Analog buffer/filter stage for CS43122 help - diyAudio
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Old 16th December 2001, 04:31 PM   #1
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Default Analog buffer/filter stage for CS43122 help

I'm designing a DAC using the CS43122. However I'm not sure how to make the analog output stage. The CS43122 has got differential analog outputs. The next stage in my signal chain is single ended, so I need an analog LP filter and a differetial to single ended converter in this stage.

I've thougt of two solutions so far:

1. Copy the (old) LC audio ZapFilter (schematics from their site).

2. Do it meself, like the AKM eval. board ( http://www.asahi-kasei.co.jp/akm/eng...df/EKD4395.pdf ). But I was told that summing the differential signals with resistors will require perfect matching, or else common mode rejection will be decreased.

So, I'd like to hear from anyone that has made such circuits and what your preferences are.

Kasper M
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Old 17th December 2001, 03:14 PM   #2
tiroth is offline tiroth  United States
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This could be the wrong way to go from an audio quality standpoint, but couldn't you use a differential line reciever like TI's INA137 et al? AFAIK these feature laser-trimmed resistors and close to 100dB common mode rejection. THD+N is about 0.002% from memory.

I'm looking for a good current-to-voltage and LP filter myself for the AD1853. The AD1853 evaluation board schematics actually have a LP filter and differential-to-single-ended converter (summing amp). However, the sonic characteristics may not be up to the standards of this forum.

My plan is actually to keep the differential signal and send it out to the amp, and do attenuation and summing there. However, I don't know enough about filter building to design a better output stage.
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Old 17th December 2001, 05:17 PM   #3
hifi is offline hifi  Sweden
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what input reciever are u using?

i would be wery interessted in looking at your design...maybe even build it if you let me =) im sitting on a few 8420 and 43122 circuits....but no time to design anything...


i wuld like to try to have a LL trafo on the output and only buffer the signal or usíng the scheme on www.ultranalog.com


/micke
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Old 17th December 2001, 06:52 PM   #4
tiroth is offline tiroth  United States
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Quote:
Originally posted by hifi
i would be wery interessted in looking at your design...maybe even build it if you let me
I'm currently designing/acquiring parts, but I'm planning on using cheap DIR1703 recievers, pass through AD1896 for jitter reduction, AD1853 for the output DAC and an NE5532 output stage. At this point I'd rather use a cheap output stage and make it modular so I can get fancy and experiment with a valve stage "in the future...."

I think even the reference design will sound acceptable. If you have any suggestions they would be quite welcome.
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Old 18th December 2001, 11:56 AM   #5
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Thank you for your replies

hifi:

I will be using the CS8414 as input receiver. To lower clock jitter an async. samplerateconverter will be used (or I will try a design similar to Marc Heijligers at: http://members.chello.nl/~m.heijlige...tml/dactop.htm ).

My filter/buffer stage will definetely be solid state and right now a LC Audio alike solution seems to be reasonable. LC will sell me the parts too.

Kasper
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Old 18th December 2001, 07:31 PM   #6
hifi is offline hifi  Sweden
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to bad.....there dosnt seem to be any reasonable design with cs43122 and cs8420 on the net...except NB:s "dac4" but the boards dosnt seem to be availible....


i got some cs8420 if you are having trouble lockating them....or they are availible from elfa......


i got the parts from ericsson early this year but i havnt got around to building something with them......thought i could find some nice layout and just etch the boards......

hmmm maybe i can do something with them in the chrismas holidays....

/micke
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Old 2nd January 2002, 10:32 PM   #7
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Default Iron dac...

You might consider an old fashioned device: a transformer. I have not played with a 122, but this is pretty generic.

Ground isolation, ultrasonic filtering, no power supply issues, neither rejection nor modulation.

Quality, both technical and subjective will vary quite a bit, but generally, something from Sowter, Jensen, or Audionote would be a safe bet.

A 10 kohm 1:1 should do the trick. One could even try a surplus 600:600 ohm line tranny.

Some prefiltering is a good idea, to keep from "pulling" the 122's at DC, say a couple hundred ohms on each leg, with a cap set for a ~~50 kHz to 100 kHz corner across the primary.

Also, if I may paint with such a broad brush, trannies are usually happier feeding a higher impedance load than spec, with loading and damping being done at the primary. Do pay attention to mechanical issues, as trannies are sensitive to vibration. Not grossly so, but in chasing the last degree of resolution.
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