[DavidK35]

http://www.ebay.com/itm/MUSE-TU-20-Russia-EH6922-smallest-Tube-Preamp-Headphone-Amplifier-Sliver-/221073309953?pt=LH_DefaultDomain_0&hash=item3378ff0101
 
Says 3Wpc on 33ohm headphone, can this be for real?

 

[CollectoR13]

Looks too good to be true.
Search for "muse portable headphone amp" here on head fi, to get impressions of the build quality of their amps.
If anybody wants to mod it, it would be a ok start.
 

 

[K7music]

2011 MacBook Pro, into Muse TU-20, into Sony MDR-XD200 headphones
 
First off, the MacBook Pro already has some pretty good sound coming out of the headphone jack... 
 
 
With regards to the TU-20
 
The noise floor is pretty substantial, I can hear the 60Hz hum just past the 3-4 volume level, and as I turn up the volume just past 5 I start hearing all sorts of buzzing.. Maybe a better 12V power supply would fix that..... 
 
I analyzed the power supply and it had a nice noisy ripple at about 71kHz.. This is typical of most SMPS but it comes out in audio.. Maybe there's cleaner 12V supplies that this can work on. 
 
And the 6V tube heater supply had a nice 1.2V ripple of around 20kHz, but that's also typical of those cheap little LM7806's... more filtering is in order in my opinion. 
 
definitely does Not work with 12AX7 tubes so much for Tube Rolling if you only have 12AX7's. 
 
Does not sound all that much better, and sadly I don't have my tube ears all tuned up so it's hard for me to notice the subtleties but it does amplify and sort of sound beefy when it's not quiet. 
 
Maybe on a different listening environment the subtleties can be noticed but in general I think it looks nicer than it sounds and I'd rather spend the $80 or so on a very clean solid state headphone amp. 
 
K7.

 

[K7music]

So I checked out the power supply..... I'm here in the US of A and the power supply out of the box was a 240V european type SMPS with a little adapter for 120VAC. 
 
The measured voltage of that supply was 11.88VDC; it's supposed to be 12V at 0.5A
 
So then I picked out a 12V 2.5A SMPS from my box of goodies and I measured it at 12.28VDC (With a FLUKE Multimeter!).
 
When I plugged it in, the noise floor reduced significantly but there was a hum every time I touched the volume pot??????? 
 
When I measured the current.... even with no input and no load (no headphones) it drew 0.545A!!  So, the SMPS that was given with the unit is under powered and noisy as heck!
 
Enough said!
 
I'm gonna see what I can do to clean it up and hack it up to something decent... After all, it is in a nice metallic box!!
 
K7

 

[bearington]

I just received mine from China. Muse TU-20  EH6922, but I will not touch it until the April 6th, for I am on the road. I have another 12 Volt supply for it too. A few decent 12AU7 tubes too, but before I do any tube rolling, I plan on cleaning up some of the circuits, maybe replace a few caps and other things.  I will figure it out when I start measuring and playing with it.   

 

[bearington]

I opened the box, the power supply was European two pin 240vac. I used one of my own PSs. The op amp is a dual 5532p, that has to go. The tube power selector on the board was soldered for the EH6922, cut that so I can roll 12AU7 tubes too, I have a few of them. Leaving the original tube and replaced the op amp with a OPA2604. Have a few dual op amps and singles on a dual Bdog adapters. The electrolytics are Elna and Rubicons, but not sure if they are knock offs. I also have a buzz on contact with the volume control, but is because there is no grounding to the chassis and no nut on the potentiometer. I usually, like to see more capacitors on an amp. Ok time to burn it in, see what it really sounds like before I pull out my soldering iron.

 

[bearington]

  Listening as I was burring the Muse TU-20, I changed the op amp again to a Dual Brown dog adapter with two LME49990. I adjusted the bios, by setting the volume to max, with a 32 ohm load. Played a 1khz -26dB sign wave. Then adjusted both channel outputs at the op amps to 6.30 Vdc. Sounds good, haven't done anything with rolling tubes, but I did add a case ground to the board, to kill the buzz.
It sounds good for an inexpensive amp. Will play more later. I only have 24 hours of burn in, should have at least 48hrs before playing.
The LME49990s are very fast and accurate, lack warmth but are very crisp when it comes to high end. I think I will attempt to soften them with the tube I select, after a good burn in. All my op amps and tubes I will roll have been burned in, they are parts from other rolling projects.    

 

[MDR30]

Received mine today. With original wall wart there was mains hum and a whistling tone (around 1 kHz or so). Tried a few other mains adapters and one simple, switched one got rid of hum and noise. The amp is powerful, drives my AKG K501 from a Sansa Clip well.
 

 

[MDR30]

I'm tempted to try other, better, op amps and wonder if it's just to remove and replace with the OPA2604 suggested above. Other good alternatives?

 

[bearington]

I tried that and a brown dog adapter with two LME49990s. Currently using two AD797AR on a brown dog adapter, with a mullard 12AU7 tube. Using a 2.5 amp ps, added chassis gnd. I had to unsolder the bridge to make the pins for a jumper viable. The unit I had was over modulating, so I lowered the grid voltage to 6.28 vdc, no load full volume. For the size, cost it sounds good, using customized denon ah-d2000, but will try my stock hd800s tomorrow. The Er4s sound good too. The source is a ak100 on the line ins on the back, or an imoded iPod on a custom dock. Currently this is the best sounding tube and op amp combo I tried, have many more tubes and op amps to audit. I need put this on a scope to find the best grid voltage ( no over modulation ). I also have an occasional noise that comes and goes, need to get rid of, other then that dead silent at full volume ( other then typical tube noise at extreme volumes. )

 

[MDR30]

I tried that and a brown dog adapter with two LME49990s. Currently using two AD797AR on a brown dog adapter, with a mullard 12AU7 tube. Using a 2.5 amp ps, added chassis gnd. I had to unsolder the bridge to make the pins for a jumper viable. The unit I had was over modulating, so I lowered the grid voltage to 6.28 vdc, no load full volume. For the size, cost it sounds good, using customized denon ah-d2000, but will try my stock hd800s tomorrow. The Er4s sound good too. The source is a ak100 on the line ins on the back, or an imoded iPod on a custom dock. Currently this is the best sounding tube and op amp combo I tried, have many more tubes and op amps to audit. I need put this on a scope to find the best grid voltage ( no over modulation ). I also have an occasional noise that comes and goes, need to get rid of, other then that dead silent at full volume ( other then typical tube noise at extreme volumes. )

Any chance of photos with explanations for us non-experts out there?

 

[K7music]

awesome work Bearington.... however for a $100 and all that work I don't think it's worth it...
 
I also purchased this little beast: 
 
http://www.ebay.com/itm/261031079874?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
 
It's about $50 and I had to troubleshoot the transformer to make sure I got the right voltages, but at least it came assembled...... MAN this thing sounds AMAZING!!!! much better than "The Quickie" which was $100 and I had to assemble the whole thing and it didn't even come with a box!!!
 
K7

 

[K7music]

here's the "HIFI stereo audio amplifier 6N3 Tube PRE-AMP Buffer" on Amazon and in the review section I explain what I did to get the right voltages from the transformer. 

 

[bearington]

K7 I wouldn't invest any money into it either, but the parts were sitting in boxes collecting dust, they were left overs from playing with a DAC. It took only a few min of work for me. When I get a chance I will post a pic, but I have to work today

 

[MDR30]

Quote:

When I get a chance I will post a pic, but I have to work today

 
Look forward to the photos with instructions on where to measure the bias. I've been listening to the amp a lot this weekend and it really shines with my AKG headphones, especially the K401 which I haven't listened to much since I bought it. It's dynamic, full-blooded and with an amazing sound stage. The upper mids are a little bit forward (quality of the headphone), but apart from that it sounds very realistic.
 

 


 
Is this the adapter you used, and does it fit in the box?