First pre phono design [newbie]

[max1979]

This design is way overcomplicated...

Yes: we complicated the design just a bit .
I started with different tubes and SRPP config because I was just looking at the high gain. The decision to go for the ECC88 as first stage and the requirement to have no less than 46-48dB, imposed to get the most from the first and second stage in terms of gain, that's why we have a beta-follower and a mu-follower. Distortion seems to be lower too - at least considering the simulation.

Anyway I have to agree: that's for sure pretty complex

 

[max1979]

Normally the volume control would be after the buffer and the output coupling capacitor.

Not sure I've well understood. If you put the volume control after the buffer stage, don't you impact the output impedence that it's supposed to be as low as possible?

 

[rayma]

Not sure I've well understood. If you put the volume control after the buffer stage,
don't you impact the output impedence that it's supposed to be as low as possible?

Sure, but a 10k control is fine, with a maximum of 2.5k output resistance (at the -6dB setting).
Your circuits all put DC on the volume control, either from the previous stage or from the next stage.
That can't happen. If you do want to buffer the volume control, there must be a coupling capacitor
between it and any DC present in the circuit.

One way to avoid two coupling capacitors (before and after the control) in your circuit, which has the
control before the buffer, is to use a negative supply for the buffer's source resistor. Then the gate
can be at ground potential, and only an input capacitor is need for the control.

 

[max1979]

I don't think few KOhm is a problem considering the final stage has an input resistance of 100KOhm.
[As in the previous schema, I used a fixed resistance as volume control just to make the simulation easier]

 

[dsavitsk]

The main thing you want with the MOSFET is low Crss (i.e., drain to gate capacitance). In my latest phono stage, I used FDPF5N50FT because Crss was low, the parts are cheap and rugged, and availability is high. Distortion was stunningly low.

FQPF2N60C has lower Crss, lower input capacitance, higher voltage, and costs half as much. No idea how it sounds or measures yet.