Need tube buffer circuit for sub-woofer out

[Gilbert]

Can anyone recommend a single stage circuit for *buffering* a signal for a sub-woofer output?

Currently building a S.E. 2A3 amp using one gain stage using the 6SL7.

I'm devoting the second half of the 6SL7 as a buffer stage for a sub-woofer output.

Need inversion so I can't use a cathode follower which is non-inverting.

Don't really need any gain. I don't think so anyway.

Thinking about a 'conertina' or split load stage to where I just take the signal off the plate with no gain.

If I set it up as a more typical gain stage, then I guess I'll need a resistive divider of sorts to bring the signal back down to 'line level'.

Probably will need a RC filter of sorts to capacitively couple it to the sub-woofer.

Any suggestions?

Thanks,
Gilbert

[Eli Duttman]

The concertina idea seems to have some promise, but high Rp/low gm types, like the 6SL7, are not so good for concertina service. If you're building a stereoblock, you could use a single 6SL7 for voltage gain in both channels and a single 6SN7 for the concertina in both channels.

Instead of a concertina, you could wire a 6SL7 section as a so called plate follower. A "plate follower" is a single stage tubed opamp that uses plate to grid NFB to produce an inverting block with little or no gain. The NFB lowers the O/P impedance, which is good for driving the SW.

[Brett]

Originally posted by Gilbert
Can anyone recommend a single stage circuit for *buffering* a signal for a sub-woofer output?

......................

Any suggestions?

Use an opamp (with a decent one, it won't make a scat of sonic difference) and parallel the 6SL7 stages to drive the 2A3.
Personally I'd ditch the 6SL7 to drive the 2A3, but that's a 'nother whole discussion........

[Sch3mat1c]

Single 6SL7 has been used for 2A3 just fine with no loss of highs.

Use shunt feedback to reduce gain. Cathodyne will have non-existant output admittance it'll suck so much.

(Admittance is opposite of impedance, I just thought I'd drag that word out because it's so annoying to have to invert other parts of the sentence when referring to inverse terms!)

Tim