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MDAC first listen (part IV)

Discussion in 'audio' started by adamlau, Feb 5, 2012.

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  1. JohnW

    JohnW Trade: Lakewest

    Hi wpope,

    The M-AMP will be released after the M-PAX (which is the add-on PSU for the MDAC).

    We should have the first M-PAX ready around the 20th (these are prototype units).

    I'd say around 3 months before the M-AMPS are ready for shipping - with a retail price under GBP500.

    John
     
  2. arthur

    arthur Banned

    That seems dirt cheap for a 100 + watt power amp John?

    I'm hoping a bridged pair might give me 200 watts a side for my second system which will be the cdq, M-amps and as yet unknown speakers. (depends on the new room.)

    PS, Is the silver colour on the m-dac an automotive paint job by any chance?

    I feel the need to respray my speaker stands and I'd like them in the same shade as the M-dac/M-amp just to be totally obsessive :cool:
     
  3. JohnW

    JohnW Trade: Lakewest

    Cost is reduce as its direct sales (within Europe) - cutting out the distributor and retailer saves a whole chunk of funds that we can put into the product instead.

    The M-AMPs should be rated at 120W per channel - so in bridged mode they will be closer to 250W - infact Peaks will be significantly higher, Long-term power level is limited by the thermal dissipation of the small heatsink area, however music peaks in bridge mode can be nearer 300W to 400W so they should make great little power houses.

    I hope they work well, as I'm disappointed with the sound of my Martin Logan's CLSII - my current amps (no name mentioned) really are not happy.

    In many ways, I'm designing the M-AMP's to drive my CLS's which are very nasty loads (0.5 Ohms at 20kHz). I figure that if an Amp can drive CLS's then it can drive almost anything.

    While simulating the output stage of the MAMP it was still very linear driving a 1 Ohm load at 3KW to 4KW!!! this can never happen in real life due to the PSU and heatsink - but its nice to see that the output stage design can handle very High peak power levels and still remain linear.

    The amplifier design is very novel, I'm very keen to "hear" it - fingers crossed!

    John
     
  4. arthur

    arthur Banned

    Now I am too even more! If they can drive half an ohm without a heart attack I imagine they'll be more than adequate for anything I'm likely to own.

    And I still volunteer as a tester kind of chap :);)

    Saving for a pair has already begun.
     
  5. dtd

    dtd pfm Member

    Has me very tempted too, and I'm very happy with my HK990 ... time will tell I guess! Finally ordered a isolator. The 4 month old Dell XPS is clearly leaking current (can feel it on the MDAC chassis!), and I suspect the PC its connected to is, just not as bad.

    Put me down as a volunteer tester too - I have a pair of Mourdant Short Performance 6's which are ruthlessly revealing yet fun.
     
  6. dtd

    dtd pfm Member

    What headphones do MDAC owners find work well with the unit? I'm going to try the Sennheiser HD650s, Grado SR325i, and the BeyerDynamic DT880s tomorrow back to back. I'm looking for a pair that are honest sounding, plenty of detail and stage but great for long term listening at night.

    (Hmm does this justify its own thread?)
     
  7. Interzone

    Interzone pfm Member

    I use Senn HD800s (and own hd600s and akg q701 which I have tried with it). It seems to do a good job. I haven't compared it with a dedicated headphone amp though but I'm pretty happy with the HP output. Maybe one for the future.
     
  8. JohnW

    JohnW Trade: Lakewest

    Well, I suggest as they are "stereo" units you try a single unit first - then you can upgrade to "Bridged" mono blocks when funds permit...

    What speakers so you have - I don't want to get too off-topic here (and there already has been a recent thread on this subject), but in the past I've found it beneficial to separate the High Current Low frequency path from the lower current Mid and High frequency paths - this can be done with Bi-Amping...

    The M-AMPS can selected for Stereo, Bi-Amped or Bridged mode with a rear panel switch (System Gain is compensated in Bridge mode).

    I believe (and I'd be interested in others opinion) that in Bridged mode the damping factor of the speaker system is reduce by half – (better system damping) as the effective impendence of the speaker driver as “seen” by the amplifiers which is the driven from both terminals is halved (Think of driving an 8 Ohm resistor from both ends – the imaginary Center-point of the resistor becomes “Zero ohms” and thus each amp drives 4 Ohms…) this must then also result in better system damping – the extra current must be doing something…

    It’s the speaker driver (system) impedance that has more of an effect on the speaker system damping then the output DF of an amplifier – 8 Ohm versus 0.1 Ohms for a typical amplifier…

    Any self respecting Rastafarian from Jamaica will tell you that lower impendence Bass Drivers will give you tighter controlled Bass – its not uncommon to hear of 1 to 2 Ohm Bass Drivers (Poor amplifiers).

    What I’m trying to say is that “Bridging” should Tighten the speakers Bass due to better system damping…

    Bridging also makes better use of the reservoir capacitors within an amplifier, normally only one Bank of capacitors are used per signal half cycle - with bridge operation both backs on each supply rail are used during each half cycle. What you loose by driving half the load impedance you make up by better utilization of the PSU.

    So to Bi-Amped or Bridge?

    The M-AMP's also have a-20dB attenuation setting, so you can operate the MDAC's Digital Pre-amplifier with less attenuation.

    John
     
  9. dtd

    dtd pfm Member

    JohnW,

    I suspect your right with re: extra current and bass speakers that have loads at the 1/2 ohm mark.

    I have a pair of B&W CM9s that were independently tested to drop as low as 1.2ohms under heavy load in the bass region. With my previous amp (CA 840a), at reasonably volumes the bass wasn't as taught nor controlled as it should be.

    The HK990 also has (independently tested!) a very low output resistance and a healthy damping factor, and happily provides 1.5kw of current under dynamic loads at 1 ohm with ease. The CA 840a could only dream about touching a 1ohm load.

    The bass quality between the two amps is night and day due to the extra current that is capable of controlling & damping the greedy CM9's woofers.

    However as with all things, worth testing with one amp. B&W do have a reputation for current greedy drivers after all.
     
  10. arthur

    arthur Banned

    At the moment I have a pair of three way AVI Trios. They are not an easy load, but I doubt they'd compete for stubbornness with you ML's .

    Though they may well be changed as the new second room may be too small for such biggies.

    In any case I'm keener on the power amps noew than I am for the m-pax.
     
  11. wpope

    wpope Member

    I have AKG 702s and find they work quite well.
     
  12. wpope

    wpope Member

    As I live in Canada, I was wondering what your distribution plans were for this country? Thanks.

    Bill
     
  13. ChrisPa

    ChrisPa pfm Member

    I believe it's the opposite

    If the output impedance of one amp is say 0.1 ohm, then when you bridge there are 2 output impedances in series with the load
    - 0.1 ohm in each amp
    - a total output impedance of 0.2 ohms, ie. twice the output impedance of non-bridged

    so the output impedance is doubled and so the damping factor is halved (ie. worse) when bridging

    for the same voltage swing you don't have twice the current, you have the same current through twice the output impedance

    If you want better damping factor, then run the amps in parallel

    Maybe the thing to do is to bridge the PSU (if you've got a twin monoblock design) to get twice the supply swing when monoblocking the amp
     
  14. JohnW

    JohnW Trade: Lakewest

    Hi Chris,

    Your correct, but your looking at the issue from an amplifier output impedance perspective, and thus miss my point (I don’t consider the output impedance of the amplifier to be the limiting “System” factor) - I'm thinking of it from the "load = Air" perspective – importantly the interface between electromechanical system and Air

    I consider it to be a felicity to consider the damping factor of a voltage drive amplifier which should be sub ohms – when the voice coil itself has such high impedance – it’s this voice coil impedance that limits the control of the driver / air interface.

    When the speaker cone is accelerated – it’s the resistance of the voicecoil that prevents the amplifier to 100% accurately “Brake” the cone movement, and reverse direction etc… Consider if the voicecoil had zero impedance (and zero amplifier output impedance) there would be perfect control of the speaker drivers cone.

    I guess the impedance match between a non-hornloaded speaker cone and air to be so poor that it’s the Mass of cone (the Cone's momentum energy) that the voicecoil impedance struggles with (simple terms impedance = resistance)…

    The Amplifiers output impedance is normally atleast a magnitude or two lower then the impedance of the voicecoil, so I consider it must be the voicecoils impedance that is ultimately the limiting factor when considering the "accurate control of air movement"

    When an amplifier is operated in bridge mode, it appears to be driving 1/2 the normal load impedance – this must also mean an EFFECTIVE halving of the voice coil impedance (resistance) – and then I suggest this results in better damping of the driver (as the voicecoil impedance limits the system damping).

    I could be wrong as I’ve never seen this mentioned – but it makes sense to me unless I’ve missed something (which really could be the case as I’m no speaker driver expert)…

    By "System Damping / Damping" I mean to describe the accurate Control of air movement via the speaker cone, acceleration and overshoot etc.

    I don’t wish to take this thread too far of subject…
     
  15. elnero

    elnero pfm Member

    I use Audez'e LCD-2 Rev.2's with mine. Originally I was using a vintage Pioneer SX-650 receiver for a headamp but the last week or so I've been happily using the M-DAC's own headphone output. I've been rather surprised at how well it holds up compared to the Pioneer and also a Harman Kardon 730 receiver.
     
  16. travelfotografe

    travelfotografe pfm Member

    Currently using Sennheiser HD800 (and previously HD650 before I sold it to fund the HD800) with the M-DAC built-in headphone amp. The M-DAC drives these 300 Ohm headphones well enough to satisfy me. Volume is loud enough with the M-DAC volume control at -20dB to -10dB (depending on material), and too loud (for me) at about -5db.

     
  17. ADL

    ADL HiFi reborn

    Dear John, I own an Arcam A38 that can be bi-wired to drive my b&w cm8.
    I know that is not like bi-amping, but can i have some benefits of this? And why?
     
  18. tkteo

    tkteo New Member

    How much power can the MDAC's headphone output section deliver? At 32, 64, 300Ohms, etc. It is not stated among the specs.
     
  19. fusion5

    fusion5 on the dark side of hifi...

    Hi John,

    regarding the M-AMP:

    1. Any chance to add a Trigger output? Would make sense if there is a Loop through output. Also this would be a great benefit for Home Theater systems.

    2. Is a three channel version (to drive center an rear speakers) or a 'stripped down' mono version possible?

    3 .Currently I'm using an "Active Tuning Module" made by my speakers manufacturer (Nubert) which is matched to my speaker model. This device is placed between pre and poweramp and limits me to RCA interconnects. Is there a great benefit from using XLR interconnects?

    The ATM is used for this:

    [​IMG]
    [​IMG]

    Regards,
    Michael
     
  20. ChrisPa

    ChrisPa pfm Member

    Hi John

    you seem to be making 2 points, and they shouldn't be mixed because they're not interrelated. I didn't miss your point about drive unit to air, I ignored it because it has no bearing on amplifier bridging.

    No. Each amplifier sees (seems to be driving) the output impedance of the speaker plus the output impedance of the other amplifier.

    In a bridged amplifier there is no 'reference to zero'. Instead, as far as each amplifier is concerned, whereas on it's own it is driving to zero, it is now driving to a floating terminal - which could be zero, 90deg out of phase, 180deg out of phase and twice the amplitude - anything.

    If we tweaked our bridged amp so that one amp always held its output terminal at zero, the overall output signal would be the same as our 'free running' bridged amplifier. And once again the single, active half of the circuit sees the same load as before - the speaker plus the output impedance of the other amplifier

    You have to look at the electrical circuit from the point of view of the electrical load. It doesn't know what type of amplifier is connected to it. With a bridged amplifier it sees the same voltage/current as it does with a single amp, but it sees it coming through twice the output impedance.

    Whatever the amplifier topology or circuit technique, once it's connected to the load it becomes one big simple amplifying block again.

    When bridged it is driving exactly the same speaker load, not half the load

    This is nothing to do with the behaviour of the speaker driver

    Off subject? Does this thread have a single topic? It's one of the most wandering threads ever :) . Yes, this should be in a separate thread, but we've started, so we may as well continue?
     
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