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MDAC First Listen (part 00100110)

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Hi guys,

I'm looking at puchasing an MDAC second hand for a good price soon. While I've been interested in John's MDAC2 project for a while, I've always found the main web page rather daunting. I apologise in advance, as I'm sure that these questions would have been asked multiple times, but I've done a lot of reading through various forums and web pages and I'm still a little unsure.

Are there still spots available to make the payment and commit to getting an MDAC2?

Do you require your own MDAC to be sent in to be upgraded, or are there still salvaged units remaining? If units need to be sent in to be upgraded, does it need to be from an address within the EU?

Is it as simple as paying the combined 1st - 4th installment of £400, then adding your name to the Wiki and awaiting further instructions?

I'm essentially interested in the L2 MDAC2, and would like to know the process for getting into the queue to buy one. If I can get an L2 MDAC2 from a salvaged unit, that would save me from buying one second hand and then shipping it over.

Thanks for any help :)
 
I have seen a set of Carver ALIII advertised locally and am wondering how these tall,slender electrostats will work with the VFETs. I am aware of the things to watch out for with them: loose ribbons (buzz) + the down firing woofer may be loose (+ could be replaced with better woofer) + crossover/internal wire may be improved.

Also they are a very difficult load, but I suppose that the VFETs would be up to that task?!

Has anyone listened to the Carver ALIII?

If they are a no go, I have my eyes on:
Amphion L3s
Revel 206s
Sonus Faber Venere 3.0
Gauder Arcona 80

These last ones ought to present friendlier loads to the VFETs.

Peter
 
Peter,

The Carvers implement a 48-inch dipole ribbon (they are not ESL's) - but they could be real fun.

If the price is decent I'm sure you would enjoy them and the VFET amps are being "designed" for such nasty loads :)

You don't mention there price, but lets say they are about 1000 Euros then you would have a hard time finding something better...

Out of the speakers you listed I'd go for the Carvers!!! I've not heard them, but being large American speakers they will not be Bass Shy! :) and Ribbons are a not too distance second best to ESLs - they will be leagues ahead of any conventional Mid / HF cone drivers.
 
Thanks John.
The seller has two sets for sale around the price you indicate. I am tempted to go for one of them just for the sheer fun of it. As for WAF, I haven't got high hopes. So they wil be for my den ...
Kind regards Peter
 
Peter,

I pretty much guarantee you will enjoy these speakers - they will open a whole new listening experience - then you will really appreciate MDAC2 / VFET amps!

They would be the kind of speaker I'd buy! forget boring box speakers!

A couple of months back I bought a pair of Acustat ESLs with the same sub-woofer arrangement, I'm really looking forward to trying them out!
 
Dear John,
This is my first post. I recently purchased an MDAC 1.
I was very impressed, but protracted listening showed noises which distracted from full fidelity. I purchased the NCRU power supply and again discovered its limits, even though it did improve the sound. I opened it and was surprised not to find a separate supply for the positive analogue supply rail and only one transformer. I subscribed to the upgraded MDAC 2. (levels one to four)
But since zero does not exist in physics and engineering. And you were intent on using the original power supply, I decided to build a 3 prong cascaded (two stages) power supply using two separate toroidal transformers one for the analog and one for the digital circuitry.
I do not like the flimsiness of the mini 9pin din connector and wonder why you did not use the ampnenol. Congratulations for what I believe good work.
The remote control does not work what is to be done about it? Thanks.
 
JohnW said:
https://dl.dropboxusercontent.com/u/86116171/Aircore Cropped.jpg

The inductor above is 10uH, the VFET's will be 1.2uH to 1.5uH so will be smaller diameter, but not that much smaller.
Click to expand...

John, you might want to be a little cautious with these inductors. In my experience they have a resistive part that increases substantially at high frequencies (I believe due to proximity effects resulting from the wide conductor). It looks like you have one on hand so would be worth a quick impedance measurement just to check.
Jack.
 
Hi Jack,

Skin effect comes in to play at increasing Frequency - the 10uH parts are 34mR at 20KHz - so I'd guestimate about 5mR at 20KHz for the 1.5uH parts or less.

Obviously these are very low figures and will be swamped by PCB tracking resistance / Output Mute Relay and Connector resistance etc.

I'm guessing your more accustomed to much larger values in the mH range for your Speaker networks where skin resistance is going to be an issue due to the much greater conductor length.
 
canofan said:
Dear John,
This is my first post. I recently purchased an MDAC 1.
I was very impressed, but protracted listening showed noises which distracted from full fidelity. I purchased the NCRU power supply and again discovered its limits, even though it did improve the sound. I opened it and was surprised not to find a separate supply for the positive analogue supply rail and only one transformer. I subscribed to the upgraded MDAC 2. (levels one to four)
But since zero does not exist in physics and engineering. And you were intent on using the original power supply, I decided to build a 3 prong cascaded (two stages) power supply using two separate toroidal transformers one for the analog and one for the digital circuitry.
I do not like the flimsiness of the mini 9pin din connector and wonder why you did not use the ampnenol. Congratulations for what I believe good work.
The remote control does not work what is to be done about it? Thanks.
Click to expand...

canofan,

Thank you for your post.

What is your main replay source - if its USB then I suggest a USB isolator as I suspect your "noise" is due to Ground noise between your USB Host device and the Audio system.

MDAC in its basic form should be good for 125dB+ Dynamic range via Balanced XLR's and around 122dB for Single-ended outputs so any noise must be externally injected.

The AC transformer has dual symmetrical windings - which from then onwards the Analogue and digital sections are completely isolated.

By isolation I mean from AC to DC rectification onwards, so separated Bulk Capacitors, Multi-stage cascaded regulation etc. - in fact the MDAC has a crazy number of onboard regulator stages - I'd have to count them again but easily over 20 stages...

Separated AC transformers would not make any difference to the MDAC design.

The MDAC2 "full sized chassis" with its HQ PSU will isolate the Digital and Analogue Ground domains - while this is technically the ideal solution I have no idea what if any impact this will have on the sound quality. MDAC2 with its "standard" PSU will be pushing towards a dynamic range of 135dB.
 
Hi John,

Yes, of course you are right - my experience was with much bigger inductors. I just remember being quite surprised by low in frequency the effect started so wanted to mention it in case it was significant in balancing the bridge. I think that the magnetic field generated by the inductor itself makes the situation much worse than you read in text books for skin effect in straight conductors.

It took me a few minutes but I managed to fine one of my measurements (from about 6 years ago!).

This data is for a big ribbon style air core 3mH inductor. DCR was around 0.4 ohms This was used on a prototype as the main LF section inductor. It took us quite a bit of head scratching to work out why we were loosing output at 250Hz - turned out to be this effect.

https://dl.dropboxusercontent.com/u/37121092/inductance and resistance.png

Your component is a completely different scale from this so probably not a problem - especially with that 20kHz resistance!
 
Yes my one "Unknown" about the air-cores is there sensitivity to external proximity effects.

I just ordered good old fashioned NOS German manufactured Silver plated "Air Core" trimmer capacitors to balance the bridge circuit - being a balanced output stages there are two Bridge circuits per monoblock!

Did you get anywhere with your own simulations? Recently I had to run some Current Dumping simulations to confirm a design aspect and remembered you.

One realisation I had is that you need to have non-linearity in your Current dumpers otherwise you will not see the distortion cancellation of the Bridge. I said my Sim was "Quick and easy" :) so I just added a pair of diodes to output of a "Perfect opamp" stage to simulate the ClassC transfer characteristics of an unbiased current dumping stage.
 
I'm still working on it when I get the chance. I have something that is starting to look fairly reasonable. If you are interested I'll email you over a schematic tomorrow when I'm in the office :)
 
Last week I had a play around with the Creek Evo 50 CD player compared to my Rega Apollo R/MDAC L3 Toy combination.

I understand that Dominik had a part to play in the development of this player. I also note that it uses two Wolfson DAC chips and has an op amp output stage.

It bettered the Rega/MDAC combination for dynamics, bass drive, Timing and tunefulness.

The Rega/MDAC were slightly ahead on texture in the midrange.

On balance the Creek was the overall winner.

Swapping the Mark Grant Oyaide digital interconnect for one by Audio Mica narrowed the gap in terms of timing and bass drive but the Creek was still ahead.

We ran out of time so I did not get the chance to try the following:

● Using the Creek as transport with the MDAC L3 Toy as a DAC.

● Allowing the MDAC to warm up for more than a couple of hours.

My suspicions are the weak link is the Rega or the data transfer between the devices. Would clock locking likely fix this?

I wanted to stay with half-width cases as they can be accommodated on one shelf but I accept that MDAC2 will eventually be a full-width design.

The Creek seems incredibly well-made and the slot - loading mechanism is great.

Despite the Rega's relative shortcomings it has bettered most PC/streamer alternatives that I have tried so far with the exception of some of the kit brought round by Mark/Item including the Aurender X10. As a main digital source I intend to stick with disc spinners.

I welcome thoughts, particularly from John himself.

Please do not contest my findings thus far because this will simply generate heat and no light. I'm looking for causes and solutions to meet MY needs.

Your mileage may differ. Obvs!
 
Steve,

The Creek CD has the advantage that we slaved the Transport clock to the DAC clock.

Using the MDAC via SPDIF and your always at the mercy of Clock jitter - this is why Async USB performs so much better (when setup correctly so Bit perfect Data and using a USB isolator to prevent Grounding issues between the DAC / USB Host).

The solution is to add a clock-lock card to your Rega which I can do. I'm sure you can find CD transports with lower Clock jitter then the Rega, but they will always still be sub optimal as SPDIF WRT clock recovery is a flawed solution, Clock-locking removes this deficiency.
 
This site contains affiliate links for which pink fish media may be compensated.
misterdog said:
Though if you are importing into the UK. Import Duty and VAT may add up to
40 % onto the cost :eek:
Click to expand...

How much is Vat in the UK thesedays? its 21% here in Czech Rep. and duty's about 2.5% to 3% so your looking at no more then 25%, its still a very good deal IMO.
 
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