Unbalanced Buffer Linestage

[Panelhead]

I am wondering if someone can recommend a DIY unity gain line stage. Since I am an unbalanced person the ability to convert back and forth between balanced and unbalanced is not important.
The unity gain is important due to the 100 dB efficient speakers I use. A normal gain linestage puts the volume pots just barely cracked open. And hair trigger pot response.
I looked at the BLS, but the gain and the recommended input impedance are an issue. Several of my sources work best if they see a 100K or so load.
The buffer at the input of the Zen V4 looks like an easy solution, but would prefer using a dual rail supply. This may allow DC coupling.
Currently I have build one using a BUF634. This is sounding nice, but a discrete circuit should perform better. There are a lot of devises inside the BUF chips. This could be done much simpler.
Also a fairly low set of rails (15 - 30v) would allow use of parts on hand.

TIA,
George

[mlloyd1]

Do you want symmetrical or single ended? bipolar, FET or Tube?

For symmetrical, take a peek at the Borbely Audio Site

And the BUF634 is really not that bad of a device. You have to be careful with rails, decoupling , etc.

Just for kicks, for my unity gain line driver needs, I've been playing around with a dual JFET source follower in front of a LM6321 buffer. Nothing fancy, but it's not bad.

mlloyd1

[Jocko Homo]

The LM6321 works fine by itself. If you can find one.

If not......JFETs! Bet Signoro Lloyd will sell you some of his.

Jocko

[mlloyd1]

Oooohhh no. They're mine, all mine and you can't have them!
ah, hah, hah, hah, hah, haaaaaaah

I'd part with a buffer before I part with a FET and you can quote me on that ....

D@mn- National discontinued the LM6321 What next ....

Oh well, go visit headfi . They keep up with buffers MUCH more than I do.

I've got a clock circuit to think about now (Thanks Jocko) Can't let them digital boys have all the fun ...

mlloyd1

Originally posted by Jocko Homo
The LM6321 works fine by itself. If you can find one.

If not......JFETs! Bet Signoro Lloyd will sell you some of his.

Jocko

[tiroth]

You can easily configure BLS with gain of 1 (read the PDF for notes). Make the load whatever is required for your source.

If you use CCS on the tails the common mode rejection is high even for unbalanced input.

I know you specified balanced not necessary, but diff. pair is a common input tool.

[Steve Eddy]

Here ya go.

<center>
<img src="http://www.q-audio.com/images/buffer.jpg">
</center>

Just about as simple as it gets.

se

[Jocko Homo]

Put R2 on the other side of R1. Or add a gate damper. <100 ohms should work.


Jocko

[Steve Eddy]

Originally posted by Jocko Homo
Put R2 on the other side of R1. Or add a gate damper. &lt;100 ohms should work.

It works fine as is. It's been out in the field for better than a dozen years and haven't had any problems with it.

se

[Panelhead]

Steve,
I will build it and compare to the BUF634 used now. It is perfect, even the rail voltage is the same. The power supply will not require a single change from the one used for the BUF's. But moving R1 should not hurt, and may help.
One question, what kind of current does this circuit draw when built as drawn up? I have the BUF634 biased to 9 ma, but they are not current limited in my simple supply.
Never used those FET's before, I will have to find a few.



George

[Panelhead]

Maybe I should be posting this on the parts page, but looking at Digi-Key, Mouser, and Allied the 2N5566 does not look availabe. Is there a better part number to search for?
I downloaded the data sheets and I like the dual chip, one for each channel in this application.

George