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Headroom Module Archive thread - Page 2

post #16 of 109
Thread Starter 

It's time to get this thread going again, so...

Without further ado, I'd like to introduce HeadRoom's latest creation, the HeadRoom Convertible!



The HeadRoom Convertable is a Desktop Portable Amp, with the Desktop DAC board and NO electronics module. Where the module would normally be, there is a rather roughly cut hole in the upper case (whoever did the drilling at HeadRoom, own up ) and a custom socket soldered directly to the board. This allows the electronics module of the amp to be changed by simply pulling out the old one and popping in a new one.

The modules I currently have are:

'03 Standard, '03 Premium, '03 Reference, '04 Prototype, '04 Coda, '04 Reference, '05 Micro, '05 Desktop, '05 Home, '05 Max, '06 Micro, '06 Desktop, '06 Home, '06 Max.

Approximate date of introduction:

'03 Modules: ? 2002 ?
'04 Modules: August 2004.
'05 Modules: gradually introduced from the middle of 2005 as each new product line began to ship.
'06 Modules: began shipping some in early April 2006, transition compmlete April 26th 2006.
post #17 of 109
Quote:
Originally Posted by TheSloth
... I plan to photograph each module (again, digicam issues...), do my best to extract the specs from the chips I can see on the board, and post my sonic impressions (using HD-650's (blue dragon v2)). This is an ongoing project to archive all the modules made over HeadRoom's nearly 14 year history.
Wow! What a fabulous idea! As a longtime HeadRoom fan, I'm most appreciative of your efforts and look forward to seeing the product of your labor.

Thanks!
Beau
post #18 of 109
That was my poor machining abilities. Actually, if I was machining, it would have been much nicer. Unfortunately all we had around was a drill press, dremel tool, and an old file. I thought it turned out rather nice considering the limited tools. I've tried to convince Tyll to buy us a small milling machine. Maybe this project will provide some good reasoning.

Enjoy,
Jamey
post #19 of 109
Man, I'd love to have a milling machine! Just figuring out how to pay for it. We will get one eventually.
post #20 of 109
Thread Starter 
Sonic impressions of the pre '04 modules. Fundamentally, the design dates back to 1997 or even earlier, however this particular version was released I believe in 2002, and discontinued in August 2004.

Standard Module:


This is based on the BB OPA604, and the crossfeed uses the OPA275. The output stage is made up of discrete transistors. As for the caps and resistors, I believe they are ceramic.

The first thing I notice about the sound is a lack of extension in both the highs and lows, as if the frequency response was compressed slightly. It has a smooth sound through the mid bass and midrange, however the high end is very slightly grainy. The sound overall is very relaxed, but slightly thin, and can be slightly congested in more complex material. Left and right separation seems to be very slightly lacking. Overall, a very pleasant but outdated sound.

Premium Module: This changes the opamp to the BB OPA627, and also seems to improve some but not all of the resistors. In terms of overall components and board layout, it is identical.

The immediate difference is an increase in detail. Bass and treble are more defined, however the mid-bass is still rather congested, and can sometimes sound a little bloated. The increased detail does however give a better sense of left and right separation. It's certainly an obvious step up in sound from the Standard Module.

Reference Module:


This is similar to the Premium Module, except that all the caps and resistors seem to be upgraded to higher spec models. The output transistors are upgraded, and the component matching is to higher spec.

This is an excellent sounding module. It seems to clear up the congestion of the two lower end models, and has beautiful detail and treble clarity. Bass is also well defined. I really enjoyed listening to this module, however it has a fatal flaw, which is a tendency to exaggerate sibilance, and even to create it out of nowhere. I remembered this from my Cosmic with Reference Module, and at the NY meet I was very impressed that Machead immediately heard the issue with sibilance, despite also agreeing that it was an excellent sounding module. From this line, this is the only module that keeps up with current sonic standards. If there were able to tweak it to deal with the sibilance issue, this would be a very competent module, especially for portable use as it's power constraints are relatively small compared with current modules. I'd guess 20 hours battery life in a Supreme/Cosmic/Desktop Portable, compared with somewhere near 8 hours with the current Reference equivalent (the Home module).

K701 update: I do not hear any sibilance with the K701, or the Ety. 4P for that matter. The sound is clean, clear and detailed, though sometimes slightly hard and lacking in space and air. I have also noticed, possibly simply due to placebo, that this module seems to perform better when it's been running for a while and has warmed up.

Update, 5/18/06: Though I still stand by my statements that this is a pretty good sounding module, I have had some time to compare it with the current low end offering, the '06 Desktop Module, and find the new Desktop Module possesses a better blend of strengths. The old transistor output stage from pre '04 seems to have a harshness that comes from some zero crossing distortion. Despite also hardly being biased towards class A, the new Diamond Buffer design seems to avoid this pitfall, having a more evenly balanced sound from top to bottom. I'm also not quite convinced by the drive capability of this older output design - it seems to lack in the lowest bass, ending up somewhat thin. It's redeeming quality though is that the old Reference presents just the tiniest bit more detail. The crossfeed is now quite a way behind HeadRoom's current standard, first implimented with the '04 revision and refined subsequently.

Next up: Coda '04, Micro '05, Desktop '05 and Home '05 Modules.
post #21 of 109
Thread Starter 
'04/'05 Modules:

Coda Module '04: (August 2004 to March 2005)
vs.
Micro Module '05: (March 2005 to April 2006)


Both of these modules make significant sonic compromises for the sake of battery life. They are both designed to run for about 20 hours off 2 9V batteries. They differ in that the Coda Module uses the BB OPA2137 whereas the Micro uses the AD822, and the Coda uses a 2 layer circuit board to the Micro's 4 layer board. The power consumption requirements are a change from any previous HeadRoom Module, involving a significant reduction in current draw. Relative to the previous best of breed, the pre '04 reference, these sound a little muddy and congested. They do not possess a sparkling clarity. Both modules actually have a similar sonic signature, with the Micro Module having a slightly fuller and more articulate sound. They shouldn't really be compared to the reference standard however, and are more relvevant as upgrades from the electronics in a Total Airhead. They are obviously significantly better sounding than the electronics of the mobile line, however are noticeably inferior to their more power hungry siblings. For those with a Coda with the original module, I don't think the Micro Module is a significant upgrade. It is better, but not by a huge margin. For those trying to decide what module to choose with their Micro Amp, I can't recommend the Micro Module unless battery life is very important to you. It gives only a glimpse of what HeadRoom amps are capable of.

Desktop Module '05: (March 2005 to April 2006)


This is the low end module in the current line up, available on all Micro and Desktop amps. It differs from the Micro Module in the use of the Burr Brown OPA2134 instead of the AD822, and has significantly larger capacitors. There may also be small differences in component selection and matching that I am not aware of.

This is a very competent sounding module, especially for the price. It offers a significantly cleaner, and to my ears more neutral presentation than the Micro Module which seems warm and slightly congested in comparison. It is also able to articulate something of the recording's soundstage. It has a clear treble response, though never seems to bring out sibilance from recordings. It is not the last word in inner detail or weight, however does make an excellent portable module for those looking for good sound before battery life. Expect 8 hours from a Micro and 20 hours from a Desktop Portable. It makes an excellent upgrade for the Coda. For older HeadRoom amps, especially home amps, it's a more complicated question - in my opinion it is able in some ways to beat the old pre '04 reference module, due to it's balanced presentation and lack of sibiliance, however it does not extract as much detail and spaciousness. Also, note that this would be a small downgrade from an '04 premium module, so if you have one of those in a portable amp, rejoice because in my opinion that's the best battery life/sound compromise HeadRoom made (please bring it back!). From any module lower down the chain than the pre '04 reference, the Desktop Module is a significant upgrade, and will not put any more stress on whatever power supply is being used.

Home Module '05: (March 2005 to April 2006)
and
'04 Reference Module:


This is a very serious module. It's clearly king of all the modules I have to play with in the 'convertable'. The first thing to point out is that it does actually sound better than the '04 Reference Module. I assumed they would be indistinguishable from one another - they both use 2134's in Class A, and they both double up on the output buffers. However the Home Module also moves to a 4 layer circuit board, completely different board layout and larger capacitors. Those seemingly small differences contribute to a noticeably fuller sound. It's hard to recommend as an upgrade from the previous reference simply because of the price, however it would indeed be an upgrade.

The Home Module takes the Desktop Module's strengths, as well as filling in some of the weaknesses. Going back to the Desktop Module from the Home Module reveals a slight thinness to the Desktop sound. The Home Module fills out the sound (possibly too much for some headphones), without sacrificing detail or extension. In fact it increases extension and detail at both extremes, as well as improving upon dynamics. Solo voices take on more life like proportions, and become believeable to my ears. With the lower modules, they sound like excellent reproductions. It starts to enter the level of fidelity where the electronics begin to disappear. This all comes at the price of current draw. Expect battery life of only 8 hours with a Desktop Portable, Supreme or Cosmic.

The Home Module is the best price/performance upgrade for any older Little, Home, MOH. Those with a Max or BlockHead would probably want to go right to the top with Max Modules. Those with a Supreme or Cosmic would have to consider how much battery life they need. If you can get away with 8 hours on 4 D cells, then go for it, but thats a hell of a lot of batteries if you use it regularly. In portable circumstances, unless you are using a very high end IEM, I'm not sure the difference in fidelity between the Home and Desktop Modules would be that audible.

One extra module: Miscellaneous prototype using TI headphone amp chip, from the R&D leading up to the '04 revision:


This module was never released, and was interesting to play with specifically because of that fact. It's a class A biased design - the gain and crossfeed stages use the BB OPA2134 in class A bias, just like the Reference '04, however the output stage is the TI 6120 headphone amp chip. Unfortunately there isn't much I can say about this, as it doesn't quite work properly - the left channel is significantly quieter than the left, I believe due to non functioning capacitors somewhere on the board. However what I can tell is that this was a somewhat thin and uninvolving module. Very clean and possibly accurate sound though, and I would be interested to hear what it could do when performing properly.
post #22 of 109
Thread Starter 
'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.
post #23 of 109
Quote:
Originally Posted by TheSloth
Reserved for future modules.
Are you expecting some new modules to review in the near future, asks he who just received his Micro w/DM yesterday?
post #24 of 109
Thread Starter 
Update, March 19 '06:

- did some pretty major spring cleaning of this thread, to remove posts I wrote which were either irrelevant or confusing. (thanks mods!)
- reformatted the text, and added pertinent photographs of the modules being discussed, also allowing other users to visually identify what module they may have. Modules are arranged generally so that the gain and crossfeed stages are on the right hand side and the output stage is on the left hand side.
- updated impressions on some of the modules for accuracy.
- corrected some typos, spelling and grammar.
post #25 of 109
I am curious about something, as a DIYer and also a Headroom owner (Micro DM and antique Supreme V1.0).....

The current DM modules uses two OPA2134 plus an Intersil output buffer per channel. That is FOUR opamp circuits per channel. What do these guys do?

Not trying to dig out trade secrets but any info would be appreciated.

Regards,
Neil
post #26 of 109
Thread Starter 
You are correct that all of the modules have 4 active amplification stages. The 4 different channels are responsible for input buffering, gain stage, crossfeed stage, and summing stage. So as you can see, there is still only 1 channel for gain, per module. This is why the Max Module had to be made on a larger board, as it has to accommodate twice the number of opamps.
post #27 of 109
Thread Starter 
25th April: Updated to reflect current '06 modules in post no. 22.



Convertible update:

Along with the new modules, Mike and I have been working on a way to get Max Modules working in the Convertible. As can be seen from the size of the opening, and proximity of the DAC board, the large Max modules would not normally fit. The solution is to place the Max Modules on double length pins, and enlarge the hole on the left hand side where the casing rises higher to allow the Module to sit down in the socket properly.

Mike has just confirmed that the Module will now fit in this configuration, however they did not have the tools to make the extension necessary, so I will have a friend with appropriate facilities make the necessary modification in the next week.

These modules do require a DPS, and so any tests will also have to wait until I am able to get hold of one for myself.

Update, ahead of schedule:

post #28 of 109
Thread Starter 
2005 brought about the advent of a completely new module, designed to work only in the HeadRoom Desktop Millet Hybrid Amp. There has been one revision since then, the '06 revision, and so there are currently 4 difference Millet Modules in circulation - '05 Desktop, '05 Home, '06 Desktop, '06 Home. OPA627 based Max Modules are not possible in a Millet due to power supply and heat constraints. As I do not have a Millet Hybrid, I will be relying on n_maher's impressions from his Millet Hybrid.
post #29 of 109
Sloth, you mention that the new modules offer more improvement to lower impedance phones. Does that mean that that a balanced HD 650 will benefit more from these changes than a non-balanced HD 650? I think I remember reading somewhere that balanced drive halves the impedance.
post #30 of 109
Thread Starter 
Quote:
Originally Posted by Luco
Sloth, you mention that the new modules offer more improvement to lower impedance phones. Does that mean that that a balanced HD 650 will benefit more from these changes than a non-balanced HD 650? I think I remember reading somewhere that balanced drive halves the impedance.
I'm glad you asked that, as I was going to mention that in the post but as I no longer have a balanced HR amp can't comment directly.

{[(Balanced drive does not halve the impedance of the headphone. It halves the output impedence of the amplifier. In a balanced configuration, each module is delivering half the current and half the voltage for the same volume level, relative to the same modules in a single ended configuration. My speculation is that the technical limitations of the HA-5002 would have been at their least noticeable in a balanced configuration, as with a balanced 650, each output buffer would be delivering only a very small amount of current.)]} <-- please ignore this, it's completely wrong.

That being said, as you can see from my headphone comparison, the old output buffer, even when operating at its peak performance as it was with the 650 still has a certain colouration. I am looking forward to hearing what the hot shot output transistor on the new Max module can do, but even the less expensive ones on the low end modules are still cleaner and clearer than the old IC buffer.
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