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MDAC First Listen (part 00100100)

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Reenberg said:
John... Happy new year when it comes. And Im looking forward to pick up a VFET amp next year :D
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Yes, looking forward to meeting PFM'ers who will be able to visit us in Czech to collect MDAC2 / VFET amps and spend a few days here :)

Reenberg said:
( I'm reading up on the current dump part from QUAD, didn't know it contained so much math *s* )
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Sounds like your reading the papers by Vanderkooy & Lipshitz's... Way too complex and I dont agree with some of there conclusions (they only consider the design in terms of Error Feedforward) - but each to there own :)

A good while back we created an Excel spreadsheet to calculate the bridge components - an thankfully with the power of today's simulators one does not need to get too involved into the very complex maths - leave that to the computer :)

It should be noted that the VFET amp differs in many respect to the Quad design, not least in that the Current Dumpers are constantly biased and not operated in ClassC of the Quad designs. The ClassC operation of the Quad dumpers causes very abrupt, non linear loading on the ClassA amp that has finite output impedance, this and other issues results in the typical high order crossover distortion spectrum of the Quad designs.

The basic principle of the VFET amp is to have the highly linear ClassA VFET stage handle the delicate signal "control" while the MOSFET non Switching Error corrected current "Dumpers" provide the "heavy lifting" - both stages are highly linear rather then with the Quad design where the ClassA sections is depended upon to correct for the ill's of the terribly crude ClassC current dumpers.
 
Yes, looking forward to meeting PFM'ers who will be able to visit us in Czech to collect MDAC2 / VFET amps and spend a few days here
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So do we :D

Sounds like your reading the papers by Vanderkooy & Lipshitz's... Way too complex and I dont agree with some of there conclusions (they only consider the design in terms of Error Feedforward) - but each to there own

A good while back we created an Excel spreadsheet to calculate the bridge components - an thankfully with the power of today's simulators one does not need to get too involved into the very complex maths - leave that to the computer
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Spot on, and yes...leave it to the PC's. They are actual quite good at that
 
JohnW said:
Fabricating semiconductor devices is a multi million dollar task...

There was a small company operating out of a University Fab plant that manufactured "Power JFET" but sadly they have gone into receivership and are no more... :(
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Hmmmm so just throwing ideas out there, perhaps like a 'burson supreme OpAmp' style design, could something larger scale be made with common components!? ...just being a hopeful, would LOVE a pair of VFETs but coming up with all the funds right now is grounds for Divorce if I attempted to raise them :-(((((
 
JohnW said:
Its not the tube, but the VFETs that limit the availability...
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would be great with a tube input/ mosfet output amp later, but price would hardly be very much lower than for the VFET amps if total numbers of amps are reasonable

Both Hypex Ncore and Holton Mosfet amps benefit sonically from a good tube preamp
 
misterdog said:
:D:D

Two other MDAC users I know (thanks to this thread :) ) are also Hypex owners, one with Lowther Horns and one with Quad ESL's.
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And another one here... With Ergo IX speakers designed by James of the DIY room.
Seriously impressive kit.
 
Sadly, Just two remaining positions for VFET amps (with one potentially reserved).

Sam,

I have a set of VFET reserved for you... no need to make any decisions at this time as I can always use them as spares :)

Misterdog,

A pair reserved for you :)
 
sam_cat said:
And another one here... With Ergo IX speakers designed by James of the DIY room.
Seriously impressive kit.
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Just built a pair of Hypex monoblocks used with an M-DAC and some modest SCM-11s. Very happy so far... VFETs sound to be great, but above my league. Still thinking about MDAC2 but so far happy with the MDAC.
 
JohnW said:
Sam,

I have a set of VFET reserved for you... no need to make any decisions at this time as I can always use them as spares :)
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Thanks John,

Its almost certainly going to be a yes, worst case scenario I sell the amp on at cost.. And that would only be *if* it didnt improve on the Hypex NC400.

Do you have enough sets so that you can have a pair of amps? It would be criminal for you to build these and not have a set for yourself (especially as you will need them for tuning the Mdac firmwares/TDac...)
 
Sam,

I'll have enough devices for 26.5 pairs of monoblocks, I'll most likely source some more devices just to be on the safe side, I'm just waiting for the devices in transit to clear customs.
 
I've some questions on the phone out of M-DAC.

1) When I use M-DAC phone out to drive a sensitive IEM (e.g. CK100pro), I clearly heard some noise produced by my M-DAC. I think that the noise level was around 20 to 30dB when a CK100pro was used, and the noise level did not vary with volume control. Is this noise level normal for M-DAC?

2) Some articles say that digital volume will distort the data (i.e. soft sounds in 24bit data become silent when attenuation reach -3x dB). Will this happen in M-DAC? Since most of my headphone are low impedance models, I use the M-DAC's phone out mostly with attenuation of <-30dB, can I ensure a high level of fidelity in this case?
 
I was thinking, as my new headphones can be used with either a normal supplied 6.35mm jack or a 4 Pin XLR, I thought I might knock up a cable and try it out. Then I thought, why not put the Mini-XLR DIN on the back panel, and wire it up. (M-DAC out of warranty now so no issue to start modding it). I'd like to be able to undo anything, so I was wondering if any rear panels are available? John?

Also what was the Pinout etc for the one on M-DAC2 (not that I plan to get one, but might as well standardise)

I've already got the Rean 4 Pin Mini-XLR, and have just ordered the Sennheiser connector from their spares shop.

rt4fc-b.jpg


1productsennheiser-hd800-plug-543688.jpg



PS - sorry, I know this info is in this thread about 5 times already, but I can't find it!
 
Whats your digital source - are you using USB?

Do you also use the MDAC's line outputs with Amplifier / speakers? as the headphone output is the same as the main outputs so any "noise issues" should be present with both Line outputs and headphone use.
 

Hi, welcome aboard.

If you convert your phones to run direct from the XLR outputs SQ should improve, it did for my Senn. 600. Though going from 3 core TRS lead to 4 core lead helps in itself.
 
ilmostro749,

How are you thinking or wiring the connector (to the MDAC's Main XLR outputs?) as the Headphone signals are only single ended in the MDAC (One dual pole relay switches the stereo headphone signals).

I don't have spare rear panels, the only panels I have are on salvaged MDAC's however these belong to customers so I have no right to scavenge there rear panels.

BTW, the MDAC2's rear headphone connector is a 5W Male Mini XLR (not 4W).
 
Hi John,

I've a had a good think about the VFETs over a few mince pies and port and have decided the timing isn't right to make that kind of financial commitment right now. I'm already off on an expensive cricket tour in April and my house needs a new kitchen! I may have a windfall in mid Feb. If that happens and you manage to source enough parts and are happy to make more, then I'll definitley be in. But it's not fair to hold a place open for me for 1 of only 20 spots, so please give it to the next person who wants them. And may their ears forever be sang sweet notes of audio heaven :)

James
 
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