His Master's Noise: A Thoroughly Modern Tube Phono Preamp

[piano3]

Sy, am I correct in thinking that you designed this phono amp for Technics EPC-305-MC?
If so could you please remind me of the tracking weight and confirm that the DCR is 15 ohms. I haven't used mine for over 20 years and I've lost the paperwork which originally came with it. I only used it for a short time as the amp I owned then had a very noisy moving coil input. In fact, it's the only LOMC I've ever owned; I bought it at great discount when I was a student.

 

[SY]

I've used it with the Technics and with a Denon 103R. Yes, 15 ohms (measured). I set tracking at 1.5 gram for the Technics.

 

[piano3]

Many thanks Sy.

 

[SY]

Je t'en prie!

 

[Freecrowder]

Just came across this article yesterday. Timed perfectly i have been looking for a high performance Phono Pre. I recently purchased a Denon 103R and am running it into Cinemag XfMR's and a Bottlehead phono pre. I was astonished of the complete lack of noise through the XFMR's. Any way to get to the point are there still a set of complete boards out there for purchase??

 

[luvdunhill]

Any problem performing the Vhk lift in the PSU chassis off the unregulated HV line?

 

[SY]

The Vhk lift is pretty noncritical, so go for it!

Freecrowder, have you contacted Jack Walton at tech-diy.com? He had boards made and I've been very happy with them.

 

[TUBESMAN]

Sy, a quick question about the FETs. I'd like to know the voltage dropped across each of them so I can size the heat sinks properly. And pick the right package. TO220 may not be needed in all spots. But if it is, well, that's OK too. Thanks!

 

[SY]

The "lower" FET has just a couple volts across it, so its dissipation is close to zip. The upper one will have 50-80V across it (depending on which stage), so is perfectly fine with a small heat sink that can get rid of a watt or two.

 

[TUBESMAN]

By lower fet you mean the one closer to the tube or ground? Right? Thanks!

 

[SY]

Yes, exactly.

 

[TUBESMAN]

One last (for now) question. The IR LED is 1.25V, I don't suppose a 1.5-1.6V LED would make a big difference. Yes? No? Thank you!

 

[SY]

It will likely require a higher B+, and increased dissipation in the first stage tube. IR LEDs are super cheap and easily available- for the initial prototype, I pulled a couple out of some old remote controls. For my nicer build,I bought them at Radio Shack.

Classy, that's me!

 

[TUBESMAN]

Yeah they are cheap but it seems they are specked at higher than 1.25V on voltage. I know you like the IR diode because of the low forward resistance. I just had an idea, how about two regular Si diodes in series to get the drop, and sets of them in parallel to get the resistance down, sort of like what you did in the RLD

 

[SY]

That won't get the resistance down because each diode will handle less current.

This one should work fine. 30 cents in onsie-twosies from Mouser.

http://www.mouser.com/ds/2/311/SFH 4141, Lead (Pb) Free Product - RoHS Compliant-532132.pdf

 

[TUBESMAN]

Ok, I will look into it. The data sheet looks good. Thanks!

 

[poli]

Thanks a lot for this fine article, Stuart!

 

[SY]

Appreciate the kind words. Update coming soon!

 

[luvdunhill]

Appreciate the kind words. Update coming soon!

Oh?

 

[SY]

In light of Merlin Blencowe's excellent JAES paper on tube noise, I'll be lowering the plate currents of the first and second stages. It won't change the performance significantly, but it will reduce heat and probably extend tube life.