Fet buffer (?) for I/V stage ?

Bernhard · 15th November 2004, 10:41 PM

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

till · 15th November 2004, 11:45 PM

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.

hjelm · 16th November 2004, 05:48 AM

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.

Bernhard · 16th November 2004, 08:24 AM

Ok, what does the low impedance of buffer help if the current flows through a 10k I/V resistor

hjelm · 16th November 2004, 01:10 PM

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?

Bernhard · 16th November 2004, 01:28 PM

Here it is, J109 and K364...

carlosfm · 16th November 2004, 02:14 PM

Those transistors are on the feedback loop, it seams like a current boost for the op-amp.

Bernhard · 16th November 2004, 02:22 PM

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.

carlosfm · 16th November 2004, 03:24 PM

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.

Bernhard · 16th November 2004, 04:50 PM

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.

15th November 2004, 10:41 PM	#1
Bernhard diyAudio Member Join Date: Apr 2002 Location: Munich	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

16th November 2004, 05:48 AM	#3
hjelm diyAudio Member Join Date: Nov 2003 Location: Västerås	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. __________________ Hjelm

16th November 2004, 01:10 PM	#5
hjelm diyAudio Member Join Date: Nov 2003 Location: Västerås	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? __________________ Hjelm

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15th November 2004, 11:45 PM	#2
till Banned Join Date: Apr 2002 Location: Germany, Clausthal	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.

16th November 2004, 08:24 AM	#4
Bernhard diyAudio Member Join Date: Apr 2002 Location: Munich	Ok, what does the low impedance of buffer help if the current flows through a 10k I/V resistor

16th November 2004, 02:14 PM	#7
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	Those transistors are on the feedback loop, it seams like a current boost for the op-amp.

16th November 2004, 02:22 PM	#8
Bernhard diyAudio Member Join Date: Apr 2002 Location: Munich	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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