Valve Buffer amp

[Brit01]

I'm in the process of gathering materials to put together an Aikido pre-amp but I would also like to learn more about buffer amps.

I have a great SS Carver pre and power amp but would like to experiment placing valves in the path somehow.

I've heard of buffer amps but don't know much about them. Would this be a valve amp with no gain, just colouring the sound with the valve??
Would this be used between the pre and power or between the source and Pre??

Are there kits available?

Cheers

[Eli Duttman]

Yes, a buffer amp is "unity" gain. Usually, a buffer is a cathode follower and they tend to be linear. You may get some benefit if a tubed buffer is located between the O/P of a CDP and the preamp.

All too often, SS equipment exhibits a nasty 10 KOhm I/P impedance. You want to use a HIGH transconductance (gm) type. High gm makes for a low O/P impedance buffer, which is exactly what the situation calls for. JJ's ECC99 is a suitable type for the job.

BTW, you should use a bipolar PSU, as that eliminates a cap. in the I/P circuitry.

AFAIK, a kit for this specific job is not available.

[Karsten Sømand]

Hi Brit01

You could also have at look at SY´s new buffer / preamp as well. This preamp is with an input transformer of very high quality (Jensen) and the circuit is with DC-servo to avoid the (big, expensive) capacitor in the outlet.

You can find a very detailed description under "The Heretical Preamp": www.syclotron.com

Kind regards

Karsten

[Geek]

Here's a great buffer:
http://geek.scorpiorising.ca/GeeK_Zo...30521#msg30521

The only mod I have done is change the 2.2M||.047 X2 cap to a 100 ohm, 2W metal oxide. Reduced hum.

Cheers!

[Brit01]

Thanks guys for the info here.

I'm a beginner so some of the info you gave was a little chinese like.

SS equipment exhibits a nasty 10 KOhm I/P impedance. You want to use a HIGH transconductance (gm) type

I'll need to do some reading about this

FYI in case this info is needed. I have a Carver power amp with 380 watts per channel at 8 ohms and very sensitive speakers (93db). Also a pre-amp with a holographic feature which I love and would like to maintain this in the path.

[Geek]

High transconductance tubes have a lower output impedance. The ECC88 buffer I posted as an output impedance of 100 ohms as tested (depending on tube variance, it can be as high as 160 ohms). It can drive even a 5K volume pot.

Conversely, low Gm high gain tubes, like the 12AX7 in buffer have an output impedance of around 5-6K and shouldn't be used to drive anything less than a 50K input volume pot.

Cheers!