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New DAC and Headphone Amp

March Audio

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#1
Its been a while since I have posted any DIY stuff, but I have been tinkering in the background. The latest project is still a bit premature to be thrown out into the wild, but still....

Anyway, a friend who knows my bent for audio electronics sort of challenged me to build him a quality DAC and headphone amp (separate boxes) that could rival commercial gear at a sensible price. Of course I took the bait :) I need an analogue input headphone amp for myself anyway....

This is the initial DAC box, a second is being made (for my friend) is about a 1/3rd less tall and looks sleeker with brushed front plate. The headphone amp box will match.

IMG_20180705_183350.jpg


IMG_20180705_185106.jpg


DAC is powered from USB,HPA will be from a wall wart.

Measurements. Im only going to post a few as Im still tinkering.

DAC output 1 kHz 0dBFS. Maybe not SOA, however pretty damn good. Note that the noise floor is in reality lower, this is an artifact of the measurement system. I need to build a notch filter which takes out the fundamental and it will drop about 20dB.

0dB.png


headphone amp with no load, same DAC feeding.

1k 0db att HPA.png


With my Oppo Planar Magnetics (32 ohm load) plugged in. SPL was 108dB ouch!

No thats not an error, its the correct plot. :) Barely no change in distortion. I need to find some high impedance cans to test now.

1k 0db att HPA with PM1s.png


DAC -60dB

-60dB (log).png


12kHz jitter (HPA output measured)

12k hpa.png



No, Im afraid Im not going to reveal the secret sauce quite yet :)

I will send it to @amirm when finished for some serious testing on his AP.

Oh yes, it does actually sound pretty good too :) !
 
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Wombat

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#2
Its been a while since I have posted any DIY stuff, but I have been tinkering in the background. The latest project is still a bit premature to be thrown out into the wild, but still....

Anyway, a friend who knows my bent for audio electronics sort of challenged me to build him a quality DAC and headphone amp (separate boxes) that could rival commercial gear at a sensible price. Of course I took the bait :) I need an analogue input headphone amp for myself anyway....

This is the initial DAC box, a second is being made (for my friend) is about a 1/3rd less tall and looks sleeker with brushed front plate. The headphone amp box will match.

View attachment 13677

View attachment 13679

DAC is powered from USB,HPA will be from a wall wart.

Measurements. Im only going to post a few as Im still tinkering.

DAC output 1 kHz 0dBFS. Maybe not SOA, however pretty damn good. Note that the noise floor is in reality lower, this is an artifact of the measurement system. I need to build a notch filter which takes out the fundamental and it will drop about 20dB.

View attachment 13680

DAC plugged into headphone amp with no load.

View attachment 13681

With my Oppo Planar Magnetics (32 ohm load) plugged in. SPL was 108dB ouch!

No thats not an error, its the correct plot. :) Barely no change in distortion. I need to find some high impedance cans to test now.

View attachment 13682

-60dB

No, Im afraid Im not going to reveal the secret sauce quite yet :)

I will send it to @amirm when finished for some serious testing on his AP.
Great. I love the hands-on projects. Insights?

Also how do you do the faceplate graphics? My friendly engraver has left town. ;)
 

March Audio

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#3
Great. I love the hands-on projects. Insights?

Also how do you do the faceplate graphics? My friendly engraver has left town. ;)

The prototype box is using Front Panel Express. Idiot proof free CAD design software and reasonable quality CNC machining. However they are damn expensive. No good for quantity.

Insights...... :)......... well, that may have to wait. This is turning out so well that Im seriously considering a small production run. Marketing logo - " Better than all that Schiit!"

:)
 
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Wombat

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#4
The prototype box is using Front Panel Express. Idiot proof free CAD design and reasonable quality CNC machining. However they are damn expensive. No good for quantity.

Insights...... :)......... well, that may have to wait. This is turning out so well that Im seriously considering a small production run. Marketing logo - " Better than all that Schiit!"

:)
Thanks. Good luck. thumb.gif
 

March Audio

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#5
OK, the DAC and headphone amp project progresses :)

Here are the new slimmer cases.

d1.jpg


d4.jpg


d11.jpg


d10.jpg


I mentioned before that every month I meet up with a bunch of audio enthusiasts at a local HiFi dealership. Its mainly an excuse for a meal and a few drinks but we do occasionally discuss hifi. :) Their systems range from the more more modest to Chord DAVE / Audio Physics high end. As I wanted a bit of feedback on the DAC/HPA performance beyond my own biased opinion I set up a simple blind test for people to take part in.

I pitted my dac/amp against a Chord Mojo. Both were hidden from view. Using my Oppo PM1 cans and a switch box the participants could select what music they liked from a wide range and play it using JRiver. Audio levels were exactly matched with a DVM measuring the amp output voltage and checked using my B&K sound level meter. They could listen to as many tracks as they liked for as long as they liked and instantly switch as often as they like between the amps.

test blurred.jpg


jr.png



They were then asked to select in an excel sheet which Dac they preferred, or if they thought there was no significant difference. The results are below. Please note during the test the DACs were labelled DAC1, DAC2 and the results were not visible.


results.png


Wasn't expecting that ! :)

Please rest assured Im NOT taking this as proof of anything - it was just a bit of feedback for me about the design that, as far as practicable, eliminated biases and expectations.

Other feedback from the participants was that only one person had a consistent preference for the Chord Mojo. One person thought it was actually the same DAC on A and B :) . Most considered it variable dependant upon the track that was played which was preferred, but ultimately with a slight preference for my DAC. However, extremely difficult to tell apart.

My main take away from the event (which yet again re-inforces my previous view) was that DACs are pretty much a problem solved. Whatever people like to think, when they are put under controlled conditions they really struggle to tell the difference. I think the group found the result a little disconcerting.

The DAC is pretty much a finished article, however I now need to design the final PCB for the headphone amp. I will then send it to Amir for proper testing and abuse :)
 
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Blumlein 88

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#7
I dig your choice in music there. And the items you've created look great. Kudos to you. Now we'll have to see if Amir can test them without messing it up. Are you going to send identical samples to Jude and atomicbob? :) :)
 

March Audio

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#8
I dig your choice in music there. And the items you've created look great. Kudos to you. Now we'll have to see if Amir can test them without messing it up. Are you going to send identical samples to Jude and atomicbob? :):)
Thanks ! :)

Yes I will send some units to Jude and Atomic Bob, with march audios marketing tag line "Better than all that Schiit" :)
 

Soniclife

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#9
Great stuff. Out of interest how many had done this sort of test before?
However, extremely difficult to tell apart.
Do you think they could really tell them apart, or are we really looking at guessing and a small sample size?
Both DACs measure very well so if there is a difference what would it be?
 

Sal1950

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#10
Any rough idea what a final sales cost would be?
Just curious for comparison sake.
 

March Audio

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#11
Great stuff. Out of interest how many had done this sort of test before?

Do you think they could really tell them apart, or are we really looking at guessing and a small sample size?
Both DACs measure very well so if there is a difference what would it be?
Well I have tried a couple of blind tests before with the guys, its very relaxed and informal so we dont (and shouldnt) take it too seriously. I dont consider it a valid statistical exercise, but it does tell me the differences are small enough !

In my own testing I really struggle to tell any difference, there is no way I could successfully ABX the devices and I dont believe the guys last night would be able to either.

Oh the difference in the DACS is obvious, its Rob Watts billion tap filter ;)
 

March Audio

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#12
Any rough idea what a final sales cost would be?
Just curious for comparison sake.
That really hasnt been worked out yet. These are just prototypes and the case cost is currently waaaaaaaayyyyyyy too high. :)

If I go ahead it will be (certainly initially) a small production run so I wont have the advantage of quantity cost reductions. What I would like to do is get the HPA board finished ( I do need to make a gain change to ensure it drives a high enough voltage for high impedance cans) and let Amir test both DAC and HPA (assuming he is willing and interested) and see just where it sits in absolute technical performance terms and compared to the competition.

It would also be interesting to send it around a few forum members to guage reaction to the sound quality.

Just out of curiosity, has anyone got any feedback on the look of the units? One change that will be made is that the headphone socket will be on the board so will be flush with the front panel.
 
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#13
If I had to guess, I might assume this is a ak4490 design with a very competent usb receiver and overall desing. (Something along the line with these "i2s over usb" boards: JLSounds) Cheap, cheerfull and high performance even for a small scale DIY. I will be most interested to see the implementation.

The amplifier could be a nice simple intrument amplifier with pretty good high(ish) current buffers. BUF634 perhaps? Either way, quite transparent at 1k (understatement).
 

March Audio

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#14
If I had to guess, I might assume this is a ak4490 design with a very competent usb receiver and overall desing. (Something along the line with these "i2s over usb" boards: JLSounds) Cheap, cheerfull and high performance even for a small scale DIY. I will be most interested to see the implementation.

The amplifier could be a nice simple intrument amplifier with pretty good high(ish) current buffers. BUF634 perhaps? Either way, quite transparent at 1k (understatement).
:) Secret sauce is staying under wraps :)
 

Sal1950

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#15
Just out of curiosity, has anyone got any feedback on the look of the units? One change that will be made is that the headphone socket will be on the board so will be flush with the front panel.
The jack change would have been my first comment. The panel is very attractive but quite spartan, though I don't know what you could add?
Model descriptions maybe?
 

March Audio

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#16
The jack change would have been my first comment. The panel is very attractive but quite spartan, though I don't know what you could add?
Model descriptions maybe?
Yeah, I wanted to keep it very simple and clean, even considered putting the headphone socket on the back panel.
 

yage

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#17
Long time lurker, first time poster because of this thread. I think your prototypes look very cool - "bada**" is the word that comes to mind. One comment - the DAC might need some sort of sample rate indicator on the front, if only to help the end user make sure they're properly set up.
 
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#18
Roger on the secret sauce. It is just fun to speculate.

Just out of curiosity, has anyone got any feedback on the look of the units? One change that will be made is that the headphone socket will be on the board so will be flush with the front panel.
I like the front panel a lot. Flush headphone jack will make it look even less diy for sure. Perhaps move the dac 1 and hpa 1 to front and lose the large text in the back. Company logo is good in the back panel, but should be in a smaller type. Perhaps use white fill in the back text and red in front to differentiate them a bit. Consider having RCA in, RCA out texts (in small type) as you have named the usb jack too. Not sure how it would work without over crowding the back panel.

Matching RCA's would be great. :)
 
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