i/v options for current output DAC chips (technical question)

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Hi all,
well I've tried several things now with my zero-oversampling TDA1541A:
- resistor conversion (20 ohm)
- resistor plus dirt cheap transformer (220>>9V mains connected in reverse, DCR 1.5k and 8R5)) to get an idea
(no output filters here)
- classical op amp transimpedance application with some OPA2134 I had lying around, with 2 pole Butterworth filter set at 22 kHz cutoff, and using a "smart" filter configuration as of BB application notes on i/v.
Results are that resistor with or without transformer gives a sweet and mellow sound with nice microdynamics, but no high or low end dynamics at all (note, this also without the transformers which evidently are no audio grade parts). In this light the microdynamics might be a psychoacoustic illusion since no macrodynamics available...
Classic op-amp i/v : very nice dynamics but return of some shrillness/blandness. Hmmmm. I like the op amp solution best after all but it's not ideal still.
Here my question: the main issue with any resistor based i/v is the limited voltage compliance of the DAC. So the resistor ideally should be zero... and subsequent amplification infinite. Not ideal. BUT since the problem is voltage compliance, why not increase voltage comlpliance in the first place - then i/v conversion could use arbitrarily high resistor values to give the desired output voltage - practically there would be no amplifiction of I(out), nor any amplification afterwards, just a current source mirror. Or am I deluding myself and it's just what the op amp did before, except in a single transistor without all the safeguards and guaranteed specs of an op amp IC?
Specific question: is it sonically worthwhile to try cascoding the DAC I(out) with a suitable JFET (idea from again, BB application notes) and using say, a 1k resistor for i/v after that to get around 2.83 V? Would a simple JFET be able to handle the situation without significant nonlinearities/distortions? This assuming one sets the reference of the JFET low enough to allow linear operation at low DAC I(out) levels.
Thanks!
MBK

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Topic - i/v options for current output DAC chips (technical question) - MBK 08:53:34 03/18/02 (8)

some i/v options for current output DAC chips (technical sugestions) - jcox 16:18:02 03/19/02 (6)

Re: some i/v options for current output DAC chips (technical sugestions) - MBK 18:14:00 03/19/02 (5)

turn op amp around in i/v circuit - jcox 10:13:12 03/21/02 (4)

Re: turn op amp around in i/v circuit. Actually... - MBK 03:02:24 03/22/02 (0)

Re: turn op amp around in i/v circuit - Just did - MBK 02:35:58 03/22/02 (2)

Happy vacations - MBK 20:48:20 03/27/02 (0)

vacationing, can send eqs after april 2 - jcox 11:20:13 03/24/02 (0)

Similar findings - Dave I 12:30:31 03/18/02 (0)

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