Your on the right track, below is an example of a similar setup using 6SN7’s this arrangement sounds fabulous, if you want to stick to 9-pin tubes I would use a 6CG7, use a MOSFET as a sub for the cathode follower.
And LM334 as a ccs.
The gain is adjustable as well.
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Quite agree, I see one problem on first glance with their scheme, the first triode needs a coupling capacitor after the 300K load resistor, over time their would be a tendency for the circuit to start motor boating!
Is there any obvious differences between 6SN7 and 12AX7 for the input
differential amplification. can we use tube as ccs to replace for the LM334
Huge difference in tubes, two different beasts, the 12AX7 requires much more feedback to achieve a reasonable gain for a line stage, and the 6SN7 is a much more linear tube to boot.
You definitely could use a tube for ccs, but you would have an additional heater supply, and a much larger negative bias to worry about and I don’t know if it would perform, or sound any better!
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Looks like something I might try. Couple of questions.
- Do you know the HV supply needed?
- No load resistor in the first triode?
- What is the gain?
Thanks.
Its also a diferential schematic, it doesn't need a resistor the CCS fixes the operating conditions of that triode, the gain depends of the tube, with a 6sn7 will be like 10 (I'm guessing
) the HT something like 100-200V (IR820 has a rupture voltage of 200V Max) you can use a DN2540/IRF710/FQPF3N60...You may look for a low Crss miller capacitance in those something like ~50 pF or lower if you use a higher capacitance one it will have a low slew rate or may oscilate with ease
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I’m running them at 250VDC, the first triode is basically a cathode follower. The gain can be set from about 12dB to about 18dB, depending on the ratio of the feedback. I think the variable resistor should be around 25K instead of 10K.
The 334 is set for a 10mA cathode current.
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I read somewhere that the 6SN7, 6SL7 internal structure was symmetrical, unlike the 12AX7. Stated they sound better?
I have heard the Octal Cornet and it was very nice. A lot of neat design features.
I also like 6DJ8 and 2SK170/417a phono stages.
BTW, I'm not promoting or knocking anyone's design, just thinking out loud.
I hope the original poster is finding what he is looking for.
I have heard the Octal Cornet and it was very nice. A lot of neat design features.
I also like 6DJ8 and 2SK170/417a phono stages.
BTW, I'm not promoting or knocking anyone's design, just thinking out loud.
I hope the original poster is finding what he is looking for.
I wouldn’t worry, we should think critically about others designs! I don’t like a 12AX7 in a line stage, for one is the higher impedance one has to work with even using one as a cathode follower. It doesn’t mate well with low impedance SS amplifiers.
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