Amp Distortion comes and goes

[Macca]

I've had my suspicions for a while but as it has now happened again I'm convinced something odd is going on.

For the past 2 weeks I've had the system sounding really good. Then, last Thursday, I'm thinking something not right, but can't put my finger on it. Then I'm playing Thin Lizzy 'Live And Dangerous' and I can hear distortion in the vocals. Now I'd only played this a week ago and that was just not there. Nothing in the system had changed in the slightest way. I swapped out CD player for another, same problem. The sweetness and clarity of the sound was gone.

As I say this has happened to me before several times. Result I am no longer attracted to listen and watch telly instead. I could never figure it out.

The other day I was reading a thread about Naim amps and a fair few Nam owners said that although they usually have their amps powered up 24/7, they occasionally felt the sound got a bit hard and congested, at which point they would power them down for a day or two, when powering up again the problem would be gone.

So instead of leaving the amp on standby I switched it off for a few days. Just powered it up and from the start I could hear it was better, didn't even have to walk from behind the speakers to hear it.

So what is this all about? Is there a technical explanation? The difference is quite marked, as in the difference between a crap system you would just switch off rather than listen to and a really good system you can't drag yourself away from. Is it indicative of a fault?

[walpurgis]

That seems very odd Martin. Nothing obvious springs to mind that could be the cause.

[Macca]

When it is off song it reminds me of the TAD system I heard at the Cranage show. Like a bad PA. It is weird but I know what I'm hearing and so presumably did the Naim users. Listening right now it is sweet as a nut. Nothing like the nasty racket it was making on Thursday night.

[Firebottle]

I've been having the same with my very lowly workshop amp for some time.
I have been too busy to get it down and have a look at it but I bet it is a dry joint that increases and decreases in resistance due to thermal effects.

I wouldn't be surprised if the same wasn't happening with your amp. It's a pity we couldn't get it apart last time I was over. Next time :thumbsup:

:cool:

[Arkless Electronics]

Are you sure it's not just you? I started a thread a while back about how every now and then the system just seems to sound crap, even though nothing has been done to it since the last time it was switched off! I put it down to having an off day.... in as much as temporarily not being "mentally receptive" to good sound for mystery reasons (which may be stress, tiredness or whatever) which would have probably resulted in my thinking the same of any system at that moment in time....

I can't say there is any likely issue with your amp. Is it the same through both channels? The odds of getting the same fault simultaneously on both channels are remote, unless it's a PSU issue.

[Macca]

Jez - I'm as sure as I can be that it is not me. It is too big a difference. I've not checked if it is just one channel, I'll do that when it happens again.

Alan - LOL two double E's respond (thanks btw) with two polar opposite answers. Could a dry solder joint be responsible if it was both channels at the same time?

[AD Audio]

I repaired a Tube Technology Unisys last week with exactly those symptoms. Nothing visible on the Scope at all, and the distortion came on occasionally and randomly when the amp was warm. I did three things to cure it without being able to isolate which one was the final cause: refloated the main joints where the amp gets hot, swapped out two psu caps in the pre section and two cathode bypass caps that looked bit weary (obviously not applicable in this case) and cleaned and refitted several tag connections again where the amp gets hot. My instinct was it was the pre psu caps failing but whilst in there made those other tweaks. Most importantly, it cured the problem!

[Marco]

Hi David,

Your dedicated room in the trade section is now ready to be used, see here: http://theartofsound.net/forum/forumdisplay.php?112-AD-Audio

Please populate it, ASAP, by starting a thread there on any subject you wish! :cool: It's important that the room doesn't lie empty, as it looks bad.

Marco.

P.S Martin, sorry to hear of your amp woes. Glad you've sorted it, though!

[Arkless Electronics]

Jez - I'm as sure as I can be that it is not me. It is too big a difference. I've not checked if it is just one channel, I'll do that when it happens again.

Alan - LOL two double E's respond (thanks btw) with two polar opposite answers. Could a dry solder joint be responsible if it was both channels at the same time?

The difference I've "heard" has been huge when I've had to put it down to it's just me having an off day! From "wow" last time it was switched on to ":scratch: how the hell did I think this sounded good last night?"... Trying it again the next day has always seen it back to normal.

[YNWaN]

This 'known' Naim issue regarding being left on for too long is a new one on me - where did you read it? Are you sure you aren't suffering from a touch of paranoia?

[Macca]

The difference I've "heard" has been huge when I've had to put it down to it's just me having an off day! From "wow" last time it was switched on to ":scratch: how the hell did I think this sounded good last night?"... Trying it again the next day has always seen it back to normal.

There is clearly audible distortion, especially audible on vocals, one night, a couple of night later, same programme, no distortion. I agree if you are not in the mood you can't get into it sometimes, but I only sit down and put music on when I am in the mood. No background music unless it is the radio. No way that this down to mood. And the 'cure', although temporary, has worked more than once now.

A former owner did say to me there was an issue with his amp with dry joints, he used to give it a good whack on the top, said that sorted it for a while.

Incidentally amp does not run warm even after several hours at high levels. Barely warm on the top case, even in summer. Have had it run a little warmer with other speakers in the past but not much.

[Macca]

This 'known' Naim issue regarding being left on for too long is a new one on me - where did you read it? Are you sure you aren't suffering from a touch of paranoia?

On PFM (or might be Wigwam but pretty sure PFM)

No, not paranoia. I don't think so. But all paranoids probably say that ;)

[Hudz]

I had the same amp as you Martin, never noticed anything unusual but then sold it to a musician friend of mine who said when his was left on for any length of time it would do exactly as you described.

There's a thread on here somewhere from a previous owner who had contacted the manufacturer about his amp, also with a similar problem and I believe IIRC he was told it was a common fault on the soldering to the speaker relays.

Can't remember exactly who posted it but it might have been Effem.

Hope this bit of vague news helps.

[Arkless Electronics]

This 'known' Naim issue regarding being left on for too long is a new one on me - where did you read it? Are you sure you aren't suffering from a touch of paranoia?

There's certainly no known technical reason for it so "Naim lore" I presume....

Martin. When I have an off day as described the "sounds like a bad pa system" you describe is about how I would also describe it.... a "wall of sound" with no separation or spaciousness or "life" to it. Turning it up to try and inject some life just makes it worse...

It may be a real fault in a shared between channels power supply though of course.

[Arkless Electronics]

There is clearly audible distortion, especially audible on vocals, one night, a couple of night later, same programme, no distortion. I agree if you are not in the mood you can't get into it sometimes, but I only sit down and put music on when I am in the mood. No background music unless it is the radio. No way that this down to mood. And the 'cure', although temporary, has worked more than once now.

A former owner did say to me there was an issue with his amp with dry joints, he used to give it a good whack on the top, said that sorted it for a while.

Incidentally amp does not run warm even after several hours at high levels. Barely warm on the top case, even in summer. Have had it run a little warmer with other speakers in the past but not much.

If there is definite audible distortion then a fault is more likely of course! I can't say I was knowingly in a funny mood or anything when I heard the things I described though...

Try a good belt to the amp next time you hear it and see if that helps.

[Macca]

I had the same amp as you Martin, never noticed anything unusual but then sold it to a musician friend of mine who said when his was left on for any length of time it would do exactly as you described.

There's a thread on here somewhere from a previous owner who had contacted the manufacturer about his amp, also with a similar problem and I believe IIRC he was told it was a common fault on the soldering to the speaker relays.

Can't remember exactly who posted it but it might have been Effem.

Hope this bit of vague news helps.

Thanks Martin. Yes it was frank Effem who recommended giving it a belt. But who wants to do that all the time? Might be time to go amp shopping.

[Macca]

There's certainly no known technical reason for it so "Naim lore" I presume....

Martin. When I have an off day as described the "sounds like a bad pa system" you describe is about how I would also describe it.... a "wall of sound" with no separation or spaciousness or "life" to it. Turning it up to try and inject some life just makes it worse...

It may be a real fault in a shared between channels power supply though of course.

Could it be the soldering in the speaker relays as suggested? That sounds like it might be an easy fix.

[YNWaN]

There's certainly no known technical reason for it so "Naim lore" I presume.....

I'm deeply familiar with Naim 'lore' and I've never heard of such a concept - rather the contrary in fact.

[Macca]

Ask on PFM. It was a recent discussion I think.

[Hudz]

Could it be the soldering in the speaker relays as suggested? That sounds like it might be an easy fix.
Easy fix apparently but a total pain to get to, if that's indeed what it is.

Mine did sound as dull as ditchwater if left on standby for any length of time and was only ok after a day or so of being powered down.

Good excuse to get yourself something shiny off Santa;)

[AD Audio]

Hi David,

Your dedicated room in the trade section is now ready to be used, see here: http://theartofsound.net/forum/forumdisplay.php?112-AD-Audio

Please populate it, ASAP, by starting a thread there on any subject you wish! :cool: It's important that the room doesn't lie empty, as it looks bad.



Marco.

P.S Martin, sorry to hear of your amp woes. Glad you've sorted it, though!

Thanks Marco: I will do just that! David

[Arkless Electronics]

Could it be the soldering in the speaker relays as suggested? That sounds like it might be an easy fix.

Unlikely. They can give trouble after time but I've never known both channels effected as there is a set of contacts for each channel. If it was the soldering to the coil then that would effect both channels and result in the relay dropping out and killing the sound to both channels.

A dry joint or worn electrolytic in a shared voltage source (such as a regulator) in the pre section or in a separately powered section of the power amps seems most likely. Not having a circuit diagram I can only guess.... It could even be something bizarre like an electronic mute circuit or overload protection circuit which shares a power supply (or some circuitry) and at times the fault causes the mute to just a say start to come on so that instead of muting it causes distortion... or the amp starts to go into partial and programme related current limiting protection just enough to cause distortion... I've seen both scenarios happen but don't know if yours even has either type of circuitry fitted!

Intermittent faults such as this can of course be a servicing nightmare if it may work perfectly for days!

[Macca]

Good excuse to get yourself something shiny off Santa;)

Yep, but that was going to be shiny 65 inch telly. :(

Thanks for everyone's input, much appreciated. I'm thinking for now I will power the amp down completely each time. Has sounded fine all tonight.