The AC gain component of the Aleph current source tracks the
output current to the speaker, and provides a fixed percentage
of that current. In this way it negatively "ghosts" the load and
lets the primary gain stage think it's driving a higher, but
otherwise identical impedance. 50% is nominally the best
figure in terms of efficiency and overall performance, although
there is no reason not to adjust to other values and see what
you get.
In reference to the sound getting worse with increased bias, it
is possible you might be encountering a stability issue at higher
currents, as the open loop gain of the amp increases with higher
bias. You might want to try increasing the two compensation
cap values, the one across the NPN transistor (or across it's
Collector-Base, usually 1 nF) or the lag cap Drain-Gate across
the negative bank of Mosfets (try 1 nF there also).
output current to the speaker, and provides a fixed percentage
of that current. In this way it negatively "ghosts" the load and
lets the primary gain stage think it's driving a higher, but
otherwise identical impedance. 50% is nominally the best
figure in terms of efficiency and overall performance, although
there is no reason not to adjust to other values and see what
you get.
In reference to the sound getting worse with increased bias, it
is possible you might be encountering a stability issue at higher
currents, as the open loop gain of the amp increases with higher
bias. You might want to try increasing the two compensation
cap values, the one across the NPN transistor (or across it's
Collector-Base, usually 1 nF) or the lag cap Drain-Gate across
the negative bank of Mosfets (try 1 nF there also).
Hello and thak you, Mr. Pass.
First, for your explanation about the way that the aleph's current source works. Simple and clear.
Second, for your advise about how to solve my problem with the bias of my amplifiers. I will try what you suggests about the value of the caps.
In the last days I've learned a lot about alephs and I think that I must work again in mines to adjust everithing in the rignt way. I'm writing a list with the things to do. By the moment, they are working and I'll wait till summer to make the chages. Meanwhile, I'll go on learning.
Thank you very much.
masfe
First, for your explanation about the way that the aleph's current source works. Simple and clear.
Second, for your advise about how to solve my problem with the bias of my amplifiers. I will try what you suggests about the value of the caps.
In the last days I've learned a lot about alephs and I think that I must work again in mines to adjust everithing in the rignt way. I'm writing a list with the things to do. By the moment, they are working and I'll wait till summer to make the chages. Meanwhile, I'll go on learning.
Thank you very much.
masfe
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