[AVAILABLE] TTSH V4 Build Thread

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resynthesize
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Re: [AVAILABLE] TTSH V4 Build Thread

Post by resynthesize » Thu Jan 14, 2021 12:56 am

ebfx wrote:
Wed Jan 13, 2021 7:23 pm
resynthesize wrote:
Wed Jan 13, 2021 10:51 am
fallout wrote:
Wed Jan 13, 2021 10:20 am
It looks like you have a reversed diode to the right of the LM301 at the top.
:doh: how did i not see that?! I’ll fix after work today and report back. thank you!
I'm curious to know if this solves your problem. The diode in question is part of the ADSR circuit so I wouldn't expect much effect on the AR operation.

I've been trying to track down a similar problem with my v4 build for a few nights now. After reviewing the v3 schematics and spending a few nights probing my board, I narrowed the problem down to the 2N5460 (Q4) in the ADSR section. I pulled Q4 from the board and put it in my (admittedly very cheap) transistor checker and it came back as a BJT instead of a JFET. So, I replaced both 2N5460's in the ADSR/AR section and everything started working as expected. You may want to check if you have a similar problem.

I checked the markings on the original transistors from Synthcube and they are definitely labeled 5460, so I suspect they either got a bad batch or I was a bit too heavy-handed during installation. My replacement NTE 2N5460's have a different pinout (S-D-G instead of D-S-G) so I had to do a bit of pin swapping on the board, but they read as P-channel JFET's on my tester and now my circuit is working like it is supposed to.
I just replace the diode and the ADSR behavior is different but still not right. The release slider is still just generating a fixed voltage at the ADSR output when I adjust it as well. Thank for the tip on the 2N5460, I'll pull that next and test it after I go through and verify the rest of the components with the unpopulated pcb photo that @fallout helpfully provided.

edit: I just pulled a 2N5460 and tested and sure enough it tests as a BJT-PNP as well. i sourced mine from utsource originally. I'll order some replacements and see how it goes. thanks!

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fallout
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Re: [AVAILABLE] TTSH V4 Build Thread

Post by fallout » Thu Jan 14, 2021 8:16 am

Thanks for the information on the 2N5460's, ebfx. it'll be something to look out for once I complete my build and begin testing. My parts are from Synthcube, FWIW.

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