Author Topic: Mmmmmmmm.... Amplifier grounding  (Read 3145 times)

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Offline icon

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Mmmmmmmm.... Amplifier grounding
« on: June 03, 2012, 09:50:22 pm »
Hi

I built an audio amp a few years ago, which consists of a toroidal transformer, a couple of independent unregulated 30V power supply modules and a couple of circuits built around the TDA2030. The circuits for the latter are pretty much the reference circuit from the datasheet for a single supply.

When I first made it, it hummed like billy-o. I fiddled with a bit, to no effect, and it then went under the bench for want of time and enthusiasm.

So, 15 years later I pulled it out from under the bench. Still hums; time hasn't improved it. I'd really like to get it working properly before I bin the TDA2030 in favour of something made this century.

Can you give me some ideas about what bits to connect to what, to shut the damn thing up? It's mounted in a metal case which is connected to mains earth and the signal leads are shielded. Plugging a signal source (my mobile phone, which I consider quite brave!) into it actually quietens it a fair bit.

Thanks
John
 

Offline david77

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Re: Mmmmmmmm.... Amplifier grounding
« Reply #1 on: June 03, 2012, 10:16:28 pm »
Grounding any kind of audio amp can be a bit tricky. Do you have circuit diagram and photos of your build? That would help immensly.

You said your case is connected to mains ground, is the signal ground also connected to the case? That can be problematic.
Also I suggest you read this article: http://sound.westhost.com/earthing.htm
and basically everything here: http://sound.westhost.com/articles.htm#s4

I've built a couple of TDA2030 amps and never had much trouble with them, even though I've always used veroboard - which certainly isn't ideal.
If you decide to use something newer instead nobody can guarantee you it won't hum again if theres a general error in your ground connections or construction ;).
 

Offline icon

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Re: Mmmmmmmm.... Amplifier grounding
« Reply #2 on: June 05, 2012, 09:30:35 am »
Hi

I had a bit of a play with the amplifier circuit, and got it to behave by moving some wires around. Because it was built from discrete modules, the circuit originally looked like this:



After a bit of reading, I decided to move the speaker's ground off the amplifier board, back to the power supply board. Also by trial and error I discovered that connecting the input cable screen to the amplifier ground at one end and to the chassis (and therefore earth) at the other seemed to be quietest. I'd still be glad glad to hear other suggestions as to how to do it properly. Other than "put a match to it".



There was a tiny bit of residual hum, but that disappears when you connect a signal source (my Squeezebox), leaving only a bit of hiss that you have to press your ear to the speaker to hear. The actual circuit is this:



And this is what it looks like:



Of course now I discover why they put inputs and speaker terminals on the back of amplifiers. Still, when I make the next one... I fancy an LM3886...


Cheers
John
« Last Edit: June 05, 2012, 09:33:31 am by icon »
 

Offline Tube_Dude

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Re: Mmmmmmmm.... Amplifier grounding
« Reply #3 on: June 05, 2012, 02:34:54 pm »
Hi

The ground side of the Zobel network, R6 C4, must be connected to the power supply board ground too.  ;)
Jorge
 


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