Proposition Squealing

[VanWhy]

I get a bad squealing/whistling when I turn the gain up at all on the Proposition Distortion. Gain knob all the CCW it does not squeal.

At first I thought it could be the charge pump but it makes the noise without it in.

Could it be bad biasing with Q1? I populated RB1 and RB2 and R13 exactly from the build doc. I just most of the components. I first wanted to ask if it was anything with that JFET first then I can start double checking values of components.

Video attached. Sorry camera is moving a bunch.

Proposition Squealing Video

 

[Cybercow]

I get a bad squealing/whistling when I turn the gain up at all on the Proposition Distortion. Gain knob all the CCW it does not squeal.

At first I thought it could be the charge pump but it makes the noise without it in.

Could it be bad biasing with Q1? I populated RB1 and RB2 and R13 exactly from the build doc. I just most of the components. I first wanted to ask if it was anything with that JFET first then I can start double checking values of components.

I've built dozens of Proposition pedals and never had one squeal like that. I won't be the JFET (Q1). My best guess would be the opamps being used. I recognize the date codes stamped on four of those TL072CP opamps and they are from a known bad batch. (I discovered them first from Tayda.) Change out the opamps and the squeal should go away.

For future reference, here is a short list of known bad batch date codes for TI TL072CP opamps . . . . .

Known Bad TL072CP Date Codes:
18MDSHY
14AP8NM
07A5L8QM
22ALE3M

 

[VanWhy]

I've built dozens of Proposition pedals and never had one squeal like that. I won't be the JFET (Q1). My best guess would be the opamps being used. I recognize the date codes stamped on four of those TL072CP opamps and they are from a known bad batch. (I discovered them first from Tayda.) Change out the opamps and the squeal should go away.

For future reference, here is a short list of known bad batch date codes for TI TL072CP opamps . . . . .

Known Bad TL072CP Date Codes:
18MDSHY
14AP8NM
07A5L8QM
22ALE3M

Good call. I did get them from Amazon so they are likely bunk. That is pretty easy so I'll try that first. I got some good ones from Mr. PPCB so I trust those ones.

 

[VanWhy]

That was it. Bad TL072's. Swapped out and it rules. Thanks @Cybercow