[dorkus]

i just got my Muse today - took a little under 3 weeks from my original order date, which seems relatively reasonable.
 
out of the box, there were a few things that didn't look so hot. the front panel has a smudge on one of the markings, as if the ink didn't dry before they handled it. there were also a lot of fingerprints on the faceplate, as if the unit was used. also the terminations are of inferior quality as people mentioned - the "gold-plated" connectors barely look like they have a gold flash on them and are already tarnished looking. the USB connector is extremely loose and doesn't seat the plug all the way. and the unit has no feet at all, allowing bare metal edges to contact whatever it's on.
 
i powered it up and plugged a pair of headphones in. the first thing i noticed was a buzzing noise - turns out it was a variable speed fan i had on in my bedroom. it probably has a noisy triac, and i imagine the stock Muse power supply (wall wart) is very poorly filtered. i turned off the fan and the noise subsided. then i tried hooking it up to my iMac via USB. i got sound, however there is a ton of clipping at even a very low volume level. this leads me to suspect a reversed part or other assembly issue. i'll have to take it apart tomorrow and check out what's going on inside.
 
so, first impressions are pretty piss poor, though for the $129 or whatever i paid i suppose it's to be expected. i have a lot of leftover parts and tools from my DIY days, so i don't mind a fixer-upper... just would have been nice to have some semblance of quality control on these things. i'm going to file a complaint with the seller now.

 

[dorkus]

i opened the Muse up to see if i could figure out where the distortion was coming from. assuming the PCB designations are correct, all parts appear to be installed correctly (though no idea if the parts values are correct). the distortion sounds a bit like what one gets when one uses a high offset current (e.g. bipolar input) opamp in a non DC-balanced circuit. i'd have to probe around to figure out if that's the case, not really in the mood though.
 
on the plus side, the seller did offer to pay for whatever repair costs. (at least, i think that's what he offered, his english is a little confusing.) but that doesn't seem realistic as any repair shop that would even touch it would likely charge in an hour what the entire unit costs. but at least he's been quite responsive to emails, and said he would contact an engineer to see what the issue may be. at this point though, it would probably be a better use of everyone's time and money to just do a return/refund.
 
the power supply circuit is interesting to say the least. in order to derive a split supply from the 12VDC wall wart, signal ground is floated at 1/2 the single rail voltage. oddly, a TA2030 amplifier chip is used to accomplish this... the output of the IC is used as the ground point. very strange, i guess it works though i can't imagine the ground impedance is all that great (because it's an audio  chip, the impedance should be fairly flat through the audio range, but that's all from negative feedback, blech).
 
parts quality is a mixed bag... the promised BB opamps and chips are all there, but the caps are a mix of just ok nichicons and some more generic electrolytics. the soldering job is pretty shoddy, with a lot of resistors crooked and incomplete flow around the joints. ah well, you get what you pay for...

 

[pp312]

Actually, you often don't, and you appear not to have.
 
Problems I encountered include a 220 ohm electrolytic wired wrong way round and a headphone socket that loses contact in one channel if you put pressure on it. The loose USB connector can actually be overcome by using a different type of plug, one intended for a phone connection, which is something I discovered by accident. Can't enlighten you any further as I never knew there was more than one of the same type of plug.
 

 

[dorkus]

update... i got a partial refund from the seller as compensation for having to service the unit... no sense sending it back given the high shipping costs. and i was able to fix the issue. turned out the output opamp (OPA2134) was fried... adding a socket and plugging in what i had on hand (OP275, AD827) fixed the distortion issue. i left the AD827 for now, but need to get something with FET inputs so i don't have to worry about offset.

while i was in there i also made a few changes:

- reduced amp gain ~ 6dB by decreasing feedback resistance (added parallel resistor) - the gain is way too high for me, with most sources i can use only the very bottom of the volume pot where it is very non-linear.

- reduced output impedance from 33 to 10 ohms. all my 'phones are low impedance and the damping factor @ 33 ohms is pretty terrible... i would decrease it even further but not sure about stability. thinking of trying 5 ohms in combination with an RC snubber to stabilize.

- changed out most of the electrolytics. mostly to Pana FM, one large nichicon HE at the power input.

the sound is very nice, if colored, via USB - certainly a big improvement over built-in audio on my Macs. it's extremely smooth and warm - a little too much so, but it helps make computer listening much less fatiguing. bass is still pretty bloated and flabby, which i'm starting to wonder is a product of the floating ground scheme. all in all it's a bit too tube-sounding for my tastes (i prefer neutral), but for the $50 net i wound up paying i'm not complaining.

i have some OPA1642 samples on the way, will see how those fare. not really looking to go too nuts with op amp rolling, just need to find something that sounds decent and will stick with that. i do need to further reduce the output gain though, it is still way too high with my 'phones... might consider rewiring the pot as a shunt and building in an additional 12dB of attenuation.

kind of curious to try the Aune now... the sound of the Muse is so much better for even the most casual background computer listening, i'm really tempted to get one for work. maybe with some light mods it could sound pretty good, and the quality looks quite a bit better than the Muse. the only reason i chose the Muse was the toslink input (to use with my PlayStation 3), i would not recommend it otherwise based on my experience.

 

[dorkus]

btw, i also would not recommend the Muse for S/PDIF input use - the sound is vastly inferior to USB, very thin and electronic sounding. sounds like a poor implementation with lots of jitter... it's good enough for video games, but i would hesitate to use it for even casual music listening.

 

[pumin]

hi dorkus,
I found Kmtang grounded his Aune on DAC chip, and he said it sounded better, please check.. 
http://www.diyaudio.com/forums/digital-source/171424-aune-mini-usb-dac-headphone-amp.html

 

[dorkus]

hi pumin - thanks, i stumbled across that post too, might give it a try.
 
my TI opamp samples arrived and i have some browndog DIP adapters on the way, will see how the FET chips sound.

 

[dorkus]

so, i played around a bit more - i socketed the DAC buffer as well, and mounted some opamps on browndog adapters:
 
OPA1642
OPA2107
AD825 (x2)
 
i also have the AD827 which i can use in the buffer (but not the HP amp due to bipolar input current). incidentally i also had some AD8620's on hand but i did not bother trying them as i have found them disappointing (bright and threadbare) in past installations (CD player output sections).
 
all chips have .01uF Pana P decoupling between V+ and V- pins on the DIP adapters (or directly on pin in the case of AD827). i replaced the .1uF bypasses on the board with 47uF Elna Silmics, since HF decoupling is now provided more effectively by the Pana P.
 
all in all, it sounds better - cleaner, more neutral and dynamic. the bass is more controlled, though i still wouldn't call it taut.
 
as for IC preference, i'll admit i'm not hearing any huge advantage of one chip over another... they all sound like IC opamps after all, and in the end i believe the surrounding circuit has far more influence on the sound than the chip itself. that said, i do hear the signature of the different topologies - the bipolar AD827 is the coolest and crispest, with a little better definition to leading edges. i've played with discrete JFET buffers before, and the AD825 has a little of that sound... smooth, a little light. the FET OPA's sound fairly similar, they have the most "air" though are a little fuzzier than the other two.
 
after trying several combinations, i settled on AD825 in the buffer and OPA2107 for the HP amp - as of now this seems to give me the best overall balance. interestingly i found the AD825 most advantageous in the buffer, where to my ears it was the winner by a larger margin than any of the other chips in either position. several years ago i had heard good things about the AD825 (primarily its unusually wide open-loop bandwidth) and so far it seems to be living up to some of the hype. it's too bad it doesn't come in a dual package, i'd like to eventually solder the SOIC's in place so i can get rid of the parasitics of the adapters and sockets.
 
i still want to reduce the gain of the HP amp so the volume pot is more usable, mulling over the best way to do that...
 

 

 

[Tacoboy]

I bought a Muse Headphone amp. ($65) about 6 months back, no complaints.
But now want to try something better?
Trying to figure out how much I need to spend to get a good improvement in sound.
 

 

[rasputyn]

Just ordered Muse MK2, I'll post the results when I receive it... It seems that there is obvious difference in comparison with MK1:
 

 
It looks like that design is somewhat different from Aune too, since Aune has some regulator connected with wires to PCB near supply connector.

 

[carsten1]

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[carsten1]

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[carsten1]

Weird?! Hmm..!
 
In Aune X1, they have changed to a lesser expensive OPA, older OPA, after making the first 300 pcs. They say it is because of wanting more "warmt" in the sound, and absolutely makes a big fuss out of saying, that it is not because they want to change the chip, because it is a cheaper chip. They actually use these very terms.
 
Aune and Muse are HifiDIY items.