'06 Modules, introduced April 2006, announced April 26th 2006 at the Head-Fi National Meet
The gain and crossfeed stages are basically identical to the '05 modules, however the output stage has been redesigned and marks a return to discrete output stages for HeadRoom (the pre '04 modules had a less advanced and less competent discrete design, as is visible in the earlier photographs in this thread). Gone is the Intersil HA-5002 buffer in single or dual configuration, replaced by a discrete transistor output design that is common to all the modules. The configuration of the modules is now:Micro '06: AD822*2 -> Discrete Output
Desktop '06: OPA2134*2 -> Discrete Output
Home '06: OPA2134*2 -> Discrete Output, Class A Biased (deeper bias than '05 Home Module)
Max '06: OPA627*4 -> Discrete Output, Class A Biased, output transistor upgraded from the one used in the other modules, with even deeper class A bias than '06 Home Module, thicker copper traces and silver solder
The discrete buffer is based on, but not identical to the Diamond Buffer design used in the PPAv2.
Mike told me that the original spur for the redesign was that they found that the Intersil buffers didn't perform/measure adequately when driving very low impedence loads (<20ohms). Both in measured and perceived performance, the output quality of the HA-5002 decreases markedly with impedance from about 100ohms. The Max module has been re-laid-out, and the removal of the second set of connecting pins that allowed the module to be stacked (which it never is for heat dissipation reasons) has allowed the overall module size to be reduced somewhat, however still not enough to fit into the smaller portable amps, or some of the older home amps (for example the Little). The output stages at the different price points are now differentiated by class A biasing, and by the quality/price of the output transistors - therefore, all the modules now have the same drive capability to handle low impedance loads.
The Micro and Desktop modules that I have photographed here are pre-production modules, so some of the solder work and component alignment is less than perfect (I rather like the impromptu pyramid of resistors in the middle of both modules). Though both boards are green, the original colour coding of the '05 modules has been maintained in the production boards. See www.headphone.com
for pictures of the final product.
I tested with my Etymotic ER4P, Etymotic ER4S, AKG K701, as well as my reference Sennheiser HD650 (stock cable (yes, I think it's pretty good!)). The power supply was either the 'brick' or the battery pack, and the source was either the internal Desktop DAC, fed by USB from my computer (iTunes ALAC, all Classical) or the line out from my 3G iPod (ALAC, Cardas HPA mini-mini). My experience with other amps includes an M^3 Steps with OPA637/627, Gilmore Dynamic with custom PSU, HeadRoom Balanced Home with '05 Max Modules.Micro '06, compared with Micro '05
Clarity! I always found the Micro Module to be somewhat undefined and unrealistically euphonic. The new output stage has really cleaned it up. The difference was especially clear with the Ety's - I immediately heard bass control and definition that wasn't there with the older module. Overall, a tighter, cleaner sound. The opamp is still euphonic, has a bit of 'grain', and doesn't give the best extension in the highest of highs, but overall it might be an acceptable trade off for 20 hours of battery life. I'm not sure it is an upgrade for someone who has an '05 Desktop Module hoping for better battery life, but it might finally be a crossgrade. It's a little clearer at the bottom end, and a little grainier up top.Desktop '06, compared with Desktop '05 and Micro '06
Again, the same differences were apparent, however not quite as strikingly - an improvement in clarity, and a small improvement in dynamics. The Desktop has over the Micro better control of the treble in particular, with no grain and extension right to the top of the audible range. The more I listen to this module, the more I enjoy it, and am able to detect nuances that were covered over by the old output stage - sometimes this is obvious, and at other times it takes a while to notice. In a sense the division between the Micro and Desktop modules has become a tiny bit smaller, making the 'Desktop or Micro Module in my Micro Amp?' threads harder to answer. The Desktop '06 is however still the better module in all senses, and I would still strongly recommend it if you do not intend to use the Micro portably. It has a smooth yet detailed sound, and the only thing bad I can say about it is a slight lack of bloom in the treble, which to my ears makes it very slightly flat sounding in that region. Overall, this module has incredible
synergy with the AKG K701.
Design change: The larger capacitors on the board for this module are now the same size as the smaller ones used on the Micro Module. There appears to be no sonic trade-off that I can detect for this change.Home '06, compared with Home '05, and Desktop '06
My immediate impression of the module is how hot it is! There is clearly a deeper class A bias on this module than it's predecessor. As it should, it shares the strengths of the Desktop '06, but again, as it should, makes up for the weakness I pointed out in my description, that being a slight flatness to the treble. The Home '06 has a sweetness and bloom in the treble, as well as a general fleshing out of the overall tone giving a deeper sense of soundstage and acoustics. Its very smooth, but not in a bad way. It has all the detail of the lower end modules, however gains a certain tube-like smoothness from it's class A bias. Unsurprisingly, it sounds like the best of the Home '05 and the Desktop '06 combined. Amazing impact and weight, especially with the K701. A clear step up from the Desktop. In reference to the '05 Home, it clears up a certain muddyness in the bass, and a bit of detail and dynamics in the treble.
It's not perfect though - as excellent as its presentation is, it is lacking in a certain reach-out-and-touch-it quality. All of the information is there, but it's behind the slightest veil. Now well into class A with a very nice discrete output stage, the limiting factors in this module are the OPA2134 opamps and the 'brick' power supply. Impressions with the Desktop Power Supply to follow, however in general expect a tightening of the bass and better control over the treble. HeadRoom have reduced the price of the Home Module to $99 on top of the base price for a Desktop Amp. With this reduction in price, it has become a very compelling upgrade over the stock model. Though it benefits from a DPS, it does not require one, giving it serious bang for buck for sound quality over and above the Desktop Module. I do not recommend it for the Desktop Portable due to serious reduction in battery life, but for the Desktop Amp it's a no-brainer if you can afford it.
Update: The DPS cleans up the sound of this Module nicely. The bass is certainly tighter, and the blacker background really helps dynamics and soundstaging. The treble is a bit more refined as well. Whether it is worth the price of admission is a personal decision, but it is a noticeable upgrade.Max '06, compared with Max '05 and Home '06
My initial impression of this new reference standard is that is by far the most neutral sounding module I've ever heard from HeadRoom. It is NOT forgiving of weaknesses in the signal chain. I am hearing deficiencies in the Desktop DAC that I hadn't heard before - traces of harshness here and there, and a slightly dry sound overall. The sound is right there, without the slightest veil, throwing at your ears whatever you throw at it. It is not inherently harsh or 'forward' however, it just seems to be dangerously transparent. I can hear the difference very easily between the optical output and USB output on my MacBook Pro. The Home Module in comparison is a little warm and fuzzy, especially in the bass, and not the last word in transparency. With lesser sources, the Home Module might be a more pleasing sounding choice to round out the sound a bit, but with a killer source (something I will lack for the forseeable future unfortunately) the Max Module is a markedly more transparent module that will let you hear the most subtle nuances of your recording, as well as cables and all the other junk that sits between the performers and your ears. It's bass response is fantastic, with amazing control over the headphone driver - my K701's produce that wonderful soft visceral feeling of the lowest bass fundamentals when driven by this module. The Max '06 seems to add or subtract practically nothing - that will take a bit of getting used to! Recommended heartily only for people with sources of equivalent quality!
Update 1: The clarity of this has proved too much for my K701's, and I'm back to 650's. It seems that I prefer my K701's when the system has a bit of extra warmth behind it, and the 650's in a more neutral setup.
Update 2: I've now had the opportunity to spend quite a few hours with the Max Module, and am more and more impressed by the refinement it brings to the performance of HeadRoom's 'cost-no-object' solution. It isn't initially particularly impressive, due to it's neutrality. But the more time I spend with it, the more I appreciate it's sonic honesty. I find the totally controlled, textured and layered bass rather addictive after a while, but it is so well controlled that it takes a while to actually appreciate what it offers - it doesn't jump out at you, it's just there when it's called for and disappears when it's not. It sounds just delicious with the 650's, and when the bass is that clean, it makes me rethink the idea of the 650's having a bass 'hump'. As I said in my earlier update, I find the K701 just too thin sounding in this setup, and find it has bettery synergy with the warmer sounding modules, and perhaps warmer sources in general (I wonder if the K701 really wants a nice tube amp). The 650 OTOH really needs incredibly clean drive to sound its best, and that's exactly what it gets from the '06 Max Module.
In comparison with the '05 Max Module, the latest revision just seems to remove a layer of haze from the sound, bringing you closer to the performers.The very short conclusion for those that can't be bothered to read everything above: the old Intersil HA-5002 output buffer has a small but detectable euphonic colouration, irrespective of class biasing or numerical doubling, which increases as headphone impedance decreases. The new discrete output stage is closer to neutral, and is more transparent to the opamp's inherent sound, as well as being better able to drive a wider range of headphones.
A comparison of the effect of the new output buffer on headphones of different impedances and sensitivities:
Having compared all the modules, I was interested to try to sonically isolate the effect of the new output stage, and evaluate the original rationale that the old output stage didn't handle low impedances well. I settled on the Desktop Module as a 'middle of the range' point of comparison as this is the most common module here at Head-Fi, and compared it with the Home '05 and Desktop '05, all of which use the same opamp and differ in output stage and class biasing.Sennheiser HD650: 300ohms.
These were the reference headphones at HeadRoom when the '04/'05 modules were designed, and it shows. The '05 Desktop and Home modules both mate well with this headphone. Comparing the '06 Desktop with these older modules reveals relatively subtle changes to the sound. The older modules give a slight (over) emphasis to the soundstage and air surrounding the notes, whereas the new module is slightly more defined, with better definition of the fundamental tone. If I had to choose a module for this particular headphone, it would either be the Home '05 or Desktop '06, The Home '05 has over the Desktop '06 a smoother, fuller, warmer sound partly due to the Class A biasing, and the Desktop '06 has over the Home '05 a bit of clarity, instrument separation and dynamics. Which is better is a matter of taste in this case. The Desktop '05 is still a decent performer here, but falls a little behind the other two (as one would expect).AKG K701: 62ohms.
. The differences between the modules are far more apparent here, with the Desktop '06 having a surprising edge other both previous modules. The Home '05 sounds congested and muddy in comparison, and lacks impact and dynamics. The soundstage is also somewhat compressed, with relatively flabby bass. It does have in it's favour the benefits of class A biasing, but they are offset by the struggling output stage. Again, this is all relative - it's not that the '05 Home module is bad sounding on its own terms, but in direct comparison it can't keep up with it's newer sibling with this headphone. Desktop '06 -> K701 is a killer combination. The Desktop '05 is quite a way behind in this comparison, with the single output buffer struggling to provide these headphones with the current they require. (I briefly tested the K501 and found the same differences to be apparent).Etymotic ER4S: 107ohms.
The differences between the modules are equally apparent here, however the softer, less dynamic Home '05 module seems to slightly tame the peaky treble and sometimes slightly thin sound of this IEM. The Desktop '06 still shows greater clarity, and possibly better extension, however this to my ears is very revealing of the headphone's treble which makes it a little bright for my ears. The (maybe artificially) fuller sound of the Home '05 is more forgiving of this headphone. The Desktop '05 on the other hand exhibits the advantages of neither module, losing out both on clarity, extension and tone.Etymotic ER4P: 27ohms.
No contest! I find it hard to listen to the old modules with this IEM any more. With this low impedance IEM, the older modules are muddy, congested, and I find low bass to be covered over and sometimes inaudible, buried under the upper bass and lower mid range. The Home '05 is obviously least guilty of this as the defects are somewhat mitigated by the doubled buffer and Class A biasing, however all of the Intersil based modules exhibit this issue. The ER4P is already a somewhat rolled off, warm headphone, and needs no encouragement to sound so. The first time I tried out the new Desktop '06 Module was indeed with the ER4P and despite having not used the convertible for a while before that, the difference was clear. I never knew the ER4P was capable of such clarity, particularly in the bass where it exhibits pretty awesome definition, texture and punch.
Some totally unqualified conjecture about other headphones: though I've never owned any, and don't care for the sound, I'm guessing these new modules will get on a lot better with Grado's, and give them the punch that people like from these headphones. UE-10's and other ultra low impedance headphones will derive a benefit even greater than for my ER4P's.
Footnote: for the sake of clarity I am probably overemphasising the differences between the new and old modules. Even where I have spoken fairly harshly about the old modules, it is simply for the sake of comparison. You may experience smaller or larger differences with these new modules, and just because there's a new kid on the block doesn't mean you need to spend your hard earned money on a module upgrade for your amp if you like the sound the way it is. The differences you will experience will vary considerably from headphone to headphone, and the higher impedance the headphone, the less difference you may experience. Upgrading to these new modules is hardly a must, and having to send in your amp for a few weeks and pay a sizeable fee is hardly everyone's idea of fun, but there's some pretty sweet sound quality to be gained if you really want it. If you received your Micro amp within the last 3-4 weeks, or any other HeadRoom amp in the last 2-3 weeks chances are it may already have a new module in it, so be sure to check with HeadRoom, or just take a look inside.
Shame on you for not noticing
A side effect of all of these upgraded modules has been that I have not once found myself reaching for my HD-650's since the headphone comparison. The K701 has, without my noticing until now, completely taken over as my reference headphone.
*A final note regarding HeadRoom Modules: This '06 revision is most likely to be the last set of modules with the current, standardised pin count. HeadRoom are working on some exciting things for the future and cannot impliment them with the number of pins currently available on the module. So this is the end of the line for the convertible, and as far as upgrading your existing amp, there is little point waiting for another revision: there isn't going to be one. If you are interested in the upgrade, just do it.