Ok, so first I would like to apologise if I am in the wrong category. I really could use some help.
I wanted to upgrade my amplifier, so I opened the box. I just want to emphasise, that I had made everything myself, just not the amp, it was a cheap one from ebay. The upgrade should have been simple, to switch the old amp into a tda7492, I think it is called. It is a fully built amp that I have bought off of ebay. I have also a preamp in this that I built myself. All of this is run off of two transformers. One is around 14-15v ac, this is the big one for the amp. The other one is 2x12v ac or something similar.
The amp worked great before the atempted upgrade. Had only a slight mains hum, because it was cramped. Could barely hear it. Now the problem is that it plays, but it has a very loud buzz. On both channels. The volume control on the preamp has no effect on the buzzing. The music plays though, just not well, through the buzz.
First I thought that this is a grounding problem, so I remade all the wiring. This did not help. Maybe I'm just bad at grounding, I'm not sure.
I then checked the preamp and the amp separately. They both worked fine, no problems. I tested the preamp through sprakers, so maybe I just did not hear the buzz, but I don't think it was there.
When I checked the voltage on the supply to the amp there was 18v dc and also 36v ac alongside that. I don't think that that is good 😀 I checked the preamp and it had alongside the dc 26v ac on both voltages, negative and positive leads. I thought that the diode brigdes broke, so I replaced them, but the same thing persists. My decoubling capacitors on the preamp are beginning to inflate, I think it is because of the too high voltage, because the caps are only 25v rated. The so called power supply is just the diode bridges connected with some decoupling capacitors.
I measured the output of the amp to the speakers. Across one output and ground There was 5v dc and 10v ac. The other output was 0v. I had no sound playing. I don't know what is the problem there. Please advise. Thank you 🙂
I wanted to upgrade my amplifier, so I opened the box. I just want to emphasise, that I had made everything myself, just not the amp, it was a cheap one from ebay. The upgrade should have been simple, to switch the old amp into a tda7492, I think it is called. It is a fully built amp that I have bought off of ebay. I have also a preamp in this that I built myself. All of this is run off of two transformers. One is around 14-15v ac, this is the big one for the amp. The other one is 2x12v ac or something similar.
The amp worked great before the atempted upgrade. Had only a slight mains hum, because it was cramped. Could barely hear it. Now the problem is that it plays, but it has a very loud buzz. On both channels. The volume control on the preamp has no effect on the buzzing. The music plays though, just not well, through the buzz.
First I thought that this is a grounding problem, so I remade all the wiring. This did not help. Maybe I'm just bad at grounding, I'm not sure.
I then checked the preamp and the amp separately. They both worked fine, no problems. I tested the preamp through sprakers, so maybe I just did not hear the buzz, but I don't think it was there.
When I checked the voltage on the supply to the amp there was 18v dc and also 36v ac alongside that. I don't think that that is good 😀 I checked the preamp and it had alongside the dc 26v ac on both voltages, negative and positive leads. I thought that the diode brigdes broke, so I replaced them, but the same thing persists. My decoubling capacitors on the preamp are beginning to inflate, I think it is because of the too high voltage, because the caps are only 25v rated. The so called power supply is just the diode bridges connected with some decoupling capacitors.
I measured the output of the amp to the speakers. Across one output and ground There was 5v dc and 10v ac. The other output was 0v. I had no sound playing. I don't know what is the problem there. Please advise. Thank you 🙂
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My thoughts too. And in the wrong forum section.
A quick scan through tells me that he fiddled with it, and now it puts serious AC hum out and has bulging PSU caps. My advice would be to ask someone else who knows what he is doing to repair it.
A quick scan through tells me that he fiddled with it, and now it puts serious AC hum out and has bulging PSU caps. My advice would be to ask someone else who knows what he is doing to repair it.
Moved to Class-DI would ask someone, but I don't have the means to, don't know such people and professional help is not worth it. This amp not very expensive and homemade. I just really don't want to remake everything. I don't have the time. The problem is very strange at least for me. Thank you for all the help. You too DF96, great help introducing to the forum and giving valid advice with quick replys 🙂
You should disconnect everything and start checking from the beginning. Check the output of each transformer. Then check the output of each rectifier - assuming you have a rectifier for the pre-amp and a separate rectifier for the amp.
You are probably connecting the ground of the preamp to the ground of the amp, so make sure that those two grounds are wired to be at the same potential.
It would also help if you can post a photo or two of your setup and a diagram of how things are connected (or supposed to be connected)
You are probably connecting the ground of the preamp to the ground of the amp, so make sure that those two grounds are wired to be at the same potential.
It would also help if you can post a photo or two of your setup and a diagram of how things are connected (or supposed to be connected)
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