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What happened to my Amp?


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One for those with real technical knowledge of HiFi electronics.

I have an old, unused Audiolab A8000a integrated amp from the mid/late 1990's (later than the early, ropey models and pre- TAG McLaren era), sitting in its box, where it has lived for about 7 years. It's in fairly immaculate condition.

Despite what many opinions might be of these amps, it used to be a very clean, detailed and transparent, but sometime clinical and occasionally slightly un-involving listen. It worked well with my other components.

The Audiolab was relegated to my second system, in our lounge in the 00's.

My wife was very wary of touching my HiFi kit, but she started getting used to playing her music on this lounge system, with its Arcam CD player. There were no problems until one day, she put a CD in and no sound was coming out of the speakers.

I'd always asked her to turn the volume right down to 0 before turning the system off and before turning it on, but on this occasion the system was already switched on from my earlier use, so she assumed there was no sound as the volume was turned right down. So she turned it up. Still no sound so she turned it up more and there was still no sound.

Then she realised the input selector was set to Aux and not CD, so she turned the knob to CD to be met by an instant, unbearably deafening blast of sound. she quickly turned it down, or off and due to the shock and panic couldn't remember what she's done. She vaguely thinks the amp may have cut out (protection???) but couldn't be sure. She was upset and angry.

When I heard about this later that evening, I went to have a look and turned everything back on., to find that something was not right at all.

Compared to before this incident, turning the volume knob up  now resulted in a very rapid increase in volume level, rather than the smooth progression before. The sound, although initial clear, sounded very hard and metallic and although not sounding distorted, was becoming unlistenable at position 2 and above on the volume control. By position 4 it was far too loud and frankly awful.

Clearly the incident had caused some serious damage. My wife was so put off by this event that she vowed never to touch any of my kit ever again, so the system lay unused for a while before I dismantled it and packed some of the components away.

After a few years I finally had time and the inclination to try and get this amp repaired, so I took it to a well known and often recommended (on HiFi forums) "specialist" in Audiolab and TAG-McLaren kit, who said he would take a look, test the kit and if I was happy, make repairs up to an agreed price. He would phone me if it was going to cost more.

When I returned to collect the repaired amp, he said he couldn't find anything wrong with it, but had upgraded and replaced some of the cheap components in the pre-amp. He then connected the amp into his own system to give me a demo.

I was very disappointed to find it sounded nearly as bad as before, but he said he thought it sounded perfectly fine and that it was a typical Audiolab sound. Well it didn't sound fine to me and it certainly didn't sound anything like it had done before. A good friend had also had one of these amps and his sounded just as good as mine.

I paid him for his work and went on my way, both very disappointed and aghast at how this guy, who had lots of various bit of Audiolab and other kit lying around and was supposed to be an expert, could find that piercing sound remotely acceptable.

The Audiolab amp was tried out at home a few times and then packed away and mostly forgotten, where it has laid for the last 7 years.

So, apologies for the lengthy ramble, but I wanted to give as clear a description of events as I could. The question is, what is the likely damage that occurred to this amp?   I could just junk it, but curiosity and the fact that the amp is in top condition has left me wondering if it could be saved.

I've looked inside and there are no signs of burn marks, scorching, heat discolouration or disintegrating or damaged components. At least not to my untrained eye. The caps all look solid and intact.

Can anybody suggest the likely cause or causes and whether this amp can be economically repaired and used, or sold on.  Many thanks in anticipation.

5

Edited by High 5
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In general, running a solid-state amp with no load is unlikely to do damage short term, whereas running a valve amp with no load can do serious damage quite quickly. Running a valve amp into a short c

I think you've confused yourself now as well as Martin 

Appreciate that neither you or Rabski might want to name names on this but to avoid any issues suggest you PM Rabski and then you can be clear about who you are both talking about and if they are in f

I take it you've used a different amp with the same speakers and all was well? Just asking as it's usually speakers that come off worst from situations like you described, and if the speakers were fine I'm surprised the amp wasn't.

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Both channels the same? If this is the case then the fault could be power supply related as this is common to both channels. If your friend has the same model might be worth checking the voltages.

Bob

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From diagrams online it shows the power rails to be +44 and -44 volts. I suspect a power issue but i would have thought your previous repair visit would have picked up the issue. There are several companies that repair and upgrade the 8000A online. I used to love the one i had in the mid 80s. If you've already spent money on repairs i suppose it may not be cost effective. Good luck 

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I’m with Martin in thinking it’s the speakers that would’ve usually suffered, most probably anyway.  Switching from Aux to CD, with a CD playing can’t cause any problems, so it must be related to the excessive volume. That would mean the output stages, and possibly the components that supply them, like the power supply mentioned above.
 
Otherwise it’s a complete mystery to me!  Did the ultra-sensitivity you report remain after the ‘repair’?  

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I expect it was the sudden burst of excessive volume, when the input selector was switched to CD with the volume set very high.

The inspection and replacement of pre-amp (or maybe it was phono amp?) components, didn’t result in any change from before I took it in to looked at.

I basically paid for his time to inspect and test the amp and to upgrade the handful of small components. No repair was carried out as the chap couldn’t find anything wrong.

Turning the volume knob results in the volume increasing very rapidly at a low setting and the sound is hard, very glaring, almost metallic. At position 4 it is unbearable and very loud. 
 

.

Edited by High 5
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Turning on an amp at full volume should cause no damage to the amp UNLESS no speakers are connected and then it will fry the output transistors at worst and blow a fuse or two at best (though usually the former) ... however some people have wrecked drive units from this situation.

So I have not a clue why it sounds off to your ears - the only way to reach a conclusion is to find a local wammer with the same Amp and compare the two in the same system.

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7 minutes ago, uzzy said:

.....I have not a clue why it sounds off to your ears - the only way to reach a conclusion is to find a local wammer with the same Amp and compare the two in the same system.

Rest assured, a comparison with a properly working example isn't going to reveal just minor or subtle differences. The amp is bu****ed for any useful purpose.

The sound is awful and the volume control only has that small range before the volume becomes painful.

You can see why I'm puzzled  about what has caused this failure. The only thing I know for sure, is what I've described in my OP.

.

One thing I haven't tried, is to use the pre and power amp sections on their own (there are pre-in and pre-out phonos), combined with another amp. I have a vague recollection that an internal link needs to be cut to allow full independent operation of the pre amp, but I'm not sure about that.

If that works, it should determine if it's a pre or power amp issue (or both). It'll have to wait until the end of this week before I can try that.

Thanks for all your replies so far.

5

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Hi,

Which inputs cause the problem - is it all inputs, or the phono only, as i recall that there is a button on the back that allows for MM or MC cartridge.

Regards,

Shadders.

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1 hour ago, High 5 said:

Turning the volume knob results in the volume increasing very rapidly at a low setting and the sound is hard, very glaring, almost metallic.

I don’t wish to appear insulting, but there’s no chance you’re accidentally putting the CD player into the phono input, is there?  That all I can think of that might account for excessive gain and glare ime.  

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47 minutes ago, Shadders said:

Which inputs cause the problem - is it all inputs, or the phono only, as i recall that there is a button on the back that allows for MM or MC cartridge.

Hi Shadders, it's on all the line level inputs, including the tape in. I haven't tried the turntable phono input.

39 minutes ago, Nopiano said:

I don’t wish to appear insulting, but there’s no chance you’re accidentally putting the CD player into the phono input, is there?  That all I can think of that might account for excessive gain and glare ime.  

No offence taken. It's a straightforward question, but no, I'm perfectly able to discern between the phono and line level inputs.

23 minutes ago, toprepairman said:

Whereabouts are you? maybe you could find someone near to you to give you another opinion?

South Coast. I assure you, I could pull in anyone off the street to listen and they'd tell you it was broken.

22 minutes ago, Shadders said:

Hi,

If components were replaced, perhaps a wrong value resistor was put in.

Regards,

Shadders.

There was no change from before that work being done and afterwards.

It appears the component replacement, which wasn't carried out to rectify any fault, has had no effect on the problem.

5

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