Valve Mc Head Amp

[Ianm2]

For Stepping Up Mc Carts.

[RobHolt]

Can this be done without generating lots of noise?

I'd be interested if it were a real possibility.

Rob.

[NickG]

I voted for the "madness" option. I think it would be next to impossible, totally impossible using valves that could used in a kit, and I am not sure what it would achieve. The two common options are step up TX's, or a jfet cascode, I don't know what the jfet sounds like, but I can't see any problems with transformers myself, and in terms of cost, to do it well enough to be of use could well cost as much as a good set of transformers anyway (maybe as costly just for a quiet enough power supply).

Transformer!

You are unlikely to give better quality/value than a cheap (~£60) pair of Lundahls that have tappings to give 5:1, 10:1 or 20:1.

[Ianm2]

hmm I have a anode follower std. commercial circuit,

but perhaps a differential pair of ecc82s with a solid state rectifer and big capacitors may work, the diff pair could cancel some noise and all that?

[NickG]

What valve does the anode follower use, and whats the noise level, and what level of MC output is it designed for?

I don't think a differential pair will help, its self generated noise thats the first problem. It will help with the PSRR but I don't think it would have any positive (and maybe a negative) effect on that noise.

[BOONDI]

Originally Posted by NickG

The two common options are step up TX's, or a jfet cascode, I don't know what the jfet sounds like, but I can't see any problems with transformers myself, and in terms of cost, to do it well enough to be of use could well cost as much as a good set of transformers anyway (maybe as costly just for a quiet enough power supply).

Did you build one of the Mc op amp circuits in issues 6 and 7 of the Suplement?

If you did and you used the AD 797 then you used a Jfet op amp.....

Am using AD 275gp op amp in this circuit for MM just now and it sounds excellent. It is a dual butler input op amp with bipolar and Jfet characteristics. It has a voltage noise of 6nV/hz over the entire 1-100k Hz range. This may be a good idea for a hybrid circuit with jfet input and valve output......

I know that most people reading this will hope I burn in hell, but these op amps cost about £2.20 each and offer exceptional performance for the money. They run on about 30 mA of current and can swing 10 V p-p.
Seems like an experiment worth trying out for someone who knows a bit more about valves than me tho......

[NickG]

Just for the record it was the Allen Wright jfet-valve type of cascode I was talking about. Of course a low noise opamp will give the required gain, but the poll was talking about a Valve MC head amp.

[BOONDI]

Not familiar with the Allen Wright hybrid, but I think this type of circuit for MC would be easy to build and give decent results.
I know that the thread is about an all valve MC stage, and you wouldn't want to get involved with a sand amp, but I think this may be the best compromise to the hiss/noise problems that occur in high gain valve phono stages.....

P.S. Correction to the post above (Because the edit button has disappeared....)
The 797 is a bipolar, The other op amp, the AD743, that was used, was the one with the fet input.

Just my 2d worth......