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.

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
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

Try 5687 or

Thatt's what I was thinkting .
Maybe the new JJ ECC99 is a good option also .
http://www.jj-electronic.sk/tube_ecc99.htm

Ronald .

"Nothing40" skrev i en meddelelse
om...
Maybe I could tweak the circuit for a 12AT7,or something that would
be a better choice for this application..

I dunno,Any suggestions?

Try to look at his little beauty:

http://www.triodeel.com/6h30.html

/ Hans

In article ,
(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.


Assuming the sound card has a moderately low output resistance, I would go
with a 12AU7, with a bypassed cathode resistor to keep the gain as high as
possible, and the output resistance as low as possible. I would then
connect an op amp style negative feedback loop around the tube, to set the
desired gain, and further lower the output resistance. The op amp style
feedback loop uses a resistor between the input and the grid of the tube,
with a second resistor connected from the output, back to the grid. You
might start with a 100k resistor from the input to the grid, and a higher
value for the resistor from the output back to the grid. The gain is
roughly proportional to the ratio of the two resistors, as long as the
ratio is small, although it is actually less because of the finite gain of
the tube.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

Behold, Ronald scribbled:

Try 5687 or

Thatt's what I was thinkting .
Maybe the new JJ ECC99 is a good option also .
http://www.jj-electronic.sk/tube_ecc99.htm

Ronald .

AHHHHHH! When did they make their website into a sucky Flash nav thingy?

:'(

--
Gregg
*It's probably useful, even if it can't be SPICE'd*