Low Volume, Low Gain G2

A

ac30irons

Member
Hey all, I know bits around this have already been asked but I’m struggling for a definitive answer.

I have just built a G2 kit from a popular and very helpful uk supplier. There was a bit of mucking about with the diodes and a couple of resistors around forward voltage but it’s built. The kit was supplied with Russian D9Ks.

On power up volume has to be a least 2/3s up to do anything and the gain all up or there is little to no sound. Through a clean amp it sounds ok but there is no where near the gain there should be. I would describe it as a bit crunchy.

I have heard of something called leakage current. I’m not very technical at all and don’t really get it all.

Are D9Ks generally leaky ? Is there an Ge alternative I should just be able to drop in ?

Bloody headache this diode thing.
 
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The diode thing is not that tough really. With a bit of reading and trail & error experimenting (aka: "Don't be afraid to "socket and see". Experiment."), the clipping element mystery (headache) can cleared up.

Here are a few good articles on clipping elements . . . .

1) Saturation Controls
2) More Saturation Controls
3) Simple Easy Mods, Tips & Techniques
4) Diode Clipping Circuits

Clipping elements can often reduce the volume of a signal, depending on what sort of clipping method is used (soft or hard clipping), but that reduction should NOT impeded the performance of the volume control. Even leaky Ge diodes should not affect a volume control.

Understanding what a clipping element does is explained in the articles posted above. Whether it's a diode, LED, PN/NP junction of a BJT/FET or some other active PN/NP junction device, the Fvd (Forward Voltage Drop) and the curve-trace of any of those PN/NP junctions is the key to having a clue what clipping elements (and their different configurations) will do in a circuit.

Not sure which "G2" build you are referring to. If it's the "Germanium II Distortion" by PedalPCB, the Ge diodes are performing "soft clipping' in the feedback portion of the 4th (Q4) & 5th (Q5) stages of that circuit. Ge diodes of most any type, for the most part are interchangeable. It boils down to their specified and measured Fvd values.

And as for better helping you suss out the issue you're experiencing with your build, schematics and good clear, detailed photos of your build would prove beneficial. Let's see some pics and power supply voltage measurements.
 
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This is the bad boy that Iv built.

shop.pedalparts.co.uk

Gee-Wizz Muff

When is a Muff not a Muff? When it's been tweaked into a cranked Marshall kind of sounding vibe. Fronted by a unity gain buffer, offering up a high impedence input, the Muff-based circuit is given some soft germanium clipping to lighten the mood, bringing it more into overdrive/distortion...
shop.pedalparts.co.uk shop.pedalparts.co.uk

So far I have swapped out D1 and D2 and dropped in some silicone diodes. There is now range in the sustain pot but it of course takes away some of the G2 ness. I have tried measuring the D9K leak resistance if that’s what it’s called and they are all around 250k. Iv done this by setting the DMM to 2M. I’m not even sure if I have done that correctly. I’m led to believe they should be in excess of 470k, ideally towards 1M.
 
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benny_profane said:
https://forum.pedalpcb.com/threads/...ornish-designs-all-a-bit-crap.9300/post-88005
Click to expand...
This is a good read if not a bit technical for an idiot like me.

I don’t believe that forward voltage is the issue. Iv done the mod with the resistors for that. I think it’s leakage.

So here is the things I think I need to know.

a - am I chasing a dream if non leaky Ge’s are so rare ?

b - if I buy a load, how do I test them on ‘resistance mode’ like I need a dummies guide.
 
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This is a big hunch, but I don't think your issue has anything to do with those diodes. Diodes with such a small forward voltage don't take much signal at all to clip the waveform. There is an issue somewhere else in the circuit, most likely in that transistor stage or before. Double check all your parts values.
 
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From the Supplier of your PCB!:
The original values for R9 and R11 are shown in blue. During test builds this circuit could sound great or be ready for the bin. Seems it’s all down to the first set of clipping diodes. If their forward voltage isn’t spot on they won’t clip, and everything goes askew after that. AionFX came up with a solution that eliminates this risk, increasing the gain in the first stage to ensure there’s enough signal to get that first pair clipping. Use 100R(680R} and 18K (15K) as shown.
 
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As cdwillis suggested, check all your Resistor values again as this Circuit is critical to components being correct!

Russian GE's are usually opposite with their Anode and Cathode but it will not effect this Build as you have each pair opposite to each other so it will still behave as normal!
 
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music6000 said:
As cdwillis suggested, check all your Resistor values again as this Circuit is critical to components being correct!

Russian GE's are usually opposite with their Anode and Cathode but it will not effect this Build as you have each pair opposite to each other so it will still behave as normal!
Click to expand...
Everything is checked multiple times, it’s all in the correct place. I also did the resistor change when first built.

It’s a well documented issue for the G2 circuit, or any other where Ge diodes are used for soft clipping. I just need to know which leads on the DMM I put on the cathode and anode and what to set the DMM too.
 
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ac30irons said:
Everything is checked multiple times, it’s all in the correct place. I also did the resistor change when first built.

It’s a well documented issue for the G2 circuit, or any other where Ge diodes are used for soft clipping. I just need to know which leads on the DMM I put on the cathode and anode and what to set the DMM too.
Click to expand...
Courtesy & Appreciation will go a long way if you want more help with your Issue.
You haven't acknowledge one reply from the Members trying to help you with a Like, Smile or whatever.
It’s a well documented issue for the G2 circuit, or any other where Ge diodes are used for soft clipping
Click to expand...
You seemed to have answered your own solution!???

Google will tell you which leads on the DMM you put on the cathode and anode and what to set the DMM too.
 
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music6000 said:
Courtesy & Appreciation will go a long way if you want more help with your Issue.
You haven't acknowledge one reply from the Members trying to help you with a Like, Smile or whatever.

You seemed to have answered your own solution!???

Google will tell you which leads on the DMM you put on the cathode and anode and what to set the DMM too.
Click to expand...
Hey there, I didn’t even realise you could like or smile. I don’t really do this online forum stuff. That doesn’t take away the ability to say thanks, which I should of done.

I really am grateful to all the people that have chimed in on the post.
 
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ac30irons said:
Hey there, I didn’t even realise you could like or smile. I don’t really do this online forum stuff. That doesn’t take away the ability to say thanks, which I should of done.

I really am grateful to all the people that have chimed in on the post.
Click to expand...

Pointer on Like & Pointer on the one you want & Click.

1685364365959.png
 
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1N4148 Si Diodes have forward voltage around 0.70 Volts.
1N34 Ge & D9K's Diodes have forward voltage around 0.30 Volts.
So basically when used as a pair of Clipping Diodes the Volume is decreased by Half when Ge diodes are used.
The Circuit has to be designed to compensate for this correctly & the G2 has not hence the Aion mod to try & improve it.
YourD9K's maybe as low as 0.25v & this will kill more volume also but it doesn't explain your Low Gain issue, that is why we need to know that your Resistor values are correct & Pictures are the Best option for us to verify this.
 
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I found some info on the vero board site. They talk about your issue also. Here’s a couple screenshots I took of their discussion. I’ll post the site in a min.
 

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tagboardeffects.blogspot.com

Cornish G2

Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 1000 verified designs. DIY your own boutique effects!
tagboardeffects.blogspot.com tagboardeffects.blogspot.com

Scroll down, and the comments section will start right after the layout, I believe.
 
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Drayve85 said:
tagboardeffects.blogspot.com

Cornish G2

Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 1000 verified designs. DIY your own boutique effects!
tagboardeffects.blogspot.com tagboardeffects.blogspot.com

Scroll down, and the comments section will start right after the layout, I believe.
Click to expand...
Iv read through this which has brought me to my conclusion about leakage. I mean who knew these things could leak.

Iv been reliably informed the ITT 1N34A black gold red are the way to go. More chance finding a yeti in the UK. Will have to buy from US and get busted for shipping.
 
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