6SN7 and DN2540's

[tmblack]

Anyone tried a 6SN7 preamp using DN2540 current source as anode load and LED for biasing?
What would gain be?
I think this would sound great if it can work.

[SY]

The ImPasse preamp is made almost exactly that way. See Jack Walton's writeup on it at http://www.tech-diy.com/Preamplifier...mpasseSaga.htm.

[tmblack]

I see the writeup but is the Impasse a commercial product?
I don't see a schematic, I'll have to build my own.

[SY]

The project was published in AudioXpress from whom you can order back issues. Jack is selling boards and kits, which come with schematics (I have no financial interest in this, other than getting a couple of free boards- Jack's profits get donated to running this forum). The performance is quite good as my measurements and his would suggest. So far, people who have built it are quite happy with the sound.

[Magz]

I use the 2C22 (which is similar to 1/2 of a 6SN7) in my preamp, with cascoded IXYS 10M45S CCS plate load and Cree SiC Schottky diode bias, running at 14.6mA plate current and 3.4V bias. First I went from a resistor + bypass cap on the cathode to the diode bias - big improvement in bass depth and overall clarity and detail. Then I added the CCS load and WOW - images just snapped into focus and everything sounded so much better. Another bonus was the increase in gain - I was able to use a single 2C22 to replace both sections of a 6SN7 (using resistor loading on plate and cathode) and still have plenty of gain for my sources.

So to answer your question, yes it works, and maybe you don't even need a dual-section tube. A 2C22 or 6J5 may be an alternative for you.

[tmblack]

Magz, good work, what voltage are you running it at and what is the voltage gain of the stage? Are you using a buffer after that?
The distortion should drop like a leaf.
I have a few 6SN7 and 6922 so I will want to use them.

[Gluca]

Originally Posted by Magz

I use the 2C22 (which is similar to 1/2 of a 6SN7) in my preamp, with cascoded IXYS 10M45S CCS plate load and Cree SiC Schottky diode bias, running at 14.6mA plate current and 3.4V bias. First I went from a resistor + bypass cap on the cathode to the diode bias - big improvement in bass depth and overall clarity and detail. Then I added the CCS load and WOW - images just snapped into focus and everything sounded so much better. Another bonus was the increase in gain - I was able to use a single 2C22 to replace both sections of a 6SN7 (using resistor loading on plate and cathode) and still have plenty of gain for my sources.

So to answer your question, yes it works, and maybe you don't even need a dual-section tube. A 2C22 or 6J5 may be an alternative for you.

this^

I have been using 6CG7 (noval version of 6SN7) with cascoded DN2540's as load and LED bias. Very happy with the results.

[Magz]

Originally Posted by tmblack

Magz, good work, what voltage are you running it at and what is the voltage gain of the stage? Are you using a buffer after that?
The distortion should drop like a leaf.
I have a few 6SN7 and 6922 so I will want to use them.

Plate voltage is about 175V. I estimate the stage gain at about 17. The 2C22 is followed by a Lundahl LL1674 amorphous cobalt core transformer wired 4:1 in a parafeed type output stage with a 1uF cap. Output impedance is about 450 ohms.

[dgta]

Originally Posted by Magz

I was able to use a single 2C22 to replace both sections of a 6SN7 (using resistor loading on plate and cathode) and still have plenty of gain for my sources.

I'd be interested in seeing that. 2 cascaded stages of 6SN7 give well over 200 gain easily. How do you get that out of a single stage/tube?

[Magz]

I don't. I didn't say I get the same gain as the 6SN7, I said I get plenty of gain for my sources. With the 6SN7 there was far too much gain, and the preamp resorted to various gain-dropping tricks such as resistors across the output transformer secondaries, and still the volume knob remained below 10 o'clock at all times. Now the knob is almost always between 11 and 3 o'clock.