ilmostro749
pfm Member
Maybe Audiolab only allow so much mark down, so the are saying return or open box to get around that. Or they just messed up, and let you have a new one so as to not upset their customer...
MDAC First Listen (part 00100100)
- Thread starter ilmostro749
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Maybe Audiolab only allow so much mark down, so the are saying return or open box to get around that. Or they just messed up, and let you have a new one so as to not upset their customer...
We had been away for a couple of days so was probably around 12C. My M-DAC (& amp) have been absolutely fine since, I'm pleased to say. As my amp was also effected, I'm willing to consider a one-off event 'cos I can't think of any M-DAC failure causing my Primare power amp to also fail. Time will tell if the failure repeats.
I wish you a productive New Year & hope your impending trip to China goes well John.
Added: All of my system is switched off last thing at night then powered back on around 5:30 via the remote RF mains switches so subjected to daily heat cycling.
JohnW
pfm member
Sooooo,
Sorry I've been quite these past few days as for a Christmas treat, I treated myself to working on the VFET amp design
(don't worry, I'll go back to the MDAC2 tomorrow).
The MDAC2 employs a totally symmetrical analogue circuit design - the positive and negative cycles of the audio signal are handled by a "Mirror image" circuit. From past experience "symmetrical" circuits sound the best. This is made possible by complementary NPN / PNP transistors & N channel / P channel fully complementary MOSFETS.
Unfortunately, Vacuum tubes do not have complementary devices as Electrons can only flow in one direction (From Cathode to the Anode). The VFET amp which uses a tube on its front end could therefore not be a symmetrical design – which troubled me.
However while lying in bed a week ago or so I realised I could mirror the current from the Cathode of the tube and then design similar fully symmetrical Gain stage as I’ve designed for the MDAC2.
I spent these past few days with the computer simulator working on the details of the new “symmetrical” tube circuit – with not only confirmed the circuit works, but also with pretty impressive results
I also spent time on designing the VFET ClassA output stage*, which resulted in a VFET / MOSFET hybrid output topology – the VFET device with its linear “Triode characteristics” compounded with a MOSFET to form an ultra linear output device.
*Before I could even start to work on the design I had to create a computer spice model of the VFET devices – as no accurate model existed for them as be last manufactured in the late 1970's they pre-date Spice simulators. I had to purchase HP / Agilent Semiconductor analyser & High performance LCR meter to create “realistic” models. These analysers cost me over GBP10K second hand Oh well, I guess I'll be even more proud of the design when its completed
Its such a shame that its not possible to “Mass Produce” such an amplifier as I’m stunned by the innate linearity of this compound output device – with an open loop (No Global Feedback) THD of lessthen 0.0005% 100W 8 ohms 20KHz (-106dB 2nd & -109dB 3rd)…. consider that the VFET amp stage will only need to produce 10W ClassA and closed loop so THD will be much lower on the final amp!
I’m really pleasantly surprised how linear this 'VFET / MOSFET' compound output device is – when I look at the bigger picture of the Amplifier design it brings a smile to my face as its such unique and “crazy” (in a good way) design
The MDAC2 / VFET amp should be a stunning combination!
Sorry I've been quite these past few days as for a Christmas treat, I treated myself to working on the VFET amp design
(don't worry, I'll go back to the MDAC2 tomorrow).The MDAC2 employs a totally symmetrical analogue circuit design - the positive and negative cycles of the audio signal are handled by a "Mirror image" circuit. From past experience "symmetrical" circuits sound the best. This is made possible by complementary NPN / PNP transistors & N channel / P channel fully complementary MOSFETS.
Unfortunately, Vacuum tubes do not have complementary devices as Electrons can only flow in one direction (From Cathode to the Anode). The VFET amp which uses a tube on its front end could therefore not be a symmetrical design – which troubled me.
However while lying in bed a week ago or so I realised I could mirror the current from the Cathode of the tube and then design similar fully symmetrical Gain stage as I’ve designed for the MDAC2.
I spent these past few days with the computer simulator working on the details of the new “symmetrical” tube circuit – with not only confirmed the circuit works, but also with pretty impressive results
I also spent time on designing the VFET ClassA output stage*, which resulted in a VFET / MOSFET hybrid output topology – the VFET device with its linear “Triode characteristics” compounded with a MOSFET to form an ultra linear output device.
*Before I could even start to work on the design I had to create a computer spice model of the VFET devices – as no accurate model existed for them as be last manufactured in the late 1970's they pre-date Spice simulators. I had to purchase HP / Agilent Semiconductor analyser & High performance LCR meter to create “realistic” models. These analysers cost me over GBP10K second hand
Oh well, I guess I'll be even more proud of the design when its completed Its such a shame that its not possible to “Mass Produce” such an amplifier as I’m stunned by the innate linearity of this compound output device – with an open loop (No Global Feedback) THD of lessthen 0.0005% 100W 8 ohms 20KHz (-106dB 2nd & -109dB 3rd)…. consider that the VFET amp stage will only need to produce 10W ClassA and closed loop so THD will be much lower on the final amp!
I’m really pleasantly surprised how linear this 'VFET / MOSFET' compound output device is
– when I look at the bigger picture of the Amplifier design it brings a smile to my face as its such unique and “crazy” (in a good way) design The MDAC2 / VFET amp should be a stunning combination!
JohnW
pfm member
Pierre,
Sorry for the late reply, I've been working on the VFET amplifier design over the Christmas period
There are 3 positions left on the VFET list - so I'm not sure how long it will be before they are all sold.
PM if your interested in one of the last pairs
PhilCTTE
Senior mumbler
Wow such expense for the bespoke analysing equipment!! It's a shame similar tubes can't be sourced for you to continue production and make a (healthy) profit. Such passion for your work!
I,m so glad I had the funds to be a part of it. Very much appreciate your relentless commitment and hard work.
Have a happy new year !
I,m so glad I had the funds to be a part of it. Very much appreciate your relentless commitment and hard work.
Have a happy new year !
JohnW
pfm member
The cost of these items new was over GBP100K! so at GBP10k its a "bargain" although I can think of many other ways to spend the such funds Part of the "Cost" of the VFET amp project is to purchase the equipment required to properly engineer the design - while my interest in the project is to be able to design reference Amps I can trust in there sonic performance.
The Phase noise measurement system I use for the MDAC2 project is worth over US$250K - its why there's so little real development in HiFi as it simply does not repay the investment to do it "correctly" - with so many garage outfits making embarrassingly Amateur designs.... (says John who purchased a pillar drill from the local Tesco stores to drill the holes for AV bypass RCA's on the rear of the MDAC)
Still its better then giving Merc GBP2K to replace a Gear shifter due to a cracked US$0.50 plastic lever!
Tubes are not such a problem as there are Russian type I can use in place of the JAN 6111 / 6112's, although ATM I refuse to have any dealings with Russia! Its the VFETs which are the "Golden devices" I'm really really impressed with the linearity of the VFET/MOS compounded topology I've developed for the Amp.
Its no so much the financial "loss" of not being able to manufacture more units, rather that so few will be able to own the amps... as they will really offer reference performance.
ATM, I'm hard pressed to recommend an amplifier whose performance I believe in, and I'll not be able to say "you should try a pair of VFET amps" with the MDAC2 / TDAC... as there will only be 20 or so pairs in the world!
Happy new Year
Part of the "Cost" of the VFET amp project is to purchase the equipment required to properly engineer the design - while my interest in the project is to be able to design reference Amps I can trust in there sonic performance.The Phase noise measurement system I use for the MDAC2 project is worth over US$250K - its why there's so little real development in HiFi as it simply does not repay the investment to do it "correctly" - with so many garage outfits making embarrassingly Amateur designs.... (says John who purchased a pillar drill from the local Tesco stores to drill the holes for AV bypass RCA's on the rear of the MDAC)
Still its better then giving Merc GBP2K to replace a Gear shifter due to a cracked US$0.50 plastic lever!
Tubes are not such a problem as there are Russian type I can use in place of the JAN 6111 / 6112's, although ATM I refuse to have any dealings with Russia! Its the VFETs which are the "Golden devices"
I'm really really impressed with the linearity of the VFET/MOS compounded topology I've developed for the Amp.Its no so much the financial "loss" of not being able to manufacture more units, rather that so few will be able to own the amps... as they will really offer reference performance.
ATM, I'm hard pressed to recommend an amplifier whose performance I believe in, and I'll not be able to say "you should try a pair of VFET amps" with the MDAC2 / TDAC... as there will only be 20 or so pairs in the world!
Happy new Year
fusion5
on the dark side of hifi...
Hopefully there will be a smaller (cheaper) non-tube version some day
davidjt
pfm Member
+1!
Not really having room for huge electrostatics, I believe I've found speakers 'worthy' of the MDAC2/VFET combination: a pair of s/h Focal.JMlab Utopias have resulted in another step-change in SQ here. So, one third of the way to my ultimate system, and even more excited, if that's possible.
Best wishes for the new year.
JohnW
pfm member
Well, I'd like to design a "system", but its hard to see how I can design an Amplifier that can compete with the performance of the VFETs... (its not the Tube, but the VFETs that are the defining factor of VFET amps).
Heres the simulated THD of the VFET stage open loop, 8 ohms 10W's...
https://dl.dropboxusercontent.com/u/86116171/VFET DB A03 THD Sim.jpg
Upper curve is 2nd order Harmonic, while the lower is the 3rd...
-106dB 2nd at 20KHz Open loop (0.0005% THD)... The VFET/MOS 'compound device' is inherently linear
-132dB THD at 1KHz!
JohnW
pfm member
I listened to a pair of JM'labs speakers at SQ's once and I was surprised how good they where - I was expected ear splitting treble but this was not so!
If I had to buy box speakers then I'd consider theses...
Best wishes for the New Year... MDAC2 and VFET amps at the very least
misterdog
Not the canine kind
I have just installed 2 monobloc Hypex n-Cores which are putting a big smile on my Quad ESL's, though as we have 75mm. of snow and zero temp. I am missing the fringe benefit of Class A.
JohnW
pfm member
I have just installed 2 monobloc Hypex n-Cores which are putting a big smile on my Quad ESL's, though as we have 75mm. of snow and zero temp. I am missing the fringe benefit of Class A.
How do they sound with your Quads?
ti33er
pfm Member
....soooo possibly a slightly silly question Mr Westlake, but could you not design and 'produce' VFET of some sort, of your own design and do the World a favour !?! ;-)
If the amps turn out to be so good, there are many people who spend silly money on audio gear that may make it worth your while!?!
£ Paul $ ¥ €
If the amps turn out to be so good, there are many people who spend silly money on audio gear that may make it worth your while!?!
£ Paul $ ¥ €
misterdog
Not the canine kind
Two other MDAC users I know (thanks to this thread
) are also Hypex owners, one with Lowther Horns and one with Quad ESL's.
JohnW
pfm member
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...
JohnW
pfm member
Someone else has a stash.
Just look at that horrid cheap computer grade ribbon cable carrying the audio signals... but an eye watering amount of VFETs!
IT's Nielson Pass's tribute to Sony, made of one of Sony's old ( the last ? ) stashes of vfet's. There is only the set at the picture
John... Happy new year when it comes. And Im looking forward to pick up a VFET amp next year.
Keep up the fantastic work, what an interesting journey it has been until now.
( Im reeding up om the current dump part from QUAD, didn't know it contained so much math *s* )
John... Happy new year when it comes. And Im looking forward to pick up a VFET amp next year
.Keep up the fantastic work, what an interesting journey it has been until now.
( Im reeding up om the current dump part from QUAD, didn't know it contained so much math *s* )
fusion5
on the dark side of hifi...
Well, I'd like to design a "system", but its hard to see how I can design an Amplifier that can compete with the performance of the VFETs... (its not the Tube, but the VFETs that are the defining factor of VFET amps).
Heres the simulated THD of the VFET stage open loop, 8 ohms 10W's...
https://dl.dropboxusercontent.com/u/86116171/VFET DB A03 THD Sim.jpg
Upper curve is 2nd order Harmonic, while the lower is the 3rd...
-106dB 2nd at 20KHz Open loop (0.0005% THD)... The VFET/MOS 'compound device' is inherently linear
-132dB THD at 1KHz!
Yes, you're right. I forgot the to mention the VFETs in my post.
But sadly I can't affort 4 pairs to run an active VFET driven speaker. And even if I could, there are not enough parts available.
Third party amps for me atm!
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