Author Topic: NomNom v.2020 passes unaffected signal when engaged.  (Read 379 times)

Robusto

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NomNom v.2020 passes unaffected signal when engaged.
« on: September 27, 2020, 05:13:00 PM »
Hello,

I am working on the latest version of the NomNom (Phase 90). I am getting a clear signal when engaged but not phasing. I have been through the board with an audio probe and the clean signal/rate pot section seems to be the problem. I have signal at the emitter of Q1, but when I move on to R25, and the other spots in that section (including the right side of IC1), I get a faint heartbeat type flopping noise that speeds and slows when I adjust the pot. The left side of IC1 is passing signal as normal, along with all the other two ICs. I've tries adjusting T1 with no change. Voltages seem okay. I've tried 4 different TL072s in IC1 with no change. Hoping this is a common thing that someone will notice right away. Thanks!

1 Spot power supply at 9.42v

On all three ICs  1-3 and 5-7 are  3.85v, 4 is 0 and 8 is 9.16
Q1 is 2.27C 2.8B 3.85E
Q2-5 all three pins are at 3.85 or very close to it


 

cooder

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Re: NomNom v.2020 passes unaffected signal when engaged.
« Reply #1 on: September 27, 2020, 05:22:56 PM »
The sweet spot on the trimmer is a pretty small window often on these, I would give it another go and take your time to check the trimmer very slowly bit by bit.
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jimilee

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Re: NomNom v.2020 passes unaffected signal when engaged.
« Reply #2 on: September 27, 2020, 06:58:44 PM »
Did you use matched 2n5457s?


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Robusto

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Re: NomNom v.2020 passes unaffected signal when engaged.
« Reply #3 on: September 29, 2020, 08:49:35 AM »
I have come back to end this thread and accept my badge of shame. Yes, I did have a matched set of JFETs. Unfortunately they were 2N5952s that I got from guitarpcb.com and I forgot to invert them on the board. Case closed.  :-[

jimilee

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Re: NomNom v.2020 passes unaffected signal when engaged.
« Reply #4 on: September 29, 2020, 09:43:14 AM »
Nice


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Haberdasher

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Re: NomNom v.2020 passes unaffected signal when engaged.
« Reply #5 on: September 29, 2020, 10:04:41 AM »
Another happy ending
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