Dr. Phybes assistance – no phasing (solved)

[Anonymous]

Hi all,

So I got my Op Amp issues sorted out. I’m getting sound coming out with the effect on but no phasing. I used an audio probe and confirmed I’m getting both a dry signal (at R17) and wet signal (at R18). I’ve tried carefully adjusting TR1 from 0v to 4.2v (Vb) and what’s interesting is I can hear the sound change as I sweep TR1 but doesn’t change over time on its own. Also changing the Rate (P1) doesn’t seem to change anything. This makes me think there’s something wrong with my LFO circuit. I’ve confirmed P1 is working and checked continuity between P1 pin 2 and R24 and P1 pin 3 and IC3 pin 6.

My voltages on IC3 (TL061) are

2 – 9v

3 – 9.1v

6 – 8.8v

Va – 9.4v

Vref – 4.2v

The voltages at IC3 don’t seem right but I’ve checked the values for R25, R26, R27, R28 and they are correct. I’ve reflowed the socket resistors and tried replacing IC3 with a fresh TL071 and I get the same voltages at those pins.

Am I missing something obvious? Anything else I should check? I’ve run into a wall here. Thanks.

[Billy]

What are the voltages on IC3 empty socket

[Anonymous]

Welp, stupid me. Thanks for the suggestion to test the empty socket. Your gentle nudge helped to save the day (again).

I had neglected to test the voltage on pin 4 before. When I tested it empty it showed 9.4v when it was supposed to be at ground. After a bit of continuity testing and then going back to the build doc I realized there was a note that I had missed that talked about making sure both ground pads MUST be connected.

Here’s the one I missed:

It also explains why my LED flasher wasn’t flashing. DUH if I had started trouble shooting that instead of the effect I would have figured it out in a second. Lessons learned.

This thing sounds awesome! Thanks again, Billy. Another one SOLVED!

BTW – my correct voltages (empty socket) are:

2: 7.7v

3: 5.5v

4: 0v

6: 7.86v

7: 9.4v (Va)

[Billy]

I thought you had it working with the previous TL074 swap

I’ll have to admit I missed it too and that’s after a few debugs where the 2nd ground not being wired was the problem so how I missed it I’ll never know!

But glad you got it fixed

When you get high readings on op amps and the empty socket like that it’s usually a faulty IC,  bad ground, solder bridge / short, bent IC pin or IC not located properly in it’s socket or dry solder joint

Here’s a link to Tonmanns op amp testing guide

https://drive.google.com/file/d/1pG8H8lyj9jUDFTqtcJ1QbHNTldIrPnP3/view?usp=drivesdk

For example If you’d have taken a resistance reading from pin 4 to ground you would have got an infinite ohms reading telling you it was open circuit ie no connection, so a very handy guide

 

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