So I just broke my practice amp

[mike313]

Hi,

Yesterday I was experimenting with a small practice amp I have (Behringer BT108) and I made the mistake of looping the out to the in: I had a cable going from the headphones out to an external audio interface and then from the audio interface back to the amp's cd player IN.
Please dont laugh too much at me, I know it is a retarded idea but I was just experimenting and didnt realized what I was doing until later.

I plugged in the bass and played some notes and obviously no sound came out of it, but i saw the audio interface clipping indicator going red for some seconds and then nothing.

Now the amp does not produce any sound at all from the speaker, even if the power light is on. If I put on headphones I can hear the bass playing at a very low volume and the sound is heavily distorted.


I wonder what did I have done? It is possible to fix it? Luckily it is just an old practice amp with no real value, but I would like to know what it is that I have broken. A fuse? The speaker? I have no idea.

Thanks for any help

[Muppet]

Have you turned it off and left it off for a while? There may be a protection circuit that has kicked in.

[mike313]

I left it turned off for the whole night....

[JapanAxe]

If you are anywhere near Swindon I would be happy to take a look at it fwiw, just drop me a PM.

[HowieBass]

Here's the circuit schematic (use the download link) as a PDF file for the BT108 http://www.electronica-pt.com/esquema/func-startdown/15960/

I think the speaker should be ok it was probably bypassed by the headphone out connection - but you might well have blown some component in the circuitry between the CD in and headphone out loop.

[mike313]

Thanks a lot to everyone for the help. Thanks JapanAxe for offering to take a look at the amp but I live far away from you, and thanks to HowieBass for the pdf, but I know nothing about circuit schematic.

Maybe I'll try to open the amp it and take a look to see if I can find the problem, but anyway it is just a small unexpensive practice ampo. Lesson learned!!

[icastle]

Looking at the circuit diagram, the most likely culprit is IC1, the passive components should have survived.

The 4580 ICs are only pennies, so well worth a punt.

http://uk.farnell.com/texas-instruments/rc4580ip/ic-audio-amp-pdip-8/dp/1755008

HTH

[tauzero]

[quote name='mike313' timestamp='1428156849' post='2738598']
Now the amp does not produce any sound at all from the speaker, even if the power light is on. If I put on headphones I can hear the bass playing at a very low volume and the sound is heavily distorted.
[/quote]

You could have damaged either or both of the ICs. You can check if IC2 is damaged by seeing if something played through the CD input comes out through speaker or headphones. If it doesn't, or if it's heavily distorted, IC2 is dead.

[rmorris]

Check IC2 as advised above (my quote thing doesn't work from this pc for some reason). But also component OP1 might be damaged ? Looks to be an optoresistor used to compress / limit.

[rmorris]

Test resistance between pins 3 + 4. Short circuit / few ohms would point to a problem (signal shorted to ground).