Right channel distortion on old system

Gwynston

20 years ago in my youth, I spent a lot on Hi-Fi separates but since getting married and having a family, I've not used them at all for the past decade or so.

We recently cleared out a lot of old stuff and decided to dust off the old stereo equipment. Although it took me a while, I was pleased that I remembered how it all goes together!

• Marantz CD-63 Mk II K.I. Signature
• NAD Amp (battleship grey :cool: )
• NAD floor-standing speakers, bi-wired with heavy duty cable, banana plugs
• Heavy duty, gold plated analogue interconnects

My kids were suitably impressed to hear how a proper Hi-Fi can sound! Unfortunately, there seems to be a sound problem in the right hand channel that I don't remember from years ago. The output is slightly duller than the left channel and if I turn the balance over to R and crank up the volume, there is clear distortion on that side.

To isolate the problem, I've swapped the speakers, then swapped the speaker cables, then changed the interconnects. All with no change, so I've concluded it must be the amp's output.

I notice that when I turn the volume dial, there is a crackling sound, and if I fiddle with the dial a bit (crackle, crackle...) the right channel will clean up a bit, almost eradicating the problem. But then adjusting again (crackle, crackle...) can bring the distortion back.

Gwynston

Now I must be getting old, because I can't remember how all this old analogue stuff works under the covers. But I do recollect from my childhood when playing with some of my parents old Hi-Fi stuff that over time the crackling would start happening with old equipment on the volume dials and also the balance.

So what I'd like to know is what causes it and can anything be done? Is the distortion in one channel a consequence? Are the dials simple resistors, or accelerometers and can they be "cleaned"?

ZENER

What is the model number of the NAD amplifier ?

It's quite possible that some contact cleaner spray will sort it as it sounds like a simple resistive analogue volume control system that has just gotten a bit grubby from lack of use.

If you give me the model number I can check and advise where to direct the spray.

Ken

Gwynston

Thanks Ken.

It's a NAD 306

Gwynston

Is WD-40 suitable for the job?

Would a grubby resistive volume control explain why only the right channel seems problematic?

I guess I could try the spray on the balance control too?

ZENER

No don't use WD40 ! WD40 is a lubricant and isn't suitable as a contact cleaner. Contact cleaner evaporates away leaving no residue.

A combination of things could cause the fault you describe including any selector switches in the signal path. Let me have a look at the amp first and I'll get back to you.

Ken

Gwynston

Thanks Ken - didn't mean to scare you there!

I had a feeling WD-40 wasn't suitable, so thought I'd throw the question out there since I have some at home! But I know you can recommend me something I can hopefully buy cheaply in my local Halfords or Woodies.

Cheers, Gwyn.

ZENER

Sorry I thought you were going to use normal WD40 lubricant. In fact WD40 do make a contact cleaner that's fast drying but a bit over priced IMO. Here's a link to their web page of contact cleaners.

Pictures of the internals of the amp are thin on the ground but any that do show the volume control seem to show a sealed unit. Difficult to get cleaner into these type but some have a small hole for getting cleaner into it. You'll need to investigate a bit but the amp seems easy enough to dismantle.

While you're in there give the tone and balance controls a good drenching doing your best to get the spray into the controls rather than just on the assembly. Obviously disconnect the power from the amp and rotate the controls while spraying them. Likewise for the switches, a good spraying and plenty of actuations in and out.

Sometimes just exercising the various controls can clear up things like this, good old fashioned friction scraping any corrosion away. Modern amplifiers use digital controls so don't suffer this problem but that amplifier is old school which is no bad thing !!

There seems to be a history of dry joints on these amps too but that's another days work

If you're in Dublin I can do the work for you if you're not comfortable doing it yourself ?

KEn

Gwynston

Thanks - I'll pop in to Maplin in Galway and get some spray.

Your comment about dry joints prompted me to go Googling, and from what I've read I hope that's not the problem!

The first time I switched it on, the right channel was completely dead. I think it kicked in when I adjusted the volume, so hopefully it is just grubby contacts and I can get at it alright. After being on for more than an hour and getting nice and warm, it didn't change behaviour anyway.

There are a lot of buttons and selectors on this amp, most of which I don't use as I've only got the CD player connected. And I activate the "tone defeat" setting to bypass the bass and treble so hopefully just going at the balance and volume will do it for me. But I guess there's no harm in giving them all a good spray.

ZENER

The tone defeat switch itself could be dirty so best to clean everything in the signal path - Bass, Treble, Balance, Loudness, Volume and source selectors and tape switching controls. Basically anything that moves on the front panel will need attention. Though, as I said above, just moving the controls and operating the various switches could help !

Let us know how you get on !

Ken

TroutMask

Spray every switch and every pot

mossym

quite possibly a solder joint gone dodgy with age, possibly on the volume pot. someone who knows what they are doing with a multimeter and a soldering iron should have it solved in short order

whizbang

I think you would be better off with WD40, rather than a pure contact cleaner.

The pots/contacts need lubrication more than they need cleaning, particularly with older stuff that may be worn.
The difficulty is getting it into the right places...

http://www.electrolube.com/products/contact-lubricants/eml/contact_cleaner_lubricants/

TroutMask

Please don't use WD-40, it's a quick fix but will create problems in the long run. The best cleaning formulae for electronic work are manufactured by Caig Labs. For everyday stuff like carbon pots, Servisol is fine, and it has a very light lubricant incorporated into the formula.

Gwynston

I bought some contact cleaner in Halfords, but have yet to give it a try yet.
I'll report back with my results.

whizbang

Please don't use WD-40, it's a quick fix but will create problems in the long run

+1 - post in haste, repent at leisure....:o