modifying the D1 I/V stage (X?, CCS?)

BrianGT · 7th September 2003, 02:55 PM

Has anyone tried modifying the D1 I/V stage? I am wondering if it would sonically benefit if it was converted to an X type setup.

Also, what about using current sources?

Here is a picture of the stage from the service manual:
( http://www.passlabs.com/pdf/d1-srv-man.pdf )

--
Brian

Algar_emi · 7th September 2003, 07:36 PM

Is it possible to use this I/V converter with just one DAC instead of two? For example by grounding the input of Q6. Will it work?

Nelson Pass · 7th September 2003, 07:44 PM

You could remove Q6 and all the circuitry around it.

jam · 7th September 2003, 07:47 PM

Brian,

You could get rid of R25 and R32 and replace them with 20ml current sources. With Mr.Pass's permission.

Regards,
Jam

BrianGT · 7th September 2003, 09:13 PM

Will this output stage work well with the AD1955, which has stereo differential current output?

--
Brian

BrianGT · 7th September 2003, 09:49 PM

The datasheet for the AD1955 says:
"8.64 mA p-p Differential Output"

Do I need to change anything in the I/V stage to account for this difference, compared to the PCM63?

--
Brian

Nelson Pass · 8th September 2003, 01:42 AM

Check the DC output requirements of the chip, but otherwise,
ther answer is (should be) no problem.

Nelson Pass · 8th September 2003, 01:44 AM

In reference to the above schematic, I should point out that
the followers are not necessary for many applications, and you
could get by with the simple diff pair and the 1.5K resistors
(capacitively coupled, of course).

Klaus · 8th September 2003, 07:12 AM

Hi,

I have also released a question about converting the D1 stage, maybe in the wrong forum part, because just one answers has come so far...

The essence of the tread below is: how to use the 0,1mA I-output of TDA1547 with a changed D1-stage? My idea is the reducing of bias current to ca. 1mA and use of a smaller FET like e.g. 2SK389. Is there any mistake in this realization? Thanks for feedback!

modify D1 stage for 0.1mA DAC?

Regards

Klaus

Nelson Pass · 8th September 2003, 09:34 PM

It seems that current output DACs are designed to
ideally operate into virtual grounds.

As the transconductance of the JFET in question goes
down, more signal voltage will appear at the source,
and any dependence of signal quality vs output voltage
of the DAC will start showing up.

That said, I would expect it to work fine.

7th September 2003, 07:36 PM	#2
Algar_emi diyAudio Member Join Date: Oct 2002 Location: Canada, Qc	Single DAC use Is it possible to use this I/V converter with just one DAC instead of two? For example by grounding the input of Q6. Will it work?

8th September 2003, 07:12 AM	#9
Klaus diyAudio Member Join Date: May 2002 Location: near Frankfurt/Main	conversion to 0,1mA DAC? Hi, I have also released a question about converting the D1 stage, maybe in the wrong forum part, because just one answers has come so far... The essence of the tread below is: how to use the 0,1mA I-output of TDA1547 with a changed D1-stage? My idea is the reducing of bias current to ca. 1mA and use of a smaller FET like e.g. 2SK389. Is there any mistake in this realization? Thanks for feedback! modify D1 stage for 0.1mA DAC? Regards Klaus

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7th September 2003, 07:44 PM	#3
Nelson Pass The one and only Join Date: Mar 2001	You could remove Q6 and all the circuitry around it.

7th September 2003, 07:47 PM	#4
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Brian, You could get rid of R25 and R32 and replace them with 20ml current sources. With Mr.Pass's permission. Regards, Jam

7th September 2003, 09:49 PM	#6
BrianGT diyAudio Moderator Emeritus Join Date: Jan 2002 Location: near Atlanta, GA	The datasheet for the AD1955 says: "8.64 mA p-p Differential Output" Do I need to change anything in the I/V stage to account for this difference, compared to the PCM63? -- Brian

8th September 2003, 01:42 AM	#7
Nelson Pass The one and only Join Date: Mar 2001	Check the DC output requirements of the chip, but otherwise, ther answer is (should be) no problem.

8th September 2003, 01:44 AM	#8
Nelson Pass The one and only Join Date: Mar 2001	In reference to the above schematic, I should point out that the followers are not necessary for many applications, and you could get by with the simple diff pair and the 1.5K resistors (capacitively coupled, of course).

8th September 2003, 09:34 PM	#10
Nelson Pass The one and only Join Date: Mar 2001	It seems that current output DACs are designed to ideally operate into virtual grounds. As the transconductance of the JFET in question goes down, more signal voltage will appear at the source, and any dependence of signal quality vs output voltage of the DAC will start showing up. That said, I would expect it to work fine.