X-Pre making strange noises!

[fanshawe]

Hi folks,

I've got an X-pre (stock, as far as I know) that I've had for several years without problems. Today it seems to have gone 'resonant' on one channel; in other words, if I physically tap on the casing or on a control, I can hear this coming through one of the speakers 

Any suggestions on how to fix? Is this what people call valves 'going microphonic'?

Thanks in advance!!

[jc]

Pretty likely it's a valve on its last legs. To double check swap the valves around and see if the problem changes channel with the valve. If yes then a new pair is recommended.
pinkfloyd has a range of GENUINE NOS valves he sells here that he matches into perfect pairs for you at reasonable prices.

Check here and contact him directly if required.

[PinkFloyd]

Oct 1, 2015 12:14:46 GMT fanshawe said:

Hi folks,

I've got an X-pre (stock, as far as I know) that I've had for several years without problems. Today it seems to have gone 'resonant' on one channel; in other words, if I physically tap on the casing or on a control, I can hear this coming through one of the speakers 

Any suggestions on how to fix? Is this what people call valves 'going microphonic'?

Thanks in advance!!

Hi Fanshawe,

The valve has gone microphonic, for sure, and if both valves have been in the X-Pre for "several years" then rest assured they are well past their best and will have drifted way out of specification. The best way to be 100% certain is to open the X-Pre up and swap the valves over..... the problem will then migrate to the other channel.

It's easy to change the valves in the X-Pre, you just undo all of the screws and slide the circuit boards out of the enclosure (pulling the front panel towards you) and then it's a simple case of pulling the old valves out and fitting the new ones. This will show you what the inside of the X-Pre looks like: rockgrotto.proboards.com/thread/9361/musical-fidelity-pre-rejuvination When you put it back together (a two minute job) remember to feed the ground tag between the rear plate and enclosure.....

This is the ground tag:

i157.photobucket.com/albums/t69/pinkfloyd2007_bucket/X-PRE%20modifications/DSCN5911_zps6e9ce641.jpg~original

It's pretty much the same for all of the X-Series and this will give you the general idea:

www.rock-grotto.co.uk/x-can-v2-tube-rolling.htm

Apologies for the picture quality, I uploaded that tutorial about 15 years ago and the best camera I had to hand back then was a whopping 1 mega pixel

The "stock" valves that come with the X-Pre are the JAN Philips 6922 but you can use 6DJ8 / E88CC / ECC88 / 6N23P to name but a few. I wouldn't be too particular about the "name" on the valve, the most important thing to ensure is that the valves you are buying are GENUINE new old stock and they measure within "as new" specs when tested.

There are a few reputable companies I can recommend (ebay is not one of them) if you choose to go down the amperex / siemens / mullard route. If all you are looking for is the best sounding, best matched pair of valves on planet earth for your X-Pre then drop me an e-mail:

rock.grotto (AT) gmail (DOT) com

Hope this helps.

All the best,

Mike.

[fanshawe]

Many thanks both for the advice - I've just swapped the valves over and the problem does indeed switch from the right to left channel. So I'm in the market for some new valves, email on its way shortly Mike!

Cheers