Have always had this issue since I built the amp. On startup the right speaker will play static for about a minute before calming down. Left speaker is dead silent. When I built each channel of the amp and tested them separately; this issue wasn't present.
Static Sound
I've tried some troubleshooting steps. When I disconnect the RCA input at the terminal block to the amp board, it's dead silent.
I tried different RCA jacks and wires, same noise.
When I touch the RCA jack the noise goes away faster.
I've used star grounding and both channels are hooked up to the same point at ground on my PSU board. Only the right channel behaves this way.
When I built the amps I checked for poor solder connections and cleaned all the flux off very well, didn't have this issue when I first tested each channel.
The only thing I can think of is, soft start module being on that side of the chassis or something with the speaker protection circuit? Not sure where to start any help would be greatly appreciated as this annoyance causes me not to use the amp as often and I just stick to a smaller cheaper amp build I got from China that works very well.
Static Sound
I've tried some troubleshooting steps. When I disconnect the RCA input at the terminal block to the amp board, it's dead silent.
I tried different RCA jacks and wires, same noise.
When I touch the RCA jack the noise goes away faster.
I've used star grounding and both channels are hooked up to the same point at ground on my PSU board. Only the right channel behaves this way.
When I built the amps I checked for poor solder connections and cleaned all the flux off very well, didn't have this issue when I first tested each channel.
The only thing I can think of is, soft start module being on that side of the chassis or something with the speaker protection circuit? Not sure where to start any help would be greatly appreciated as this annoyance causes me not to use the amp as often and I just stick to a smaller cheaper amp build I got from China that works very well.
It does kinda behave like a cap issue because there's a time constant. Also if i turn the amp off and back on, it does this for a shorter period of time.
Im stumped because i tested all the caps before installing them. They're all good quality caps straight from the bom too. Since it's only 1 channel, I guess it can be narrowed down to a cap on that amp board?
This won't change anything but do you have a 'scope that you could use to view and characterise this noise? It might give you more clues in that minute, to what causes it and why it would then fade away.
I do have a scope, might try that but don't know if I'm experienced enough to interpret what's going on from that.
This is a great place to start thanks. I'm avoiding taking the amp off the heatsink as I don't have fresh heatsink compound at the moment, but I may need to. C1 is a film cap, going to try heat and cold spray on it to see if it changes symptoms. Also I'll try disconnect a few things such as soft start and speaker protect board. Thanks a lot for your help 😀
Did you use two separate soft start modules, one per each channel? Or is it a common one for both channels? If so, where does it's ground relate to?
Best regards!
Best regards!
There's one soft start circuit connected to ac and the transformer. It is a floating ground not connected to chasis. I made this long ago, but I remember there being complaints about the design. The small yellow disk cap is not in circuit the way its connected right now if i remember correctly. It just goes to one pad that isnt connected to the ac input. Asked why the board was layed out like this' no responses.
Attachments
Sorry, I have to admit that I've muddled up a soft start with a speaker protection unit. So my question doesn't make any sense at all.
Best regards!
Best regards!
Static usually means a bad connection, perhaps inside a transistor. Cold spray is used to locate the offending area. Tapping things with a plastic handle may find it too. Perhaps you are heating up the Jack with your finger? Retouch (melt) the solder, with flux if possible.
No problem, i jumpered the softstart likely not the issue.
I was just about to update that the static returns when i blow air on the following area of transistors.
Attachments
I don't have any shorting plugs, but I used a jumper lead. The static is gone and replaced with hum that the longer lead wire is likely picking up.
Look for bad or loose connections on the input circuitry to Q1. Is the offset affected at all by the noise?
If it were a bad common connection there would be hum/buzz as well as the noise.
But also check the connection to the ground loop breaker.
Post some clear, close photos of all the input circuitry and the related wiring.
Seems like a solder joint, but also could be a defective part, including Q1.
But also check the connection to the ground loop breaker.
Post some clear, close photos of all the input circuitry and the related wiring.
Seems like a solder joint, but also could be a defective part, including Q1.
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The bias behavior is likely to be normal.
At this point the brute force method is best, since there are only a few parts.
Replace the input C1 first, because that's the biggest suspect.
If that doesn't work, next replace R1, R2, R3, R4, R5.
If that doesn't work, then next replace Q1/Q2 and C3.
At this point the brute force method is best, since there are only a few parts.
Replace the input C1 first, because that's the biggest suspect.
If that doesn't work, next replace R1, R2, R3, R4, R5.
If that doesn't work, then next replace Q1/Q2 and C3.
I think you're right. I was hoping it was something simple, I dread taking this chasis apart but might have to. Lol
I probed around with my scope but the second the probe touches anything on the input side the sound goes away.
Here is a link to the waveform on the output.
Noise waveform
Never saw anything like that.
Once I built a tube preamp, all new parts. Crackling noise in the phono stage.
After some irritation, the input plate resistor, a Dale metal film CMF55, was implicated.
I called the factory and had a discussion. Turns out someone handled the bare elements
with their hands before assembly. A whole lot were bad.
Once I built a tube preamp, all new parts. Crackling noise in the phono stage.
After some irritation, the input plate resistor, a Dale metal film CMF55, was implicated.
I called the factory and had a discussion. Turns out someone handled the bare elements
with their hands before assembly. A whole lot were bad.