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New Practical Devices XM6 Amp/DAC (The Complete Review)

post #1 of 557
Thread Starter 

It seems all the well known portable amp manufacturers are doing a refresh of their product lineup.  There are some really interesting possibilities coming down the pipe.  I have had some great experiences with Practical Devices XM4 and XM5 amps, allowing me to roll opamps and tailor the sound to my tastes.  I have enjoyed the products and service that James Forest at Practical Devices has provided.  While I previously sold my XM4(s) and XM5 while exploring different amp options, I found myself missing the sound of the PD amps (and the DAC on the XM5 was a bonus).


I recently e-mailed James to inquire if he had anything new coming down the pipe and to my surprise, he responded with an offer I couldn't refuse. Practical Devices is set to release the XM6 Amp/DAC and I was given the opportunity to try out the first production model.  Needless to say, I accepted.  I now have the opportunity to evaluate it and post my impressions. 


The Review, Part 1 (Exterior):

Of course, most people are going to look at the XM6 as just an evolution of the XM5.  That’s what I was expecting when the amp was being shipped out.  Obviously there were going to be a couple of extra features, but I was not sure how much of an improvement the XM6 could be over the XM5.  The XM5 has a lot of excellent features that make it a great go-to amp when you want to tailor the sound to your tastes; bass and treble boost options that didn’t overwhelm the sound quality, a 10dB gain boost button (actually, according to James, 9dB and some change), a 75 Ohm attenuation button that allowed you play extra sensitive in-ear monitors, an adjustable cross feed setting, and finally, OpAmp and Buffer sockets for each channel.  This made it one of the most versatile portable amps I have ever seen; giving you the option to change the sound in so many ways.  Not only that, but it also featured a Digital to Analog Converter (DAC) that allowed you to bypass a laptop’s sound codec for higher quality sound, at least in theory.  The DAC, however, was considered the weak point of the XM5; using a PCM2704 USB DAC from Texas Instruments, it was not a bad performing chip but really wasn’t a hit with a lot of reviewers and users (including myself…I hardly used it).


So, how does Practical Devices improve an already excellent amp?  Well, they start with fit and finish.  The earlier XM4 and XM5 were identically constructed, using an extruded aluminum Hammond enclosure with a flat rear end plate with appropriate holes cut out.  The front was made of thin aluminum that had screen-printed lettering and was secured by a plastic bezel.  While, tough and durable, they had a bit of a do-it-yourself feel to them.  Not so with the XM6!  When I first took it out of the box, it seemed smaller, because there was no plastic bezel and the front end plate was a thick piece of aluminum that closely matches the rest of the enclosure in finish and color (oh yeah, did I tell you that you can get the XM6 in different colors?).




The fit and finish of the enclosure is excellent! 

From Camera 018.JPG  

From Camera 020.JPG


While the body of the XM6 is still the same Hammond style as the previous amps, the end plates have been beveled on the edges and for each of the holes.  The volume knob is an excellent match with the finish as well.  One note: to remove the front cover plate, you must remove the volume knob as well, but James includes a small hex wrench for it (does take a bit of finagling, though).

From Camera 019.JPG


The XM6 is available in a variety of anodized colors including blue, black, red, and gold (picture at top).  This adds an additional degree of finish.  Lastly, instead of the screen printing, the plates have embossed lettering.  Overall the amp looks very professional on the outside.

Amp pictures 001.JPG


The amp came with the following components (note that I already attached the rubber feet):

From Camera 025.JPG


Let’s take a look at the inside, shall we?:


The Review, Part 2 (Interior):

Having had the XM4 and XM5, I had a reasonably good idea what the amp components would be like. (The following two pictures courtesy of the Practical Devices web site)

XM5 Interior 2.jpg


XM5 Interior 3.jpg


So, I have to admit that I was not prepared for this…

Amp pictures 005.JPG


Amp pictures 004.JPG


The workmanship is excellent.  The interior no longer appears stuffed with components and yet there is significantly more electronics in the XM6; a large portion for the DAC, the shuttle (which I will get to) and the Aux plug.  I build computers as a second hobby and the PCB (printed circuit board) looks professionally manufactured; head and shoulders above the XM4 and XM5.

More XM6 001.JPG


As you can see, James went with a dedicated battery instead of options for swappable 9-volt batteries.  With the additional PCB, a conventional 9-volt could not fit.  This battery is rated at 8.5 volts (tested as 8.3 according to the built-in tester).  The good news is it is easily removable and replaceable, so I am sure PD will make it available for purchase or at least provide a source for replacements.

Sorry for the fuzzy picture, but you can get a good view of the small surface-mount components.

More XM6 005.JPG


More XM6 002.JPG


Impressive…most impressive!

You can see the replaceable OpAmps and buffers.  The arrangement is identical to the XM5; the two Opamp sockets towards the front of the amp and the buffer sockets to the rear.  I received the XM6 populated with two OPA134 OpAmps and two BUF634 buffers.  PD did include the little copper wire busbars for the buffer sockets in case you want to roll your OpAmps.

The bottom of the PCB is finished just as professionally as the top.  The solder points for the larger components are actually flattened (sanded down?) and the PCB has a layer of copper in it to provide some RF shielding so the amp shouldn’t pick up your cell phone or laptop (or vice-versa).

Amp pictures 013.JPG


Amp pictures 011.JPG


One last thing on the PCB, it was obviously designed specifically to use the Wolfson DAC, because there is a small screen printed wolf’s head and “24bit @ 192kHz” logo.  I just wish my camera could have caught it.  So the bottom line for me is while I have seen some other manufacturer’s well-made amp interiors, this is one of the best component arrangements I have (personally) seen.


OK…OK…It’s got my vote for PlayAmp of the Year, but HOW DOES IT SOUND?


The Review, Part 3 (Amp):

This portion of the review will be a little unorthodox.  The biggest appeal of the Practical Devices amps is the ease in which you can roll different OpAmp chips (and buffers) to change the overall quality of the sound to suit you, then use the bass/treble boost buttons and other front panel buttons to alter the sound even more.  I will give you a little of my experience with the stock chips, but realize it is only the beginning of the possibilities with the XM6 and not the end by any means.  I will say that right now I don’t have any other chips to roll into the amp, but with the XM5 I had great results with the AD8065 WhiteCat OpAmps before settling on a combo of the AD8397 Doublecat and copper busbars in the buffer sockets (the 8397 has a built-in buffer).  I’m sure the XM6 would be no different but YMMV and your taste in sound quality may dictate a different amp/buffer set-up.  Therein lies the beauty.  I’m sure James at PD will be happy to give you the option to choose a different amp/buffer combo when you order the XM6.


I was sent the default OpAmp option of OPA134s.  It also came with BUF634 buffers (I am not sure if they will be included in the default configuration, but will certainly be an option if not).  I also receive the little copper busbars for future OpAmp rolling.  My current equipment set-up is a little limited right now, with a Cowon S9 as the analog sound source, the XM6 amp, and Markl-modded LA 2000 Lite Headphones w/ Jarrah woodcups.  The mods allow these former Denon AH-D2000 cans to have a much better extended range while reigning in and tightening the still excellent bass.  They have J$ earpads as well.



I use music encoded as flac files on the S9 with a variety of types from movie soundtracks (LOTR) to 60’s/70s/80s rock (Moody Blues, ELO, Alan Parsons), to Manheim Steamroller’s Fresh Aire Series.  I used no EQ on the source.  When I first started burning in the XM6, I gave it a quick listen and found it had a nice musical quality although a little light on bass in most tracks.  However, when I played a bass-heavy track (Blue World by Moody Blues), the bass sounded muddy, almost like it was a bit distorted (disclaimer: that particular track has given me issues with amps before, but I have listened to it on a full-size solid state amp on these cans with no problems).  SO, I let the amp burn-in over 50 hours and the muddiness disappeared and smoothed out (no more distortion sound).  So sitting down for a real listening session, I have come to the conclusion that the OPA134/BUF 634 is a good starting or baseline configuration for this amp.  I was asked by an early poster in this thread why PD didn’t just use the 8065 or 8397 as the default setup, so I asked James and was told, “OPA134: it is still quite a good chip by today's standards - excellent distortion numbers, low noise, reasonable  power consumption, and good performance when paired with the BUF634's.  And of course, they can be rolled out for anyone who wants another amp chip.” (Thanks, James, for the reply).  I have to agree, it’s not a bad combination and many owners will perfectly happy with the config.


One thing I did notice was that it sounded musical and fairly natural sounding (to these old ears).  The BUF 634s provided plenty of power to drive the LA2000s (not that they are that difficult) but I did notice the bass, while tight (after burn-in) and able to hit the low notes without difficulty or muddiness, really didn’t give the punch I wanted in some of the tracks where I want to really rock.  So, as my finger hovered over the bass boost button, I wondered what I was in for: another mudfest or some serious rocking.  When I hit that button, I was immediately hit with some significant bass presence.  The manual states that the boost adds 6dB to the low frequencies and I have to agree that the increase is very noticeable.  James has had the bass boost button on his amps since the XM4 and the implementation has always been excellent; the same holds true for the XM6.  I went back and played my bass heavy tracks and commenced a rockin!  There was no muddiness or distortion or anything but tight punchy bass (I think my cans were craving the power earlier).  The same can be said for the treble boost button.  While only increasing the upper range by 2.5dB, it helps the high end fill out a bit without being shrill or piercing.  I have read that some people on the forum would prefer a bit more treble boost, but I think the increase would overwhelm the rest of the sound.  The bass boost adds increased punch while the treble helps round out the sound.  So my default settings are with the bass and treble boost buttons on, which makes the current OpAmp/Buffer arrangement just fine for me (right now).  The crossfeed works just fine as well with a dial on the back of the Amp that can adjust the sound from mono to almost stereo image.  I use it on rare occasion, but I know it’s there when I need.  The +8 dB gain boost will help with high impedance cans or cans needing more power (LCD-2, anyone?) and the 75 ohm resistance switch will let you play those sensitive IEMs (Ety EM-4Ps).  Overall, this an extremely well rounded amp that can satisfy a lot of listener’s needs and give the Head-Fi’er a chance to tweak the sound to suit their needs.


But wait, there’s more!


The Review, Part 4 (DAC): 

Compensating for something...

As you can tell so far, the XM6 is a refined version of the XM5 with a much nicer external finish and well implemented electronic components.  As you can read from my impressions, there really isn’t any significant way to improve the amp.  It truly is and can be what you make of it.  So how can the XM6 be considered a significant improvement over the XM5?  The DAC, of course!  While many of the reviews of the XM5 lauded the quality of the amp, the Digital-to-Analog Convertor (DAC) was never really a favorite of the reviewers.  Don’t get me wrong, it wasn’t badly implemented; it worked fine, it just failed to impress a lot of users enough to switch from their laptop on-board sound output to make use of it.  The XM5 used the Ti PCM2704 (and previously the PCM2702) 16 bit DACs with a 48KHz max sampling rate and a 98dB signal-to-noise ratio (reference: http://focus.ti.com/docs/prod/folders/print/pcm2704.html).  It’s a good DAC, but many of the players and laptops already met or exceeded its performance.  So, how to improve?  Well let’s see: I have a full-size stand-alone DAC with the Wolfson WM8740 at its heart, a new Digital Audio Player (DAP) just released (and another due for release) with a Wolfson WM8740 for its DAC, and the XM6 with a…sense a pattern here?


So, the XM6 is equipped with a Wolfson WM8740; what makes this DAC chip so special?  Let’s start with the fact that it is a 16-24 bit DAC with 8-192KHz sampling rate and 104-120dB signal-to-noise ratio (those stats are taken directly from the Wolfson Web Site: http://www.wolfsonmicro.com/products/dacs/WM8740/).  In addition to that Practical Devices incorporated a Texas instruments SRC4192 192KHz Asynchronous High-Performance Sample Rate Converter for sound up-conversion.  What does that mean to me?  That it better sound a whole heck of a lot better than the XM5’s DAC!


And it does!  It’s a USB DAC so it installs painlessly (don’t forget to set the switch on the back of the XM6 to USB or you get no sound…ask how I know).  The first thing that impressed me was I had to turn all the volume sliders down to at least half before even adjusting the volume of the XM6 (I about blew my cans before I realized it).  To test the DAC, I listened (and watched) the BluRay versions of The Dark Knight, Wall-E, Cars, and Up!.  I also watched some DVDs and listened to some of my music using the AIMP2 software player.  I was very impressed with the sounds from the BluRays, the sound quality was outstanding and made good use of the WM8740’s capabilities.  DVD’s sounded almost as good, but I could hear a difference.  For movies, especially HiDef, the XM6 easily surpasses the laptops regular audio output.  My music is encoded in flac (which AIMP2 supports) and sounded very nice although in this case I had to turn on the bass and treble boost to get the sound I liked (no EQ on the player, though).  Of course that eats into battery life.  I haven’t been able to get a good read on battery life using the DAC yet.  But I am through two movies right now and I just went below 8 volts on the tester.


While listening to music with the DAC, I had the chance to use one of the new features James put on the XM6; the jog-shuttle (or joystick, according to the manual).  Now looking at the back plate, you may notice something a little odd; the previous and next track icons seem to be reversed.

From Camera 020.JPG


That’s because you are supposed to use the control with the front facing you; reach behind the amp and jog left=previous track, jog right=next track, push straight in to pause or play.  It works and is easy once you get used to it.  Most software audio players should be immediately compatible but James does include guidance on enabling the controls in WinAmp.

So the DAC is the thing that makes the XM6 so much more capable that the XM5 and comparable to other high-quality DACs.  The fact that it is combined with an excellent customizable amp is a huge bonus!  Practical Devices definitely made up for the weaknesses of the XM5 and took it up several notches.


The Review (Conclusion):

Wrapping up the fanboyism...…

There is one last feature on the XM6 to be addressed.  As you can tell from the photo above, there is a plug socket labeled Aux.  I emailed James to find out if there is anything that can take advantage of the Aux and was told, “We have a medium-term plan to release an AuxConn-to-2xRCA line out adapter, so you can use the XM6 if you want a 24bit/192kHz USB source for your living room stereo, for example.  Alas, we don't have a release date yet”.  He also told me they were planning to publish the pinout (which was in my draft of the manual) and I was allowed to post it (Thanks again, James).

XM6 Aux Pin-Out.jpg

(Posted with permission from Practical Devices)


So, you DIY’ers will have the chance to rig something up for yourselves (or the rest of us ).  I’d love a little remote control for shuttling back and forth when the DAC is sitting on the table next to the laptop and I’m sitting in my comfortable easy chair with my cans on, just out of reach of the controls…  One note: the socket looks like it takes the type of pins used with computer jumpers (or the pins connecting the two PCBs inside the amp itself).


I am very impressed that James at Practical Devices was able to take a great Amp/DAC and make it even better.  The XM6 easily surpasses its predecessors and adds a couple of new features that provide even more potential.  I can’t wait to try running my digital CD transport through the XM6 and compare it to my full size DAC to see how it fares.  Based on my current experiences, I think the XM6 would easily be up to the task.  It's an excellent Amp/DAC!


Fanboy?  Not really, I just like what I see (and hear) in the XM6.  Is it perfect?  If I had to pick a nit or two, I think the XM7 needs to support optical input as well.  Also, the Aux connector is really going to need to be utilized by PD (and others) to be useful, and only time will tell.  


I’d like to thank James Forest at Practical Devices for giving me the opportunity to provide my impressions on the XM6.



The XM6 has been released with a starting price of $395 with upgrade options available on the Practical Devices Website...


Right now, the XM6 appears to only be available in Blue or Black... 



-HK sends

Edited by HK_sends - 5/27/11 at 4:49pm
post #2 of 557

post #3 of 557

As a PD long time user, I am glad to see they finally get around with a new amp. The back of the XM6 should look interesting...

post #4 of 557

I've been wondering when this would happen. The new amp looks good. I look forward to your impressions and info on the new tricks she can do.

post #5 of 557
Thread Starter 

I've been curious about the features on the back as well.  James did mention a couple of things; "24-bit @ 192kHz upconversion to a Wolfson DAC" and OpAmp rollable (of course).  He said he would send me a copy of the manual (a work in progress) to explain the other features as well. I am curious about the capabilities myself.


If anybody is interested, I did ask about the 8dB button: Any driving reason for the bias boost being set at 8dB as opposed to 10dB?

"No reason.  If was just what common component values worked out to.   IIRC, the XM5's actual was 9-point-something (which rounded to 10), and the XM6's is eight-point-something, which rounded to 8 - so there is very little difference."


Lastly, he said I was free to take lots of pictures including the insides, so I will try to provide good coverage.


I will let everyone know as soon as I get it.



-HK sends

post #6 of 557

Look forward to your impressions, having owned a couple of PD gear I hope they have another hit with the version "6".

post #7 of 557

HK_sends, id just like im jealous and i hate you 

post #8 of 557
Thread Starter 


Originally Posted by mark2410 View Post

HK_sends, id just like im jealous and i hate you 

I seriously just got lucky with the timing...


Now, if I could just be so lucky with cars, lotteries, women, and LCD-2s...


Besides...they'll make more...



-HK sends

post #9 of 557

Have they gone too far & tried to cram too much in there? There looks like a lot going on. If its implemented well without compromising on quality then it looks like it could be awesome to have all those features. Definitely looks interesting.

post #10 of 557

XM5 doesn't suck, so I doubt this will.

post #11 of 557

i was hoping their next outing would have a mid boost too, that way you could apply any 2 to effectively produce a bass or treble reducer option.  i would greatly welcome that, this at first glance im not seeing why i should want one of these over the very nice XM5?


also i wouldnt mind seeing them make a nice little desktop amp

post #12 of 557

I imagine that Aux-in in the back is for an adapter so the XM6 can be used to control an ipod's playback.

post #13 of 557

yeah i was hoping for more along the lines of like an xm5 bug bigger internally so i can play about changing opamps nice and easily

post #14 of 557

They probably left that in.  Hopefully.

post #15 of 557
Thread Starter 

I wish I could tell you but it still hasn't arrived and Monday is a federal holiday (no mail).  I was hoping to be able to play with it this weekend.

James is sending the manual with the amp so I will hopefully have some answers for you when it arrives.


As for the Aux input, I hope it will work on other sources besides iP*D because I don't use Apple...I currently have a Cowon S9 for a source (and my laptop to test the DAC function).


I'll let you know as soon as I can.



-HK sends


PS - At least the DAC sounds like a significant upgrade (he said it's a Wolfson).  I also know it will have buffers because he's sending some BUF634 chips as well.  And, of course, it has the standard lithium battery/charger as the XM5.

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