Parallel stage in a Liverpool

[Gibsonman63]

Has anyone tried this? I would think that the first stage would bring the best results in terms of noise reduction.

So V2a moves to V2b and V1a moves to V2a, then V1a/b get paralleled?

I brought Merlin's preamp book to work so I can do a little light duty design work at lunch. If I get far enough I will scan and post my revised circuit.

[billyz]

I have not done a liverpool but, I did it to an Express. It works great, no downside that I can tell. Remember to cut your plate load in half as well as the cathode resistor. I used parallel resistors to not only obtain the correct value but further reduce the contact noise.

Theoretically you also increase the cathode capacitance to double, but I can not hear any improvement from doing so. I leave the cathode with 25uf bypassed.

[Gibsonman63]

Thank you BillyZ. I saw your comments on a recent thread and was inspired to try it. I am at a point in my build where I can do this without having to backtrack, so now is the time.

[Gibsonman63]

A little light-duty design work. Let me know if I missed something.

[Tone Lover]

Being that its headed into the tone stack has anyone tried using a cathode follower for the extra stage and would this change how the tone stack interacts with the circuit. in other words would i need to change any values to get it to sound the same with the tone controls.
Thanks Bill

[billyz]

Being that its headed into the tone stack has anyone tried using a cathode follower for the extra stage and would this change how the tone stack interacts with the circuit. in other words would i need to change any values to get it to sound the same with the tone controls.
Thanks Bill

I have tried it as a Cathode follower into the tone stack as well as into the PI. I did not feel there was much to be gained there.
Cathode followers work well to drive long cable runs though. Low impedance output. I think a cathode follower would be better used as a line out.

[billyz]

Gibson man, your link is not working for me.

[Gibsonman63]

It's a PDF and it pulls up here. Suggestions? I can email it to you if you want to PM me.

BTW, I forgot to add the paralleled resistors. I'll touch it up when I get a chance.

[billyz]

It downloaded now. Looks good to me. Try it and report back.

[Gibsonman63]

Absolutely. I am getting slammed at work at the time being, but I do manage to solder a bit most evenings. Probably another week give or take before I am ready to smoke test.

[passfan]

I recently applied this mod to a newly finished Liverpool and noticed a decrease in noise right away. I feel it is worth the effort for the return.

[Markusv]

Applied it to my Liverpool a few months ago
Settled it right down. It's almost as if the amp is less susceptible to problems with the V1 tube.

Subsequently used it for a customer's Liverpool as well as a 6SN7 output express- 'ish amp

I am pretty convinced now

Markus v