I had a bit of a brainwave regarding bitstream dacs.
(note: I know little about them, being an inveterate multi-bit tinkerer)
As I understand it, a bitstream dac works by converting the digital data into a pwm waveform that is then filtered.
Does anyone know if this is always filtered on the chip, or are there any bitstream dacs that expose this pwm waveform?
Want to build a "digital amp" heh ?!
Old types are, see: http://www.fortunecity.com/rivendell...da/vasfda.html
"As a result many designers screwed up their analogue stages for the early Timeslicing DACís up so badly that most DAC Manufacturers started integrating various parts of the analogue stage onto the chip to avoid this (notable exception - Nippon Precision Circuits - NPC). ---> e.g. the CD63 DAC IIRC
Later Phillips Bitstream Chipís (like TDA1547) are famous for having been crippled sonically by some Idiot who integrated a analogue stage based on the NE5532 Op-Amp onto the silicon. Another DAC vendor who really made a sonic mess is Cirrus Logic (under the Crystal Brand).
-->After their superb CS4303, which offered pure digital outputs (and which almost no-one got to sound good as the analogue stages could not cope with all that RF Noise) and the CS4328 which implemented an excellent internal analogue stage, all their other DACís (CS4327, 4329, 4390 and so on) have incorporated switched capacitor lowpass filters (sonic poison) and lousy CMOS Op-Amp output buffers. "
So CS4303 is one. Best browse through (old) datasheets!
There must be more.
It is sad that it's not necessarily the digital oversampling and whatnot that is ruining the sound, just a cheapo analog stage that's included so that the chip specs right in any circuit.
The new generation 24/192's could probably sound amazing if they offered an output before all the crappy internal filtering was done.
Had a look at the 4302 datasheet and the evaluationboard (only papercopy)
The last one is special: they reclock ... AFTER the DAC !!!!
DAC - Optocouplers - Reclocking FF - outputcircuit (opamps)
Remember, the output of the DAC is a signal with "logic" signallevels, so 0-5V. The info is within the timedomain.
So they can use optocouplers for fast digital signals and normal FF's.
As for the 4328, it DOES have a switched cap filter network inside, followed by a MOSFET output stage (IIRC).
Ehh i meant 4303 ..
i made a dac with the old 4303 some years ago, with ECC82 tube summing/out amp, wich works fine , because tubes are not sensitive to rf noise.
If you wannna try a dac like the 4303, go (ebay...10 eu) for an old JVC cd player, the series XLZ431 have a dac named JCE4302, prob a clone of the 4303 (?), has also 4.order noise shaper, 20 bit, direct 5V level dig outputs;
or the XLV-164 /174 series, dac data about the same, called MN35500 DD-converter;
with a new output filter and a fine master clock (guido...) they sound very good, and the try would not cost a lot...
I know I'm about two months late but I'm new to the forum and found this thread while searching for this topic.
I have a Philips CD624 which uses a SAA7321/2/3 chip. These chips allow you to access the signal before the onboard opamps and filtering. Apparently similar chips were used in the Philips CD 615, 618, 634, 824, 834 and Marantz CD41, 42, 43 and others like the Rotel 965 and QED digit, I think.
Does anyone have a suitable alternative to the onboard opamps and filter?
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