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Old 14th April 2014, 01:10 AM   #1
r010159 is offline r010159  United States
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Default Quality differences between DACs

Hello all!

I have a question for you gurus. Can the differences between properly designed DACs be audible? Does each DAC have its own unique sound signature? And how much does jitter play a role in all of this? Would the answer be different if we are talking about USB DACs?

I have an ODAC and I am trying to determine if a purchase of a more expensive DAC is worthwhile. I am wondering if the differences will be aparent to me. Maybe instead the money should go into the headphones.

Thank you very much for any replies!

Bob Graham
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Old 14th April 2014, 01:36 AM   #2
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I've spent the best part of four years in my development of a DAC. I abandoned sigma-delta DACs (the current fashion technology) a few years back as they didn't sound as clear as multibit DACs.

Jitter does not in my experience play a role when using multibit DACs, but I understand its crucial if the DAC is sigma-delta.

What does 'properly designed' really mean? Designed to give a certain array of numbers (THD, SNR, freq response etc.) or designed to give listening satisfaction? The digital source (USB, S/PDIF) doesn't impact the sound quality of a DAC in my experience, provided common-mode noise issues are addressed.

Your ODAC can be improved with a mod to the power supply for relatively little money. The designer appears to have ignored the DS for the Micrel regulator's output capacitor meaning it has only marginal stability.
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Old 14th April 2014, 02:20 AM   #3
r010159 is offline r010159  United States
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Quote:
Originally Posted by abraxalito View Post
I've spent the best part of four years in my development of a DAC. I abandoned sigma-delta DACs (the current fashion technology) a few years back as they didn't sound as clear as multibit DACs.

Jitter does not in my experience play a role when using multibit DACs, but I understand its crucial if the DAC is sigma-delta.

What does 'properly designed' really mean? Designed to give a certain array of numbers (THD, SNR, freq response etc.) or designed to give listening satisfaction? The digital source (USB, S/PDIF) doesn't impact the sound quality of a DAC in my experience, provided common-mode noise issues are addressed.

Your ODAC can be improved with a mod to the power supply for relatively little money. The designer appears to have ignored the DS for the Micrel regulator's output capacitor meaning it has only marginal stability.
I thought designing to give a certain array of parameters is adequate for a DAC? Also I thought designing a DAC to these parameters is a straightforward process? I thought the "magic" (creativity needed to balance trade offs) would be found in the amplifier part? Does each DAC actually have its own sound signature?

I apologize for my ignorance. I remember very little fron my EE courses.

Bob Graham

PS: Please point me to the instructions for modifying my ODAC (it is actually the ODAC/O2 combo unit)
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Old 14th April 2014, 02:37 AM   #4
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What's adequate for a DAC design depends on the goals the designer sets for him/herself. The ODAC's designer bought a fairly expensive bit of measuring kit (a dScope) so it kinda makes sense to justify that expenditure by designing according to the numbers it produced.

In my experience of designing DACs, yes DACs do sound different in terms of listening satisfaction. I've spent several years increasing the listening satisfaction of my designs. I don't yet know how to quantify those differences in terms of measurements, though I do have one or two ideas.

I'm unaware of anyone else noticing the design error in the ODAC and I've not published any instructions for modifying ODACs. But if you were to put up a photo of the PCB around the analog power regulator I could probably indicate what's required.
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Old 14th April 2014, 09:29 AM   #5
Julf is offline Julf  Europe
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Quote:
Originally Posted by r010159 View Post
I thought designing to give a certain array of parameters is adequate for a DAC?
Are you looking for opinions, or objectively verified information?
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Old 14th April 2014, 02:32 PM   #6
r010159 is offline r010159  United States
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Quote:
Originally Posted by Julf View Post
Are you looking for opinions, or objectively verified information?
I am looking for opinions based on experience. Do all DACs basically sound the same, or does each have its own sound signature? Are there trade offs to be made in the design of a DAC that produce an audible result?
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Old 14th April 2014, 02:38 PM   #7
Julf is offline Julf  Europe
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Originally Posted by r010159 View Post
I am looking for opinions based on experience.
A lot of people claim DACs sound different. Very few have verified it using controlled, double-blind conditions, and even fewer have tried to isolate the actual DAC parts from the inevitable analog stages associated with the DACs.
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Old 14th April 2014, 02:56 PM   #8
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Originally Posted by abraxalito View Post
I'm unaware of anyone else noticing the design error in the ODAC and I've not published any instructions for modifying ODACs. But if you were to put up a photo of the PCB around the analog power regulator I could probably indicate what's required.
Interested to hear your opinion, or if you can tell us the part numbers of the regulators so we can go read the datasheets for ourselves..

Click the image to open in full size.

/Nevermind, just noticed the part numbers are on the schematic http://www.yoyodyneconsulting.ca/dow...AC-release.pdf

http://www.micrel.com/_PDF/mic5205.pdf I assume you are talking about the absence of the 470pf caps on Pin4?

Last edited by mcandmar; 14th April 2014 at 03:08 PM.
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Old 14th April 2014, 03:56 PM   #9
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No, what I'm talking about is the wrong kind of cap (ceramic, low ESR) being put on the output of the MIC5205-3.6. Here's what the DS (page 8, left column) says -

Ultra-low ESR capacitors can cause a low amplitude oscillation on the output and/or underdamped transient response.


The 22uF ceramic specified as the output cap qualifies as ultra-low ESR.

To correct this you could remove C101 and fit a tantalum cap in its place. However I'd suggest putting a ferrite bead in series with the track between the reg (U101) and the offending cap (C101). This requires a scalpel cut in the track and scraping both sides to accept solder tinning then a bead (0805 or 0603 size) across the cut.

Last edited by abraxalito; 14th April 2014 at 04:01 PM.
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Old 14th April 2014, 04:06 PM   #10
Eldam is offline Eldam  France
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cutting the trace and put 0.5 to 1 ohm 0.5 W resistor between the output of the micrel and the ceramic cap could be a solution. And of course put > 2.2 uF (micrel datasheet) ceramic or acrylic PPS from Cornell Dublier (1210 case) instead the ceramic cap?

or // with a tantal the ceramic existing one ?
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