Any schematics for balanced line driver using 6922?

[leadbelly]

I think the subject says it all: I have 6922's, I'd like to make a unbalanced-to-balanced preamp for my Aleph-X...any help is welcome.

Oooh, my first post in the Tube forum...fun!

[runeight]

How much gain do you need?

If you don't need gain, many on this forum would suggest a good audio transformer. Jensen is a good place to start.

If you need gain, the design depends on how much you actually need.

[leadbelly]

Originally posted by runeight
How much gain do you need?
If you need gain, the design depends on how much you actually need.

I would be happy with unity gain. I know my options in transformers or solid state, so it is not a question of my thinking this is the path of least resistance. I think it would be a great, simple tube project that might just sound wonderful.

[runeight]

If you don't mind cathode followers (and I don't when they're biased correctly), you can try something like this. It's a simple split load phase splitter driving two CFs as output buffers.

It does need a few different supplies, but they're easy to make.

[leadbelly]

Thanks! It looks great.

The number of voltages required is a drawback as I was hoping to use transformers out of my parts bin. Would halving all of the voltages (-50, +50, +100) be a bad idea not even worth trying?

[runeight]

I think that halving the voltages would be sum-optimal, although 6922s don't mind low voltages too much. The performance, especially the THD, will likely suffer.

You can buy 120VAC Triad transformers really cheap. You would only need two of them to provide +/- 100V and the +200V could be had from a voltage doubler. You can even use VR tubes to regulate. 0B2 will regulate at about 108V. Close enough for this amp.

[leadbelly]

Hmmm, I think I can make do using multiple surplus transformers.

I was planning to use CLC regulation. Is that OK?

And what kind of transformer current draw would I be looking at for 2 channels (3 tubes)?

Lastly, if I only get close with voltages, which would be better: under (-85, +85, +170) or over (-115, +115, +230)?

[fdegrove]

Hi,

And what kind of transformer current draw would I be looking at for 2 channels (3 tubes)?

Running every triode on an average of 15 mA would give 6*15 =90 mA without the VR tubes.

Add another 15mA for every VR tube used.

Lastly, if I only get close with voltages, which would be better: under (-85, +85, +170) or over (-115, +115, +230)?

The latter would be far better: don't forget either that the VR tubes need some extra voltage for the gas to ionise ( striking voltage).

Cheers,

[leadbelly]

Thanks!

And another thing I just thought of: where would I put a volume control pot, on the unbalanced or the balanced side, and what value?

[fdegrove]

Hi,

where would I put a volume control pot, on the unbalanced or the balanced side, and what value?

I'd put a 100K log pot right infront of the 1M gridleak at the input.

Cheers,