Some help please with Wharfedale 2050A.

[robgilmo]

Hi , New to the forums and need some help with an old (1992) wharfedale 2050A amplifier.
Apparently it was designed by Quad and isnt a bad little amp, certainly not high end though.

My problem is it is dual mono however the volume shifts or at least cuts out on one channel intermittently. The worrieng bit is it does this on both channels on both CD and Phono. I dont know if it happens on other sources as I only use CD and Phono.

I had a look on google and found an old E Bay add for the same amp.

Wharfedale 2050A, A rarity+ TEN Audio upgrade, Warranty | eBay

I contacted Ten Audio and asked them what modifications they did to the amp and got this reply, I hope they dont mind me posting this up,

Power supply bulk capacitors changed to BHC/Aerovox, power stage local power supply caps changed to Rubycon ZL (10 x the old value)
changes to NFB loop, changes to biasing circuit - in effect different bias settings
and a few more "secrets" (different volume pot, re-engineered voltage gain stage)
Nothing really wrong with soldering quality in Wharfedale, but very poor volume pot and a few more "bits" - it is a excellent performing amp, after upgrade easily leaving behind mid-end valve amps and most of transistor "stock" and I am not talking about £200 units

So guys is this something a complete novice can take on? Or would it be best left to someone who knows what they are doing? Indeed is this amp worth upgrading like this? I do know that these amps were pretty good in their day.
Any thoughts?

[wintermute]

Welcome to diyAudio robgilmo

Just to clarify are you asking whether it is worth performing the same mods that TEN Audio did to another similar amp?

Certainly if your amp is standard, then based on the TEN audio comments I would say your problems are quite probably related to the volume pot. At nearly 20 years old it is certainly also a bit long in the tooth for the electrolytics so a recap may not be a bad idea. It would probably be a good idea to practice desoldering and soldering on something disposable before tackling this yourself though if you are not experienced

Tony.

[robgilmo]

Hi Tony, thanks for the quick response.
I would indeed like to perform these mods on my amp, desoldering and soldering isnt an issue. Changing the caps sounds easy enough , do I just change like for like by reading the values on the side of the can?
The volume pot was my suspect also as it seems to fix itself if I play with the volume, where can I get a new/better volume control pot?

Also Ten Audio spoke of changing gain settings etc, I guess I would need a bit more than a soldering gun and some pliers to do this?

Rob.

[wintermute]

Hi Rob, as long as you change the caps to the same value/voltage rating you shouldn't go too far wrong.

I have a vague recollection that the NFB cap can benefit from changing to a bipolar and increasing the voltage to a higher value, I can't remember where from though... could have been something from Doug Self's blameless amp... but don't hold me to that! Many will say that different brands of caps will alter the sound of the amp. Some of the favourites are Elna Silmic II's and various Nichicon's. Panasonic FM and FC are also highly recommended. Go with a brand name and you shouldn't go too far wrong. I don't claim to hear differences between cap types, but I do buy (not outrageously expensive) Nichicons, Panasonics, or Elna's

The main issue with changing the volume pot will be finding something that is physically compatible. There are many options available, and some are very expensive. you could try looking for some ALPS pots at rs-components it will almost certainly be an audio taper one, could be anything from 10K to 100K but should be marked. POTS are horrid in my experience, I've never had a good one (tracking differences between the channels have always been the problem with ones I have purchased, but to date they have all been cheap ones). I've bought a cheap stepped attenuator from HK (about $15 including shipping) but still haven't tried it out yet, one of those projects on the backburner

Changing the gain setting will more than likely involve changing one or two resistors in the feedback section of the amp (though if it is an integrated amp then they may have changed the gain in the preamp section as well). A circuit diagram of the amp will probably be necessary here. If you want to read why you might want to do this check out Michaels excellent article on gain structure

Tony.

[robgilmo]

Thanks Tony. The pot in question is dual concentric. I dont really need to be able to adjust the balance providing the pot can provide me with a good equal balance however I would rather have it and not need it than need it and not have it.
Do I look for conductive plastic or is carbon OK? I know Alps do dual concentric shaft pot in carbon but I cannot find anyone in the UK who sells them, also is it possible to get an RK27 with a dual concentric shaft?

[wintermute]

Hi Rob, sorry I haven't been checking my subscribed posts

Interesting pot I haven't come across one of those before but it would certainly fix the main gripe I have with all the pots that I've had, ie poor channel to channel tracking!

A lot of people say that the prefer the conductive plastic, I've only ever tried carbon (and I suspect with my tin ears I would not be able to hear any difference anyway )

I'm not sure what to suggest, ordering from overseas can be expensive for the shipping, but may be your only option if you want the dual concentric. Someone else might chime in

edit: as a last resort you could try some of the non-residue CRC CO contact cleaner, but it is important it is the non-residue type. This might get a bit more life out of the existing pot, but as I said it is a last resort.

Tony.