SOLVED Frost Drive Gain Pot Not Working

[noak]

Hey everyone, pretty new to pedal building so pardon my ignorance.

Just finished up the Frost Drive and everything seems to be working except the gain knob. Turning the gain knob has no effect on the level of distortion and the pedal seems stuck at one gain setting. Would love to be able to adjust it because its way high gain right now .

I am using a A1M pot instead of the D1M in the spec sheet due to availability. I have confirmed with a multi-meter that the potentiometer is changing resistance when I rotate it.

Thanks in advance for your help!

 

[jwin615]

What value did you use for R7? Can't really see well for be sure...

 

[jwin615]

R7 and R8 kinda look like 47ohm
YPBkGl

 

[noak]

R7 and R8 kinda look like 47ohm
YPBkGl

I am pretty sure it is correct at 4.7k

Correct me if I am wrong, however.

 

[jwin615]

I am pretty sure it is correct at 4.7k

Correct me if I am wrong, however.
View attachment 84624View attachment 84625

Are you using 5% resistors?
I read it as gold and brown reversed for 1%.
Yellow, purple, Black, Gold, Brown
But if it's brown brown, your good. Hard to see on the phone, and in general.

 

[jwin615]

Looked like 2 different shades here...

 

[noak]

Are you using 5% resistors?
I read it as gold and brown reversed for 1%.
Yellow, purple, Black, Gold, Brown
But if it's brown brown, your good. Hard to see on the phone, and in general.

Brown brown. Multimeter also confirms 4.7k.

 

[Robert]

Turn the Gain pot all the way down and measure the resistance between pins 1 and 2 of IC2 (the upper opamp).

Then turn the Gain pot all the way up and measure again.

 

[noak]

Turn the Gain pot all the way down and measure the resistance between pins 1 and 2 of IC2 (the upper opamp).

Then turn the Gain pot all the way up and measure again.

While the circuit is powered or unpowered?

 

[noak]

Turn the Gain pot all the way down and measure the resistance between pins 1 and 2 of IC2 (the upper opamp).

Then turn the Gain pot all the way up and measure again.

Unpowered:
Gain all the way down: 4.4k
Gain all the way up: 51.1k with red probe on pin 1 and black probe on pin 2; 90.6k with black probe on pin 1 and red probe on pin 2.

 

[Robert]

It looks like you have a 10K resistor installed for R5, which should be 1K.

 

[noak]

It looks like you have a 10K resistor installed for R5, which should be 1K.

View attachment 84627

I am using R5 as 10k because I am using a C100k Dual instead of a C10K Dual:

 

[Robert]

Hmm.... Did you insulate the dual-gang pot?

It's sitting right behind the gain stages in question...

 

[noak]

Hmm.... Did you insulate the dual-gang pot?

It's sitting right behind the gain stages in question...

I put some electrical tape over the pot and on the pcb. However, I imagine it could have easily puncutred. I guess I'll take it out and double check and upload some pictures of the back side.

Any recommendations besides electrical tape for insulation? Dust cover wouldn't fit on the dual gang pot.

 

[noak]

Hmm.... Did you insulate the dual-gang pot?

It's sitting right behind the gain stages in question...

In addition, is there a way to check this with a multimeter before I pull the pot off?

 

[Robert]

It's a little tough to measure because any combination of component leads under the PCB could be shorted together (or to ground) by the metal casing of the pot.

It'd definitely be worth making sure there is something substantial in there, when it comes to troubleshooting threads if there's a dual-gang pot it's almost always the dual-gang pot.

 

[Nic]

And there is almost always electrical tape involved ...

 

[noak]

It's a little tough to measure because any combination of component leads under the PCB could be shorted together (or to ground) by the metal casing of the pot.

It'd definitely be worth making sure there is something substantial in there, when it comes to troubleshooting threads if there's a dual-gang pot it's almost always the dual-gang pot.

That seemed to have done the trick. Just put some cardstock paper underneath the dual gang pot because I didn't have a solder sucker to take it off. Thanks for your help!

 

[jwin615]

That seemed to have done the trick. Just put some cardstock paper underneath the dual gang pot because I didn't have a solder sucker to take it off. Thanks for your help!

A chunk of old gift card or similar material works well. No long-term guarantees on cardstock. A little dab of liquid tape to hold it in place and Bob's your knuckle.

 

[noak]

A chunk of old gift card or similar material works well. No long-term guarantees on cardstock. A little dab of liquid tape to hold it in place and Bob's your knuckle.

I'll keep that in mind if the cardstock fails at some point. Thanks!