amplifier problem - sound deteriorates and gets very poor

[Linusswe]

tda7294 amplifier 12v

Hi!

guess this is the right forum for my question.

got a problem with a amplifier I built.

the amplifier is the kit from kitsrus nr 106 :https://kitsrus.com/pdf/k106.pdf consisting mainly of the IC: tda 7294


I get sound out of the circuit. BUT after a short while the sound deteriorate and gets very poor and distorted. if I disconnect the power and immediately connect again the sound gets clear but again distorted after a short while.

if I turn up the volume on the input pins it also clears for a short while. why?

anyone got any clues what this might depend on?

I power it from 3st 12v batteries because its used in a portable soundsystem. I use the 2 pins called +34v and -34v but leaves out the middle 0v. I gues 0v is used for some kind of stabilising if using unfiltered DC current?

Would be great with some support! my knowleadge of audio amplifiers are very limited.

thanks! //L

 

[VVV]

Re: amplifier problem

I think your problem is the missing 0V connection. In this schematic it is used to balance the internal circuitry (my guess is pin 2 does that). And then pin 4 has to be referenced to 0V.
So you will have to add it somehow. The easiest way to do it is to use a transformer and power the amplifier from that, rather than batteries.

 

[FvM]

amplifier problem

Minimum supply for TDA7294 is +/-10V, so it can work with two 12V batteries (with much lower output power), better 2x2 or 2x3 batteries.

 

[bws]

amplifier problem

what you call 0V its proberly gnd, i would place bateries like this.:

but i dont know how much power i can draw from that konfiguration, perhaps if it can´t give enough, place a 12V battery parralel to every battery on the picture for more power ...

 

[Linusswe]

amplifier problem

Hi!

yes I just tried that after similar tips from others. the result: my IC exploded! why?

I used 2 21,6v batteries instead of 3 12v but as someone pointed out the IC could run on as low as 10v. it should also have shortcircut-protection.

I know it was stupid to try it without a amp meter connected serial, that would have blown a fuse but not my IC

any suggestions why this setup does not work?

 

[bws]

amplifier problem

it still sound to me like you got the wrong reference point on the TDA7294 GND pin, so you got 43,2V(21,6*2) on your supply pin, making the current to high, max voltage for the TDA7294 is +/-40V

other wise you could have placed a speaker whit to low a impedanz, for the TDA7294 to take...

perhaps you could draw a picture off your setup, from the batteries to speaker !??

 

[Linusswe]

Re: amplifier problem

Hi!

Thanks everybody for the response! very effective forum this.

I finaly solved the problem. replaced the burnt IC and connected it with 2 12V batteries as you described in this thread.

Im very happy with my portable amplifier. its built around 2 4" hi-fi car speakers from dls and cased in a plywood "box" wich looks much like an old ghettoblaster in shape.

Have been using it at roskilde festival before and my camp mates reaction on the plywoodbox was
" that piece will survive anything" but sadly the car radio I used as amplifier was very battery thirsty and after 3 hr needed recharge. the people in the "load your phone" tent started to loathe me after a while I think and we relied on the classic cassete decks everyone had in the camp.

thanks! /L