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Jay 25th September 2005 06:15 AM

SRPP + Gainclone
I use Peter Daniels' NIGC circuit, driven with 6SN7 SRPP (mu-follower). My POT is B20K. I put the pot between the SRPP and the Gainclone. The input on 6SN7 plate is 220R and 100K to ground.

I haven't had time to draw the circuit, but my preliminary question is, where should I put the 20K POT, before 6SN7 or after?

Another question is what should be the correct resistors circuit and values to provide for good impedance matching? And then how to arrange for star grounding. But these need picture....

morfeas 25th September 2005 03:17 PM

SRPP will be a waist of gain, gainclone been easily driven.

I would suggest a cathode follower. Look up the JLTI amp for ideas. Don't miss

The pot should be placed before the tube stage.

Jay 27th September 2005 02:45 PM

Thanks morfeas. You're right that the Gainclone doesn't need too much drive. But my experience with BOZ told me that this is crucial for dynamic capability.

I couldn't find the JLTi schema, I mean the one with transistor current source (I don't like usual CF). A friend promised me to send a schema. He said the sound is soo good. But because we have different liking, I have no comment yet. He said that the function of the buffer is simply to inject 2nd harmonic. I said I don't like second harmonic and he said that if I don't then I don't need the tube. I cannot agree with this because I don't think that the tube is merely for adding 2nd harmonic.

Oh, is there a reason why the 20K pot should better be placed before the tube?

morfeas 27th September 2005 03:10 PM

Consider that your comment on "dynamic capability" maybe due to the previous stage (pre or source) unable to drive the low input impedance of the gainclone. A tube will help on this having much higher input impedance so it's easier to drive.

The actual JLTI schematic is copyrighted. But i think you get the main idea.

As for the tube related harmonic stories, they can varry depending on design.

The pot is best before the tube just because the opamp doesn't like it otherwise. See relative posts in the chip amps section.

Shoog 27th September 2005 06:27 PM

Hi there,
Unless you really want to experiment with valves I would point you to the discrete bipolar buffer which can be found on Decibel Dungeons website. To my taste this certainly sounds better than the basic JTi buffer which to my way of thinking doesn't use high enough voltages.
If you want to try a good valve buffer then think at least 100V's otherwise you will probably be dissapointed. Also think CCS loading.
I would agree that there is nothing in a valve circuit that needs to introduce harmonic distortion, if its done correctly.


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