Aion Cygnus (Cornish G-2) Low Volume

[Fingolfen]

So I finished up an AionFX Cygnus (Cornish G-2), and the pedal sounds good, as long as I have the volume at or near full and the sustain is at least half way up. I contrast that to an Effects Layout P-2 I built where if I don't turn the volume down to around 9:00 or 10:00 I'll blow people out of the room - even on my practice amp.

I've back traced the circuit, and I can't find any dead transistors, etc. For the build I hand selected 1N34A diodes with a forward voltage >0.3V (most were in the 0.34-0.35V range). As such I stuck with the original 15K value for R18 and 680R for R19. I'm wondering if I should have gone with the increased gain on the pre-diode stage using 18K for R18 and 100R for R19.

Has anyone tried this both ways??? Thoughts? I may try subbing out the resistors (though de-soldering on a double sided board is such a PITA).

 

[benny_profane]

Your problem is most likely due to diode leakage:

What's All This Stuff About Germanium Diode Leakage?

Like Germanium transistors, Germanium diodes are leaky. They behave like they have a resistor in parallel and in many cases, that resistor is less than 50K. The higher the leakage, the lower the resistance. Two questions that keep popping up are: How much leakage is too much? How do we...

forum.pedalpcb.com

 

[Fingolfen]

That's a good thought... I didn't test the off-state leakage of the diodes, just the forward voltage as I'd used these diodes (1N34A) in several builds without issue. What would be the easiest way to test it now that the diodes are in the circuit???

 

[benny_profane]

That's a good thought... I didn't test the off-state leakage of the diodes, just the forward voltage as I'd used these diodes (1N34A) in several builds without issue. What would be the easiest way to test it now that the diodes are in the circuit???

The least invasive way would be to test other diodes in the bunch to get a general idea—but that won’t tell you about the ones in-circuit. To get an accurate reading, you will need to desolder one lead to ensure you’re not getting an errant reading.

Edit: You’ll need to remove them and test them as described in the linked post. The circuit discussed there is very similar to the G2 (i.e., modified BMP).

 

[Fingolfen]

The least invasive way would be to test other diodes in the bunch to get a general idea—but that won’t tell you about the ones in-circuit. To get an accurate reading, you will need to desolder one lead to ensure you’re not getting an errant reading.

Edit: You’ll need to remove them and test them as described in the linked post. The circuit discussed there is very similar to the G2 (i.e., modified BMP).

Yeah.... that's what I was sort of afraid of...

Looking at the table in the file, the 1N34As he tested were all fairly leaky, and now I think I know why any G2 demo I've seen has the volume cranked to at least 8....

 

[benny_profane]

1n34A is a rather generic part number made for many years by many manufacturers. That table is not intended to be a definitive reference resource—just a collection of data points. To be sure about any specific device, you'll need to test it. The G2 can certainly behave like a BMP with Si diodes (albeit with a different compression and lower output due to the lower Vf of the diodes), but the Ge diodes must be appropriate for the circuit in order for it to work as intended. When Ge diodes are shunted to GND for hard clipping, this isn't a concern. Here, though, the resistance has an appreciable impact on the gain of that stage.

 

[moonlightpedalbuilds]

try 1n914 or 1n4148 on the first stage.

 

[Fingolfen]

try 1n914 or 1n4148 on the first stage.

I may go that route eventually, but honestly I'm trying to get as close to the original in the clone as possible.

 

[Fingolfen]

1n34A is a rather generic part number made for many years by many manufacturers. That table is not intended to be a definitive reference resource—just a collection of data points. To be sure about any specific device, you'll need to test it. The G2 can certainly behave like a BMP with Si diodes (albeit with a different compression and lower output due to the lower Vf of the diodes), but the Ge diodes must be appropriate for the circuit in order for it to work as intended. When Ge diodes are shunted to GND for hard clipping, this isn't a concern. Here, though, the resistance has an appreciable impact on the gain of that stage.

So I pulled out several additional diodes from the set I used for the build... you nailed it... leakage is terrible. I found some 1N270s with very low leakage, but the forward voltage was low, so I had to change R18 and R19 to 18K and 100R from the original 15K and 680R spec... thing absolutely howls now. It sounds like a muff, but with more low tones... I honestly like it a lot. It's a bit to the dark side.

 

[bruddy]

I've added a linear power boost circuit in front of the effect to solve the low volume problem. Works well.

 

[bruddy]

I've added a linear power boost circuit in front of the effect to solve the low volume problem. Works well.

I've added a 100k trim pot to it so you can adjust the gain to your liking. It has a very robust sound to it that you can dial back if you want. Sounds great.

 

[Feral Feline]

I like Schottky: find one that has a similar [edit: forward-]voltage to whatever Ge you have in place, and replace.

Schottky are stable, don't drift with temperature changes.

Sound? That's in the ear of the beerholder.

 

[Flashheart]

So I finished up an AionFX Cygnus (Cornish G-2), and the pedal sounds good, as long as I have the volume at or near full and the sustain is at least half way up. I contrast that to an Effects Layout P-2 I built where if I don't turn the volume down to around 9:00 or 10:00 I'll blow people out of the room - even on my practice amp.

I've back traced the circuit, and I can't find any dead transistors, etc. For the build I hand selected 1N34A diodes with a forward voltage >0.3V (most were in the 0.34-0.35V range). As such I stuck with the original 15K value for R18 and 680R for R19. I'm wondering if I should have gone with the increased gain on the pre-diode stage using 18K for R18 and 100R for R19.

Has anyone tried this both ways??? Thoughts? I may try subbing out the resistors (though de-soldering on a double sided board is such a PITA).

Does EffectsLayout still offer the P2? Don’t see it in the shop? Thanks.

 

[Fingolfen]

Does EffectsLayout still offer the P2? Don’t see it in the shop? Thanks.

They don't have the board anymore, though you can find the layout. However the EL P-2 is not accurate... both PedalPCB and AionFX now offer accurate P-2 boards. I've only built the PedalPCB one... and I love it... I've built a few at this point...

 

[jimilee]

They don't have the board anymore, though you can find the layout. However the EL P-2 is not accurate... both PedalPCB and AionFX now offer accurate P-2 boards. I've only built the PedalPCB one... and I love it... I've built a few at this point...

I believe guitarpcb.com still has one.

 

[Fingolfen]

I believe guitarpcb.com still has one.

I know they have a G-2 board. AionFX just modified their G-2 board to be a G-2/P-2 board so if you grabbed the instructions from Kevin you could probably make any G-2 board build a P-2