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Old 20th October 2003, 09:37 AM   #31
Werner is offline Werner  Europe
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Not at all!
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Old 20th October 2003, 09:38 AM   #32
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Quote:
Originally posted by peranders
Q1, Que? I'll gues the schematic is drawn wrong?
No, it has a purpose. Think about it. Otherwise, you can find
it in an earlier thread, I just don't remember which one now.
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Old 20th October 2003, 09:40 AM   #33
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What is Q1 doing then?
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Old 20th October 2003, 09:44 AM   #34
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The point is to try getting a constant supply current draw to
the input stage. It is just a dummy load intended to approximate
the inverse current draw of the input JFET.

I see now that Werner has edited and modified the schematic
slightly. It was perhaps a little bit more obvious in the earlier
one where V1 was a chain of RC links from the supply.
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Old 20th October 2003, 09:49 AM   #35
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Quote:
It is just a dummy load intended to approximate
Fascinating. Is the effect clearly audible? Why is C1 so small?
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Old 20th October 2003, 10:02 AM   #36
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Quote:
Originally posted by analog_sa


Fascinating. Is the effect clearly audible? Why is C1 so small?
Well, don't ask me, I haven't tried it. Achieving a constant current
draw should be beneficial for low level amps in general though.
As I said, there was a thread a while back discussing this
general principle and various ways to achieve it. As I remember
Jonathan Carr was quite enthusiastic about it, saying that the
major advantage was that one can get away with simpler
power supplies. He said that the choice of caps in the PSU
was not so important anymore.

I don't know about the C1 value. Maybe a typo? Werner?

This is not only relevant in audio. We used to have a company
called Facit here in Sweden which was quite big and advanced
in computer peripherals. In the 70's they tried to get an order
for printers to Pentagon. However, Pentagon did not accept the
printers after testing them, since they claimed it might be possible
to monitor the noise on the mains line and figure out what was
printed. These were dot matrix printers, so Facit made a special
military version of it, by simply adding an extra dummy print
head which was fed with the complementary data of the ordinary
one. The power demand thus summed to a near constant one.
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Old 20th October 2003, 05:09 PM   #37
jcarr is offline jcarr  United States
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Default Caps in the PSU

Bulk of discussion in this thread:

http://www.diyaudio.com/forums/showt...006#post135006

With additional comments here:

http://www.diyaudio.com/forums/showt...531#post193531

As always, YMMV.

regards, jonathan carr
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Old 20th October 2003, 05:22 PM   #38
Marinos is offline Marinos  Greece
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Hi all,

Werner explains this setup at his site

http://www.geocities.com/Hollywood/H...33/design.html

"........Since this scheme would result in a high power supply source impedance at low frequencies, the supplies load must be kept constant relative to the music signal. This is done hanging a source follower off the first stage's transistor which runs at the same current, but inverse in polarity. The follower can be filtered at its gate to restrict its operation to low frequencies only. ".

I think that the last sentence explains C1 operation.

Don't forget to give me some help about the "integrated preamp" (see previous post) guys.
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Old 21st October 2003, 05:53 AM   #39
Werner is offline Werner  Europe
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No. The load at Q1's source is there to simply mirror the load at the front-end transistor's drain.

That 100nF and 750R at Q1 stems from part of the RIAA filter. We don't copy the whole RIAA as the bulk of the current flows in the 750/100nF pair anyway.

I make no claims as to the sonic benefits of this scheme. I expect it to depend heavily on the type of voltage supply anyhow. Some of you may want to try it, though.
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Old 21st October 2003, 08:28 AM   #40
Electrons are yellow and more is better!
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Quote:
Originally posted by Werner
I make no claims as to the sonic benefits of this scheme. I expect it to depend heavily on the type of voltage supply anyhow. Some of you may want to try it, though.
Werner we have a discussion about the Jung regulator with extremely low output impedance (and the importance of it), your power supply seems to be very week since you need current compensation?? Isn't low impedance of the power source essential at all times?
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