View Full Version : LCR Phono stage

03-12-2008, 10:28
Hi folks, here's my new project, completed yesterday!

It's an LCR phono stage using Silk 10k RIAA modules and Western Electric 448A tetrodes.

There are a couple of issues - it's microphonic as all hell, and needs some screening as it seem to pick up radiated hum from just about anything. Still, I'm liking the sound (a lot! :) ) I'm sure I can solve the microphony and hum problems in time. :scratch:


03-12-2008, 11:16
Wow - sexy and very professional looking! :youtheman:

I'm sure some of our resident experienced D.I.Y-ers will offer their advice on how best to cure the hum and microphony issues.


03-12-2008, 11:21
Wow - sexy and very professional looking! :youtheman:

I'm sure some of our resident experienced D.I.Y-ers will offer their advice on how best to cure the hum and microphony issues.


Thanks Marco!

I'm open to suggestions on the hum and microphonics!

03-12-2008, 12:24
Super work as always Pete. :)

Taken from Linktech:

In some circumstances tubes can start ringing when they are subjected to physical vibrations, we have done a lot of tests to determine what is the best way to cure these microphonic vibrations. Avoid hard mounting the tube as this will stop vibrations from being transmitted into the internal tube structure. We have tested many combinations of mounting techniques and have found that the best dampening material is expanded foam Neoprene tubing. The tube is mounted into a cylinder of this material and then clued down. The other source of vibration is the tube connecting wires, these are rather rigid and any vibration will travel up them into the Tube.

We found that by cutting the Tube leads and installing very fine (like hair) soft Copper wires allows for no sound vibrations to get into the tube. This makes the tubes near noise free and is great in the recording studio or other audio applications that need the best sonic performance.

03-12-2008, 15:10
I like it, and want one! I've mumbled about an LCR phono stage before. :)
I heard Andrews at the Chester meeting and was very impressed.

The valves on mine poke out of the top of the case just like yours and pick up just about anything, seemingly for miles around!

Cured by using 'Pearl Valve Coolers' which seem to work nicely as screening cans and tube dampers at the same time.


03-12-2008, 15:29
Interesting - mine varies and it seems that you can tap the chassis and send it off oscillating. I've clipped off the extra cathodes from the 448As and that helped, but it still seems to be borderline stable. :scratch:

I've read that excessive microphonics can be due to oscillation, and that seems to be the case here. When it's behaving, the microphonics aren't too bad. :steam:

03-12-2008, 16:08
Wow looks really impressive!!
How did you get on with the Silk transformers
Hope you manage to overcome the hum issues might be worth speaking to SAC I found the owner/designer to respond quickly to questions in the past
Once its all sorted do you mind writing a report I think you will have something that is very special

03-12-2008, 18:57
Hi John, The Silk seem pretty good, at least I like what I'm hearing very much so far! It's early days yet, but it compares favourably with my P10 in my previous stage. Then again, it cost more in parts than the P10 does retail!

The only problem is that it occasionally misbehaves, breaking into oscillations or becoming really microphonic. It seems better now that I have re-soldered the grid stoppers as close as possible to to the pins, and clipped off the extra cathode pins. I think it's basically borderline stable, perhaps some screen stoppers are next or maybe increasing the value of the grid stoppers.

04-12-2008, 16:59
After much faffing I discovered the problems were due to one of the tubes. The farting noises are now gone and it's sounding nice!

07-12-2008, 23:36
When troubleshooting like that always check the tubes first, dude ;)


pure sound
08-12-2008, 09:29
I heard this at the weekend. Its very, very good.

purite audio
08-12-2008, 09:39
Of the Allnic stages I prefer the LCR eq 1500, how much of the SQ is the LCR module responsible fo do you suppose?

pure sound
08-12-2008, 12:19
Alot if its done well. Pete has modelled quite a number of different existing LCR circuits in SPICE and most of them are actually quite inaccurate with regard to the RIAA curve. His looks very accurate and the Silk modules also seem pretty good. There may be some further tweakery that can be done with a few passive components & possibly the power supply but the basic design seems very close to where it would want to be. Possibly the best phono stage I've heard.

08-12-2008, 13:57
Any chance of a schematic and parts list please? :)


08-12-2008, 19:02
Wow! Thanks for the compliment Guy! NOt sure it's *that* good, but I'm very happy with it.

Mike, you have PM.