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Old 30th May 2004, 05:19 PM   #1
Fuling is offline Fuling  Sweden
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Default New output stage for PD-S707

Hi.

I have a Pioneer PD-S707 that is becoming a subject for severe modifications. Next in the line is a new output stage.
My first idea was a 6C19 (low µ triode) mu follower but that one got ditched for various reasons, mostly space and heat issues.

The original stage (drawing "a)") has a gain of x2 and puts out 2 Vrms, but I realize that I can live with only half of that (gain can be had later in the signal path). I can also loose the muting circuit since my amps are tubed and takes way longer to warm up than the CDP takes to stabilize.

What I want is a bit of lowpass filtering (there´s a lot of noise coming out of the DAC) and a buffer to drive whatever comes after the CDP. Preferably direct coupling, I can live with, say, 200mV offset if necessary.

The DAC has a +2,5V DC-offset, which is too low to get a Mosfet up and running. This is where the BF245B enters the arena, simply as a level shifter to elevate the Mosfet´s gate to about +4,3 volts where it starts to conduct.
Output offset is (should be?) adjustable by adjusting the current through the BF245B, and hence the Vgs.

Have a look at drawing "b)" to get an idea of what I´m rambling about, and feel free to comment.
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Old 1st June 2004, 06:37 AM   #2
hjelm is offline hjelm  Sweden
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Looks neat!
It is a single ended mosfet follower?
Just a question. It is the rebranded PCM1716 in that player i.e. voltage out?
I would like to know if anyone has loaded the output of it with a CCS since it is a OP driving the output (and a cmos one at that) i would imagine that there should be a benefit in loading it with a CCS.

Shouldn't this thread be in the digital area?
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Old 1st June 2004, 11:36 AM   #3
Fuling is offline Fuling  Sweden
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A single ended J-Fet/Mosfet follower it is, yes.
I don´t know anything about the DAC except that it´s a SMD device that puts out 1,4Vpeak at max signal into a 27k load.

I guess I could have a deeper look into the schematic and find out more about the DAC, hmm...

Maybe it should be in the digital area but the relevant circuits are very analog, so I put it here
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