Noise problems with TDA7294

Hi!
I just finished my gainclone, but I got some problems. I have two tda7294's in BTL running my sub. when the big heatsink becomes hot and the 7294's producing a lot of bass, I get some "krrrrrr" noises. this just happens when the heatsink is becoming hot (appr. 50 deg C or so)

Whats wrong? shound it make that kind of noise?
 

Arty

Member
2011-02-24 5:04 pm
1 heatsink, 1 IC.
consider, 0.7 C/W.
Ambient temp. 25 C.
power : 50 W
calc.:
50*0,7 = 35
35+25 = 60 celsius.
That is only 50 watt heat dissipated, barely i would consider it for 1 single lm3886.
majbe a jet-propelled supersonic fan can help you :D
but i would rather just get moooar of heatsinks like that.
one of those heatsinks + fan is okay for 1 chip.
 

Arty

Member
2011-02-24 5:04 pm
read the datasheets.
the tda 7294 has 50w dissipation at max.
it may seem to be a large heatsink.but it is not.
it can hold a single tda7294 cool without a fan.
if you are not pushing them too hard, then maybe i would risk 2 of them sharing the same sink.
but then again.. better to be sure.

---
update.
I did re-read the datasheet.
The lm3886 has a power dissipation of roughly 120 watt at max.
You have 2 of them, thats 240 watt.
50 watt for the tda7294.
You allso have 2 of them.
so that is 100 watt.
Total of 340 watt at absolute maximum.

If you would like to use a single heatsink, and not get over 80 celsius at 25 celsius ambient temp...
then You has to have a heatsink with 80-25 = 55 celsius, 55 C /340 W= 0,16 C/ W heatsink. (or make it K/ W mathers not.)
the math is simlpe. This would be a rather big sink. Let us allso consider that You do not push all amps at the same time to the absolute maximum.
So lets say that 340 watt is no more than 270 watt (80%) and You allow max 100 celsius at 25 Celsius ambient.
it comes to 0,27 K /W heatisnk.
The closes one to match this on the page You posted a link for is
https://www.elfaelektronikk.no/elfa3~no_no/elfa/init.do?item=75-641-31&toc=20476
thisone.
If you want to use a single large heatsink, this will do.
2450 gramms, 100x83x300mm.
even so i would risk a thermal controlled fan to turn on if the heatsink goes over 60 celsius.

A cheaper solution is to scavange some computer cpu heatsinks.
With the fan, naturally. One may make a temp. enabled fan controll, over 60 celsius the fan should kick in till things go below 40 celsius.
 
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