Croft preamp whistling.

[fiddlemaker]

Hi All,
I have a croft micro, upgraded by Glenn a couple of years ago to 25r spec. Over the weekend it's started to make a loud whistling sound through the speakers. It's present on both line and Phono inputs, and is insensitive to volume control position even when set to "zero". It does, however go away when the "mute" switch is engaged. Initially suspected a microphonic line stage valve, but replacing this didn't help. Anyone have any ideas?
Cheers
John

[farflungstar]

Is it on one channel or both? Have you swapped out all valves?

[Arkless Electronics]

Probably a power supply regulator issue. Not a user serviceable problem I'm afraid.

[fiddlemaker]

Is it on one channel or both? Have you swapped out all valves?

On both channels. As it's present when the line input is selected I'd assumed (perhaps incorrectly?) that the phono stage valves couldn't be the problem.

[fiddlemaker]

Any good amp fixers in Sheffield? (Or maybe I should send it to Mr Croft).

[Audio Al]

Any good amp fixers in Sheffield? (Or maybe I should send it to Mr Croft).

This :)

[fiddlemaker]

This :)

Cricket season, though.:)

[Audio Al]

Or Alan ( Firebottle )

or Ampregen http://www.ampregen.com

I have used Graeme he rebuilt my AI500 :)

[struth]

Yes sounds power related

[simon e]

I'd email Glenn, he is normally pretty good at replying. He confirmed a suspected transformer fault on my micro 25 and offered to repair or supply a replacement if I was happy with a soldering iron.

So 15 minutes with the iron and pre amp back running perfectly.

Sent from my SM-G930F using Tapatalk

[Arkless Electronics]

Or Alan ( Firebottle )

or Ampregen http://www.ampregen.com

I have used Graeme he rebuilt my AI500 :)


Any good amp fixers in Sheffield? (Or maybe I should send it to Mr Croft).

I can also fix it of course... as I'm sure Audio Al intended to mention if it hadn't slipped his mind....

[Audio Al]

I can also fix it of course... as I'm sure Audio Al intended to mention if it hadn't slipped his mind....

Are you a valve amp specialist Jez ? wasnt aware of that if you are .

[Audio Al]

John

Just out of interest what tune is it whistling ;)

[fiddlemaker]

On both channels. As it's present when the line input is selected I'd assumed (perhaps incorrectly?) that the phono stage valves couldn't be the problem.

Well, it looks like it was indeed a dodgy phono stage valve. I replaced these and the whistling seems to have gone (hesitate to say for sure, as the noise tended to come and go.....).
Thanks to all for the helpful suggestions.

[Haselsh1]

Brilliant John, so glad you got it fixed so easily.
;)

[Arkless Electronics]

Are you a valve amp specialist Jez ? wasnt aware of that if you are .

I do all types of amp other than class D... triode, tetrode, pentode valve, silicon bipolar transistor, germanium bipolar transistor, fet, mosfet igfet, vfet and anything else not yet invented... so long as it's analogue :)

[fiddlemaker]

Ah well, thought it was fixed but the whistle came back after the preamp had been powered up for a while.
:(

[Jimbo]

Ah well, thought it was fixed but the whistle came back after the preamp had been powered up for a while.
:(

Just send it back to Glenn, he is certainly the best person to sort it.

[fiddlemaker]

Just send it back to Glenn, he is certainly the best person to sort it.

yes, sent him an email to hopefully make arrangements.

[fiddlemaker]

Now fixed by Glenn, at no charge.
Gentleman, scholar, legend.

[Jimbo]

Now fixed by Glenn, at no charge.
Gentleman, scholar, legend.

Glad you got sorted John.

He is certainly one of the best and as you say a true Gent.