Anyone used a PCM1794A with balanced output?

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hifimaker

hifimaker

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#1
Has anyone tried using a single PCM1794A with it's balanced outputs connected to a Pass I/V stage?

Looking at the TI app notes, they recommend op amps for the I/V stage and as an unbalanced to balanced converter.

http://focus.ti.com/lit/ds/symlink/pcm1794a.pdf -page 18

Probably no problem using the Pass D1 I/V circuit, but can the unbalanced to balanced converter be omitted and the I/V circuit connected directly to a set of right and left xlr connectors?

Does anyone have experience with this chip driving balanced outputs?

I'm open to other chip recommendations.

Thank you,

-David
 
#2
I've done it with a PCM 1702

I've done this with a PCM 1702. Inside a Denon DCD S10. As part of an upgrade I bypassed the stock analoge stage and connected a Zapfilter from LCaudio. This buffer allows current or voltage input, balanced or unbalanced. So I hooked this directly on the DAC output using the balanced current input configuration. It worked well and still does several years after.
 
#6
dw8083 said:
There are a lot of people using TDA1543 & TDA1541 DAC chips. I wonder why more people are not using the PCM1792 or PCM1794 chips?

-David
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Personal preferance for the NOS sound, philisophical reasoning that doing less to the signal sounds better (KISS), availibility of existing designs, or maybe because it is a hell of a lot easier to solder DIP than SSOP. I havnt build a dac with either yet (its on my to-do list), but those are the reasons I can see.
 
#8
dw8083 said:
Has anyone built a DAC with the 1794?

-David
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I've built a combo DAC/headphone amp using the 1792. I'm pleased as punch with the sound, and the Audio Precision at work is fond of it too.

SSOPs aren't that hard to solder. I use a homemade miniwave tip on my Hakko 936 station with separate flux. Lay flux, place chip, wipe the tip past the pins and you're in business.
 
#10
dw8083 said:
Has anyone tried using a single PCM1794A with it's balanced outputs connected to a Pass I/V stage?

Looking at the TI app notes, they recommend op amps for the I/V stage and as an unbalanced to balanced converter.

http://focus.ti.com/lit/ds/symlink/pcm1794a.pdf -page 18

Probably no problem using the Pass D1 I/V circuit, but can the unbalanced to balanced converter be omitted and the I/V circuit connected directly to a set of right and left xlr connectors?

Does anyone have experience with this chip driving balanced outputs?


Thank you,

-David
Click to expand...

Not sure if I understand Your question here !?
The D1 shoud be able to convert the signal coming from the pcm1794, but this chip put out a "little" bit more current than the original D1-dac (PCM63...). Think there are some values that had to be altered, but don't know which.
When it comes to balanced mode...the D1 IV is born balanced...and so is the PCM1794...!?

Lyra
 
#11
dw8083 said:
Hi gmarsh,

Would you happen to have a link to a schematic for your DAC or know where to get design ideas? I've found a lot of articles on unbalanced designs, but there is little published on balanced designs.

Thank you,

-David
Click to expand...
I made a thread about the DAC when I finished it... there's Eagle files posted in the thread.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=59357

The output stage is stolen from the TPA6120A2 data sheet - PCM1792 feeds a OPA4134 which acts as a balanced I/V, and the TPA6120 is configured as a differential-to-single-ended amp. DON'T use 1kohm load resistors in the I/V as the TPA datasheet suggests - this will cause the OPA outputs to hit the negative supply rail! I used 681 ohm resistors instead.

There's also a different output stage shown in the PCM1792 which uses NE5534's for I/V. You could probably just build that part of the I/V and drive a XLR cable directly with that, though there will be a negative voltage offset on each pin.
 
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