Aleph P or BOSOZ variant

[stefan]

Hi all,
I think some time on preamplifier and modify Aleph P schematic. In result may be I'm closer to BOSOZ.
OK, here is my latest schematics.

As you can see there are several specialities:
1. I use bipolar current sources. They are simpler than sources in Aleph P and are (may be) better.
2. Instead of zener diodes I think that ordinary diodes (D103, D104, D105, D106) can be used to protect MOSFETs. Do you think I'm right?
3. I use assymetric power voltage (+25 / -15V). It's chosen to minimize power dissipation for negative current sources (Q12, Q14) and to provide larger output swing.

I still made this only for simulation.

Any opinions are greatly appreciated.

[eLarson]

I'm not sure if D102 and D104 are needed, and I'd be afraid of clipping with regular diodes between the source and gate of the MOSFETs. If the input is less than a half a volt or so, I guess it wouldn't be a problem, though. Give it a shot and see what happens. You could always drop a zener in later.

I am currently planning a BoSoZ (Zen Daughter-in-Law) with constant current sinks connected to the source pins of Q1 and Q2. I'm going to start with the 750 ohm resistors for the drain load, though.

How much gain do you anticipate using the current source load?

Erik

[stefan]

I use current sources because I want to use this preamplifier mainly to convert unbalanced input to balanced output. The gain can be adjusted with R19.

Protecting diodes will conduct if input voltage is less than -4V or greater than Us+0.6V. These situations are unusual and in normal work diodes are not conducting.

[eLarson]

"I use current sources because I want to use this preamplifier mainly to convert unbalanced input to balanced output."

I'm using the "tail" current sinks for the same reason. I have a number of single-ended sources (chiefly a tuner and a TV) to go along with a balanced source (CD). Ultimately I'll have an amplifier that will take a balanced input (I'm thinking of a 10 or 20 W Son of Zen) which will make maximum use of that feature.

As for the current sources for the drain load, I'm not sure I'm going to need the extra gain they will provide. I may try it down the line, though, just for fun. If it works out well for you, let us know.

Erik

[Nelson Pass]

Looks great!

[jwb]

I think it will sound great. It does remind one more of BoSoZ. I noticed you have specified 47µF output capacitors. Are you able to get quality capacitors in that size, and if so, where do you get them?

[skaara]

Is the rule for output caps, "the bigger the better"?

[stefan]

It depends of load impedance.

When load is bigger than 1k 30uF are enough.

I didn't find still good capacitors for outputs,
If you have some ideas all will be appreciated.

[eLarson]

I used 51 uF Solen film caps that I had scavenged from a previous project. They worked out pretty well. (Solen had some larger sizes, too, but I had to draw the line at cost.)

I had picked them up at a Parts Connection "garage sale" in Oakville, ONT a couple years ago. Unfortunately I think the Sonic Frontiers is out of the parts business now. Once all of their existing stocks of parts are gone, there will be no more.

Erik

[Peter Daniel]

I think that in most cases, even 10uF is too much. Go for quality and not the size.