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Old 7th April 2011, 11:03 AM   #1
Ivchikx is offline Ivchikx  Latvia
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Unhappy Hum on TDA7294

Bought this 4x TDA7294 kit from ebay & hooked it up to 2x24 600VA toroidal transformer. When I powered it up, it works, but also produces hummmm sound in speakers with & without anything connected at input. What could be a problem?

Also, how to increase bass response?

Last edited by Ivchikx; 7th April 2011 at 11:27 AM. Reason: added info
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Old 27th June 2011, 04:23 PM   #2
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Default Increase the value of Bootstrap Capacitor, It should be 110uf minimum 220 uf better

Quote:
Originally Posted by Ivchikx View Post
Bought this 4x TDA7294 kit from ebay & hooked it up to 2x24 600VA toroidal transformer. When I powered it up, it works, but also produces hummmm sound in speakers with & without anything connected at input. What could be a problem?

Also, how to increase bass response?
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Old 3rd July 2011, 12:26 AM   #3
gootee is offline gootee  United States
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Quote:
Originally Posted by Ivchikx View Post
Bought this 4x TDA7294 kit from ebay & hooked it up to 2x24 600VA toroidal transformer. When I powered it up, it works, but also produces hummmm sound in speakers with & without anything connected at input. What could be a problem?

Also, how to increase bass response?
A picture of your setup would probably help.
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Old 15th October 2011, 08:27 AM   #4
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Hello all!
If you can a little explanation, what serves bootstrap electrolytic capacitor C5=22uF at TDA7294?
(see datascheet for TDA7294)
thanks

Last edited by formula 22; 15th October 2011 at 08:31 AM.
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Old 15th October 2011, 09:33 AM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Ivchikx View Post
.......... it works, but also produces hummmm sound in speakers with & without anything connected at input. ...............how to increase bass response?
increasing the Bass response could make the Hum sound Louder.

You almost certainly have an error in the grounding or in the PSU.
Read
Audio Component Grounding and Interconnection - diyAudio
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regards Andrew T.
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Old 15th October 2011, 02:12 PM   #6
Einric is offline Einric  United States
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I purchased one also a while back and it hums too.
I enjoyed the strong bass performance but it was really too annoying.
I moved on, I'd love to see what you discover.
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Old 15th October 2011, 03:50 PM   #7
gootee is offline gootee  United States
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Quote:
Originally Posted by Ivchikx View Post
Bought this 4x TDA7294 kit from ebay & hooked it up to 2x24 600VA toroidal transformer. When I powered it up, it works, but also produces hummmm sound in speakers with & without anything connected at input. What could be a problem?

Also, how to increase bass response?
Click the image to open in full size.

Make sure that the AC pair is twisted tightly together, right up to the screw terminals. Also twist tightly together your input pairs, right up to the terminal block. And ditto for your output pairs. (Or use shielded twisted pair cable.)

Make sure none of those three pairs get near each other, or any other part of the circuit.

What are the values of the two large-ish red box capacitors, near the input terminal block? And what are the values of the six electrolytic capacitors that are in a line, near the four chipamps?

Last edited by gootee; 15th October 2011 at 03:54 PM.
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Old 22nd October 2011, 05:26 PM   #8
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What is the input load?
Typically either a potentiometer or just some resistors?

If its running without an input load, well that's going to make noise.
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Old 22nd October 2011, 06:02 PM   #9
Ivchikx is offline Ivchikx  Latvia
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I've moved on to APEX TDA7294 amp design, works perfectly. But, if it is possible to debug this one, why not.

If memory serves, large-ish red box caps are 2.2uF Small ones are 22uF.

About twisting cables etc - it isn't that kind of hum. It's constant, quite loud and annoying. Maybe theese TDA7294 chips are fake or the PCB design is bad one.
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Old 24th October 2011, 09:22 PM   #10
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Hi there,

I have the same board with exactly same problem as you described. I think the amp is self-oscillating, it is dependent on what is connected to the input and also on type of PSU. To me it is something between the hum and a high freq buzz. The heatsink become quickly hot (in comparison with 3875/3886 gainclones).
On PSU side I've tried different R-Core and toroidal transformers (2x15, 2x18 and 2x24V, 200-500VA) and also replaced the transformer with the 2x24V/6A switching power supply.
The type of transformers has very little influence, but with the SPSU the hum was almost gone, the buzz were still there.
I've tried then to add more smoothing caps (2x20,000uF/40V) but it had again a little or no influence on the humm/buzz.
Maybe a wrong PCB design/wrong parts? - I haven't had a chance to investigate deeper for the moment...
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