The effect of the ac current gain in Aleph

[Peter Daniel]

I would like to try converting the Aleph output stage into a simple current sourced stage. All the feedback around the current source, the out series resistors, all the parts hanging on the output are influencing sonics in some way. A simple Mosfet with a fixed current source should sound probably better. I do lose the power into 4 ohms and lower but this is not an issue here.

Natural progression of course, is SOZ with single resistor for current source, but at the cost of efficiency. So I would be leaning towards simple, active CS.

Anybody tried doing that already?

[Henrik]

Peter
Gray did this nice job:
Pass Son of Zen w/current sources (etc.)
and you can X it if you want, but the cost is lower inputimpedance if you dont want to use a buffer.

[Peter Daniel]

Thanks for a link, somehow I never got to see that thread. But it's more of a variation on SOZ design.

What I'm looking for, is a modified Aleph, with mosfet as a current source, but without the circuit associated with active current gain. I'll be using that amp in tri-amp system with efficient drivers, so I don't need extra power and if I'll be able to achieve better sonics, it's worth it.

[uli]

Hi Peter,
Take any Aleph and throw out the outputresistors and the RC
back to the CCS (C10, R21 in Aleph2) thats it!

Uli

[Henrik]

Peter
It is. Obvious I misunderstood you. But Uli is right.
I have used that circiut topology (changed the outputdevices to irf610´s) to drive a push pull outputstage.

[uli]

Henrik,
how does it sound compared to an Aleph?

Uli

[Steve Eddy]

Originally posted by Peter Daniel
What I'm looking for, is a modified Aleph, with mosfet as a current source, but without the circuit associated with active current gain. I'll be using that amp in tri-amp system with efficient drivers, so I don't need extra power and if I'll be able to achieve better sonics, it's worth it.

If the drivers are efficient enough, why not use a simple source follower?

se

[Peter Daniel]

Because I'm sentimental about Alephs. And I would like to use X topology, and experiment a bit with the boards I got.

[Nelson Pass]

It will not surprise you to imagine that I have
worked with this a bit.

There are occasions when a constant current source
or even a resistor will sound better, but this is highly
dependent on taste and having the proper speaker.

A good example is a nice efficient horn midrange or
tweeter. If you don't need the power, you have less
need of gain in the circuit.

pass/ - likes a good horn now and then

[Steve Eddy]

Originally posted by Nelson Pass
A good example is a nice efficient horn midrange or
tweeter. If you don't need the power, you have less
need of gain in the circuit.

Yes, especially if you already have a preamp in the loop, which for loudspeakers in the 95dB+ wouldn't necessarily require any additional voltage gain. And if you don't need any voltage gain, the circuit can reduce to an emitter/source/cathode follower, which is simpler, more linear and has a lower output impedance (assuming an active current source).

se