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MDAC First Listen (part XXVI)

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sq225917 said:
They will be able to do all that crap in DSP on the FPGA, should the demand arise.
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Beat me to it :) Dominik's was a big headphone fan - so I'm sure he has his own personal interest to add a Crossfeed mode with later FPGA firmware :) that's the beauty of having the FPGA on the board.
 
jirij said:
I can confirm that.

Most of the issues I had when using my recabled/balanced K702 disappeared over some weeks of using the MDAC with a different kind of headphones, could the initial "run-in" / "burn-in" take that long? My first listen to the upgraded MDAC was after good 5-6 hours of playback - perhaps it wasn't enough.
Needless to say, the recabled AKG K702 are not really forgiving when it comes to bad/mediocre/decent recordings, which I have lots of - it takes quite a lot of effort to fill the L-R "range" so that it sounds like a room with musicians. The lack of reflections and the extent of instrument separation really got me there. However that's a good thing when it comes to a DAC, right?

I borrowed older Sennheiser HD600 headphones from a friend and the sound is indeed more "pleasant", so I guess it was just me having headphone problems with the upgraded MDAC. :)
Sorry for the false alarm.
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Its the nature of HiFi - all about balance and matching!

I still want to get your DAC back here for a few hours to perform a small modification that I've been adding to recent units :) so maybe one weekend soon... :)
 
JohnW said:
Malyq,

I've been told by many that the headphone output is even better on the Fusion'ed MDAC - your unit is in the next batch so looking forward to your feedback :)
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These are really good news, John - and something to looking forward to, when I am back from vacation in two weeks... :)
 
JohnW said:
Its the nature of HiFi - all about balance and matching!

I still want to get your DAC back here for a few hours to perform a small modification that I've been adding to recent units :) so maybe one weekend soon... :)
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I'm quite sure we'll see each other sometime during November at least as I also need some time to develop a viable linux kernel based USB testing platform, suitable for my laptop, so that we can simulate at least some commonly used linux-based NAS boxes and other devices when testing the prototype board.
However I hope to visit you sooner than that. :)
 
JohnW said:
The only area where the MDAC2's "Original" headphone amplifier would have be less then optimal would have been into very low impedance loads where beyond about 100mA the output stage would drop out of Pure ClassA operation into ClassB.

This would never be be an issue with normal use - but very low impedance headphones current requirments could exceed 100mA - such as the HiFi Man ribbon headphones which really need a small power amplifier.

The idea is to design a "sliding class A circuit" where the heat dissipation can be kept under control - but if current is required beyond 100mA the circuit would insure the output stage remains in classA operation...

I'm also going to try using a MOSFET output stage... so ClassA Mosfet design...
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Am I right that low impedance headphones would run better with the discussed tuning of the headphone amp section? If yes, it may help the Grado Headphones (32Ohm) I am using daily. So, yes!!

Jansen
 
JohnW said:
Question:-

For MDAC2 how important is the headphone output? - should I devote a little effort to making it a substitute for an ultra high end headphone amp?
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Yes please! Would help to drive also Audeze HPs I guess.
Hopefully it won't degrade overall SQ in any way when feeding amps/speakers, but as we know you John for being perfectionist, I believe it wont :)
 
JohnW said:
I'm also going to try using a MOSFET output stage... so ClassA Mosfet design...
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Can you avoid the problem of such a stage constantly drawing lots of power (and getting rather hot) when the user may not actually use the headphone facility from one year to the next?
 
Plutox said:
Can you avoid the problem of such a stage constantly drawing lots of power (and getting rather hot) when the user may not actually use the headphone facility from one year to the next?
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Well that's the idea behind the sliding ClassA - under normal operation I'll bias the FET's at 50mA each on 10V rail - so 0.5W dissipation per device which is easily manageable - with the sliding bias circuit modulating the standing current if required (important to remember that a standard AB circuit will dropout of ClassA at about 2x standing current so 100mA without the bias modulation).
 
Only me seeing some derailing from what I think at least some of us agreed upon i.e. KISS.

Only trying to protect the project ... ;-)

/Lars
 
LarsS said:
Only me seeing some derailing from what I think at least some of us agreed upon i.e. KISS.

Only trying to protect the project ... ;-)

/Lars
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Lars,

If your worried about a circuit perspective its quite simple - I'm using a circuit I'd worked upon for the MIMP - I'm just investigation wither its feasible with the MDAC's lower rail voltages.

Target is say to maintain ClassA operation upto 500mA - you would be able to drive horn speakers at that level :)
 
shaolin said:
Yes please! Would help to drive also Audeze HPs I guess.
Hopefully it won't degrade overall SQ in any way when feeding amps/speakers, but as we know you John for being perfectionist, I believe it wont :)
Click to expand...

The Audeze LCD-3 are rated at 50ohms - Fusion'ed / TOY MDAC's can already drive these - anyone know how much voltage swing is required?
 
John,

Only talking as a Project Manager (in IT), have no idea about electronic circuits any more even if I used to work with radars in the 70's.
However I do have long extensive experience from skilled IT subject matter experts and creative proposals which sometimes lead to scope & time schedule creep. I do appreciate your creativeness, skills and have no intention in trying to stop that, on the contrary. Let's await your final design and make that happen.

/Take care
Lars
 
LarsS said:
John,

Only talking as a Project Manager (in IT), have no idea about electronic circuits any more even if I used to work with radars in the 70's.
However I do have long extensive experience from skilled IT subject matter experts and creative proposals which sometimes lead to scope & time schedule creep. I do appreciate your creativeness, skills and have no intention in trying to stop that, on the contrary. Let's await your final design and make that happen.

/Take care
Lars
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Apprecatied - you can see my weakness :rolleyes:
 
John,

would it be OK if I join the regular MDAC2 upgrade list (including installments) for a salvaged unit? I need a 2nd DAC for my desk.

Michael
 
LarsS said:
John,

Only talking as a Project Manager (in IT), have no idea about electronic circuits any more even if I used to work with radars in the 70's.
However I do have long extensive experience from skilled IT subject matter experts and creative proposals which sometimes lead to scope & time schedule creep. I do appreciate your creativeness, skills and have no intention in trying to stop that, on the contrary. Let's await your final design and make that happen.

/Take care
Lars
Click to expand...
I too was initially kind of baffled why John implements anything almost anyone comes up with - from a PM perspective, that's nonsense, increasing the costs / time with no interest scoping, possibly leading to features that negatively affect the entire project. I don't think he has done a proper WBS decomposition, basic Gannt chart or risk analysis for the MDAC2 project. Am I wrong?

Then I understood how he works, his rather personal approach to the entire thing, found out more about the "man-day" to "john man-day" ratio, ..., and realised that his kind of business actually works in this community. Apparently quite well, I should add. :)

All the management stuff isn't really *that* useful for a team of 2-3 people (counting Renata) anyway. And as long as one can stretch the "when" in the triple constraint, more energy can be focused at "what", eg. increasing the quality, which is what matters to people here. :)

In the end, I guess everybody wins.
 
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