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Old 20th April 2004, 01:35 PM   #11
Mike C is offline Mike C  United Kingdom
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Quote:
Originally posted by Eli Duttman
The icing on the cake would be CCS loading the cathode follower with a pentode.

If one were to go to the trouble of adding another valve, especially
a pentode, I'd suggest using this as an anode load above the first
valve and of course removing the cathode follower.
This of course gives a Kimmel mu stage.

Then throw away the poor sounding 12AU7 and use say an E80CC instead
and you'll have a really fine sounding preamp.

It's called Nina, and the circuit and details are are on this board!
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Old 20th April 2004, 10:11 PM   #12
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An Alan Kimmel mu stage is TOO linear for my purposes, I want a SMALL amount of 2nd harmonic distortion.

I suggested a 'CG7 as the tube, not a 'U7.

CCS loaded cathode followers sound BETTER than resistively loaded CFs do. Pentodes make good current sinks, as do N-channel FETs and NPN BJTs. Why use "sand", when a tube will do?
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Old 21st April 2004, 08:00 AM   #13
Mike C is offline Mike C  United Kingdom
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Quote:
Originally posted by Eli Duttman
An Alan Kimmel mu stage is TOO linear for my purposes, I want a SMALL amount of 2nd harmonic distortion.
OK, I understand, so a normal triode with anode load resistor it is then.
Quote:

I suggested a 'CG7 as the tube, not a 'U7.
Oops, sorry, I was looking at the original cct.

Quote:

CCS loaded cathode followers sound BETTER than resistively loaded CFs do. Pentodes make good current sinks
Fine, I accept this totally.

One thing to consider; how about just using a pentode as a cathode
follower? As I see it, the very high voltage gain gives good linearity,
and the generally highish Gm (relative to similar size triodes) will
give a low Zout, I think.
I wonder if, compared to triode CF with pentode sink, less might be more
if you see what I mean. I have no idea if that's right, just idly
speculating ...
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Old 22nd April 2004, 01:24 AM   #14
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"One thing to consider; how about just using a pentode as a cathode
follower? "

So here is your perfect exceuse to stock up on the 12BY7. Use 'em in the Cit.II or your linestage output. reisitive load will do the trick nicely, and at ~100 ohms output z, should drive your opt just fine.
regards,
Douglas
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Old 22nd April 2004, 01:36 AM   #15
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Hi,

Quote:
CCS loaded cathode followers sound BETTER than resistively loaded CFs do.
Don't you mean CCS sunk CFs here?

I just want to avoid confusion before anyone asks where to put the CCS here.

Cheers,
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Old 22nd April 2004, 02:04 AM   #16
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In the case of cathode followers, CCS means constant current sink. Putting a CCS in the "tail" of a Schmidt phase splitter is the same thing, a current sink.

If it's in the plate circuit, it's a current source. If it's in the cathode circuit, it's a current sink.
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Old 22nd April 2004, 02:23 AM   #17
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Default THE CONVENIENCE OF THE "S"...

Hi,

Eli,

What I meant is the use of the verb "to load" in conjunction with the CF's CCS.

With the anode follower the CCS (Constant Current Source either way to make my life easier) is used as a replacement load for the commonly used anode (plate to you) resistor.

Whereas in terms of a cathode follower the CCS is used to sink current away from the cathode so it replaces the commonly used cathode resistor that's usually tied to ground.

It's a matter of semantics, I know.

Cheers,
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Old 22nd April 2004, 02:35 AM   #18
EC8010 is offline EC8010  United Kingdom
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It's a "source" if connecting its far end to 0V causes a regulated current to flow, and a "sink" if when connected to 0V, no current flows, but when conected to an appropriate (non-zero) potential, a regulated current flows. How about that? There's a really easy-to-follow, succinct description! No wonder there's confusion.

Pentodes cathode followers don't work quite as well as their high mu promises. Even after the voltage between g2 and cathode has been arranged to be (nearly) constant. A bit of a disappointment, really.
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