overall volume.

100pF : brighter, snappier, somewhat less full sounding, and more output volume.
470pF: a good inbetween value.
1nF (stock) : actually quite good, a well chosen value, though maybe a little too warm.

I'm going to do some testing at high volume soon to decide what value is best.

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Post by HydrozeenElectronics »

Can some on help me figure out why R11, R12 and R13 are connected to positive voltage and not just ground? I can see that they are part of some sort of boot strapping configuration to boost impedance I'm guessing but why the DC positive wouldn't the AC input just float right over the top of it to ground? I've really been trying to wrap my mind around this for a while now and any help would be appreciated.

Thanks

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Post by Dirk_Hendrik »

HydrozeenElectronics wrote:Can some on help me figure out why R11, R12 and R13 are connected to positive voltage and not just ground? I can see that they are part of some sort of boot strapping configuration to boost impedance I'm guessing but why the DC positive wouldn't the AC input just float right over the top of it to ground? I've really been trying to wrap my mind around this for a while now and any help would be appreciated.

Thanks
Which schematic are you referring to when you mention these resistors?
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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Post by HydrozeenElectronics »

Dirk_Hendrik wrote:
HydrozeenElectronics wrote:Can some on help me figure out why R11, R12 and R13 are connected to positive voltage and not just ground? I can see that they are part of some sort of boot strapping configuration to boost impedance I'm guessing but why the DC positive wouldn't the AC input just float right over the top of it to ground? I've really been trying to wrap my mind around this for a while now and any help would be appreciated.

Thanks
Which schematic are you referring to when you mention these resistors?
It's the buffer stage of the G2 pedal that is in the downloadable pdf at the beginning of the thread.

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Post by BaldPaul »

File unavailable. What gives?

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Post by Dr Tony Balls »

Does anyone have this schematic still? I have a printout hat I can either scan or just redraw if needed.

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Post by Intripped »

i have this - should be correct
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G2 sch.png

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