The $95.00 Xiang Rong Audio XR010 tube amp Updated With Photos
Jul 26, 2008 at 10:59 PM Thread Starter Post #1 of 12

roger_s

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About 10 days ago I dropped a note here asking if anyone had seen this HA:

Single End Tube Head Phone Amp Kit - Plug and Play

I didn't get any responses but then I'd never seen mention of it so I wasn't surprised. The vendor's got good feedback, charges very reasonable shipping from HK (19 bucks!) so I figured what the heck and bought one.

It arrived yesterday. The bottom line, it's a decent amp if you're willing to invest some sweat equity.

I took it out of its shipping box (the top had not been taped shut, it was held together by a tab/slot bit that somehow managed to stay together from HK to ABQ. Amazing), plugged in the 6DJ8 tube--the markings are rubbed off, don't know it's lineage--and fired it up. With my DIYmod iPod Mini or my iMod 4G I got hum and not-so-hot sound from my HD-650's. There was noticeable distortion, unfocused bass, and only OK imaging. My ears said "the input's over driven".

I also wasn't too happy plugging everything into 1/8" jacks. I knew about them going in and already planned on replacing them. So I set about mounting it in a Radio Shack project box. I removed the 1/8" jacks and the Alps volume control/power switch and soldered in some Navships teflon insulated wire. On went RCA jacks, a proper 100K pot, a power switch and a 1/4" phone jack paired with a 1/8" jack that's disconnects when a 1/4" plug is in use. I floated the RCA jacks from the aluminum top plate with shoulder washers and didn't ground the PCB to the plate.

Another plug and play and still hum and still not so hot sound. Back under the soldering iron I tied the PCB ground to the plate. The hum was much improved. There's still some with the iMod or the DIYmod but I pretty much expected that since they're not grounded to anything and the XR010 likely isn't getting much grounding from its power supply.

Time to tackle that lousy sound. I scrounged up a couple of 470k ohm resistors and tied the inputs to ground through them. Wow, was I right about it being over driven. What a difference. The bass is much improved, tighter, more slam. The opening of k.d. lang's "Luck In My Eyes" really shines. It took everything Jimmy Smith's Hammond B3 could toss at it. It's not perfect, it's not as articulate as my Bottlehead S.E.X and certainly not as transparent or detailed but at 1/4 the price I'm very impressed. Next up is to replace the coupling caps. I suspect even a pair of Solens will take this little amp up a notch or two.

It plays well with my HD-650s, K-240Ss, V-Moda Vibes but not so much with my Shure E3c's. They sounded rather tinny compared to the others.

If you opt to get one, be prepared to fire up your soldering station and your solder sucker. A few hours of elbow grease make for a pretty decent amp. Right now mine's serving duty as the audio for a Hackintosh that I use as to convert reel-to-reel and cassette tapes to CD. No hum to speak of now that it's tied into a properly grounded source.

EDIT: You really don't won't your phones on when powering on. There is a very pronounced power-on pop.

Roger
 
Jul 26, 2008 at 11:19 PM Post #3 of 12

roger_s

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I'll see if I can't get some pictures up. Right now I plan to leave it in its RatShack box--I did paint the top plate blue. It'd be easy enough to build a wood box for it but that's for another day.
 
Jul 27, 2008 at 1:10 AM Post #4 of 12

928GTS

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You've got me interested in one of these amps,if you could include a little bit of detail about the mods you made. Basically more or less what did you connect to where so I can repeat these mods whenever I manage to get this amp. Sounds like a fun project!
 
Jul 27, 2008 at 1:34 AM Post #5 of 12

roger_s

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Pretty easy. Take a look at the link to the photos on eBay. The two 1/8" jacks come off along with the volume control. Replace all of those wire on the PCB and hook up RCA jacks, a volume control, a 1/4" headphone jack, and a power switch. Getting the input levels down requires soldering a 470k ohm resistor from the positive side of the RCA jack to ground. That attenuates the input (WARNING: ASCII art ahead):

Do this to both channels:

RCA Jack Center Hole
+------------ To PCB Input
|
\
/
\ 470K ohm resistor
/
|
------- Ground
-----
---
-

I'll work on getting some photos up but for less than 10 dollars worth of parts on top of the 95 dollars to buy the thing you should have a pretty decent headphone amp.

Mine came with a schematic and the PCB is labeled. Between the two the mods are dead simple. Even I could do them!



Quote:

Originally Posted by 928GTS /img/forum/go_quote.gif
You've got me interested in one of these amps,if you could include a little bit of detail about the mods you made. Basically more or less what did you connect to where so I can repeat these mods whenever I manage to get this amp. Sounds like a fun project!


 
Jul 27, 2008 at 6:01 PM Post #6 of 12

roger_s

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Here's the attenuated input. That's a 470k ohm resistor running to ground

amp-3.jpg


Here's the top with a set of AKG 240-S phones for scale

amp-1.jpg


The bottom end of things

amp-4.jpg


And another shot of the top

amp-2.jpg
 
Jul 28, 2008 at 1:31 AM Post #8 of 12

roger_s

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I did that initially. I soldered in 2k resistors. It made no noticeable difference so I didn't include that effort in my write-up. I decided to bring out the big guns after that failed rather than chase resistor values.

I suspect that this thing's designed for folks who'll just plug into it via a headphone jack rather than a proper line-in. They can fiddle with the volume on their source to get whatever quantity/quality of sound they want.
 
Jul 28, 2008 at 1:49 AM Post #9 of 12

nikongod

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Something to note:
The input RCA's should ground to the ground on the PCB. It looks like the copper wire grounds to the chassis. Although the chassis should be grounded for safety, it should not meet up with signal ground except for at a star ground point.

As a point of anal retentivity: It looks like the red twisted pair is power going to the switch up front. cool deal, but I would re-route these wires away from the pot if possible. I have seen DC lines leak noise into the signal. If its not nice and quiet after setting up the ground, try this too.

edited:
Your casework looks quite nice. The holes are alllllll nice and clean and lined up.
 
Jul 28, 2008 at 2:36 AM Post #10 of 12

roger_s

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That was my original setup. The RCA's are in shoulder washers to isolate them from the chassis. The hum was very noticeable in that configuration. Also, it's not very easy to spot in the photos but there is a green wire that ties the PCB ground to that copper ground wire. Nice and quiet in that configuration.

I always twist my power leads--even for DC. There's no obvious noise from it but I'll do a bit better routing when I take it apart for its cap upgrade. I've ordered some Obbligato copper case caps from DIY hifi. 630v caps should run pretty cool in this thing!

Thanks for the case compliments. The holes were an afterthought--tought after I ran it for a bit without any ventilation. Those voltage regulators get toasty fast! Ventilation is aided by a gaping hole in the back of the case. The power supply's plug is right-angle--it wouldn't have made a connection even if I'd postioned the PCB next to the box. Eventually it'll find itself in a better box. Heck. I'm already thinking about buying another even though I have absolutely no use for it.

The more I listen the more I like it.

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif
Something to note:
The input RCA's should ground to the ground on the PCB. It looks like the copper wire grounds to the chassis. Although the chassis should be grounded for safety, it should not meet up with signal ground except for at a star ground point.

As a point of anal retentivity: It looks like the red twisted pair is power going to the switch up front. cool deal, but I would re-route these wires away from the pot if possible. I have seen DC lines leak noise into the signal. If its not nice and quiet after setting up the ground, try this too.

edited:
Your casework looks quite nice. The holes are alllllll nice and clean and lined up.



 

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