My amp has melted - advice please

lbr

lbr

monkey boy
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Oh bugger, my amp has just melted in a billowy cloud of smoke. I was listening to some music, heard crackling noises coming out of the speakers and jumped up to turn everything off by which point the listening room was hazy with the charred innards of my amp! I'd be really grateful for any considered input as to why and what I could/should do now!

Amp (was) a DPA 50S, speakers are Martin Logan CLS iiz. I know these can present a difficult load and like a fair whack of power, but enough to melt my poor power amp?!

Piccies of the disaster zone below...

A few questions that I'd really appreciate your thoughts on:

  1. What could have caused this?
  2. Could it have happened while the amp was on standby or only when listening to music?
  3. Could the speakers be damaged now? I don't now have an appropriate amp to test them with and I'm loathe to plug them into anything too exotic in case they are root cause
  4. What factors should I be considering in the choice of a replacement amp (with a view to ensuring a repeat performance does not occur)

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Thanks for any help :)
 
Hi Lbr

Don't know where you're based ''in a happy place'' could be anywhere !

If near Milton Keynes, feel free to send me a PM. I have a spare amp I was going to put into service for system C.

It is a Sansui, and could be yours for a whopping £30.

If you a) live nearby b) want something cheap to listen to music on until you buy something new c) just want to check your speakers

..send me a PM

Hope this is helpful - nb the amp looks 'goosed' Im afraid to say..

If not , no worries...system 'C' shall progress as planned !
 
Thanks for the links guys

Bottleneck - I'm in Andover, so not that close I'm afraid. I have another system that'll see me good in the meantime, but I'll definitely keep a look out for something cheap and local to check the speakers out on before doing anything more permanent. Thanks for the offer though - much appreciated.

Goosed indeed I fear...
 
Oh dear :( - I hope the speakers are ok.

Martin (felix) is your man here where DPA is concerned so perhaps send him a PM.

On first sight it looks like an exploded electrolytic cap, however I think I can see remnants of rectifier diodes on the charred area of the board. Those can vapourise if the caps following them go short circuit. If it was one of those big encapsulated rectifier bridges it could certainly make such a mess.
Odd that the internal fuse didn't blow in time.
 
Crumbs.

That's the old 100S-based board design, and it looks like the bias controller has gone or, more likely, some emitter resistors have cooked-off... Damn shame!

With these amps its usually the emitter resitors in the o/put stage start going, which cooks the remainders (they are several SMT devices in parallel per o/put TR); and the way this stage design works, if you loose one half, the other can turn on hard...pop.
Later amps use some bigger (thermal rating) parts here.

It's an age&heat- related failure rather than load IME; these amps can even tolerate a dead short otherwise (BT, DT...)

If the board can be cleaned and some of the tracks are still in place it can be rebuilt as new - the transistors are available and not expensive. But that does not look good, I must say. Happy to take a look if you are anywhere near Bath...


PS looks like only one channel is damaged. Attached speaker might have briefly seen 40v DC, but if you didn't hear a deafening 'crack' through the speaker, I wouldn't worry about that.
 
Thanks Rob and Felix, really helpful. Looking at it, I'm not at all hopeful of a rebuild I'm sorry to say. Real shame as it was a cracking amp [rose tinted flashback - I remember visiting the DPA "factory" when I lived in Cardiff around '95 (IIRC, basically a prefab on an ind est in St Mellons) to have an Enlightenment DAC looked at - nice guys and very helpful. Sold that DAC recently and regretted it since...].

I didn't get any "crack" from the speaker at all - a fairly benign crackle from the right hand speaker actually; much less dramatic than the smoke pouring from the amp!
 
OK, this morning's mad idea if the amp is dead:

What you have leftover is a very nice case, all socketry (and your existing cables), mains wiring complete and a chunky power supply.

You could just pretty much drop a pair of UCD180 Hypex modules in there and be up and running with a beefy Class D amp very, very easily. It would be subtly different, but shrug off your speakers as a load, and run cool. Just a thought :)
 
looks to me like an output device gone short or bias controller as previously mentioned, then because of that the emiter resistor has totally disintergrated. it might not be as bad as you think, a good clean up and maybe only a few quids worth of parts.
 
might have being the caps, that they could not handle such a lower load of ohms,
nando
 
Looking again in detail, the caps are fine,- just smoke damage (cosmetic). That black 4R7 resistor thats exploded is the key - the output dumper emitter resistors have cooked off over the years. BT, DT...
 
felix said:
OK, this morning's mad idea if the amp is dead:

What you have leftover is a very nice case, all socketry (and your existing cables), mains wiring complete and a chunky power supply.

You could just pretty much drop a pair of UCD180 Hypex modules in there and be up and running with a beefy Class D amp very, very easily. It would be subtly different, but shrug off your speakers as a load, and run cool. Just a thought :)
Click to expand...

Way beyond me I'm afraid! To be honest, even if I did get it fixed, there's no way SWMBO is going to let it back in the house again after last night's smokey adventures :SWMBO:

If you think it's salvageable, you are more than welcome to it, FOC. You are right though - there are lots of nice parts still intact.
 
Wow! - in that case, I would like to accept with the intent of trying the 'mad idea' and posting results. I'll PM you later.
 
felix said:
Wow! - in that case, I would like to accept with the intent of trying the 'mad idea' and posting results. I'll PM you later.
Click to expand...

I have a pair of old Goldmund Telos 5000 monoblock's that went quiet on me, would you like .................................................................:D just joshing :MILD:

good look with the rebuild, looks viable :)
 
Crikey billyo you really cooked that one Lee! Good luck Felix, be interesting to see what you come up with.

nice caps!

I thought amps had an emergency cut out / fuse thing, am I wrong?
 
The Deltecs all have a thermal cutout related to case temperature (the round thingy on the baseplate near the mains socket, bottom left) but ...only the later versions have fuse on the speaker lines. Not that such would prevent this sad occurrence, which is down to trying to use SMT resistors as emitter resistors in a power amp. :(

Long ago modded my (later version) 50S amps to use gurt big, heatsinkable caddock bits instead!
 

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