6SL7 diff pair - how to set up????

[fdegrove]

Hi,

The paraphase divider is 470k/58k/470k. The 58k is the value that has to be tweaked, depending on gain of the stage. I have both srpp cathodes bypassed. The divider is on the 2a3 side of the capacitor. I also used 470k grid leaks and 1k grid dtoppers on the 2a3's.

Meaning you have the gridleak resistors (470K) in // with the voltage divider (470K/58K/470K)?

Cheers,

 

[JimW]

paraphase

Yes, I am using the same arrangement as your sample circuit, just different values.

 

[fdegrove]

Hi,

Yes, I am using the same arrangement as your sample circuit, just different values.

O.K...I figured as much.
However, nothing spectacular but, the voltage divider/gridleak and " gain correction" resistor, for want of a better word, can be simplified by referencing the divider network to ground like TD does here:

MUPP

As the author explains in the accompanying text, the mu-follower already reaches the maximum gain so there's no need for the bypass cap across the cathode resistor of the bottom part of the paraphase splitter.
Also, as he wanted to use the 6SL7 iso the ECC88 he chose to use a mu-follower to arrive at the lowest possible Zout for that stage to overcome the Miller capacitance of the 2A3s.

The same idea could of course be applied to the ECC88 at the expense of another twin triode which of course has to be fed as well....
I like the simpler approach better but that's my POV.

Cheers,

 

[JimW]

simpler approach is often best

I arrived at my scheme because I had as a starting point 2 stereo srpp set's, which I converted to push pull just to see if it would work. I have thought of building the Td/FdG circuit to see how it sounds. Frank you said you have built it - how did it sound?

 

[fdegrove]

Hi,

Frank you said you have built it - how did it sound?

It sounded way better than the original setup which had 1/2 of a 12AX7 for voltage gain and the otherhalf wired as a cathodyne splitter driving the PP pair.

It is however a bit short on gain so it can do with a line level preamp quite nicely.....
Meaning you don't actually have to dump all the gain on the attenuator....

All in all it's not state of the art but it does throw up the sonic differences between various brands of ECC88s and 6922s, always a good sign in my book.

Let me know what you think of it should you try it one day.

Cheers,