Amp sounds different after repair!!??

mattc76

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Hi all!

I've recently had my NAD C352 in for repairs when I suddenly had no sound out of one channel. When it came back there was a note saying - "faulty transister replaced - tested ok".

Anyway I've had it for a few weeks and I'm sure its lost some of that NAD warmth that I really like. It seems brighter and a bit harsher!!?? Am I going mad? I'm using B&W 686's with silver cable (cant remember what its called but its about £5 a meter with airlocks on the end!). Before it went away it was all just right ie nice and detailed yet warm and nice to listen to - now it seems too bright!? Due you think I just need to get used to it?

Cheers
Matt
 
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Anonymous

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Well, I don't think that one transistor will need burning in!

Maybe it was always slightly faulty?

Might be an obvious question but have you changed anything else like cabling, positioning of speakers?

I would give it some time first - at least a week and maybe have another word with the dealer - something might have been knocked inside, although it's a long shot.
 

Tony_R

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I've had instances where after repair the amp appears to be working fine... However... it depends if proper measurements have been taken and if the amp was setup correctly after repair. The output transistors require bias adjustments after replacement for example.

One thing you could try, is to provide the amp with a mono source (does this amp have a 'mono' button?) and then listen to each channel in isolation on each speaker in turn. It would also be useful to switch the speakers between channels, if you hear any differences between the channels during the mono tests.

It is a possibility that the blown transistor may have damaged some other component. In the past I have repaired amps, only to find that they don't sound quite right, and further investigation has revealed additional 'leaky' (i.e. partially faulty) transistors - so the amp works, but doesn't meet it's original specification. This can also often be revealed by astute voltage measurements around various parts of the circuit comparing them to those on the circuit diagram.

Even failed capacitors can give the kind of symptoms you describe - and if a component (whether it be capacitor or transistor) has been exposed to excessive voltage / current due to the failed transistor, this could be the cause of the odd sound.

Sorry for the slightly technical explanation and hope this helps.

--Tony.
 

mattc76

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Tony, thanks for the reply.

What you say is slightly worrying because I can see the potential hassle it may cause: numerous phone calls / parcelforce sending etc etc.. I don't have a mono button but I have listened to both channels independently and although the difference is slight there is the suggestion of more treble coming out the repaired side - it could all be placebo BUT now whereas before I could listen to almost anything comfortably, now there are some tracks that are almost unlistenable because of harshness / brightness. This is not what I remember my NAD amp sounding like. One other thing - when I listen to tracks that i know very well they don't sound QUITE like they used to. For example Jack Johnson Sleep through the static track 13 "Monsoon" right at the start there should be a REALLY subtle bit of open high hat (or ride or whatever its called) on the left side that is almost inaudible depending on the speakers (one of my benchmarks for comparing speakers) - now it is easily audible out the R channel.

Bottom line is my NAD and B&W no longer sounds warm - but harsh.

Trouble is they're gonna think I'm bonkers when I phone up and say: thanks for repairing it - its working but it doesn't sound quite right 'specially on that Jack Johnson track....you know the one i mean....you know that bit of hi hat.....etc etc....I'll end up sending it back numerous times them testing it and not finding anything wrong....! Trouble is its bugging me now and it never used to...

Cheers,

Matt
 

Tony_R

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Hi Matt,

It's important to bear in mind that stereo recordings can sometimes have a different tonal balance between channels, depending on stereo effects etc. that were added during production. This is why I suggested checking with a mono source - as it can be misleading at times.

If you can't get a mono source - a good test if you have an FM tuner, is to deliberately put it in between stations to get the hiss (this usually requires pressing the 'mute' (un-mute) button on the tuner), and then comparing the tonal balance between the two channels.

It can even be useful to use a pair of headphones at this stage - as any differences in sound will be readily identifiable with hiss (white noise). But even speakers can be ok in the absence of headphones, although it would probably help to have someone switch the balance from left to right for you, in order that you can remain in the same position.

If you don't have an FM tuner, you could plug a computer into the amp and playback a .mp3 or .wav file. Shouldn't be too difficult to track down a "white noise" (or even "pink noise") .wav on the internet. Pink noise has slightly different characteristics, but will server the intended purpose. NOTE: Keep the volume down as low as possible during these tests.

By the way - if you have a surround amp with a speaker setup facility - that most likely makes use of either pink noise or white noise (hiss!).

Cheers,

Tony.
 

mattc76

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Tony

Thanks I'll try that.

Just been listening to Police Every Breath You Take - previously it was warm and lush - now i'd describe it as frankly metallic sounding. It seems to have lost its midrange warmth, and has less base and sounds frankly metallic with unnatural sounding hi's. There's definately something fishy going on (and I'm not talking about the contents of Baldick's apple crumble...) and its really bugging me!!

Its still under warranty but I can't face the hassle of another repair (superfi online) - they had it for 4 weeks last time and didn't refund my parcelforce postage and I'm convinced they'll say there's nothing wrong with it anyway....Trouble is I really like the amp it took me months and months of trial and error until I found a combo I was really happy with.....now it is out of production so I couldn't simply have an exchange.

I'm dreading the prospect of sorting this out :(

Cheers all

Matt
 

mattc76

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Just been listening to some of these tracks on my headphones from a different source. I'm now realising that the amp could have been faulty right from the off and possibly not playing the treble quite right (albeit REALLY subtly) in that R channel. (That previous very quiet hihat in L channel which is now more prominent in R channel after repair, seems to be just as prominent in my ipod!?) Maybe it was faulty out the box before it finally snap crackle and popped!? Is that possible or am I truly mad? Anyway it all seems a bit bright now!?

I don't suppose some kindly sole would look at my system (Listed below) and say if it screams BRIGHTNESS to you? Thanks - much appreciated!

Matt
 
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Anonymous

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Well I've got that amp and I've used it with the 686 speakers before with that speaker cable, can't say it was bright at all to be honest. To be honest, I would probably try and live with it for a couple of weeks to see if it settled down or if I got used to it. If after that I still wasn't enjoying it I would put it on ebay and look for something else and avoid the potential hassle of sending it back and forth and being told there's nothing wrong with it.ÿ
 
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Anonymous

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And this is the second faulty NAD thread on here this week so I'm getting a bit nervous!
 

mattc76

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Stereolad:Well I've got that amp and I've used it with the 686 speakers before with that speaker cable, can't say it was bright at all to be honest. To be honest, I would probably try and live with it for a couple of weeks to see if it settled down or if I got used to it. If after that I still wasn't enjoying it I would put it on ebay and look for something else and avoid the potential hassle of sending it back and forth and being told there's nothing wrong with it.

Hmmm the ebay option had crossed my mind to be honest.

I just find it all a bit bizarre really - I can't believe that it was faulty out the box because it worked so well, I was so pleased with it and my initial reaction was that it was all nice and warm. BUT I also can't believe that one faulty transistor being replaced would change things so much. The fact is that it IS much brighter almost as bright as my old CA and MS902i setup which I had to get rid of because it was too bright - if I turn the treble knob (on the NAD) down by a quarter then it almost sounds like it used to!??! (maybe my ears are going funny)
 
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Anonymous

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Flog it and get a used Rotel RA-03. If you can't find one, go for the RA04 or 05. Very smooth, detailed for the price point and gutsy. They're not at all bright or harsh. I'll struggle to part with mine when the time comes.
 

mattc76

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I think I've been an absolute idiot...

I've just noticed that one of the gold links on the back of the speaker was loose (not the bit where the cable plugs in but the other bit which is why i didn't notice it before). Have given it a good tighten and I think everything's back to normal! Everythings nice and nice again - no harshness at all. What a n*b! And to think I almost sent it back! Just goes to show - connections connections connections....

Thanks for your comments anyway!

Matt
 

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