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DAC chip differential output

cromodora

cromodora

foshfishfie
I would like to try bypassing the output opamps of my soundcard.

According to the datasheet*, it has a differential output.
The analog output legs are R+,R-,L+,L-.

Can I just wire them direct to RCA sleeve and tip or is there more to converting to single ended?

*The analog outputs are full differential outputs and 2.4Vpp (typ@VREF=5V) centered around VCOM. The differential
outputs are summed externally, VAOUT = (AOUT+) - (AOUT-) between AOUT+ and AOUT-. If the summing gain is 1, the
output range is 4.8Vpp (typ@VREF=5V).
 
cromodora said:
I would like to try bypassing the output opamps of my soundcard.

According to the datasheet*, it has a differential output.
The analog output legs are R+,R-,L+,L-.

Can I just wire them direct to RCA sleeve and tip or is there more to converting to single ended?

*The analog outputs are full differential outputs and 2.4Vpp (typ@VREF=5V) centered around VCOM. The differential
outputs are summed externally, VAOUT = (AOUT+) - (AOUT-) between AOUT+ and AOUT-. If the summing gain is 1, the
output range is 4.8Vpp (typ@VREF=5V).
Click to expand...

There is more to converting to single ended.

The simplest op-amp free technique is probably to use a transformer.
 
I wouldn't just bypass it, as you need to filter the digital junk coming out of the DAC.
Yair
 
To get a single ended output, you need to take one of the phases and connect it via a capacitor e.g. 4.7uF in series amnd a resistor e.g. 100K to ground.

Different chips have different levels out ultrasonic noise on the output. Some of the Wolfson and in particular AKM converters need little to no filtering. Try it and see how it sounds.
 
Thanks for the replies guys.

After PD mentioned transformers, I looked up Lunhdahl, Sowter and Jensen sites. Went googly eyed, got confused with the wiring permutations and put off by the cost involved.

The soundcard is my ole reliable Emu 0404 PCI the sound of which I prefer over the Benchmark DAC. Also its quite versatile allowing me to sit in on bass thru the digital input whenever I feel like playing along to some easy tunes.

It has an AKM4395 DAC with differential output. The datasheet recommends filtering to get rid of out-of-audio-band junk. Emu does this by buffering the AK's output with two JRC2068 (dual) opamps then a filter network before sending it on to another JRC 2068 for single-ended output.

I figure why not skip the three opamps and tap the outputs direct from the AKM legs and send the signal neat to my Naim 32.5 or Starfish. These have 729 input buffer stage to provide the bandwidth filtering.
 
I came across this DAC when playing with the Logitech Transporter (which is actually using the pin-compatible 4396). I just replaced the op-amps with Burson buffers and changed the coupling caps. At the same time a friend tried skipping the op-amps all-together in another Transporter. The conclusion was you just can't skip them - they add some gain and clean the junk.
A good thing though will be replacing them with some of the better op-amps around, and add good regulators.
Yair
 
Yair,
Are you using a Naim preamp with the input filter stage?

Sparts,
Thanks for the link.
Reassuring that its not a sow's ear project.

So, numpty me summarising,

R+ add 100R in series --> R channel HOT
R- add 100R and 4.7uF in series, 100k to ground --> R channel GRND

L+ add 100R in series --> L channel HOT
L- add 100R and 4.7uF in series, 100k to ground --> L channel GRND
 
For Single ended use, just take the + output, 100R + 4.7uF in series and 100K to ground. Connect the ground of your interconnect to the ground of the sound card.

Personally I wouldn't go the transformer route unless you are happy to shell out for a good one - cheap transformers will produces masses of distortion, especially in the bass.
 
Sparts155 said:
For Single ended use, just take the + output, 100R + 4.7uF in series and 100K to ground. Connect the ground of your interconnect to the ground of the sound card.

Personally I wouldn't go the transformer route unless you are happy to shell out for a good one - cheap transformers will produces masses of distortion, especially in the bass.
Click to expand...

Woohoo!
Its Alive!
Sounds clean so far. Will give it a proper listen tomorrow.

I've fitted the 4.7K caps only.
Will try with resistors when I have quality ones at hand.

Thanks Sparts. I'll give cheap transformers a miss.
 
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