WARNING: TECHNICAL CONTENT
I have to admit that, despite my love for analog, I am fascinated by digital, its challenges and immense complexities. Leaving a DAC component's analog sections aside, the rest of it is a complex maze of digital circuitry, with noise and jitter lurking all over, where slew rates are also a critical aspect (as in analog circuits), which brings me to the current/voltage (I/V) conversion stage of a DAC.
The following paper http://electronicdesign.com/analog/designing-high-speed-current-voltage-conversion is typical and written by an Analog Devices engineer in their High Speed Amplifier Group, and in it basically covers noise in the I/V stage and also states that slew rates following the DAC chip's output must be fast enough: "the op amp needs to slew at least 300V/µs. If it can’t, slew distortion will slow waveform edges and generate code-dependent jitter in the output" - I redacted the "300" because it may not be literally applicable to audio and the main point is in bold typeface, and as he says elsewhere, "the op amp used for the transimpedance amplifier needs to slew fast enough to match the DAC’s output"
Lately, I've been reading up on the Esoteric K-01x and the upcoming K1 players, and the K-01X is using a MUSES 02 bipolar op amp for the I/V conversion - and not the allegedly superior MUSES 01 which is a JFET op amp - while the Grandioso K1 will be using the new MUSES 03 JFET op amp. The MUSES 01 has a stated slew rate of 12v/usec, the 02 5V/usec, and the specs for the 03 are not available yet. Nonetheless, 5 or 12V/usec are not really fascinating numbers. Having said that, the players are claimed by Esoteric to offer intrinsic slew rates of "2000V/usec" in the analog output buffer, which is extra-ordinarily fast. Meantime, a few other manufacturers use discrete I/V conversion (of unknown slew rates), and yet others a simple resistor.
So the questions are:
1) which I/V design is superior and why
2) why wouldn't everyone use a simple resistor
3) given that the MUSES 01/02 are just similar in price, is there a benefit of one over the other; some DIYers claim the 01 is really the superior choice for this application
4) what are good slew rates for this part of the circuitry as well as the DACs themselves
5) On diyaudio.com, Wayne of Pass is quoted as saying that op amps like the MUSES "don't fit" in their discrete-circuit design philosophy (analog or digital, though Pass don't do digital), so why wouldn't everyone design a discrete I/V?
I am looking for real, honest answers, not google parrotisms - Artificial Intelligence is always apparent.
Thanks
-ack
I have to admit that, despite my love for analog, I am fascinated by digital, its challenges and immense complexities. Leaving a DAC component's analog sections aside, the rest of it is a complex maze of digital circuitry, with noise and jitter lurking all over, where slew rates are also a critical aspect (as in analog circuits), which brings me to the current/voltage (I/V) conversion stage of a DAC.
The following paper http://electronicdesign.com/analog/designing-high-speed-current-voltage-conversion is typical and written by an Analog Devices engineer in their High Speed Amplifier Group, and in it basically covers noise in the I/V stage and also states that slew rates following the DAC chip's output must be fast enough: "the op amp needs to slew at least 300V/µs. If it can’t, slew distortion will slow waveform edges and generate code-dependent jitter in the output" - I redacted the "300" because it may not be literally applicable to audio and the main point is in bold typeface, and as he says elsewhere, "the op amp used for the transimpedance amplifier needs to slew fast enough to match the DAC’s output"
Lately, I've been reading up on the Esoteric K-01x and the upcoming K1 players, and the K-01X is using a MUSES 02 bipolar op amp for the I/V conversion - and not the allegedly superior MUSES 01 which is a JFET op amp - while the Grandioso K1 will be using the new MUSES 03 JFET op amp. The MUSES 01 has a stated slew rate of 12v/usec, the 02 5V/usec, and the specs for the 03 are not available yet. Nonetheless, 5 or 12V/usec are not really fascinating numbers. Having said that, the players are claimed by Esoteric to offer intrinsic slew rates of "2000V/usec" in the analog output buffer, which is extra-ordinarily fast. Meantime, a few other manufacturers use discrete I/V conversion (of unknown slew rates), and yet others a simple resistor.
So the questions are:
1) which I/V design is superior and why
2) why wouldn't everyone use a simple resistor
3) given that the MUSES 01/02 are just similar in price, is there a benefit of one over the other; some DIYers claim the 01 is really the superior choice for this application
4) what are good slew rates for this part of the circuitry as well as the DACs themselves
5) On diyaudio.com, Wayne of Pass is quoted as saying that op amps like the MUSES "don't fit" in their discrete-circuit design philosophy (analog or digital, though Pass don't do digital), so why wouldn't everyone design a discrete I/V?
I am looking for real, honest answers, not google parrotisms - Artificial Intelligence is always apparent.
Thanks
-ack