Hi Phil,
My question is due to the fact that I need to cut down the power drawn
by the electrostatic headphone hybrid amp I've asked about previously on
this group. I didn't talk about the amplication in my initial post
since I didn't want people to start discussions about the amp not
relating to my question; I've already built the amp and I need to change
operating point.
http://www.headwize.com/images5/gilmore4_1.png
Ignoring all but the output stage, V1/2 Q8/15
The designer claimed he had chosen operating point so that the tube's
non-linearity in this configuration was roughly canceled by the driving
source follower's nonlinearity.
My problem is I have to reduce power supply voltage and current a bit.
When I built the power supply transformer, I didn't realize that I
should give it enough margin voltage so that as my mains voltage varies
(up to 10% in my house, even if rarely), the raw supply could drop below
the power regulator's voltage.
So my concern is how much to cut the idle current by when I reduce
supply voltage by a given amount, so as to preserve the rough inverse
matching of the nonlinearities of the two devices. Or do I change the
operating point of the MOSFETs instead. The reason I wanted to see the
curves is to compare how the nonlinearity changes with varying the
voltage and current through the tube.
My aim here is to retain the 40 ppm THD measured with the original while
just reducing the power of the amp (it's kind of overkill since 1500 V
peak to peak drives the Stax a good deal louder than I'd normally listen
to).
Thanks.
"Phil Allison" wrote in
:
"Prune"
Also forgot to add it's for under constant current operation; I need
plate voltage vs cathode voltage.
If such data can't be found, is there a way I can derive it from
other curves?
** The basic plate current V negative grid voltage curves still apply.
Just that with cathode drive, the varying negative grid voltage is
actually a varying positive cathode voltage ( all voltages relative to
chassis).
The whole game ( linearity wise) depends on the performance of the
actual scheme used for driving the cathodes - ie how accurately does
it convert the input signal voltage to proportional changes in cathode
current.
How about you describe yours ?
....... Phil