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MDAC First Listen (part 00100110)

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If I where to design the SPDIF interface today [...] I'd scramble the Audio data during transmission to de-correlate such second order effects. This would also greatly help the Clock recovery circuits (PLL's) who have a hard time attenuating these correlated audio data patterns.

You could scramble in a proprietary stage after having acquired the data from SPDIF, at the cost of some latency.
 
SPDIF is a far simpler interface with significantly simpler decoding circuits, and can be decoded at a fixed Clock rate with oversampled statistical analysis (IIRC so long as you can sample the edges at 3 - 4 times the data rate you can recover the Data "clockless".

The USB interface requires magnitudes greater circuit complexity, the more circuit devices you have operating at the USB Host data rate the more greater the level of PSU & Ground noise will can be injected into the system. This opens the door for a "Distortion" mechanism that allows the PC's operating domain to enter the Audio domain.

The Ideal solution is to remotely situate the USB input circuit external to the DAC chassis, and connect via optical links. The DAC can provide the Reference Master clock so the USB port is operated Asynchronous in the correct sense.

Yes, very much so, and the reason the MDAC2 has the advanced clock option where we can eject a controlled amount and spectrum of "Jitter" to de-correlate such effects.

A problem with SPDIF and to a degree USB is a that the "Energy spectrum" of the Data is strongly correlated to the transmitted Audio data. If I where to design the SPDIF interface today (Silicon area is so much cheaper today then when SPDIF was first conceived) I'd scramble the Audio data during transmission to de-correlate such second order effects. This would also greatly help the Clock recovery circuits (PLL's) who have a hard time attenuating these correlated audio data patterns.
thanks John for the very helpful answer. I guess there's a trade off between wanting to put the receiver off board and finding a way to receive the data from the off board receiver without going back to square 1. Is the plan still to have some sort of (optional?) off board input pod with the M dac 2? Or did that idea get shelved.
 
Is the plan still to have some sort of (optional?) off board input pod with the M dac 2? Or did that idea get shelved.

Yes, once I've laid out the USB input PCB section on the MDAC2 digital PCB, I can copy the section and design the external pod with little extra effort.

The Pod can also be used with the MDAC1 adding a clock-locked ASync isolated 192KHz USB port.

It might make a good SMD PCB production trial run here in Czech Rep - the pod would cost less then GBP100 - and bring the MDAC1 upto date with 192KHz USB support :)
 
Yes, once I've laid out the USB input PCB section on the MDAC2 digital PCB, I can copy the section and design the external pod with little extra effort.

The Pod can also be used with the MDAC1 adding a clock-locked ASync isolated 192KHz USB port.

It might make a good SMD PCB production trial run here in Czech Rep - the pod would cost less then GBP100 - and bring the MDAC1 upto date with 192KHz USB support :)
Maybe on MDAC3, we can have the optical connection between the digital PCB (which would be in charge of the front panel, etc.) and the analog one. :)
(Perhaps with the option of using a separate PSU for the analog PCB.)
(And an amplifier with good PSU noise rejection.)
 
I am looking forward to the MDAC2 L3 (+ TDAC) and the VFETS immensely. Now I have ample shelving and some nice speakers in place (Amphion Argon 3L). The speakers are a compromise but I think they will be absolutely fabulous-sounding with the VFETS and MDAC2 as a pre/dac from my computer source. Now I have time to run in the speakers and adjust my hearing to their voicing before I receive the MDAC2 and the VFETS. And I look forward to the day when I will drive down through Germany and further on into the Czech Republic to pick up the MDAC 2 and VFETS.

Do you have any suggestion as to which speaker cable to use?
I have two lengths of QED XT400 that seem to work fine, but I am always open to suggestions from your hand.

Also: what sort of power cables will be suitable for use with the VFets?

I really enjoy the discussions here and your calm and considered answers and progress reports!

Kind regards,
Peter
 
Maybe on MDAC3, we can have the optical connection between the digital PCB (which would be in charge of the front panel, etc.) and the analog one. :)
(Perhaps with the option of using a separate PSU for the analog PCB.)
(And an amplifier with good PSU noise rejection.)

The MDAC2 will implement a Galvanic isolation barrier between the Digital & Analogue Domains. It might be necessary to charge extra for this option - it just depends on costing if we have the budget it will be included as standard.

Full galvanic isolation will require the full size Chassis with its separated Analogue and Digital PSU.
 
I am looking forward to the MDAC2 L3 (+ TDAC) and the VFETS immensely. Now I have ample shelving and some nice speakers in place (Amphion Argon 3L). The speakers are a compromise but I think they will be absolutely fabulous-sounding with the VFETS and MDAC2 as a pre/dac from my computer source. Now I have time to run in the speakers and adjust my hearing to their voicing before I receive the MDAC2 and the VFETS. And I look forward to the day when I will drive down through Germany and further on into the Czech Republic to pick up the MDAC 2 and VFETS.

Do you have any suggestion as to which speaker cable to use?
I have two lengths of QED XT400 that seem to work fine, but I am always open to suggestions from your hand.

Also: what sort of power cables will be suitable for use with the VFets?

I really enjoy the discussions here and your calm and considered answers and progress reports!

Kind regards,
Peter

Peter,

The VFET design has progressed significantly this past month and is now taking its "final" form - its pretty cool to start seeing the design coming together.

I've been purchasing NOS components in Bulk for the VFET project (not just the VFETs), items like the really really nice Bargraph displays, very high quality silver plated Air core trimmer capacitors for the Bridge balancing etc.

I'm really really excited about the VFET amps as they are just so different and so advanced to anyother analogue amplifier design on the market.

I also managed to source a few more pairs of VFETs :) I'm jealously guarding them :p

I'm not the one to ask about Speaker cables, I've been using Solid Flat core cable I had as free samples back in the early 90's... but I do recommend Bi-Wiring if your speakers allow.
 
Thanks John. The Amphion Argon 3Ls are not bi-wireable, alas. I will stick with the QED XT400 speaker cables then ...

I saw your posts with the Bargraph displays - I like the look of them. I follow this thread religiously every day, so I am up to speed with regard to your progress. At times, however I too lose track of some of the info you provide because the thread sometimes moves in mysterious patterns that conceal while revealing new info.:D

By the way, I am curious to know what pattern you decided on for the sides of the VFETs. But I suppose you will let us know when that happens.:)
Peter
 
Thanks John. The Amphion Argon 3Ls are not bi-wireable, alas. I will stick with the QED XT400 speaker cables then ...

I saw your posts with the Bargraph displays - I like the look of them. I follow this thread religiously every day, so I am up to speed with regard to your progress. At times, however I too lose track of some of the info you provide because the thread sometimes moves in mysterious patterns that conceal while revealing new info.:D

By the way, I am curious to know what pattern you decided on for the sides of the VFETs. But I suppose you will let us know when that happens.:)
Peter

I've still not settled on the heatsink side panel pattern yet - rather I've concentrated on internal design, PCB layout & the front panel design which I still have to slightly tweak to allow the slot loader on the matching full width MDAC2 chassis to be nicely positioned.
 
A quick update on the MDAC2 Analogue stage testing.

The MDAC2 is the first product that I've designed almost ground up with the aid of computer simulations.

Now that I have been able to re-establish my lab, I've had the chance to verify some of the more difficult to measure simulation results.

Working on the first version of the MDAC2 ClassA output stage had me worried for the past few days as the measured results and simulated results where very different. I had no way of knowing if it was a measurement or simulation error.

Dominik made the rather obvious suggestion to measure an off-the-shelf commercial Opamp and compare my measured results with the manufacturers Data sheet.

So I built a simple test circuit and was able to confirmed its a measurement system error - which I've now resolved.

Back to measuring the MDAC2 PCB and the results are now within the "correct ball park" the simulated results are still better, but I'm now able to optimise the component values on the PCB to achieve the design targets.

I'm chuffed that I can now "complete the circle" and confirm / tweak the "real hardware" so that I can close the gap with the simulated results.

The MDAC2 design is so complex that it can only be designed with the aid of the computer simulator so it was important that the real world and simulated result agreed with each other - otherwise I'd be in real trouble!

I hope that by the end of this month I'll have the most "feared" part of the analogue board tested and debugged.

I'm leaving confirmation of the clock performance for last as parts of the new test system are still in shipment - components of the system are so large and heavy that they are being shipped via Sea Cargo.

I'm not concerned about the clock performance at this stage, the design has been confirmed "Good" with the earlier Prototype PCB. Really the purpose of the new system is just to optimise the clock design - its "great" as it is, but I'd like to be sure its optimised to the very best performance the design allows. The clock performance is so fundamental to any DAC's performance that we want the very best - and to be able to provide the measured results to prove it!

Fingers crossed for the MDAC2 analogue stage!!! atleast I have access to the lab once again to confirm and debug if I encounter any difficulties and its reassuring to see that "So far" the simulated results are "workable", while not totally accurate they are still an important design tool.

The VFET amplifier circuit has also be designed and optimised via the use of the simulator, so again the results of the MDAC2 analogue board will help be critical to the "confidence" of the VFET design - pushing boundary requires support! :)

I'm very much pushing the boundary's of my design abilities with the MDAC2 / VFET amplifier circuits - so its really important that I can trust the simulation results.

Wow - after all of this work, they had better be stunning! I've been working for more then 3 years on the MDAC2 project, that's a far chunk of my working career.... Yes, I'm getting nervous as its all starting to come together finally! :)
 
Lovely to hear this progress John, well done!

I'm really not enjoying my Music these days and eagerly awaiting your Masterpiece!!!

Best regards

Paul

Ps. I am curious about the BiWire statement you made recently; not intending to sound sceptical but how does BiWire benefit? I stopped BiWiring (not BiAmping though) because I was playing with some Canare Quad core cable a few years ago, Shotgunning from a Tag 250MR monoblock to B&W 804S vs. twisting both 2.5mm core ends to make a single thicker 5mm core - I was bemused to find (in this particular instance) that the Shotgunned approach made the treble sound screechy and mids thin !!! It was unbelievable and the only time I have ever really heard speaker cable make a real difference ...besides QED Silver Anniversary which has a similar sCREECHy effect on full range speakers treble..because the gauge is too thin IMO ;-)
 
Wow - after all of this work, they had better be stunning! I've been working for more then 3 years on the MDAC2 project, that's a far chunk of my working career.... Yes, I'm getting nervous as its all starting to come together finally! :)

We trust in you! :)

Thanks for the update!
 
John,

Regarding the new clock circuit. Do you think an external 10MHz master clock could be beneficial for a single MDAC2 or a slave configuration?

Michael
 
John,

Regarding the new clock circuit. Do you think an external 10MHz master clock could be beneficial for a single MDAC2 or a slave configuration?

Michael

Michael,

I'm presuming your thinking of a GPS derived 10MHz clock or rubidium?

The shortterm phase noise (the Jitter that matters the most) is determined by the MDAC2's internal clocks performance the external clock is only used for longer term (think in orders of Seconds and greater) synchronization.

My gut reaction is to say there will be no benefit, but the proof will be in the listening.
 
Lovely to hear this progress John, well done!

I'm really not enjoying my Music these days and eagerly awaiting your Masterpiece!!!

Best regards

Paul

Ps. I am curious about the BiWire statement you made recently; not intending to sound sceptical but how does BiWire benefit? I stopped BiWiring (not BiAmping though) because I was playing with some Canare Quad core cable a few years ago, Shotgunning from a Tag 250MR monoblock to B&W 804S vs. twisting both 2.5mm core ends to make a single thicker 5mm core - I was bemused to find (in this particular instance) that the Shotgunned approach made the treble sound screechy and mids thin !!! It was unbelievable and the only time I have ever really heard speaker cable make a real difference ...besides QED Silver Anniversary which has a similar sCREECHy effect on full range speakers treble..because the gauge is too thin IMO ;-)

I can only speak from personal experience and Bi-Wiring has always improved matters. I can think of a handful of times I tried it on my own speakers, but mostly with systems at shows.

I Bi-Wired my own ESL's (as they had separated transformers for Bass + HF) and it made a big difference.

OTOH, I've read many negative comments about Bi-Wiring here on PFM which really surprised me in light of my own experiences.
 
I can only speak from personal experience and Bi-Wiring has always improved matters. I can think of a handful of times I tried it on my own speakers, but mostly with systems at shows.

I Bi-Wired my own ESL's (as they had separated transformers for Bass + HF) and it made a big difference.

OTOH, I've read many negative comments about Bi-Wiring here on PFM which really surprised me in light of my own experiences.

John, there are three wiring configurations for loudspeakers using single amplification on each channel:

1) Single wiring via the jumper bars joining the HF and LF terminals at the rear of the speakers.

2) Removing said jumper bars and bi-wiring.

3) Single wiring, removing the jumper bars and replacing them with proprietary short runs of cables terminated with quality connectors.

The third option is better, IME for dynamics and timing.

These are mine:

 
Agreed, but I'm not sure if I can face another round of the Wailin Jennys - they bring back to many bad memory's of the hard time at IAG China when we developed the 8200CD / MDAC and the Huge listening effort required during the original MDAC upgrade process.

You should try some classical music John. :D :D :D
 
That never works for me: if it's a favourite, I forget I'm supposed to be in 'critical' mode and just enjoy the music. Could try early Baroque, I suppose. :)
 
That never works for me: if it's a favourite, I forget I'm supposed to be in 'critical' mode and just enjoy the music. Could try early Baroque, I suppose. :)

There is a third mode:

Being critical of any changes that may be more enjoyable.
 
There's another theory that says you should listen to something in your collection that previously you have been disappointed with, such as tracks by a favourite artist that haven't hit the mark for you. I suppose the idea is that this might make it easier to detect improvements.
 
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