Tube phono stage build

[kevinkr]

Have a look over in analog source for alternative designs from Salas and myself.

 

[PRR]

> keep the investment in parts minimal in case things go south.

I may be mis-remembering the bad old days.

But I think by "going cheap" you are already on the south-bound ramp.

Also not keen on "small chassis". If you plan to put the PT on there, you'll have hum problem.

 

[Eli Duttman]

FWIW, I strongly prefer LR8 regulation, with an IC dedicated to each channel. Take all legitimate steps to minimize residual hum. Separate regulators improve channel separation.

While AC heating is possible, don't go there. The challenge is TOUGH, for a very experience builder. Build a proper, regulated, 12 V. DC heater supply. You need 300 mA. of 12 VDC current. Voltage doubling 6.3 VAC requires a filament winding capable of 1.2 A. TANSTAFFL! An example DC heater supply is provided. The same topology with different parts is what you use in the B+ PSU.

 

[creeve]

FWIW, I strongly prefer LR8 regulation, with an IC dedicated to each channel. Take all legitimate steps to minimize residual hum. Separate regulators improve channel separation.

While AC heating is possible, don't go there. The challenge is TOUGH, for a very experience builder. Build a proper, regulated, 12 V. DC heater supply. You need 300 mA. of 12 VDC current. Voltage doubling 6.3 VAC requires a filament winding capable of 1.2 A. TANSTAFFL! An example DC heater supply is provided. The same topology with different parts is what you use in the B+ PSU.

Thanks! The transformer that I have has a 6.3v secondary at exactly 1.2a so I assume I can use that and build both heater and B+ supply in the same box?

 

[Eli Duttman]

Thanks! The transformer that I have has a 6.3v secondary at exactly 1.2a so I assume I can use that and build both heater and B+ supply in the same box?

Correct.

 

[creeve]

So I have ordered the parts for Eli's version of the RCA phono stage. In the mean time I put together the PSU and just for the entertainment and educational value I put together the schematic that I originally posted because I had those parts. Anyway I am shocked. It has issues but in a lot of ways sounds excellent!! It is quiet, awesome detail and resolution, good soundstage but the trouble is there is virtually no bass. Either that or the HF is overpowering it. It has a ton of gain in fact way too much. I actually see potential in this thing. Does anyone have any suggestions on what may be causing too much gain, too much treble and lack of bass? Maybe this could be the start of a really good sounding pre.

 

[Sodacose]

Regarding knocking the B+ down to ~250Vdc, I had success using 0D3 and 0C3 regulator tubes in a shunt configuration for a phono preamp (also a pair of 12AX7s and a MOSFET like Eli's design). They also look very cool: