Fet buffer (?) for I/V stage ? - diyAudio
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Old 15th November 2004, 10:41 PM   #1
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Default Fet buffer (?) for I/V stage ?

Hi,

in Pioneer PD9300 with 2 x Pcm58-K there are complementary (selfbiasing (?)) fets on the op amp output, drains to V+/V- , gates together to op amp output , sources together form output, no other parts, very simple.
Same for filter stage.

What is that good (?) for ???
Can it raise distortion ???

Btw. 8 PCM58 I have, measure all worse than PCM56, lower noise but more distortion
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Old 15th November 2004, 11:45 PM   #2
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i suspect it is good for giving your CDP a low output impedance. And, yes, it does add ~~~ distortion ~~~ (feel fear now)

But i suspect the distortion added will be much less than from the opamp, or the opamp with a high output impedance driving a following lower input impedance stage.
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Old 16th November 2004, 05:48 AM   #3
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It sounds like pedjas (i think it was at least) IV stage.
It has the benefit of giving a very low input impedance for the DAC to feed. As for distortion it should be very small since the DAC will try to feed the current through the transistor.
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Old 16th November 2004, 08:24 AM   #4
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Ok, what does the low impedance of buffer help if the current flows through a 10k I/V resistor
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Old 16th November 2004, 01:10 PM   #5
hjelm is offline hjelm  Sweden
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If it is before the buffer nothing.
If it is after everything, in this case the dac will se 0 ohm resistance while the current is still terminated by the resistor.
Could you draw a schematic?
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Old 16th November 2004, 01:28 PM   #6
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Here it is, J109 and K364...
Attached Images
File Type: jpg iv.jpg (22.6 KB, 913 views)
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Old 16th November 2004, 02:14 PM   #7
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Those transistors are on the feedback loop, it seams like a current boost for the op-amp.
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Old 16th November 2004, 02:22 PM   #8
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The op amp is a 5532 and should be able to deliver that one mA for the DAC, so I kick the FETs out and measure again.
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Old 16th November 2004, 03:24 PM   #9
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Quote:
Originally posted by Bernhard
The op amp is a 5532 and should be able to deliver that one mA for the DAC, so I kick the FETs out and measure again.
I would do that.
That player could sound less... yellow.
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Old 16th November 2004, 04:50 PM   #10
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Quote:
Originally posted by carlosfm


I would do that.
That player could sound less... yellow.
Never listened to that player, bought it for the PCM58-K.

Could be it sounds green.
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