MDAC First Listen (part 00100100)

[JohnW]

Wow so many VFETs on the amp. Are they using all VFETs for the output stages ? How does it the sound like ? Would also cost a lot, right ?

IIRC, There was talk of US$100K a pair - it used the last of Sonys VFET stock.

John, would you experiment with an all VFET design on the Reference VFET Amp ?

The elegance of the topology I'm using is that the "low power" extremely linear Class A VFET stage determines the sound quality, its always in control of the speaker load and live its "stress free" life believing the world is a simple 10W load - its being "buffered" from higher load currents by the MOSFET current dumpers.

An all VFET design would require the rather delicate VFETs to operate into a far more complex load, they do not posses much internal gain and are rather Non Linear when faced with higher current demands.

In our design they are protected from adverse loads and can operate under ideal "sanitised" conditions

 

[ChrisPa]

Can someone please remind me what the maximum bit/depths/rates are on each input interface, please.

I believe it's:

USB - is 1.1 so limited to 24/96
SPDIF coax - 24/192
SPDIF optical - 24/96, but may be 24/192 dependent on the actual performance of the optical input device

Is that right?

Thanks

 

[JohnW]

Can someone please remind me what the maximum bit/depths/rates are on each input interface, please.

I believe it's:

USB - is 1.1 so limited to 24/96
SPDIF coax - 24/192
SPDIF optical - 24/96, but may be 24/192 dependent on the actual performance of the optical input device

Is that right?

Thanks

Correct, why are you experiencing issues?

 

[ChrisPa]

Correct, why are you experiencing issues?

No, not at all

I've just been configuring my system so that for the first time I can start playing hi res (> 16/44.1) files.

I've just set up my SqueezePlay OS Joggler up to use the USB input and the SBT EDO plugin. 24/96 is coming through immediately , and some claimed 24 bit tracks are coming through as 16bit .

So I wanted to check whether I should be able to play 192k before I went chasing any further configuration on the Joggler and LMS.
And therefore also how to work out an effective way to get 192k into the MDAC.

I also have a dedicated PC in the hifi, with USB and optical SPDIF, so I'll probably pursue that a little further (but probably not tonight)

 

[jamjar784]

IIRC, There was talk of US$100K a pair - it used the last of Sonys VFET stock.



The elegance of the topology I'm using is that the "low power" extremely linear Class A VFET stage determines the sound quality, its always in control of the speaker load and live its "stress free" life believing the world is a simple 10W load - its being "buffered" from higher load currents by the MOSFET current dumpers.

An all VFET design would require the rather delicate VFETs to operate into a far more complex load, they do not posses much internal gain and are rather Non Linear when faced with higher current demands.

In our design they are protected from adverse loads and can operate under ideal "sanitised" conditions

Hi John

I came across a German company Progressive Audio who claim to use Silicon Carbide semiconductors in their A1 and A2 amplifiers. http://www.progressive-audio.com/ Until this discussion I didn't know this was aka VFET. I wonder where they're getting them from

KR

 

[JohnW]

A few company's produce Silicon Carbide devices for RF applications - but they don't come in complementary versions - so you have to design a non symmetrical output stages (as was typical in the early transistors days when you could only source NPN power transistors) - by my standards as a designer this is a massive no no.

Review here:-

http://www.audio.de/testbericht/progressive-audio-a1-im-test-1216858.html

Distortion performance is truly horrendous and I quote "ONLY costs 12,000 Euros"

Forgive me, but I don't find this acceptable.

Ps. the review suggest (mentions) the SemiSouth devices... which are no longer available...

 

[iansr]

Yep - its true you can all blame Ian for instigating the VFET amps (Ian gets Serial #1 & #2) and we all know never to buy a new model car in its first year of release

[v/QUOTE]

I suppose you think that's funny . . . .

 

[JohnW]

Yep - its true you can all blame Ian for instigating the VFET amps (Ian gets Serial #1 & #2) and we all know never to buy a new model car in its first year of release

I suppose you think that's funny . . . .

Yep indeed, a fleeting moment of fun - because I know how it will end up, that I'll never have the time to build my own units!

 

[ljmac]

Just to clarify, the "Silicon Carbide" devices Progressive Audio use are the same as the Power JFETs Nelson Pass uses in the First Watt J2, correct?

 

[JohnW]

Just to clarify, the "Silicon Carbide" devices Progressive Audio use are the same as the Power JFETs Nelson Pass uses in the First Watt J2, correct?

No, the review mentions the SemiSouth Corporation devices but does not specifically state there use in the Progressive Audio design - but that said the designer of Progressive Audio mentions he is a fan of Nelson Pass designs, so its a good bet that its shares its heritage with NP circuits...

We do not us the SemiSouth devices as they where only available in Nch Devices, we use the ORIGINAL Sony fully complementary VFET Devices.

 

[ilmostro749]

Yes, this will work - wire the relay coil up with the current Headphone Relay.

What is the relay part I need to get John?

 

[JohnW]

What is the relay part I need to get John?

PM you address and I'll post one out to you.

 

[ilmostro749]

Thank You very much - very generous of you!

 

[JohnW]

Thank You very much - very generous of you!

No Problem - Have your address, I'll post a couple of relays when we are next at the PO.

 

[JohnW]

Does anyone know of a good Speaker terminal brand? I'm thinking of the speaker binding posts you see on the rear of flagship Amps with Tap size tightening posts.

I had a quick look at the WBT website and felt like projectile vomiting - and that's before I noticed the price!

I'd like quality terminals not because I believe they have such a dramatic impact on sound quality, but connectors and users controls are the owners "interface" with a product and should reflect the quality of the design.

The user controls on HiEnd cars feel so cheap these days...

I'll use touch sensitive "buttons" on the Glass panel for the VFET Amp / TDAC (and later MDAC2 chassis) as I have bitter experience of getting the fit and feel of buttons / knobs correct!

 

[ChrisPa]

HiFi collective have a good range

http://www.hificollective.co.uk/components/binding_posts.html

 

[jackocleebrown]

Sorry John, not familiar with any brand other than WBT.

We stopped using WBT on our stuff because of the high cost and the increasingly plasticy cosmetic. We found that we could have very nice custom terminals made for the same cost. In their favour, WBT are totally shrouded there is less chance of an accidental short.

The nicest terminals that I've come across were on a pair of speakers from Japan (sorry can't recall the brand) they were very simple/conventional but chunky and with a clamping nut that could be tightened with a spanner.

Personally, I've always fancied an amp with solder tags on the back but I don't think that is the look you are going for in this case!

 

[iansr]

The best ones I've seen are made by Cardas and they basically act like a clamp so that you bolt together 2 pieces of metal (gold plated copper?) with the bare speaker wire between them. The idea I think is that you make a reversible cold weld. They are however very expensive. Maybe you could find someone to fabricate something similar at a much lower price?

 

[iansr]

Found them. You can use spades as well:
http://www.cardas.com/cpbp.php

 

[JohanH]

Does anyone know of a good Speaker terminal brand?

Hirschmann?

https://www.conrad.nl/nl/sks-hirschmann-pkni-20-b-poolklem-zwart-63-a-1-stuks-733808.html