Hi all, just got myself my first amp board to play with. It's the TDA7293 dual channel power amplifier board off ebay for the cheap and it's giving me buzz on both speakers especially on the right channel. I'm already using shielded input cable. I think it's related to ground loop and I'd figure I need a star ground? How do I fix this on this board? TIA!
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Hi all lol of course I installed the caps. They are in place just not in these photos The amp works properly playing music but there's a low hum when not playing music.
Hi
Look at the isolation behind the chip. on the pics - it looks like you get contact with the heat sink. please check if the chip is fully isolated.
chris
Look at the isolation behind the chip. on the pics - it looks like you get contact with the heat sink. please check if the chip is fully isolated.
chris
They're isolated (checked continuity before turned on) otherwise the negative rail would be on the sink and the chip would be toasted I supposed? Everything works fine except there's low hum I think it might be 60hz hum? It's nothing serious I can hear the hum maybe 10-15cm away from the tweeter but pretty quiet farther away.
I'm thinking maybe the AC input is too closed to the signal input? How do I star ground this board?
Updated photos with more info.
I'm thinking maybe the AC input is too closed to the signal input? How do I star ground this board?
Updated photos with more info.
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Its looks like (hard to see for sure) that the output of the rectifier goes to the chips before the filter cap. It needs to go to the filter cap first, and be routed from the filter cap to the chip, otherwise the charge-pulses between rectifier and filter caps will be imposed on the chip's rails.
Also the ground plane is labyrinthine on the reverse, hard to see how it routes, but the regular arrangement of components is a bad sign, placement is clearly not according to circuit function but visual aesthetics, quite possibly leading to capacitive pickup from the ac input which is way too close to the low voltage input section.
Also the ground plane is labyrinthine on the reverse, hard to see how it routes, but the regular arrangement of components is a bad sign, placement is clearly not according to circuit function but visual aesthetics, quite possibly leading to capacitive pickup from the ac input which is way too close to the low voltage input section.
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Yeah its a pretty awful layout. Normally you keep the AC supply as far as possible from the inputs but here they're right next to one another.
If you really want to salvage it and the other tweaks suggested don't do the trick, you could use a seperate board (or point-to-point) for rectification and filtering, feeding the DC supply rails where the + and - terminals of the bridge rectifier are currently. Put some smaller bypass capacitors (maybe 100μF?) where the main ones were.
If you really want to salvage it and the other tweaks suggested don't do the trick, you could use a seperate board (or point-to-point) for rectification and filtering, feeding the DC supply rails where the + and - terminals of the bridge rectifier are currently. Put some smaller bypass capacitors (maybe 100μF?) where the main ones were.
My suggestion is to move the rectifier bridge and smoothing reservoir capacitors to another PCB. Instead of the smoothing reservoir capacitors that currently reside on the amplifier's PCB, use two 10uF capacitors to decouple the effects of the rails and ground interconnecting wires.
ubergeeknz said:
You are breaking rule number 1.
Meaning of 'snap!'
Which means, you directed an insult to me, which is against the rules.
Shame on you.
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My apologies! I actually did not mean any offence at all. I meant it as in the child's game, Snap! ... As we had both posted the same thing at basically the same time (i.e. the cards match).
Snap (card game - Wikipedia)