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GAD's review of five headphone amps

GAD's Headphone Amp Reviews

[ RSA Tomahawk | RSA Hornet | RSA SR-71 | RSA XP-7 | Practical Devices XM-4 | Headroom Micro | Pimeta ]


This review was written in May of 2007. I had purchased a Hornet headphone amp from Ray Samuels Audio, and through a fluke, had to wait for parts to be delivered before it could be shipped. Due to my inability to wait, I dropped a load of cash on a bunch of RSA amps because I couldn't wait for my Hornet to arrive. Details of my inability to wait are found in this humorous thread on head-fi:

Lucky me, they all came within two days of each other, so it's been a bit of an amp-fest here for the last few weeks. I purchased, in the span of one week, the following RSA amps: Tomahawk, Hornet, SR-71, and XP-7. The Hornet was bought new, while the rest were bought used from the fine members of head-fi. My goal is to audition these great amps, in addition to the ones I already own (Headroom Micro w/desktop module and the Practical Devices XM4), and decide which one or two I should keep. The plan is to then sell the rest back into the wonderful head-fi community. While all of this was going on I also traded for a Lavry DA10 DAC. The Head-fier who traded me let me try his Mr X built Pimeta which will also be reviewed.

A word on brands

There are many fine headphone amps out there, and this is by no means a wide selection of them. At the time that I was buying these amps, there just happened to be one of each RSA amp that I was interested in for sale on head-fi. Had a Xin SuperMacro-IV or a LaRocco PRII been for sale I probably would have jumped on them, but there weren't any. This is not a scientific test, and it's not supposed to be anything other than my views on the amps in my possession. Please don't email me asking why I didn't review x,y, or z amp. I just told you why. :)

A word on words

I'm not really an audiophile. I might pretend to be one, but I *am* a gear-head. You will not see words like "airy" or "forward" or "recessed mids" in my review, because honestly, I don't know what those words really mean (yes I've read the glossary, and I'm half kidding). I'm a writer, and one of the things I've had drilled into me is to *not* use words like "muddy" for sound. Why? I can't remember, but my knuckles still hurt from the ruler so I try not to do it. Seriously though, I will attempt to review these amps more for their intended purpose than their sound. I know - this isn't what you're used to seeing, so if this review isn't useful for you, then I apologize. I will try to convey if one amp sounds better than another, but I'm really more interested in practical concerns like "will it fit in my pocket". All of these amps, with the possible exception of the XM4, are highly regarded amps. They all sound great.

A word on "portability"

There seems to be two camps; "I'll bring an RSA B52 with me if I can power it - sound is king!", and "sub-atomic isn't small enough". I'm willing to make sacrifices. Sacrificing sound for size, battery life etc. is a way of life when it comes to portability, but where do we draw the line? Only you can answer that question. You must define, for yourself, what portability means to you. Do you want to take an amp with you for the plane, hotel or work? Maybe you want an amp that you can jog with. Perhaps you want the best quality you can get, but you just won't be near AC power?

Each situation has a different solution. If you're going to try and satisfy them all with one amp, then you will probably be disappointed some of the time. In this case, you need to decide what is most important and go from there. For me, as I've posted elsewhere, I could easily keep them all and apply them differently. To help clarify my views, here is how I listen with headphones:

Home while writing/working
Sound:portability ratio: 100:0
Here, size is no object and I'll sacrifice greatly for sound quality. Sound is king at home, and portability is not an issue. Battery power is not a requirement for me at home.

At work while working
Sound:portability ratio: 80:20
Here, sound is important, but portability is also important in that I take my amp to and from work every day in my backpack. I'm a consultant, so I may be someplace different every day. I need an amp that runs on mains or has great battery life, but I'll live with swapping batteries for better sound. I usually listen with full-sized open headphones with high impedance, but if I'm travelling I'll only take my IEMs.

Mowing/Working outside
Sound:Portability ratio: 50:50
Here, sound is important, but portability is important too. If I'm mowing, I'm bored, and I can focus a bit on the sound. If I'm using a weed-trimmer, then I need all the cords/amps/players hidden and out of the way. I can strap a rig to my belt without a problem. I usually listen with IEMs.

Sound:portability ratio: 50:50
I walk during lunch. If I'm in the city, I'm walking to/from work, and I'm on mass transportation. Here, sound quality is not as important as portability, but I'm willing to sacrifice a bit of portability since I usually have pockets, or can strap something to my belt. In the winter I'm wearing a heavy coat with even bigger pockets. I usually listen with IEMs.

Sound:portability ratio: 10:90
I'm not as active as I used to be, but anything I do that's more intensive than my "normal" walking I call exercise. Biking, running - whatever. Here, sound is secondary to portability. Chances are the music will be affected by outside noises, and I may need to hear those noises for safety (biking on a street for example). I usually listen with IEMs which directly contradicts my need for safety. More money than brains = me sometimes.

I will rate each of the amps on a similar scale. In the case of amps, I will weigh the sound quality vs portability. A perfect balance would be 50:50. An awesome sounding amp that isn't very portable would be 90:10 while an average amp that's very portable would be 10:90. If two amps sound identical, but one is huge while one is small, they will have different ratios, even though they sound the same.

Equipment used

I only have four headphones worth testing with: Sennheiser HD580 (HD600 grilles and cord), Sennheiser HD650, Beyer DT880 and Etynomics ER4P IEMs. I did not use filtered power, did not treat these amps special, did not fill them with super-duper batteries or do anything I would not do if I were using them like I normally would.

Sources: 5.5G 80G iPod (Native and Rockbox), 8G iPod Nano (Native), My PC (FLAC)
DACs: Headroom Micro DAC, Lavry DA10
Interconnects: ALO Cryo Dock, DIY Jena Cryo dock (x2), DIY Jena mini IC, Cardas mini IC

All my DIY interconnects use Neutrik and Switchcraft plugs and are built using Cardas solder. Sure I could have probably had better sound with a high-end DAC and CD player or turntable or whatever, but people generally don't want to use these little portable amps to listen to their turntable. People want portable amps for portability - hence, I used them in normal day to day living. When using the XP-7and Micro amp at home, I fed them with the Lavry DA10 or Micro DAC using my own DIY Jena-wire cables. When using them in the office, I fed them directly from the line out of my iPods with my own DIY cables.

None of the equipment in my reviews was provided by the manufacturers. All of it was either purchased new or used by me through normal channels.

Music used

I have very eclectic tastes in music. I like just about everything with the exception of hard-core rap and some country music. For the most part I listened to the following while swapping between amps:

Norah Jones - Come Away with Me
Natalie Merchant - Ophelia
Pink Floyd - Dark Side of the Moon
Phantom of the Opera - Original Cast Soundtrack
Les Miserables - Original Cast Soundtrack (3 disc)
Evanescence - Fallen
AC/DC - Jailbreak
Dokken - Under Lock and Key

Most of these were chosen because I like them. Seriously, I'm very familiar with them and can spot differences easily. All of these I have in FLAC and MP3 (320k CBR). I did not listen direct from a CD player because I don't have one I can use with an external DAC. In fact, I don't have a portable CD player. The *only* way I listen to music is via computer or DAP anymore. I have a DVD-A player in my car which is pretty sweet, but finding discs is a pain. But I digress...

RSA Amps

Generic Feedback

All of the RSA amps I auditioned are fabulous. They're tremendously well made, sexy as hell, and sound fantastic. ANY of them should be in your final choices. They are all that good. None of the RSA amps ever produces any hiss or noise that I ever noticed. The only exception was when I'd plug in my ER4Ps and forget that I left the gain switch on high. This combination would produce some hiss which was completely silenced when setting the gain properly.

I would feel completely safe recommending any of the RSA amps for almost any situation. They all drive my ER4Ps as well as my HD650s. They all sound great, and they all look great. They all have their strengths and weaknesses, which will probably be what you base your decisions on, which is fine. Hopefully this will help you do exactly that.

I've posted a size comparison thread on head-fi that can be found here:

None of the RSA amps include features like crossfeed. While I'm a fan of crossfeed, I find that I don't really miss it unless the recordings have very distinct separation.

RSA Tomahawk

Price: $295 + shipping
Pros: Damn it's small! Battery Life is amazing
Cons: It's not small enough. :)
Sound:Portability ratio: 40:60

The Tomahawk (TH) is an awesome little amp with great sound and HUGE battery life. It runs on two AAA batteries and runs for literally hundreds of hours. The sound to my ears was the same as the Hornet, only just a bit less... "Hornaty". That is until I burned in the Hornet, at which point the Hornet pulled a way a bit more. Again, you'll be happy with the sound from the TH. You'll only know there's a difference if you hear the Hornet and the TH side by side. Even having both, while walking with the TH I never said to my self "I wish I brought the Hornet".

The TH has two gain settings. This little amp drives my Sennheiser 580s and 650s with ease in addition to my ER4Ps. Though the TH is designed for IEMs, don't think for a minute that it won't also drive your big cans, 'cause it will. This is really a fabulous little amp, but I think it's smallness is almost pointless, especially if you have an iPod (except for maybe the shuffle). Still, for the smaller is better crowd, this one sure is smaller!

The real problem with really small amps is the interconnects. The RSA tomahawk with an iPod Nano is an awesome combination, but the line out (dock) connectors just plain suck on the iPod because they're too damn big. I've made a slew of my own iPod dock connectors, and with something the size of the Nano, they ruin the portability of it all. The honest truth here is that if I'm going to jog/bike/work out with my Nano, I'm leaving the amp at home. It's hard to beat the Nano's size, and if I'm bouncing my fat ass on a treadmill, the last thing I need is an amp, no matter how small, bouncing with me. When an amp is made that is the same form factor as the Nano, we'll be in business. It's all about compromises. In the realm of exercising I'll give up sound quality for portability. That being said, while walking, the TH is just that much smaller than the Hornet, making it a more comfortable rig to jam in a shirt pocket. For me, the Hornet is small enough.

RSA Hornet

Price: $350 (batteries are $15, colors are $15)
Pros: Very small, AC power, recharges NiMH batteries while playing, three gain positions, cool lighted switch
Cons: price is about all I could come up with.
Sound:Portability ratio: 50:50

There's a reason everyone on head-fi raves about the Hornet. It's an awesome sounding amp in a very small package. It delivers - pure and simple. The Hornet is a similar size to the Practical Devices XM4, but the XM4 is a little thinner and longer. That's where the similarities end though, as the Hornet sound blows the XM4 away when it comes to sound quality. It also looks a lot more refined (because it is). Of course it does so at over 3X the price.

I could say that the Hornet lacks the finesse of the SR-71, but remember, the Hornet is about 1/2 the SR-71s size, and the SR-71 is a dual-mono design, where the Hornet is not. The hornet also runs on a single 9V while the SR-71 takes two. This amp gets a sound:portability ratio of 50:50 for me. I think it is truly the best balance of sound, size, features and performance I've yet seen. You would be hard pressed to do better than this amp.

I'm also here to tell you that burn-in is not a myth. Taking the advice from head-fi, I set to burn in my Hornet for 400 hours. For those of you who hate math, that's 16.6 days of use non-stop. Instead of plugging it into a CD and letting it repeat forever (no CD player remember), I took it with me everywhere I went, and plugged it into my PC at night. This allowed me to do two things. First, I got a feel for how long the battery would last. Second, I got a feel for how difficult it would be to swap batteries when the need arises.

Battery life on the Hornet worked out to be 8-10 hours for me playing constantly with ER4Ps. My only peeve with RSA amps is the way in which batteries are swapped. Two tiny thumb nuts have to be removed (they are very easy to drop and lose). After the nuts are removed, the back plate is removed and the battery can be replaced. If you put the battery in backwards you can destroy the amp, so pay attention - details of the battery's polarity are on the plate and on the board inside the amp. Screwing the tiny nuts back on the amp can be frustrating, especially for a lummox like me. Of course if you're near AC power and you have NiMH batteries, just plug the Hornet in and change. You can even play while charging.

The volume knob on the Hornet is stiff which is *wonderful*. You will not blast the volume by accident when you put your player in your pocket. This is a very cool, very well thought-out feature. I added a couple of small o-rings to the knob which makes it easier to grip with my lummox-sized fingers.

Coupled with an iPod Nano and a line-out cable, the Hornet pumps out a serious amount of excellent sound. If I had to recommend one amp from the list that can be used for all needs, the Hornet would be it.


Price: $395
Pros: Sounds amazing, ergonomics
Cons: No AC power or charging, no gain switch
Sound: Portability ratio: 70:30

Probably my favorite sounding amp in the bunch of "real" portables (I don't consider the XP-7 to be really portable). "Silky" is the best word I can come up with. Everyone at work (non-audiophiles all of them), picked the SR-71 every time (excluding the XP-7) regardless of cans used. I really can't stop gushing about this amp's sound. If it had AC it would be perfection for me, but alas, it does not. For me, to compensate for the lack of AC power, I'd need to invest in 4 9V rrechargeablesand a charger. For LiPo batteries this runs about $100 from Thomas Distributing (today being May 2007). That's $100 over the price of the SR-71, which isn't cheap. Still, battery life is surprisingly good. I've used the SR-71 regularly for almost three weeks while testing (probably 1-3 hours each weekday), and haven't killed the two alkalines in it yet.

The ergonomics on this amp are better than the TH or Hornet because of its size. Being a larger amp, the knob is easier to grasp and control. This is a big deal for me at work because I am constantly tweaking the volume for different passages in songs. I don't do this while walking or exercising but when I'm sitting I do it constantly. There is no gain switch on this amp, but I never found this to be a problem. The amp drove all my cans with ease. This amp fits in my shirt pocket, but I look like a headphone-amp-toting-dork with it in there, and it doesn't really leave any room for my 80G iPod, though of course the Nano fits anywhere.

Though it's not as small as the Hornet, I imagine that this would be an awesome travelling amp. Sitting on a plane with the SR-71, an iPod stoked with lossless audio, and your favorite IEMs, and I think you'd have an awesome flight. As an only amp, I think it's tremendous sound is undercut by its lack of AC power. This amp was designed for sound. It is the only small portable in the bunch that is dual-mono.

Side by side, this amp sounds closest to the Headroom Micro (both having been fully burned in). The Micro has AC power, crossfeed, and better ergonomics, but isn't as sexy. Still, over and over, though I swore they sounded the same, I'd pick the SR-71's sound every time. Maybe it's the dual-mono design - I don't know. All I know is that the SR-71 sounds amazing. On a strictly emotional level, I would pick this amp as a portable. Logically, the Hornet wins.


Price: $695 w/power supply
Pros: Sounds amazing, runs on AC or 2x9V, takes 1/4" plug, takes 2xRCA in, ergonomics
Cons: BIG!, takes 1/4" plug, 2xRCA in.
Sound:Portability ratio: 90:10

This amp is in a different class than the others. Mine came with both the stock OPA627 opamps and AD797 opamps. One of the things I don't fully understand is how an amp can change the perception of how big the empty room in my head is. This amp has a HUGE sound. After listening to the smaller amps all day I come home to this and every day I say "wow!". My Beyer DT880s really shine with this amp. Where I thought the Beyers were to bright (ow - my knuckles!) with the rest of the amps, the mix of Beyer sound with XP-7 sound is wonderful. This amp changes the way all my cans behave when compared with the smaller amps.

While this can be considered a portable amp because it takes 2x9V, I can't imaging actually taking it anywhere. To give you an idea of its size, it is pictured here with the three other RSA amps I've reviewed sitting on top of it. The case beneath it is the matching power supply. Someone on Head-Fi suggested that it would be the perfect home amp because it takes batteries and they could take it outside with them while they work in the garden (or something similar - sorry if I confused the details). I can see this point. It would be an awesome amp to sit with on the deck with a beer. Damn... now I want a beer.

OK - got a beer.

This amp is a big, smooth, wonderful volume knob which allows for some very fine adjustments. Nice quality feel to the entire thing. My only wish is that the power cord to the power supply was longer. Still, it looks pretty impressive stacked.

Most of the time I spent listening to this amp was spent with the Micro DAC and Lavry DA10 DAC feeding it FLAC files from my PC. I did use my iPod, but an amp like this deserves the best source you can feed it.

The amp is very well laid out internally, and rolling opamps is quite easy. I actually preferred the stock opamps over the AD797, possibly due to the fact that I listen mostly with my Sennheiser HD-650s. With the AD797s installed, it was all too warm (I can't help it - it sounds warm!), though the AD797s did make the DT-880s sound a bit deeper. In the end though, I'm not a "roller" kind of guy.

Non RSA amps

Practical Devices XM4
Price: $135 (charger and battery $22 extra)
Pros: small, adorable, many features, price
Cons: not built as well as higher-end units, icky jacks (to be fixed by manuf)
Sound:Portability ratio: 20:80

My initial impressions of the XM4 can be found here: Those impressions still stand. The fact the Practical Devices has come forward and offered a free upgrade to the jack problem is impressive. Still, it simply cannot compare with the RSA stuff. Then again, it's not meant to. Though it is similar in size to the Hornet, it cannot compete in the sound department, which is why it gets a 20:80 sound:portability ratio.

Still, this little amp is loaded with features. When you turn it on, it reports the battery voltage. It has an auto power-off feature with variable time (very cool), and even has a flashlight mode where it lights up both LEDs on max brightness. Bottom line is that if you're looking for super audiophile sound, you'll need to spend more than $135 (unless you build your own). If you're looking for an amp, and your not sure you want to spend over $300, then the XM4 is a great choice.

One of the great features of this little amp is its variable auto-off. When starting the amp, you use a certain number of button pushes to configure an auto-off timer. One push enables auto-off for one hour. This is a really useful feature for people like me who can't seem to remember to turn anything off.

Headroom Micro amp with Desktop module
Price: $299
Pros: great sound, AC power, crossfeed, great company, Ergonomics, cool styling
Cons: goofy styling :)
Sound:Portability ratio: 75:25

This was my first headphone amp and I love it. Mine has the '06 desktop module and is well burned in. If I had to compare it with any of the RSA amps, it would be the SR-71. This amused me, because I was gushing about how great the SR-71 was, and found a pretty close sound in the amp that sat quietly on my desk while I went nuts looking for better amps. Some have challenged my saying they sound similar, and that's great - we all hear differently. Still, to me, this amp sounds awesome AND it runs on AC power. It doesn't charge batteries, but I still get months from a pair of 9V because I run on AC 90% of the time.

This amp is portable in the sense that the SR-71 is. Sure you can take it with you, but it won't fit in your shirt pocket. I used to walk in NYC with this amp in the winter when I had big pockets in my big coat. Once it got warmer, I started leaving the amp in the office. This is an awesome office amp, but a bit large to be used while walking.

This amp in includes headroom's awesome crossfeed feature. On this amp the crossfeed is very subtle and very enjoyable. It takes the edge off of recordings with extreme separation in the left and right channels. Another awesome feature of this amp is the fact that all of the controls are up front. Since this amp spends most of its time sitting on my desk, it's nice to have the controls up front where I can get to them. That being said, it's not like I'm constantly flicking switches, so it's probably a dubious benefit. Still, all those switches force the volume knob to be further from the input and headphone jacks. This allows more room for my fingers which makes it easier to tweak the volume.

Headroom makes a very cool accessory that allows you to now only attach your digital audio player, but to tilt it up for use on your desk (shown here). This attachment is very well thought out. I wish there was something similar for the SR-71 (I tried it - it's too big).

Bonus Amp

Pimeta DIY Amp (Mr. X Build)
Price: $Variable
Pros: great sound, AC power, DIY - make it how you like it!
Cons: No support other than you or whoever builds it for you
Sound:Portability ratio: 90:10

This amp was lent to me from someone I was trading equipment with. The fact that someone would lend me an amp from the other side of the country is a testament to the people on head-fi. Too cool.

Anyway there's not much to say other than the amp sounds great. Not quite up to the XP-7 sound, but I was impressed with how good this little amp sounded. I will definitely have to build one for myself. I gave this amp a 90:10 ratio because it can be built to be used with batteries. The one I have was not built that way however.

For those of you wondering if a home-built amp can sound any good, this amp is proof that it can.


So what will I keep? Let's go back to the sound:portability scale I used earlier. Here is the use, followed by the sound:portability ratio:

Home while writing/working:  100:0
At work while working: 80:20
Mowing/Working outside: 50:50
Walking: 50:50
Exercising 10:90

Here's how I rate the amps I have. I'm not downgrading the sound in any of these, but rather showing how I balance the benefit of the sound compared with the benefit of portability. Again it's amp, then sound:portability

RSA Tomahawk: 40:60
RSA Hornet: 50:50
RSA SR-71: 70:30
RSA XP-7: 90:10
PD XM4: 20:80
Headroom Micro:  75:25

Given these ratios, the perfect portable amp is the RSA Hornet. It sounds great, it's really small, it runs on AC power, and it has a built in charger. What's not to love? To be more specific, the numbers would indicate the following choices for me:

Home while writing/working:  100:0 - RSA XP-7 (90:10)
At work while working: 80:20 - Headroom Micro (75:25) or SR-71 (70:30)
Mowing/Working outside: 50:50 - RSA Hornet (50:50)
Walking: 50:50 - RSA Hornet (50:50)
Exercising 10:90 - No amp

The last entry was most closely matched by the XM4, but the Tomahawk has much better sound and is substantially smaller. For exercising any amp is too big as I've stated before. Still, when it comes to audio, emotion rules the day, and all these numbers mean nothing. I tried to be logical, so logically, the Hornet is the perfect amp because it has the perfect balance of sound and portability. Of course, as with all things in my life, it's just not that simple.

The RSA XP-7 will remain my home amp, displacing the Headroom Micro amp. I may eventually replace this with a tube or balanced amp since I now have a balanced DAC, but we'll see. If I replace the XP-7 at home, it will probably become my permanent office amp. As for now, my home rig consists of:

Source: PC (FLAC w/Foobar2000)
IC: DIY RCA S/PDIF w/ LOK connectors
DAC: Lavry DA10 DAC
IC: DIY Jena XLR-RCA w/Neutrik connectors
Amp: RSA XP-7
Cans: Senn HD-650 & Beyer DT880

I am still torn between the The Headroom Micro amp and the SR-71 for my office. Logically the Micro is the better choice since it has AC power, but emotionally the SR-71 just has something the Micro doesn't. I may invest in the 9Vs and charger so I can use the SR-71 in the office.

For now, here's my office rig:

Source: iPod 8G Nano or iPod 80G 5.5G Rockbox
IC: DIY line out dock w/Jena wire and Switchcraft or Neutrik plugs
Amp: RSA SR-71 or Headroom Micro
Cans: Senn HD-580 w/ 600 grilles, 650 cables & Jena DIY 1/4 - mini adapter

The RSA Hornet wins for my portable/walking/mowing amp. Sure the Tomahawk is smaller, and sounds almost as good, but I don't see an environment where the additional smallness is necessary. Thus, here is my portable rig:

Source: iPod 8G Nano
IC: DIY line out dock w/Jena wire and Switchcraft or Neutrik plugs
Amp: RSA Hornet
Cans: Etynomic ER4P

Bottom line

I need a therapist...

Seriously, All of the RSA amps reviewed here provide awesome sound, sexy packaging, and can drive any headphone you probably own up to 300 Ohms with ease. If you're in the market for an RSA amp, pick the one that fits your need or lifestyle. No review can tell you how to do that unfortunately, though hopefully I've helped provide some insight.

The Headroom amp and DAC are awesome devices. They sound great, aren't quite as sexy as the RSA amps, but still look pretty darn good. Of course beauty is in the eye of the beholder, so my opinions mean naught. I would recommend the Micro stack in a heartbeat, and often have.


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