DAC Differential Outputs

Xittenn · 24th November 2020, 06:02 AM

I bought a DAC AK4490EQ not knowing it has differential outputs. I was planning on creating a class A output stage using 2SA1313 to power some HIFIMAN HD5SE, but I don't know what actually comes out of a differential output? I am aware of the recommended circuits.

PRR · 24th November 2020, 08:21 PM

> [i]I bought a DAC AK4490EQ[i]

The bare chip? Or a boxed product including the AK4490EQ chip?

Use of the differential outputs on the chip is covered in datasheet, page 62-.

Xittenn · 1st December 2020, 10:08 AM

The bare chip. I'm building my own module for a Raspberry Pi 4 B 8GB sweet, this will simply be a DAC Amp module. I want to run pure class A on the output. This was the first time I'd looked at a DAC. I didn't expect a differential output, and I'm still not entirely sure which of several types of out is this differential output?

Is it a positive and a negative swing?

Is it they swing at the same time but in opposite directions?

I hear that there are design concerns because either the positive or negative are dominant over the other, is this an issue?

The recomended circuits requires an op-amp Low Pass Filter and a differential in single-ended pre-out. I considered alternatives and they weren't very good. I would've just used a coupling transformer but well I haven't given up on using a coupling transformer, but probably not.

PRR · 1st December 2020, 11:07 PM

Why do many DACs have differential output? - Electrical Engineering Stack Exchange

chris719 · 1st December 2020, 11:40 PM

Quote:

Originally Posted by Xittenn

The bare chip. I'm building my own module for a Raspberry Pi 4 B 8GB sweet, this will simply be a DAC Amp module. I want to run pure class A on the output. This was the first time I'd looked at a DAC. I didn't expect a differential output, and I'm still not entirely sure which of several types of out is this differential output?

Is it a positive and a negative swing?

Is it they swing at the same time but in opposite directions?

.

It is described completely on Page 61 of the datasheet and on Page 9. They are 2.8 Vpp centered on half of the reference voltage.

AOUT (typ.@0dB) = (AOUT+) - (AOUT-) = +/-2.8Vpp * (VREFHL/R - VREFLL/R) / 5

The outputs are 180 degrees out of phase with respect to each other.

Xittenn · 2nd December 2020, 12:00 AM

lol . . . written in japanese

Xittenn · 12:59 AM

The little formula wasn't obvious to me, and the literature I read, though mostly supported the idea of a 180degrees out of phase, still didn't leave me with a solid answer.

At any rate thanks for clearing that up.

chris719 · 2nd December 2020, 02:10 AM

You don't technically need to use both outputs, especially if you are not looking to preserve the best measured performance. It is highly recommended, though, since there is probably a lot of common-mode output that AKM intends for you to cancel.

Xittenn · 2nd December 2020, 02:13 AM

As far as I understand, yes there is. . . .. my 1313's just came in yay.

24th November 2020, 06:02 AM	#1
Xittenn diyAudio Member Join Date: May 2020 Location: Vancouver	DAC Differential Outputs I bought a DAC AK4490EQ not knowing it has differential outputs. I was planning on creating a class A output stage using 2SA1313 to power some HIFIMAN HD5SE, but I don't know what actually comes out of a differential output? I am aware of the recommended circuits.

2nd December 2020, 12:57 AM	#7
Xittenn diyAudio Member Join Date: May 2020 Location: Vancouver	The little formula wasn't obvious to me, and the literature I read, though mostly supported the idea of a 180degrees out of phase, still didn't leave me with a solid answer. At any rate thanks for clearing that up. Last edited by Xittenn; 2nd December 2020 at 12:59 AM.

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24th November 2020, 08:21 PM	#2
PRR diyAudio Member Join Date: Jun 2003 Location: Maine USA	> [i]I bought a DAC AK4490EQ[i] The bare chip? Or a boxed product including the AK4490EQ chip? Use of the differential outputs on the chip is covered in datasheet, page 62-.

1st December 2020, 10:08 AM	#3
Xittenn diyAudio Member Join Date: May 2020 Location: Vancouver	The bare chip. I'm building my own module for a Raspberry Pi 4 B 8GB sweet, this will simply be a DAC Amp module. I want to run pure class A on the output. This was the first time I'd looked at a DAC. I didn't expect a differential output, and I'm still not entirely sure which of several types of out is this differential output? Is it a positive and a negative swing? Is it they swing at the same time but in opposite directions? I hear that there are design concerns because either the positive or negative are dominant over the other, is this an issue? The recomended circuits requires an op-amp Low Pass Filter and a differential in single-ended pre-out. I considered alternatives and they weren't very good. I would've just used a coupling transformer but well I haven't given up on using a coupling transformer, but probably not.

1st December 2020, 11:07 PM	#4
PRR diyAudio Member Join Date: Jun 2003 Location: Maine USA	Why do many DACs have differential output? - Electrical Engineering Stack Exchange

2nd December 2020, 12:00 AM	#6
Xittenn diyAudio Member Join Date: May 2020 Location: Vancouver	lol . . . written in japanese

2nd December 2020, 02:10 AM	#8
chris719 diyAudio Member Join Date: Jun 2004 Location: Connecticut	You don't technically need to use both outputs, especially if you are not looking to preserve the best measured performance. It is highly recommended, though, since there is probably a lot of common-mode output that AKM intends for you to cancel.

2nd December 2020, 02:13 AM	#9
Xittenn diyAudio Member Join Date: May 2020 Location: Vancouver	As far as I understand, yes there is. . . .. my 1313's just came in yay.