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Temp "Time Format" issue Fix in Discussions

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Messages - Fdesalvo

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OK for posterity's sake, looks like the master is controlled by a TC9176P chip @ U13.  I'm just not sure how I damaged the board by installing the socket.  All traces are in tact.

I'm used to tracing signal flow through potentiometers, so I'm at a loss with where the master sits in the circuit.  I'm sure the issue is pre-master, so can you tell me where the master's circuitry is on the circuit board?

Anyone else have any ideas?  Desperado!

Hey there.  I just put the 5532 back in and same issues. Noises persist even with the header removed from the tube board and u4 removed.

Preset 6 for example.  Loud mororboating. Master led illuminated. OD1 no impact. Od2 no impact. Master at 9.5. Adjusting down to zero changes pitch of noise and silences it at the bottom, but master led stays lit.   

Ha!  My apologies, it's an MP-1.  I understand I can add a small cap in parallel with the IC's fb resistor, but that's not worth the trouble.  I'm going to put in a lower noise version of the same opamp back into the socket.  I was perplexed because the OPA2604 is part of the noise mod and suspected something was wrong in this particular MP-1.

Thanks for taking a swing!

I posted this in the wrong area prior.

After installing a socketed OPA2604 into U4 the following occurred:

-On some patches, Master and EQ LEDs would light up. On some, the master led would turn off after lowering the master via the front panel.
-No changes in noise level when adjusting OD1 via the front panel
-Low, pulsating bass tone/oscillations on some patches

After installing the socket, I used a meter to confirm continuity between the pins and traces and also between the opamp legs and traces. I have a 4 pack of new BB/TI OPA2604AP’s and each one responded the same way.

Any idea of similar experiences?

Thank you for your advice. I’ll give that a whirl.

Yes these are 2SK364 (in rare cases 363), but why do you want to change these?
Same with Q3/4, no need to change them, if they work they work.

Thanks for the response. I can’t imagine how busy you are.  I’m looking for other areas to reduce background noise if possible. 

Hi, all.

Long time lurker. So glad this site iis back up.

Ive got a v2 MP1 and am refreshing the caps and have moved on to the fets/jfets/etc. I have a couple of questions due to my ignorance of all things FET and the dearth of info for the v2 online.

1. I am unable to locate replacements for Q1/2: K364 GR91. Are these “2SK364’s” that I’m seeing referenced elsewhere?  I have some updated equivalents on hand (LSK170’s) if this is the case.

2. Q3/4 are MPSA92’s. I have these on hand, but is there a higher performing equivalent out there?

Many thanks for the help/education. I build all analog vacuum tube amps and do restorations on a variety of preamps, but venturing into the digital/ss realm has been eye-opening, if not exciting.

Best regards,

“Ruining good moments since 1975.”

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