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Amplifier repair guidance


Stephen Willis
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I live north Herts and Bedfordshire border and looking for a repair on a faulty phono stage on a Harmon Kardon PM655. I bought this new 30 odd years ago and it’s starting to show its age. The speaker terminals need replacing as the plastic is breaking down. Powers up all other functions work perfectly, just hooking up to a TT and I get a sound like blowing down a microphone intermittently.

thanks in advance 

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16 minutes ago, Stephen Willis said:

I live north Herts and Bedfordshire border and looking for a repair on a faulty phono stage on a Harmon Kardon PM655. I bought this new 30 odd years ago and it’s starting to show its age. The speaker terminals need replacing as the plastic is breaking down. Powers up all other functions work perfectly, just hooking up to a TT and I get a sound like blowing down a microphone intermittently.

thanks in advance 

Sounds like you’ve had your money’s worth out of this amp….. I’d say it may be time to move on to pastures new!

An amp of this age will probably need treating to a full service, replacing all caps and other components that may be past their best, which is unlikely to be economical i.e. cost more than the amp is worth. 

Edited by robbie010
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Equally if you like the sound and you like keeping things going rather than replacing them then it's what the service is worth to you that matters.

You could try Armstrong in Walthamstow, I've not used them myself but they get good reviews.  And they've got a coffee shop you can go to when you drop off :)

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Thanks everyone, this amp is pure nostalgia and not my main amplifier.

I bought it new from Tottenham court rd with my first saves pay packet after starting work.

taught me to save up and wait for things I wanted.

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13 hours ago, Stephen Willis said:

Thanks everyone, this amp is pure nostalgia and not my main amplifier.

I bought it new from Tottenham court rd with my first saves pay packet after starting work.

taught me to save up and wait for things I wanted.

Recently I had to get my amp fully serviced or more accurately repaired.  It is a similar age to yours give or take a few years. Frankly it was the  best £500 I have spent on audio equipment.

It was a very good amp in the first place and I did not want to contemplate the sort of money I would have to spend to replace it. Also didn't want to change the system synergy. 

So if you like the amp for it's qualities and you are willing to spend a certain amount of money, then it can be rewarding when you slot it back into your system all singing and dancing with the relevant parts replaced.

The next stage is to find someone you feel you can trust to do the work. There is always an element of risk, but that's one of the decisions that only you can make.

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I remember when I blew the transistors in my Nad 350 and 370 when a biamping experiment went wrong (jumpers still fitted ouch - protection circuits can't help with this, lesson learnt!!). It cost me £150 each which was about the going rate for them s/h, but I was damned if I was going to skip them or sell them as "maybe an easy fix".

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Totally disagree with the post about dumping it. Expensive amps of high quality that age are worth repairing and would cost a lot more to replace with something modern. Modern ones due to current circuits manufacturing technique are probably unrepairable.

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Thanks for your messages I am dropping it off to a repairer in Bedfordshire tomorrow.

He has a 1981 Harmon Kardon amplifier and is confident he can get it sorted.

he said they are well built and repairable.

Fingers crossed

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I learnt so much about how a system works as a whole functioning unit when I had my amplifier repaired.  I bought the system as a complete set, ie, CD player, amplifier and speakers a long time ago.

Over the years I experimented with cables and isolation pods under the Cd player and this helped control high and low equencies etc. 

Eventually I started to spend more money on having the Cd player serviced and upgraded. I really commend Restek for offering this service, 20 years after purchase.

I'm not sure there are many manufacturer's that would upgrade and service a Cd player, let alone a whole system as Restek do. 

I then bought an out board Dac from Restek, as I wasn't convinced about how the system was sounding as a whole unit.

I still felt the signal wasn't somehow coming through as it should, but it all worked ok, and I am happy as long as I can play my music.

Eventually the amplifier shut down one sunny June day in 2020. It was 22 years from purchase by this time. 

I found a good service engineer whom told me there was a lot needing repair and although he said, it wasn't an easy fix, after many months of persevering, he finally completed the job.

When I slotted the amplifier back in the same system, the signal was pushing through the amplifier in a cleaner and more transparent way.

I would suggest the sound cleaned up and fed the signal at least 20% more with all the necessary parts replaced. 

I talked this experience through with the engineer and he said, amplifiers do need servicing to keep them on song.

So I have learned that everything in the audio chain needs attention eventually.

It's easy to neglect the amplifier as I did, but the deterioration over 20 years was there, and it affected the sound of the system, until it was repaired. 

Consequently I will be getting the amp serviced if I hear it going off again. 

Edited by hiesteem
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I learnt so much about how a system works as a whole functioning unit when I had my amplifier repaired.  I bought the system as a complete set, ie, CD player, amplifier and speakers a long time ago.
Over the years I experimented with cables and isolation pods under the Cd player and this helped control high and low equencies etc. 
Eventually I started to spend more money on having the Cd player serviced and upgraded. I really commend Restek for offering this service, 20 years after purchase.
I'm not sure there are many manufacturer's that would upgrade and service a Cd player, let alone a whole system as Restek do. 
I then bought an out board Dac from Restek, as I wasn't convinced about how the system was sounding as a whole unit.
I still felt the signal wasn't somehow coming through as it should, but it all worked ok, and I am happy as long as I can play my music.
Eventually the amplifier shut down one sunny June day in 2020. It was 22 years from purchase by this time. 
I found a good service engineer whom told me there was a lot needing repair and although he said, it wasn't an easy fix, after many months of persevering, he finally completed the job.
When I slotted the amplifier back in the same system, the signal was pushing through the amplifier in a cleaner and more transparent way.
I would suggest the sound cleaned up and fed the signal at least 20% more with all the necessary parts replaced. 
I talked this experience through with the engineer and he said, amplifiers do need servicing to keep them on song.
So I have learned that everything in the audio chain needs attention eventually.
It's easy to neglect the amplifier as I did, but the deterioration over 20 years was there, and it affected the sound of the system, until it was repaired. 
Consequently I will be getting the amp serviced if I hear it going off again. 
Restek are German aren't they did you have to send them there?
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20 hours ago, Lawrence001 said:

Restek are German aren't they did you have to send them there?

Yes indeed they are. I sent the CD player back to them as they do a complete upgrade service for it.

Restek keep most of their old electronics serviced. They have a list of the old amps  and Cd players that they service and repair for a fixed price. 

This includes replacing the dac for a new version, "Burr brown",  and HDCD filter, replacing any parts that need replacing, this includes the remote control.

The Cd player was back in my living room completely upgraded within 14 days.

The amplifier I had repaired by an audio engineer in Kingston Upon Thames. Restek would of done it but we were in lockdown at the time, so decided to stay local.  He did a great job, but took a long time as he had to source  the parts, some of which were from abroad.

I tend to let people know about Restek as they are little known over here and their electronics really are that good.

Edited by hiesteem
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