Nothing40 wrote:

Hey gang..

I just got a new soldering iron,and I need to break it in!
I thought modifying my little "copper critter" preamp might be a good
project.
A small preamp I made to use between my PC,and stereo preamp,as my
sound card has a low-ish output level.
Currently it's a pretty plain 12A_7 stage,1 triode per channel, 100K
plate load, .1uf coupling caps,cathode bias,ermm.. about 1.5Vk.
I was thinking of changing this to a cathode follower,or something
similar,so it would have a lower output impedance.(so I can drive
*flamesuit on* SS amps!) Problem is,I need gain,and only have a single
9 pin socket!
Maybe I could tweak the circuit for a 12AT7,or something that would
be a better choice for this application..

I dunno,Any suggestions? Patrick.

I'd go with a 12AU7, run fairly hard (about 150v, 10 mA), with a lot of
cathode feedback. For instance, about 10k plate load and 2.7k cathode
resistor (unbypassed). This'll give you a gain of about 10 dB, which I'm
presuming will be enough, and a fairly low output impedance (well under
10k) with tons of headroom.

You can do a bit of tube-rolling with 12AU7's and 12AT7's, though with
that much local feedback I doubt you'll hear a significant difference.

Cheers,
Fred
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