Lead Solder Buzz

[jimilee]

This is what it does past about 7 o'clock. I still have distorted audio and this.

https://soundcloud.com/jimi-lee-2%2Fnew-recording

 

[jimilee]

@jimilee did you put a wire or a cap between pins 1 and 2? I thought you had meant a wire—which would essentially turn that stage into a non-inverting voltage follower (i.e., a buffer).

Wire.

 

[jimilee]

Ok, update. I removed the jumper. It did serve a purpose, it narrowed down the problem area to a hand full of parts. I replaced the 100P with a silver mica, no joy. I removed the 1uf, no buzz. I tried a non polarized and a tant 1 uf, got buzz. I connected the side of the 6k8 that originally connected to 1uf, to ground. Still no buzz. So as it stands no buzz with the 1uf removed. I’m getting correct gain control. What is the 1uf (c7) doing?

 

[benny_profane]

What is the 1uf (c7) doing?

It’s part of the RC network making an active high pass filter. Similar to what’s going on with a RAT.

EDIT: it strikes me as odd that that would cause oscillation. You’re filtering out low frequencies (Fc=23Hz) and proving a path to ground for DC voltage so it’s not amplified.

 

[music6000]

Ok, update. I removed the jumper. It did serve a purpose, it narrowed down the problem area to a hand full of parts. I replaced the 100P with a silver mica, no joy. I removed the 1uf, no buzz. I tried a non polarized and a tant 1 uf, got buzz. I connected the side of the 6k8 that originally connected to 1uf, to ground. Still no buzz. So as it stands no buzz with the 1uf removed. I’m getting correct gain control. What is the 1uf (c7) doing?

Did you test to see if C7 + pad is going to Ground ?

 

[jwin615]

It’s part of the RC network making an active high pass filter. Similar to what’s going on with a RAT.

EDIT: it strikes me as odd that that would cause oscillation. You’re filtering out low frequencies (Fc=23Hz) and proving a path to ground for DC voltage so it’s not amplified.

The cap isn't oscillating. The mis match of the caps and resistors are causing the opamp to oscilate. See the link I posted to the ti article previously.
Could be stray capacitance in the pcb playing a part too.
I wonder if scaling the values and/or altering that part of the circuit layout would be a good idea.
Maybe even just rescaling the resistors in the feedback network would help.

 

[jimilee]

Did you test to see if C7 + pad is going to Ground ?

I did.

 

[jimilee]

The cap isn't oscillating. The mis match of the caps and resistors are causing the opamp to oscilate. See the link I posted to the ti article previously.
Could be stray capacitance in the pcb playing a part too.
I wonder if scaling the values and/or altering that part of the circuit layout would be a good idea.
Maybe even just rescaling the resistors in the feedback network would help.

Possibly. I’ll mess with it a little and look at changing some values.

 

[comradehoser]

I am looking forward to the conclusion of this exciting episode

 

[jimilee]

I am looking forward to the conclusion of this exciting episode

Me too.

 

[Giorfida]

Are you positive the toggle switch isn’t touching the bass pot legs? I know with mine it was touching and I saw it just before firing up. Made a fishpaper condom for the switch body so it didn’t touch the pot.
Not sure this is your problem but it’s cheap insurance form other issues.

 

[jimilee]

Are you positive the toggle switch isn’t touching the bass pot legs? I know with mine it was touching and I saw it just before firing up. Made a fishpaper condom for the switch body so it didn’t touch the pot.
Not sure this is your problem but it’s cheap insurance form other issues.

Yessir. I have foam tape under it.

 

[jwin615]

Any luck here @jimilee ?
Hoping to start my PCB in a week or two, depending on how my misadventures in etching 2.0 goes.

 

[jimilee]

Any luck here @jimilee ?
Hoping to start my PCB in a week or two, depending on how my misadventures in etching 2.0 goes.

Yessir, I bought a built one from a forum member, I give up. I’ve tried everything I know to do and that has been suggested.