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Senn PX100/Sony D66SL & LDM+/PengAmp

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The Low Volta

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The big Sony D66SL, Sennheiser PX100 / portable preamps (Little Dot Micro+ and Pengamp) comparison

sorry for this very long and wordy post... I won't make it longer anymore by adding pics, I promise :D for pics, I'll gladly point you towards my various pictorials: Sennheiser PX100 pictorial ; Sony D66SL pictorial ; Little Dot Micro+ pictorial and PengAmp pictorial

Disclaimer: these are just a few of my impressions, written down from a “take them or leave them” point of view. This does not mean in any way that you are not free to add you own experiences or even question mine in a polite debate. Please just restrain yourself from any flaming/handbags/… as the main point of this thread is to inform ppl…


This is just a ‘short’ intro to contextualize where I’m writing from. I’m an audio product from the late 80’s / early 90’s (last bits of punk & new wave, start of grunge, LP, cassette walkman, first CD) and I always focussed on the music (content) and not on the technology. I was very happy with my parents’ shoddy phono player connected to a kenwood amp, my own pioneer midi tower and my walkmen (cassette: sony, pioneer, JVC; PCDP: Panasonic). My first introduction to decent headphone equipment (Sennheiser HD497) stems from my late student years (2002) as, after moving into a larger student home (with thinner walls), I couldn’t play my music at decent levels anymore without upsetting my fellow students. These headphones (though they might sound ok) scared me away from the idea of upgrading equipment for a long time as they really hurt my ears and I have never been able to keep them on for even half an hour…

In 2004 I was introduced to Hi-MD out of need… I needed to record some interviews for my Masters’ thesis but soon I noticed that this little wonder (NH900) could also deliver portable audio at great quality!

It didn’t really take long till I got rid of the stock earbuds (in favor of the Sennheiser MX350 and quickly after that MX450) but this was mainly for the long cord which I favour over short types. I noticed improvement in SQ, but not really drastically. Then I bought some Panasonic RP-JE50’s as I was going to travel a lot by plane and the isolation was a big benefit. I again noticed some improvement in SQ (also over the Senn MX series) but again some impracticalities popped up (too isolating which results in self-noise and is also dangerous in traffic + the Pana’s ‘whistle’ in the wind when I’m outdoors).

Late 2005, I started working and earning money (after 9 years of poor student life) so I immediately embarked on a spending spree… first, buying lots of CD’s and attending lots of concerts (both of which I could never afford before) but also my interest in better quality audio gear was aroused (mainly by visiting this site a lot and reading discussions between mods/habitués like Atrain, Ishii, Camille and lots more about the best phones etc). Still, I have had to work for my studies/living for 6 years so I’m not really a big spender yet and I decided the to go with the ‘best headphone under $100’ (according to a couple of sources, YMMV and mine maybe also :lol: ): the Sennheiser PX100 (BTW: as I live in four different cities with lots of travel in between, I’m actually only really interested in portable gear)

Then, this summer, the ‘eggo’-bug bit me and I had to have the D66SL’s… and I did…


Well, now I’m the proud owner of the Senn PX100 and Sony D66SL (eggo) and I was also reading quite a few posts on head-fi (bad idea if you do not like spending money :P ). Somehow I got convinced by all this audiophile mumbo-jumbo that these very portable headphones (heck, they are designed for portable use!!) needed a portable amp to deliver their true sound. I checked here and even though some co-owners of these phones said ‘no’ I just had to find out for myself and I ordered a ‘Little Dot Micro+’. At the same time, a very good friend (and fellow gizmo-nutter) decided to surprise me by donating his brand spanking new PengAmp (semi-Cmoy) he never really used (but of course only after I had just ordered an amp myself :P )… so after years of ‘audio-illiteracy’, I’m suddenly presented by the opportunity to compare two great and relatively low-cost portable phones and also two portable amps. This simply was an opportunity to great to miss out on, so here it goes, an un-audiophile venture into the world of ‘portable audiophilism’… I’m sorry cause I will probably use quite a few audiophile (sounding) terms and even more because I probably won’t use them correctly :D

PX100 vs D66SL

As I’m still a practical-minded joe (besides self-proclaimed semi-audiophile :D ) I will discuss not only audio-aspects, but also a couple of other (IMHO) important bits…

Description (stolen from sites)

Sennheiser PX100

Sensitivity: 114 dB

Frequency Response: 15 - 27,000Hz

Impedance: 32 Ohms

Cord length: 1.4m

Sony MDR-D66SL Eggo

Sensitivity: 106 dB

Frequency Response: 10 - 25,000Hz

Impedance: 40 Ohm

Cord length: 0.5m (Single connection to phones) (Remote friendly) + extension


Let’s get on with the big’un: SQ… well, they are different! I can’t say one’s better than the other, but they definitely are different.

The PX100 is a very ‘pleasurable’ phone. It sounds great (especially coming from my phone-background) and it has lots of bass for such small phones. The mids are still pretty clear and the highs are still not really muffled. As opposed to the MX-series it is like they simply added the sub-100HZ frequencies without taking anything away. It does sound like a very complete headphone, but slightly (ahum) coloured. It is definitely a warm sounding headphone. I do enjoy the sound on a lot of tracks that just need that extra low-frequency ‘oomph’ to shine completely (I’m thinking about DFA1979, DJ shadow, some tracks of Millionaire, surf rock like fifty foot combo, hip hop like Dr. Octagon or the Beastie Boys and some types of electro/techno and even stoner bands kyuss and their follow-up QOTSA). Part of this enjoyment comes from the liberties the PX100 takes with the lower frequencies. In other words, to say that it is a pleasure to listen to doesn’t mean it is a realistic phone. The PX100 does ‘add bass’ which on the positive side creates the warm effect, the depth of certain tracks and even a good compensation of its bad isolation (on which more further). But on the other hand this colouration can be very disturbing on music that is meant to be tight, strict and even cold. I listen to a lot of Tool, The Mars Volta, Explosions in the Sky, Sigur Ros, certain jazz performers… and those types of music need to keep (at least a bit of) the sharpness, coldness that was put in, IMHO.

The we get to the Sony D66SL ‘eggo’ phones: they are not bass heavy (not bass-lacking like the Senn MX-series) but they provide the listener with very tight but non-‘pounding’ bass notes; not a bass ‘oomph’, not even a general ‘bass’, it simply represents the notes without any blending to provide impact. These phones really shine in the mid range, which is spot-on while their highs are sometimes considered overly shrill even though I personally don’t think so, but this may be cause they are a bit thin at the lower end. To me (as an audiophile-amateur) these cans called up the image of ‘analytical’ headphones: you can hear all that’s present, but you get no guarantee it will sound pleasant. I personally do like this kind of idea: you’ll hear what was put in… this is a parallel with my EQ-use… as little as possible. But then again, I often find myself adding a bit of lower freq’s with my NH900/RH1 (through the brilliant greenmachine eq-setting) just to achieve a greater level of engagement which IMHO a purely clean/analytical sound can’t reach.

So if we were to ‘score’ them side by side, this would be it for me: (PX100 >< D66SL)

High freq’s: more than adequate (though slightly hidden by other freqs) >< good (this is my opinion of course, others sometimes even report shrillness with the D66SL)

Mids: good >< great (there simply is no other way to say this, the Sony phones make voices shine)

Lows: very present but slightly flabby/loose >< not so present and very tight

“Yeah Volta, that’s great, but there still is no ‘winner’ presented”… well, no there isn’t! :lol: I love both, but for different reasons and with/for different music… and other aspects only enhance this feeling, which brings us to…


Even though they are both meant to be portable phones and they both have some sort of ‘foldability’, the PX100 have at first glance a slight edge over the D66SL here. The PX100 fit into a small ‘case’ 15/8/3cms and the D66SL ‘roll up’ to a ball or better a disc-ish shape with 12cm diameter and 8cm thick, but the biggest difference is ruggedness! The PX100-case is plastic, but it looks and feels like it can take a bit of abuse. I wouldn’t recommend dropping it, but it can safely be wedged between books etc. The D66SL comes with a felt bag (much like the Hi-MD felt pouches, but slightly bigger and shaped specifically for the phones), which provides zero protection (not even from dust really). This really hampers the D66SL’s portability as you cannot wear them around your neck (the headband curls too much and chokes you) and they are too big to fit in a safe trouser/jacket pocket and you can’t just toss ‘em in the bag as they will surely ‘break under pressure’. Still, a lot of this could be negated if one can find a good decent case for the rolled-up D66SL… but I haven’t yet (still searching and open for suggestions).

But we have to incorporate another aspect which is very important for portability in my opinion:…

Lightness /wearing comfort

Here both phones score almost equally well, though each with their own specific characteristics and personal taste might make you strongly prefer one over the other I guess. The PX100 is a very lightweight supra-aural phone with two smallish (4cm diameter) ‘cups/discs’ covered with foam on the inside that rest on your ears. They are fitted on a single (thin) headband with split pleather padding. The D66SL is a small (think large egg for size ref) circum-aural phone with two felt-lined cups that fit over the entire ears but without the drivers actually touching anything (unlike the Senn HD497 where the idea is the same, but the foam surrounding the driver isn’t thick enough so the driver actually squashes the ear). The cups are fitted to a double headband made of two very thin rubber covered bendy/curly thingies (well, they are kinda hard to describe).

Supra-aural phones have a tendency to start hurting after a while as they press on the ears all the time, but the Senn PX100 doesn’t do this at all. It is light and the headband doesn’t create much pressure at all (unlike with all bigger Senns I have tried) not on the side of the head, nor on the top (though at first you are well aware that there’s something sitting on your head). This makes the PX100 very comfortable to wear and after wearing them for a bit of time, one might even forget they are on (on which I will come back later) but still each time again, for the first minutes or so, I have to get used to the phones sitting on my head/ears.

Circum-aural phones can differ greatly: the best designed are with the most comfortable and engaging phones I know, the worst are worse than bad supra-aural phones as they not only hurt your ears but heat them up as well :lol: The D66SL fortunately fit the first category! If one ever wonders whether Sony designers/engineers ever think of real ppl when designing stuff…they sure did with this one. The cups are very light and the drivers are angled so they: 1) do not touch your ears and 2) ‘aim’ the music directly in the right direction. The headband (if one can call it that) is so thin and light that you really do not notice it at all. It creates a very light lateral pressure, not annoying, but just enough to keep the cups in place, and absolutely no pressure on the top of your head. The combination of band and cups makes that these phones seem really light (even lighter than they already are) as they provide just enough pressure to keep the cups in a position that only the very comfortable felt-covered rim touches the skin around your ears (this goes for my head: medium, for my girlfriend’s: small and for my dad’s: large head). The only possible discomfort I can find with the D66SL’s is that they (like all circum-aural phones) can make your ears hot. They close-in your entire ears and trap body heat. But unlike the HD497’s that use pleather to cover the rim and feel like a sauna after five minutes (BTW, I don’t really like the HD497’s, if you hadn’t noticed yet :lol: ) the choice of felt-lining slows down this process. Besides, this isn’t really a drawback here in Belgium as we have horrible weather and the D66SL’s will often serve as ear-muffs and phones at the same time :D

But still, to be able to have an informed opinion on these two headphones for portable use, there is still one major aspect that needs to be addressed…


And herein lies the main difference between both phones for me personally. The PX100 are an audio-sift: they do not isolate you from any external sounds. On the positive side they are like having a soundtrack to your everyday life, which is great in certain circumstances (like days at work when I’m alone in my bureau and I still want to be able to hear if someone knocks at the door or the phone rings etc.) but for real portable use (i.e. walking around Brussels, Antwerp or any other busy city) one is inclined to raise volume to unhealthy levels as they don’t lock out traffic noise at all. A strange side-effect of the lack of isolation combined with the ‘you forget that they are on’-comfort has made me try to move away from my mac at work three times already without taking them off first, almost dragging my computer to the floor or even me talking to other ppl about the music playing and forgetting that they cannot hear it… really, you sometimes forget that the music you hear is coming from headphones :lol:

They do not really leak that much noise to the environment as far as I know, well at least my girlfriend hasn’t complained about my music yet with those phones.

The D66SL do isolate a bit more. Not in a Panasonic RP-JE50 way in that they do not negate external noise without music playing, but music at modest levels can easily drown out conversations, telephones and even traffic. As far as I have had the chance to test, they do leak out a bit more than the outside-in isolation would make you expect but I guess still less than the PX100, so it is still no real problem (not anything like those annoyingly bad earbuds that work as speakers for an entire train compartment sometimes). I think they isolate more than adequately for portable use, but I’m not sure whether they are up to the job in closed noisy situations like planes with boring ppl and LOUD babies etc, but then again, this is pure speculation, as I haven’t had the chance to test this yet.

For me this is the aspect which mainly determines which one I’ll use. I tend to grab one or the other depending on where and how I expect to listen even more than on which music I expect to listen to. The PX100 quickly have become the desk pair as I simply can’t risk to be ‘locked out the outside world’ too much at work. The eggos are by far my favourite city-pair, also just for their looks! They scream ‘Japanese import’ (or ‘alien’, which isn’t that different for most ppl here) and ooze some sort of geekish style, while the PX100 have a nice retro look but mainly surprise ppl as they didn’t think such cheapo looking non-stylish phones can sound this good…which is a good indicator of how ppl perceive them :lol:


One last aspect of the phones themselves I’d like to address shortly is durability. I must immediately warn you that I haven’t performed any tests at all as I’m very, very, VERY careful with all my equipment and I haven’t even dropped one of them from as low as 10cm yet, nor bent them in any unintended way or anything else… so this part of the review is pure subjective ‘gut-feeling’.

The PX100 has more metal parts and is less ingeniously thought out and therefore I expect it to last longer. Still the locking system for the cups (that turn 90° for storage) feels kinda loose and I expect those to be the first parts to fail.

The D66SL isn’t a phone for rough use I think (I could be wrong though) as it has lots of plastic parts and feels more brittle overall. The biggest worry is how to safely store them when not in use. The felt bag simply is inadequate and I’m still searching for a decent strong but small case for them.

Portable amps

As said before, I recently got hold of two portable amps: the Little Dot Micro+ and a PengAmp. The LDM+ is a Chinese-made very pro-looking small (7x5x1.5 cm) amp with internal LiIon battery and a charger. The PengAmp is a pseudo-Cmoy (a home-made amp but not really following the Cmoy outline) that comes in a Penguin-mints’ tin (10x5x1.5 cm) and uses 9V batteries (D-type) and has a DC-in for internal charging of a NiMH D-battery. Keep in mind that both are in fact bigger by extruding parts (gain knob and when in use mini-jack cables).

I won’t go into any further technical details, as I do not know them, understand them or really care about them.

Looks and practicality

The LDM+ looks like a standard factory-made little aluminium box, with a strong volume/gain knob that serves as on/off-switch as well and two 3.5mm sockets (audio in + audio out) and a blue power-led all on one (small/narrow) side. The sides are a bit sharp and could use a bit of sanding. It isn’t welded shut but uses tiny screws that allow you to replace the battery yourself when needed. The gain-knob is smooth metal and only 0.5cm diameter, which makes it kinda hard to twist especially as the audio-in cable sits right next to it when in use. The dc-port is on the opposite side. Text (brand/model-name + in/out indication) looks remarkably shoddy compare to the overall construction. It looks like they were ‘rubbed’ on with cheap transfers.

The PengAmp looks more like handy-crafts on the outside, but the inside reveals an optimized circuitry that is not messy at all (unlike lots of handmade electronics). On one narrow small side there are the big gain knob flanked by two 3.5mm ports and on one long narrow side there’s an on/off switch and a blue power-led. The dc-port is only accessible when the lid is open, which isn’t very practical to use the amp with external power. All elements that stick out of the tin are very well secured ad screwed solid to the tin, which looks pretty strong. There’s no text on the tin except for the text already present on a mints’ tin, but as you get a decent manual with it, it is still easy to use (though this might be confusing if you haven’t got the manual nearby). The metal gain knob is nice and big and has two small rubber rings and is easy to use (though the lack of quiet>loud indication could cause surprises and one has to learn to turn the volume down before storing it). The biggest drawback of the PengAmp is the on/off-switch: a 0.5cm thin metal switch sticking out the side which makes it a bit more awkward a shape to store.

They were both easy enough to use so that I, an electro-illiterate, could use them right away (though I needed the PengAmp manual to know what was which, input or output, but that was easy enough).


One of the first questions I want to address here is “do I need an amp?”… well, there is no one true answer for that. First an easy one: if you want to use a full sized phone meant for home use that is inadequately driven by a portable device: yes, get one and you can finally enjoy the music as intended. But if you use portable phones (like the ones I described above), what then? Well, unless you have a Euro-unit and you really want to destroy your hearing, the HiMD will be able to drive those phones adequately (loud enough without introducing hiss or deforming the sound). What a headphone amp does do, even with adequately efficient phones, is widen the soundstage. Both headphones did seem to be a bit more spaced (more distance between things centred in your head and outside). Also the extreme frequencies (high and low) are supposed to perform closer to the intended sound, although I can’t really say that I notice this significantly (still, I find it pretty hard to ABX or switch-test headphones/amps as there’s lots of unplugging/plugging involved and a real side by side is pretty hard that way).

Both amps can handle a pretty low incoming signal without producing hiss. I must say that I only have got a few items with a real(ish) line-out (the RH1 and NH900) so that the signal isn’t amp’ed twice. I am going to get an external soundcard for my portable computers with a line out someday, but I haven’t yet.

What I do notice however is that both amps have very different sound (colouration). The LDM+ is a pretty cold/analytical amp. It really shines from the middle frequencies up while the lower frequencies are present, but rather tight. It allows you to hear each bass-note played separately. The PengAmp on the other hand is warmer overall and even emphasises bass a little (though without muffling the higher frequencies at all). Well, if you have made it to here reading the entire piece, you should be able to guess what this means…


Yes indeed, one of those audiophile concepts I saw a lot at Head-Fi and always wondered about whether it actually meant something (other than that a certain amp and certain headphones looked great next to each other :lol: )…

I must say, I now have a clue what they’re going on about…


These two items simply complement each other very well: the weakness of the PX100 - its slightly flabby bass - gets tightened by the LDM+. The sum is a very rich sounding but pretty well controlled headphone that is very comfortable, still portable and delivers surprisingly good sound for its size (and price, I got the PX100 for €40 and the LDM+ for €50).


Well again, what one lacks is compensated by the other. The D66SL are often described as cold and shrill phones and while I do not really think that is completely correct, they gain quite a bit of warmth and bottom frequency punch by coupling them with the PengAmp. This combo is slightly more costly than the other (I paid $110 for the D66SL (shipped) and got the PengAmp for free but they are about €90 ‘buy it now’ on ebay) and really it sounds great. I’m listening to my own PCM-recordings of Pukkelpop (Belgian festival) this year and it really is like I’m standing there again…


Unfortunately these just enhance or better emphasize each other’s lesser aspects. The PX100 become little bass-monsters when coupled with the PengAmp but they sound too muddled for me personally (though I definitely am no bass-head so YMMV).


While I expected the D66SL to sound overly shrill with the LDM+, I was actually pleasantly surprised. They are clean and pretty bass-light phones, but this last bit isn’t really further enhanced by the amp. They sound incredibly clear and I personally do not dislike that sound.


I think it is very hard to select favourites, but after long deliberation I must say that I love the D66SL phones while I merely like the PX100 very much :lol:

As far as amps go, I don’t really know… I do like the PengAmp/D66SL-combo a lot, but the LDM+ does sound good (but different) with both phones, while I do not like the PengAmp/PX100-duo. Also the internal LiIon battery of the LDM+ is very handy. Furthermore, I have read up on the D66SL and I found a (reversible) mod that gives them slightly more bass while not disfiguring any other freq ranges, so the main plan now is to perform the mod, test a bit further and probably keep the LDM+ and sell the PengAmp.

All in all, I still don’t know whether a (Hi-)MD needs an amp… I do like the sound (a lot), but unless you use a (Hi-)MD with a line-out, you still have the colouration/noise/…from the MD’s amp. On the other hand, when you use the line-out of the RH1, you lose almost all navigational functions and track-title display as well… I tested both amps with the remote attached as well and while I realize this isn’t the way it is meant to be, I didn’t notice much detrimental effects and the ‘profits’ of full powered phones (soundstage, clear highs and lows) and the sound colouration remained. One idea (mainly when one can speak of some sort of synergy between headphones and amp at least) is to use the amp as a sort of external eq which allows you to keep the (Hi-)MD’s eq flat or even to use the RH1’s normalisation-function which is impossible to combine with an eq-setting.

I hope that this long story 1. makes some sense to y’all, 2. was mildly entertaining and 3. provided some insights into portable phones and amps…

Feel free to discuss, ask questions and share your own experiences/ideas

*edit: added links to various related pictorials

Edited by The Low Volta
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  • 1 year later...


Great writing!

It´s what I was looking for today.

I've a MDR-D77 and we all know it sounds great but the only drawback I find

is the presure it used to put on my ears, I found the solution bending a little bit

the steel headband taking care not to damage the cable that goes to the

right earphone.

It works for me but it also has an cracking sound between the ''U'' shaped plastic holder of the earphone


Anyway I like it very much.

Edited by Aleko
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