Fet buffer (?) for I/V stage ?

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Bernhard

Bernhard

Member
Joined 2002
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 :bawling:
 
T

till

Banned
Joined 2002
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

hjelm

Member
Joined 2003
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

Bernhard

Member
Joined 2002
Here it is, J109 and K364...
 

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jean-paul

jean-paul

Disabled Account
Joined 2002
Those FETs are indeed for boosting maximum output current. This seems common knowledge to me, max. output current of opamps is 20 to 50 mA with modern opamps in general with distortion. It also gives the opportunity to write "class A output stage" on the case ;)

In time I have had several Pioneer oldies ( like the very nice PD-8500 ) with those magnificent linear transports and auto-servo electronics ( no potentiometers inside except for laser current ). They always sounded better without the buffer and even better with better opamps ( and a better clock but one does not have to believe that ).

These series also have the too large 1000 or 2200 uF caps behind the regulators. Please measure the supplies and don't be surprised if they "motorboat" during startup. 100 uF was enough for them. Removing the digital volume control can't hurt either ( PD0026 ??? ).

I stopped using them as their laser dies earlier than the old Philips types and the lasers are more pricey too.
 
C

carlosfm

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Joined 2003
jean-paul said:
Sorry, I meant the models that had linear transports with "floating" laserunit. Not that Stable Platter things that make a normal person mad with the need for putting the cd in upside down ;)
Click to expand...

It made me mad for some time, true.:D
But the first generation Staple Platter mechanism on my CDP was very sturdy, mostly metal construction.
The player had two quite big trafos inside.
Never had a problem with it, sold it to a friend and he still uses it today.
 
Bernhard

Bernhard

Member
Joined 2002
carlosfm said:


You are taking side steps, as you need players with PCM56s, you have to collect 64 of them.:cool:
Click to expand...

It would be 2 x 64 =128 as PCM56 is a mono DAC.
But I doubt if I take the risk that the glue logic will not work or will disturb sound more than it helps.

So it looks like I will end up with something like 20 or 30 per channel.

My current stock is around 25 :rolleyes:
 
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