Need some help troubleshooting, what is breaking my ICs

[bobert]

Hello everybody!
I recently finished soldering a pcb and its been giving me some trouble for about a week. I tried troubleshooting it but at this point I think the problem is deeper than my understanding of electronics.

The circuit is a Darkglass Microtubes B3K, a distortion for bass. Here's a link to the layout:
https://tagboardeffects.blogspot.com/2017/05/darkglass-microtubes-b3k.html

Instead of the two J201 I have 2n5458 which I think should be an OK replacement, but correct me if I'm wrong.

The problem is that when the pedal is engaged, the distorted tone is only there when you really slam the strings and then it cuts out like a noisegate after the volume decreases past a certain point.
If i set the blend pot to half, the clean tone will always be there regardless of the volume but the distorted tone will cut in and out.

I followed the advice on http://www.geofex.com/fxdebug/fxdebug.htm for blatty and gated sound.

It says that the situation is a dead giveaway that something is not properly biased. However I'm still unsure what and where, nor does the layout call for any trimpots or biasing.
I've included the measurements on all the pins of the fets and ICs.


Power Supply = 9.19v

Top Left 2n5458
D = 8.93v
S = 6.05v
G = 4.26v

Bottom Left 2n5458
D = 6.05v
S = 1.28v
G = 0v

TL072
1 = 4.50v | 8 = 8.93v
2 = 4.50v | 7 = 7.23v
3 = 4.06v | 6 = 4.52v
4 = 0v      | 5 = 4.20v

TL074
1 = 3.8 to 4.0v  | 14 = 4 to 4.2v
2 = 3.8 to 4.0v  | 13 = 4.09v
3 = 3.8 to 4.0v  | 12 = 4 to 4.12v
4 = 8.94v        | 11 = 0
5 = 4.2v       | 10 = 4.03v
6 = 4v              | 9 = 4.10v
7 = 3.95v |       8 = 4.06v

4049
1 = 8.87v | 16 = -0.02 to 0.04v
2 = 4.55   | 15 = 8.80v
3 = 4.59v | 14 =  0
4 = 8.83v | 13 = -0.02 to 0.05v
5 = 0v      | 12 = 8.8v
6 = 8.8v   | 11 = 0v
7 = 0v | 10 = 8.8v
8 = 0v | 9 = 0v

(note the right side of the TL072)

I traced the input signal like the following screenshot:




everything is fine with the signal when it reaches the gate of the bottom 2n5458, what the fet does with the signal is beyond me but i assume its to do with the switches for treble and bass cutting/boosting. The signal then continues to the 2nd input of the TL072 where I found the problem to be.

Probing the respective output (2nd) of the TL072 gives the blatty/gated sound, or rather just harsh noise when the strings are strummed hard. And silence when the strings are strummed soft.
Probing the input is just the clean sound of the bass, but it's pretty quiet.(I don't know how big of a role the volume has at this point)

This obviously indicates a faulty IC and I've tried a replacement with the following voltages:

***Replacement TL072
1 = 4.5v | 8 = 8.95v
2 = 4.5v | 7 = 6.4v
3 = 4.5v | 6 = 4.49v
4 = 0v | 5 = 4.17v


Obviously both are bad, my question is if I put in a third (presumably working) one will it break and behave like these two?
Or is it just a coincidence that I have two TL072s whose left side works perfectly, but the right side is dead on both.

What could be the issue causing this?
I am going to get a new TL072 but until then I want to get a second (third/fourth/fifth...) opinion on this.

[Neil mcNasty]

Probably not your issue, but still good knowledge:
CMOS chips are know to be sensitive to electrostatics.
Example: wearing a wool sweater while soldering is not a good idea... It can kill the CMOS chip.
Some wear anti-static bracelets while working with CMOS IC's

The J201 has a louder output than most other JFet's, so you could try swapping to something closer to the J201 specs. It could be an issue with not passing over the threshold needed for the next gainstage.
CMOS are known for it's gating capability as far as I have seen in other circuits (parasit studio builds comes to mind)

If any of this does not solve your issue, at least I hope that it might help in a future build!
Cheers! Hope you solve your issue!