Beginner issues with eBay chip amp

[Jcanderton]

Hi everyone

I bought one of these from eBay

100W Mono Audio Power Amplifier Board TDA7294 HUS | eBay

Thought it should be as simple as wiring it up, but it doesn't seem so. I've checked the voltages on the pins and they appear correct, I'm supplying a signal strong enough to drive a set of headphones, but getting no sound out of this at all?

Not quite sure what the relay is in there for?

Anyone got any ideas or a link to where someone's successfully used one of these boards?

Many thanks

 

[bmwparts]

Do you hear the solenoid click closed after you apply power?

 

[Jcanderton]

Do you hear the solenoid click closed after you apply power?

No, I hear nothing

bTW. I'm using a 24v ac laptop ps with no center tap, will that matter? I could create a center tap with 2 100 ohm resistors if needed

 

[richie00boy]

That's your problem! The advert states it requires a 28-0-28 transformer.

Its also not really intended or ideal for driving headphones.

 

[Jcanderton]

That's your problem! The advert states it requires a 28-0-28 transformer.

Its also not really intended or ideal for driving headphones.

I'll try an artificial CT with two resistors

Sorry, I wasn't clear, I'm not using it to drive headphones, I was just saying that my audio ip signal was high enough to just drive a set of headphones. I've got it connected to an 8 ohm speaker

Thanks for the reply, I'll let you know how I get on

 

[Jcanderton]

Just tried it with an artificial CT, each side of the AC tied to ground via a 100 ohm resistor, and still not a sausage

 

[johnr66]

Obtain a center tapped transformer of proper voltage and current. Be sure to add a large heatsink to the IC.

Also these things are cheap with free shipping for a reason. They are junk.

 

[Jcanderton]

Obtain a center tapped transformer of proper voltage and current. Be sure to add a large heatsink to the IC.

Also these things are cheap with free shipping for a reason. They are junk.

Cheers. Heatsink on there, why wouldn't it work the way I have it wired?

Yes in appreciate for £10 they aren't gong to set the world on fire, maybe just my house, it was just for a try-out

 

[Mark Whitney]

This amp is designed to be powered by a two times 28 Volt AC transformer. This will produce a positive and a negative voltage of 39 Volt DC. (39 0 -39)

If the PSU you have used does not have the correct voltages and polarity the amp will not work. For one thing, the relay needs the higher voltage and there may be an under-voltage protection.

 

[Jcanderton]

Many thanks - I'll get a proper power supply and try again

 

[Michael Bean]

Also these things are cheap with free shipping for a reason. They are junk.

I agree...I hope you're not planning to drive a valued set of speakers, it could end in big disappointment.

Mike

 

[Jcanderton]

Im just messing around really, the idea is for a small backup power amp for guitar in case my main one dies, not that it ever has! Don't expect it to be the greatest

 

[Jcanderton]

Quick question, can I use a transformer with dual 28v secondaries? Or do I specifically need one with a centre tap?

Anyone know any UK suppliers?

 

[richie00boy]

Dual secondaries can be wired very easily as a centre-tapped transformer. Rapid and CPC are good for toroidals.

 

[johnr66]

Quick question, can I use a transformer with dual 28v secondaries? Or do I specifically need one with a centre tap?

Anyone know any UK suppliers?

Yes, bond two of the secondary leads together so that you get 56 volts across the open two leads. It may read higher unloaded.

 

[Jcanderton]

Thanks for that, do I need two 28v secondaries or 2 14v ones?

 

[fastfolkert]

Thanks for that, do I need two 28v secondaries or 2 14v ones?

To get 28-0-28 AC; you need to pot two 28V secondaries in "series" and use the connection between them as "0".
BTW; the chip might possibly work on lower voltages as well; so if you have a 18-0-18 or 24-0-24 lying around that might work too.

YMMV.

 

[Jcanderton]

Thanks a lot for the advice. I'll need to buy one, just making sure I get the correct one

Cheers

 

[Michael Bean]

Hi Jcanderton,

I would recommend NOT using a 28-0-28 transformer. At that voltage level you're risking a possible over-voltage situation if the mains voltage is running too high. Worst case could end up with rail voltages as high as +/- 44 volts which would exceed the limits of the chip.

Mike

 

[Jcanderton]

Thanks Mike, what voltage would you suggest?