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MDAC First Listen (part 00100100)

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ChrisPa said:
I keep thinking about minimum phase margin sounding best.

It doesn't innately feel right.
Artificially "Peaking" the signal seems like compensating for something which may be deficient elsewhere.
I don't dispute what you've observed.

I assume you're referring to phase margin in the output amplifier stage?
I guess though it also depends on what phase margin at what frequency, and also on the overall loop bandwidths, open and closed
Click to expand...

I do agree, if only because its technically wrong (and feels like cheating), during simulations I target over 75Deg to approach critical damping - the only mention I could find about PM and sound quality was a rather Cryptic quote along the lines:-

"Everyone's aware that 82Degs sounds optimal..." Well I certainly was not, and considering I could find no other reference to PM and its relationship to SQ I'd be keen to hear from other designers with there own experiences.

Interestingly, 'Unity Gain stable Op-amps' seem to target 45Deg PM at Unity Gain, and this is too tight IMO - 45Deg PM results in well over 20% overshoot.

Every designer is aware that over compensating an amplifier kills the sound, but what's 'Optimal' from the perspective of SQ? some would say the least you can get away with - which makes me wonder if a little "peaking" is preferred as I would theories it subjectively enhances detail. (I'm not suggesting this is a valid approach, but its an interesting observation if true).

You are correct that I could be compensating for the MDAC's design or my systems defiances... which is one of the reason I've built a listening room above the lab where I can install my ESLs + designing the VFET reference amplifiers + MDAC2 :)

Once the labs installed I've got a HP / Agilent network analyser (and small signal Current probes) and plan to break the MDAC2's FB loop to see how close the hardware matches the simulation results - and how stable the PM is between boards.

Yes - I'm referring to the MDAC's gain stage PM. The CL phase response within the audio BW is practically flat.

The MDAC2's Bode plot is rather odd as its a 2nd order multiple nested feedback design - which I could only consider designing (and optimising) with the aid of computer simulation.

Maybe on the MDAC2 we can adjust the Q of the Digital filters to see its effect on SQ - also the Q of the NS modulators at a later date...
 
Hi John, did you manage to get to the post office at all? You were going to send me a couple of M-DAC relays! :D . Don't worry if it takes a while, as I've got other things to do.
 
ilmostro749 said:
Hi John, did you manage to get to the post office at all? You were going to send me a couple of M-DAC relays! :D . Don't worry if it takes a while, as I've got other things to do.
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Oh, I'm so sorry, totally forget, and the reallys have been bugging me on the lab bench.

In the next couple of days I'll be shipping a MDAC - I'll post your relays then - Can you please PM or Email me your details once again.
 
JohnW said:
Oh, I'm so sorry, totally forget, and the reallys have been bugging me on the lab bench.

In the next couple of days I'll be shipping a MDAC - I'll post your relays then - Can you please PM or Email me your details once again.
Click to expand...

There's probably one dated 31/12/14 in your inbox. If you PM me your email address, I'll send you the details.
 
Hi everybody, i rarely post on this forum, but i try to follow the posts every week and the progress of the MDAC2 project.

First, i have to say that i very happy with the stock version of the MDAC. I use it with a restored QUAD 909 (with attenuators) and a pair of ATC 40 SCM. Sound is really great.

I have 2 questions to ask to the forum :

1) I meet problems with the RCA digital output slots. Since they are not screwed onto the chassis, the both are now pulled out, and not fixed, just put on the chassis. That work anyway, but for how long time ?
My question is : what do you think about replacing the original digital RCA slots by robust BNC slots, screwed and 75 ohms certified ?

2) I'm really interested by an updated MDAC L2 Toy with AV bypass. Is it still possible to order this upgrade ?

See you.
 
John, Could we have an update please on MDAC2? When can we expect to see the boards and instructions being shipped?

Thanks
 
Hello,
there seem quite a lot of satisfied hypex nCore users in the MDac crowd. I never heard someone mentioning Abletec/Anaview boards which seem to be quite promising (and cheaper) in comparison. Very good user reviews here http://www.diy-hifi-forum.eu/forum/showthread.php?t=7552 for example, especially with the latest AMS 1000-2600 amplifier board. The units are used in several commercial amps and active speakers.

Has someone used that with MDac?

What troubles me a bit is that the best amplifier technique by Anaview is only available as stereo unit, so building mono blocks is not possible (except with bridging 2 stereo amps which seems to be quite overkill with 900 W each). Previous top end ALC 0300-1300 seems to be inferior, although some thought better than nCore 400 :eek:.

How much can be lost by using stereo amp in rack with long speaker cables instead of long XLR/short speaker cables at mono blocks?
 
pdes said:
John, Could we have an update please on MDAC2? When can we expect to see the boards and instructions being shipped?

Thanks
Click to expand...

pdes,

I'll be issuing the Analogue board PCB files within the next 2 weeks, I'm in the process of completing the board, tidying up small areas and double checking the design - this is a major design goal, the digital board should be completed within 2 months, once I've built and tested the Analogue PCB.

I month or so ago, I posted a detailed reply with the remain stages.
 
Asphaltradler said:
Hello,
there seem quite a lot of satisfied hypex nCore users in the MDac crowd. I never heard someone mentioning Abletec/Anaview boards which seem to be quite promising (and cheaper) in comparison. Very good user reviews here http://www.diy-hifi-forum.eu/forum/showthread.php?t=7552 for example, especially with the latest AMS 1000-2600 amplifier board. The units are used in several commercial amps and active speakers.

Has someone used that with MDac?

What troubles me a bit is that the best amplifier technique by Anaview is only available as stereo unit, so building mono blocks is not possible (except with bridging 2 stereo amps which seems to be quite overkill with 900 W each). Previous top end ALC 0300-1300 seems to be inferior, although some thought better than nCore 400 :eek:.

How much can be lost by using stereo amp in rack with long speaker cables instead of long XLR/short speaker cables at mono blocks?
Click to expand...

Abletec once visited us in China, and while there modulator has some merits (no modulator beating between channels), I don't see them as a major advanced over NCores.... and they are expensive.

There THD figures are inferiour to Ncores / UCD.
 
John, my M-DAC is on its way out to you. Says 3 days, so Thursday with any luck. Let me know what I owe you for return postage. The little rDac is trying its best but can't do the job as well. Cymbals are really compressed and the sound stage all thin. Not a fair comp though as I'm using the volume on the sonos so it's not bit perfect.
 
pdes said:
John, Could we have an update please on MDAC2? When can we expect to see the boards and instructions being shipped?

Thanks
Click to expand...

This is what you are looking for

JohnW said:
Bob,

A far question :)

To save further embarrassing myself with timescales its better to detail the remaining project stages:-

1. Issue prototype Analogue PCB (files target Jan 30th) PCB revision A01 (GBP100 L2 payment requested at this time).

2. Visit China to arrange MDAC2, MDAC2 Slave, TDAC & VFET amp chassis, and also during this trip meet with Dominik to finalise the schematic blocks of the Digital section.

3. Upon return form China (About 7 day trip) Build and test Analogue PCB, update any corrections / modifications issue production Analogue PCB V1.00

4. If reasonably confident in updated analogue PCB designs, create paperwork and technical data for Preproduction of the Analogue PCB

5. Maybe fly to China for a couple of days to approve Chassis for MDAC2 (rear panel), MDAC slave and VFET / TDAC etc.

6. While the Surface Mount PCB production vendor starts the production cycle of Analogue PCB (place component orders etc) – I be designing the Digital PCB (it’s a much sampler design to the Analogue PCB, thus quicker about 2 months required)

7. Issues Digital Prototype PCB files Rev A01 (GBP100 “L3 ADC versions” Payment requested)

8. Build test and correct any design errors on Digital PCB (Dominik will have “test” MDAC2 software at this stage).

9. Start Prototype production of digital PCB.

10. Test Pre Production analogue boards.

11. Test Pre Production Digital boards / Completed MDAC2 assembly.

12. Full MDAC2 production.

First “Demo versions” of MDAC2 around April / May – with full production units no later then June.

June might sound a long way away, but the project will accelerate once the Analogue PCB files have been issued, as the design of the Analogue board is by far the most challenging stage of the project – I’ll (we) will be able to have a “first listen” of the MDAC2 in very basic form once I build the prototype A01 Analogue board, sometime in late February – from then on the project will progress rapidly.

I'll also need about 2 weeks at sometime to install the equipment in the new lab which will is required for production testing of MDAC2 and VFET amp etc.
Click to expand...
 
therixonator said:
John, my M-DAC is on its way out to you. Says 3 days, so Thursday with any luck. Let me know what I owe you for return postage. The little rDac is trying its best but can't do the job as well. Cymbals are really compressed and the sound stage all thin. Not a fair comp though as I'm using the volume on the sonos so it's not bit perfect.
Click to expand...

I'll turn your unit around the same day it arrives :)

I'll forward the return postage cost once Renata's posted it :)
 
Rune,

Thank you for digging up the post, I've got my head so buried in the PCB design that my minds rather "single tracked" ATM - I felt bad that my answer to pdes was brief and lacked relevant information.
 
tull_hifi said:
Hi everybody, i rarely post on this forum, but i try to follow the posts every week and the progress of the MDAC2 project.

First, i have to say that i very happy with the stock version of the MDAC. I use it with a restored QUAD 909 (with attenuators) and a pair of ATC 40 SCM. Sound is really great.

I have 2 questions to ask to the forum :

1) I meet problems with the RCA digital output slots. Since they are not screwed onto the chassis, the both are now pulled out, and not fixed, just put on the chassis. That work anyway, but for how long time ?
My question is : what do you think about replacing the original digital RCA slots by robust BNC slots, screwed and 75 ohms certified ?

2) I'm really interested by an updated MDAC L2 Toy with AV bypass. Is it still possible to order this upgrade ?

See you.
Click to expand...

try this link to the board page and paypal payment section

http://mdac2.lakewestaudio.com/
 
@JohnW Could I make a couple of constructive suggestions?

1) Update the mdac2.lakewestaudio.com page with best guess dates
2) Put something in your signature on the forum that has a link to that page, e.g. "to find out how the MDAC2 project is coming along, click here"
3) Once a month, take 5 minutes to glance over the dates on the mdac2.lakewestaudio.com page, and update as necessary


I think this would make the natives happy, and reduce the number of times people have to ask about this.

Just my thoughts. Personally I am relaxed about it, but it's hard to know how the people who have made the first payment are feeling right now. It doesn't need to take a huge amount of time.
 
wintoid said:
@JohnW Could I make a couple of constructive suggestions?

1) Update the mdac2.lakewestaudio.com page with best guess dates
2) Put something in your signature on the forum that has a link to that page, e.g. "to find out how the MDAC2 project is coming along, click here"
3) Once a month, take 5 minutes to glance over the dates on the mdac2.lakewestaudio.com page, and update as necessary


I think this would make the natives happy, and reduce the number of times people have to ask about this.

Just my thoughts. Personally I am relaxed about it, but it's hard to know how the people who have made the first payment are feeling right now. It doesn't need to take a huge amount of time.
Click to expand...

Taken Constructively :)

I'll aim to follow that suggestion as soon as the Analogue PCB had been issued - especially updating the webpage.

Once the PCB has been issued then project progress will be far more rapid :)
 
JohnW said:
Tweaking component values that effected the Phase Margin of the design had a profound effect on sound quality

Lowest Phase Margin sounded the best - Greatest detail etc...

PM was a balance between "Bass impact / foot tapping inducement" and fine detail / sound stage... unfortunately with the MDAC design they seem to be diametrically oppose each other - I'm not sure if this is always the case, I'd certainly like to believe not :) - especially for the MDAC2 :)
Click to expand...

Would there be a possibility to include some kind of user tweakability in order to make up for component drift (without box intrusion, that is)?
 
Hi John,
Looks like i need a new cd player as my pink triangle litaural has started to die after nearly 20 years of great trouble free service. I'm on the list for m and t-dacs.
Any advice re new cd player-
Should I go for stand alone transport(optical /coaxial /balanced?). Is it worth hunting down a player with clock lock function like my old litaural?.
I see audio lab have a transport out-is it likely to be good enough for the mdac2?
Or is a any cheap cd/ dvd player with digital out good enough?
At the other end of the transport world there are the likes of the cyrus signature -any thoughts would be much appreciated,
cheers.
 
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