Clicking Croft Micro Basic Volume knob - HELP!

[Wakefield Turntables]

Hi,

Can you solve this problem? I posted my old Croft micro Basic to another forum member and the volume button now seems to be clicking. I presume it's either a dirty volume pot or a dodgy valve.


I really want to get this sorted for Lawerence (who bought the amp).

Thanks

Andy

[The Black Adder]

is it in the left or right channels?... or both?

[Lawrence001]

Thanks Andrew

I think the starting point would be to clean the volume pot and see what happens. There is some debate as to whether contact cleaner is actually bad in the long run and compressed air is the way forwards. I would be interested in opinions. Also whether deoxit which I think is Amwrican is less "invasive" than servisol which may be greasy and leave a residue that is not good in the long term.

Also I noticed when I checked the valves that some of the wires and "clamps" they are soldered to come out from the valve holder when you remove the valve ie they are only held in place by the force of the valve pins, which is also a worry unless this is by design. Might also be a contributory factor.

Lawrence

[Wakefield Turntables]

fine. Keep me posted.

[The Black Adder]

Thanks Andrew

I think the starting point would be to clean the volume pot and see what happens. There is some debate as to whether contact cleaner is actually bad in the long run and compressed air is the way forwards. I would be interested in opinions. Also whether deoxit which I think is Amwrican is less "invasive" than servisol which may be greasy and leave a residue that is not good in the long term.

Also I noticed when I checked the valves that some of the wires and "clamps" they are soldered to come out from the valve holder when you remove the valve ie they are only held in place by the force of the valve pins, which is also a worry unless this is by design. Might also be a contributory factor.

Lawrence

FYI The valve base connections are designed to move slightly when plugging in/removing valves.

Back to my original question, are left, right or both channels crackling?

[Lawrence001]

Oh thanks Josie it's very loud on the right channel, if there is any noise on the left its drowned out by the right. Reminds me of a problem I saw with an MF A100 a few years ago, designed by TdeP and I think based on a valve circuit. As I understood the volume control was at full when no contact hence a dirty pot made a very loud pop, which is what I am getting now. If this is a similar circuit it would explain the loud noise. Otherwise if changing the potential across a faulty valve can make a crackle then that might be it. There are no microphonic issues I can discern from a few gentle taps.

[The Black Adder]

ok... then first of all, try swapping the valves over and see if the noise switches channels.

[PaulStewart]

If using switch cleaner, Caig DeOxit is the best on the market. Servisol is greasy and will hold dirt in the pot if it gets in later.

[Lawrence001]

I thought of switching the valves but there is a single double triode (ecc82) on the pre (buffer) stage so it's not an option unfortunately. there are 2 Ecc83s on the phone stage but I'm not sure they are configured one L one R, and as there is noise on CD too they are my last resort.

Thanks Doc that confirms my thoughts so deoxit it is then unless there is a contrary opinion forthcoming.

[Audio Al]

Send it back to Glen for the check over

[Lawrence001]

That would be the ideal solution but it's really up to Andrew if he wants the expense and hassle for the sale of a bottom of the range amp. I would imagine Glenn doesn't do the work for peanuts but I will say his amps do seem to represent great value!

[Wakefield Turntables]

As stated in our emails Lawerence try the deoxit and than as a last resort new valves, other than that I'm quite happy for it to be returned and I'll re-use in my third system.

[Firebottle]

If the deoxit doesn't work completely there is another course of action.

If the disturbance is still present the 'crackling' can be prevented by the addition of two resistors on the volume control.

The line stage valve is 'biased' via the connection through the volume control to ground. It sounds like the bad contact on the right channel volume is causing the valve to intermittently lose its correct bias, thus causing the loud crackling that you hear.
If a high value resistor, 820K or 1M ohm is connected from the centre pin of the volume to the ground pin, then the biasing will not be lost and the crackling should disappear.

:)

[The Black Adder]

Send it back to Glen for the check over


+1 The only thing to do... Glenn won't charge a lot for it so don't worry. He will know how to fix it even before it's got to him.

[Lawrence001]

Ok looking at the responses I think the best options are to try deoxit then a new ECC82,but given the cheapest deoxit spray I can find is £19.95 on ebay, I'll understand if you'd rather I just returned it Andrew.

[Lawrence001]

Ok deoxit ordered from audio affair (ebay shop was out of stock - has someone just beat me to it??) and I will post an update when I finally get it. Feeling pretty hopeful as I had thought the noise was too loud just to be debris in the pot but the post from firebottle (thanks for that) on the tube bias effect would explain how this can make such a loud noise.

[Lawrence001]

Happy Christmas to everyone!

Once I've cleaned the pot I'll post an opinion of the amp, but I can already say from initial listening that it will be rather positive. I've also got a pair of one off KT66 monoblocs ( well actually the gentleman I bought them off said when he bought them from the maker there was a second pair) that I may need some advice on. In particular biasing and what speaker loads might be optimal (as it has only a single pair of speaker taps).

[Lawrence001]

Deoxit worked a treat and the amp sounds stunning thanks for everyone's advice. it's still growing on me with its completely effortless, relaxed but detailed sound with a great sense of presence and ambience.

[Wakefield Turntables]

:gig: FAN BLOODY TASTIC! Nice to hear that it's sorted, I'll paypal you some money.

[Lawrence001]

Thanks Andrew please let me know when you have done it
so I can check it came through Ok.


:gig: FAN BLOODY TASTIC! Nice to hear that it's sorted, I'll paypal you some money.

[Lawrence001]

Received with thanks