Greetings fellow worker bees and electronics wizards! I just had ANOTHER one of these come to my bench (yaaaaaay) So everything except V1 is lighting up. No sound when plugged into the input. So I turned the effects loop on and plugged into the effects return. Bam! I got sound! And pretty decently clean luscious tube sound for a BV. Anyway. So I take the preamp tubes out and I noticed some cracked solder at pins 4 and 5 so I reflowed all the tube socket pins. Aaaaaand we have a working preamp now! BUT!!! There is this.... unGodly loud white noise/ hum that only gets louder as one increases the volume. (As is expected) When I plug into the effects return it isnt there. And, plugged into the input, the clean channel in the preamp sounds....anemic compared to direct into the effects return. Any ideas? Has anyone seen this before? The dirty channel sounds good but that white noise/hum is just way too overbearing. Dude that owns it says he can just use a noise gate but I REALLY dont want to give him back an amp that is obviously not fully repaired. Thanks for looking guys! And gals!
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Crate BV120H (older blue tolex) noise problem
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A good SIDAC should have no effect at all below its breakover voltage (120V). That high voltage across the heater winding would require a lightning stroke.
If you're curious, lift one end and see if it makes a difference.
What resistance do you measure between V1 pin2 and ground with nothing plugged into input?Last edited by Helmholtz; 04-20-2021, 04:40 PM.- Own Opinions Only -
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I might try lifting it. Would unplugging and re-plugging the speaker while shifting the impedance do that? Apparently dude did that. I just talked to him. I am FULLY aware that is bad. Very bad. But would that have killed the sidac? It didn't affect the OT apparently. The power tubes sound quite delicious.
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Originally posted by Danglin' Fury View PostI might try lifting it. Would unplugging and re-plugging the speaker while shifting the impedance do that? Apparently dude did that. I just talked to him. I am FULLY aware that is bad. Very bad. But would that have killed the sidac? .
Also a fault in the heater supply might cause buzz but not white noise.
Check if the R106/R107 are good and measure DCFIL1/2 voltages.
But I actually suspect your input jack switching contacts.- Own Opinions Only -
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Sorry if I missed it but I didn't see if you tried a different tube in V1 position?
I had one of these with a SIDAC problem, I think it was hum, but some kind of noise. Like Helmholtz said, just disconnect one of the legs to see if it is the cause of the noise.Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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I tried a different tube in V1... no joy. I replaced the input jack... no joy. It sounds like... white noise bit it ebbs and flows, if that makes any sense? I can hear it with all the volume controls off and even when I pull the cable out of the input. What about those opto isolators? Why do they even have those in there? Could the one around V1 be causing my issue?
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Originally posted by Helmholtz View PostNo answers - no fun.
I prefer a methodical approach by eliminating possible causes starting from the input.
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I will continue when I have answers to my pending questions.
Also it's not clear how control settings influence the noise. Is it silent with volumes a zero?
I could imagine that a leaky coupling cap causing DCV across an Opto LDR might cause strange noises.- Own Opinions Only -
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Sorry man. I have been running ragged between my day job and my Mom breaking her hip, I'm just now seeing all the questions you asked. I will most certainly have the answers to said questions after I leave work today. I will have a meter in that amp around 6:30. P.M. Central time (U.S.) and thank you again for all your help.
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Originally posted by Helmholtz View PostI will continue when I have answers to my pending questions.
Also it's not clear how control settings influence the noise. Is it silent with volumes a zero?
I could imagine that a leaky coupling cap causing DCV across an Opto LDR might cause strange noises.
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