Replacement volume control for early Pure Evoke-1 DAB receiver.

[Sylvain VAN DER WALDE]

Hello all.

At the present time I'm not trying to get it from the distributor, although I may not have any choice. Now, we're not dealing with the usual volume control (potentiometer) which has 3 terminals (one connected to a wiper, and the others connected to each end of a resistive track). No, this damn "little critter" has 7 terminals and 2 mounting lugs (printed circuit mounting). It has a blue body measuring 16x15x5 millimetres. Looking inside: the metal wiper assembly is attached to the plastic spindle, and has 2 separate sections (one with 3 wipers, and the other with 2). It looks as if there are 3 or 4 resistive tracks (it's difficult to be precise without spending more time to observe them). Has anyone seen or heard of such a volume control? Is it a proprietory (I'm not sure of the spelling) or a standard part? It's completely sealed, so I couldn't use my switch cleaner (which has always worked for me). Anyway, I've had to snip though the terminals and mounting lugs, as it's the best way to deal with a "plated through" PCB. Can anyone understand/explain the design theory behind this item, and/or suggest source/s of supply? P.S. I believe that the receiver is designed in the UK, but it's made in China. P.P.S. If it had been any other fault, I would have sent the radio to Pure for repair (if such a repair was deemed economical). I have many radio receivers.

Thanks in advance.

Sylvain.

[Frank Erskine]

At work I once had an oscilloscope which developed a fault with a switch/pot. I simply contacted the importers who gladly sent me a replacement part foc, which I fitted myself.

The scope was still under warranty, but they didn't seem to mind me "doing it myself".

Try to speak to Pure about a replacement.

[Graham]

It sounds to me that the "resistive tracks" are in fact on/off contacts and the device is in fact an "encoder disk" The microprocessor looks at the state of the switches in real time and can determine the direction and speed you are turning the knob and adjust the volume accordingly.

Usually there is no need for a mechanical stop, as on a pot.

Does that make sense?

[Sylvain VAN DER WALDE]

Wow! That was quick! :)

I wonder how long ago that was? There is no doubt that spares for radios, televisions, VCR's, etc.. were easy to get (via the "Television" (formerly "Practical Television") mag. adverts, in the first instance. But my understanding is that manufacturers eventually became very inflexible in supplying spares, even to qualified repairers. They had their (limited) group of distributors, and dealt only with them. I'm talking of TV spares in particular, and that was already quite a few years ago. Anyway, I do intend to do as you suggest, if I really have to. P.S. I'm intrigued (spelling?) by the design of that component, and am keen to get some replies on that.

Sylvain.

[Sylvain VAN DER WALDE]

Actually, there are stops on this one. If there had not been any, then I would have known that this component was (as you describe above) an "encoder disk". Nevertheless, I believe that you may still be correct in your assumption.

Ha! Yes! I think that we may be getting somewhere. I know only a little about such things, but enough to believe that you are on the right track (I believe that my communications receiver has a _rotary frequency control_ that works on that principle, and has no stops). Let me tell you why I wanted this "volume control" changed: On that radio, the volume goes up _immediately and rapidly_ as you rotate the knob. The fault is, that at the _very start_ of rotation the volume control works intermittently, making it difficult to get an acceptably low but adequate sound output (at night time). At the usual daytime sound levels, the volume control works OK. If you have any further remarks about this, I will be pleased to hear them.

Sylvain.

[Graham]

Looks like ebay is your friend tonight Sylvain.

[Dave Plowman (News)]

Might be some form of loudness control rather than simple volume?

[Sylvain VAN DER WALDE]

Paypal account which I've only used once or twice before). I'd thought several times about registering on Ebay, but never did. This might start me off with some careful buying.

Thanks again.

Sylvain.

[Sylvain VAN DER WALDE]

It may well be, for all I know; but Graham has located the correct part on Ebay for me. The seller provides precise information and a very clear picture (photo) of the item. I've already paid for it (immediate payment was requested by the seller to guarantee dispatch to myself).

Thanks for your reply.

Sylvain.

[meow2222]

for future reference often repairing these custom jobs is easiest. Squeezing up the track end connections often works, and a track cracked across can be repaired with pencil lead or aquadag along the crack. The wiper will remove it in one area but not for the rest of the width of the track. I would not use those conductive silver paints, they oxidise.

NT