In article , h.tees
wrote:

It is the volume control that needs replacing. It's a very common
problem in most audio circuits of that age and the design of the control
doesn't help. No need to bin the preamp, just find another volume
control. Maplin will sell something suitable for around £2-3.

Erm... IIRC the Quad 34 uses a special version of the Alps 40mm detent
stepped pot/attenuator. I doubt you will find one from Maplin for 2-3 quid!
( If so, it is about time I sent them an order for a dozen. :-) )

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Woody
wrote:
"h.tees" wrote in message


I don't think that may necessarily be the case. Quad were quite good
with their circuit design, and if the volume pot interfaced to a high
impedence load then it may not be the pot as such circuits were not
prone to that type of noise.

Unless the unit has been badly mistreated I also have doubts that the pot
is to blame as they are quite high quality stepped attenuators. More likely
a poor connection or dud cap elsewhere.

I suspect the problem here is dried out and/or leaky electrolytic
capacitors. Clicks whilst playing are typical of capacitors that are
leaking and affecting d.c. bias conditions.

I also suspect something like that.

I would agree that crackles whilst playing are also typical of a volume
pot that has gone noisy, but it should not do it at minimum volume where
the pot wiper is effectively earthed.

The loss of one channel that plays when the mono button is pressed says
one pre-amp is not working. I had a Q33 which had plug-in circuit
boards: it is just possible that this unit may be of the same
construction and that the boards have become dislodged. It might be an
idea to get the lid off and see if this is the case - if it has plug-in
boards even remove them, clean the contacts if necessary and put them
back. It might just cure everything.

I'd also recommend that.

I am trying to recall if early 34s had their ICs in holders. If so,
something like that is a candidate.

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article , Rob
wrote:


OK, thanks. Thing is, it looks to be quite a unique part - Alps, with a
nice feel and little indented bumps as it turns. However, I'd be pretty
certain that they're available somewhere. I don't think I'd do it
myself, and there might be a 'good money after bad' type situation
building up ...

If you find a current UK supplier for small quantities of the Alps 40mm
stepped attenuator series, please let me know! I have a few I obtained
about 10 years ago, but have not been able to find a seller since!

In this case, the simplest best would be to buy a replacement pot from Quad
*if* it turns out to be the pot that is at fault - which I do doubt at
present.

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

In article ,
h.tees wrote:
It is the volume control that needs replacing. It's a very common
problem in most audio circuits of that age and the design of the control
doesn't help. No need to bin the preamp, just find another volume
control. Maplin will sell something suitable for around £2-3. I would
solder it in or get a friend who can - you will save a fortune.

I'd be very surprised if Maplin sell a suitable replacement.

--
* I like you. You remind me of when I was young and stupid

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Jim Lesurf wrote:
Unless the unit has been badly mistreated I also have doubts that the
pot is to blame as they are quite high quality stepped attenuators. More
likely a poor connection or dud cap elsewhere.

Is it a stepped attenuator or just a normal pot with mechanical indents? I
suspect the latter.

--
*Just remember...if the world didn't suck, we'd all fall off*

Dave Plowman London SW
To e-mail, change noise into sound.

In article , Dave Plowman (News)
wrote:
In article , Jim Lesurf
wrote:
Unless the unit has been badly mistreated I also have doubts that the
pot is to blame as they are quite high quality stepped attenuators.
More likely a poor connection or dud cap elsewhere.

Is it a stepped attenuator or just a normal pot with mechanical indents?
I suspect the latter.

IIRC the 40mm series of this type is a stepped attenuator. Metal landings
with resistive elements between them, and the wiper moves across them. This
was how Alps were able to sell versions laser trimmed to a given balance
and attenuation spec. Hence why they were also very costly even in
low-commercial-production quantities... and why they vanished from the UK
as an single item purchase. Cost too much to make import/sale worth the
effort when most people would buy something cheaper.

The volume controls I chose for the ancient Armstrong 700 was a stepped
attenuator from Alps of the kind I have in mind. With a laser trim to quite
close tolerances. Cost a fortune at the time! But I felt it was worth it
just to have the balance stay put as you wound the volume up and down over
the range. Has also proved its worth since when I do measurements as I can
accurately adjust and reset levels.

They also did a 4-gang version at one time so you could control i/p and o/p
level together! This turned up on a few amps from people like Pioneer, etc,
IIRC, but was very expensive even without special trimming, so only on
'flagship' designs.

Above said, for all I know they changed the design later on after learning
how to get the same accuracy from a continuous track!

The smaller Alps pots are a continuous track with a detent collar to mimic
the behaviour, but not the precision of the results. Much cheaper to make,
and so lower cost. Hence turned up on far more kit, and other mass
production makers did similar, cheap, pretend attenuators using a collar.

Alps probably would also do 40mm continuous with collar if wanted, so
the 34 control *may* be that, but I think it is a discrete attenuator. If
all that was wanted was a stepped action then the smaller pots with collar
will give that at lower cost. The 40mm size costs cash, but gives space for
the landings and elements, etc.

However I've not cut open one of the controls from an old 34, so I may be
being over-generous to PJW, Mike Albinson, etc. But I suspect not. :-)

That said, if the faulty 34 that started this thread was sent to me, and
I found that the control *was* to blame I could cut it open and report
what I found. But I'm not going to buy one from Quad just for that! ;-

Slainte,

Jim

--
Change 'noise' to 'jcgl' if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Rob wrote:
h.tees wrote:
"Rob" wrote in message
...
I've just plugged in a Quad 34 preamp that's been unused for a few
years. When I turn the volume control up there's a series of loud
high pitched clicks through the speakers, a bit like LP static
discharge maybe. It was fine last time it was used.

Does this sound like an expensive problem, or would I be better off
punting it on ebay, and buying another (about £80 it seems)?

Thanks, Rob

It is the volume control that needs replacing. It's a very common
problem
in most audio circuits of that age and the design of the control doesn't
help. No need to bin the preamp, just find another volume control.
Maplin will sell something suitable for around £2-3. I would solder
it in or
get a friend who can - you will save a fortune.



OK, thanks. Thing is, it looks to be quite a unique part - Alps, with a
nice feel and little indented bumps as it turns. However, I'd be pretty
certain that they're available somewhere. I don't think I'd do it
myself, and there might be a 'good money after bad' type situation
building up ...

Rob

There seems to be a lot of guessing going on. Why don't you just send it to
Quad Service Dept. and get it fixed properly. It won't cost an arm & a leg
- standard service charge is UKP48.00 and for that you get a FULL service.
Defective parts over the value of UKP1.00, Freight & VAT are charged in
addition. They guarantee labour & parts fitted for one full year.
Furthermore they always use new packing material for the return journey if
you haven't got the original packaging. So you end up with a properly
functioning unit AND the correct packaging for that unit. Prices may have
changed slightly since earlier this year, but you can always phone to
confirm beforehand.

"Jim Lesurf"


Erm... IIRC the Quad 34 uses a special version of the Alps 40mm detent
stepped pot/attenuator. I doubt you will find one from Maplin for 2-3
quid!
( If so, it is about time I sent them an order for a dozen. :-) )



** The Quad 34 does not use a stepped attenuator.

http://www.geocities.com/quad_esl63/...atic/pre34.jpg

The Volume control ( RV1a and RV1b ) is wired in the inverting feedback loop
around ICs 9 and 10.

The gain characteristic of this arrangement is quite unlike that of a simple
attenuator as it effectively converts a linear curve pot to log.

So I strongly suspect RV1 is a dual gang, continuous track, *linear* pot of
about 10 kohms.

Gives a lost cost volume control with predictable log curve and good
tracking.

PW would not be able to resist it.




...... Phil

Mike Coatham wrote:
Rob wrote:
h.tees wrote:
"Rob" wrote in message
...
I've just plugged in a Quad 34 preamp that's been unused for a few
years. When I turn the volume control up there's a series of loud
high pitched clicks through the speakers, a bit like LP static
discharge maybe. It was fine last time it was used.

Does this sound like an expensive problem, or would I be better off
punting it on ebay, and buying another (about £80 it seems)?

Thanks, Rob

It is the volume control that needs replacing. It's a very common
problem
in most audio circuits of that age and the design of the control doesn't
help. No need to bin the preamp, just find another volume control.
Maplin will sell something suitable for around £2-3. I would solder
it in or
get a friend who can - you will save a fortune.



OK, thanks. Thing is, it looks to be quite a unique part - Alps, with
a nice feel and little indented bumps as it turns. However, I'd be
pretty certain that they're available somewhere. I don't think I'd do
it myself, and there might be a 'good money after bad' type situation
building up ...

Rob

There seems to be a lot of guessing going on. Why don't you just send it
to Quad Service Dept. and get it fixed properly. It won't cost an arm &
a leg - standard service charge is UKP48.00 and for that you get a FULL
service. Defective parts over the value of UKP1.00, Freight & VAT are
charged in addition. They guarantee labour & parts fitted for one full
year.
Furthermore they always use new packing material for the return journey
if you haven't got the original packaging. So you end up with a properly
functioning unit AND the correct packaging for that unit. Prices may
have changed slightly since earlier this year, but you can always phone
to confirm beforehand.

Thanks Mike - I've just had a confirmation from Quad that that is,
indeed, the deal.

Seems amazing value - labour fixed at £48 plus VAT whatever needs doing,
plus parts. Last time I took something in for repair to a local place it
cost £50 just for them to look at it.

I'll report back.

Rob

"Rob"

Thanks Mike - I've just had a confirmation from Quad that that is, indeed,
the deal.

Seems amazing value - labour fixed at £48 plus VAT whatever needs doing,
plus parts. Last time I took something in for repair to a local place it
cost £50 just for them to look at it.


** Return to factory service is NOTHING like what your local repair tech
has to do in order to fix something.

For one, the factory generally has the needed PCBs, on hand, aplenty.

For another, they will not bother attempting the time consuming, highly
skilled job of diagnosing exactly which components are faulty - but rather
will have low skilled " monkeys " swap PCBs about until it goes again.

Or doesn't.

As a result, you pay a low or fixed labour cost but a get very steep parts
( mostly unnecessary) bill instead.

Eminently repairable gear is often declared to be uneconomic or impossible
to fix by this primitive method.

Once the stock of PCBs for old models dries up - they are ****ed and so are
you.




...... Phil