New M-dac power supply

[Marco]

Yes to the last one, and no to the first one. Everytime I compare it with something modern, and arguably technically 'better', the old timer has the audacity to win!!

So it gets bored trying... Both Nick and Anthony have heard my DAC and know of its sonic capabilities.

Perhaps this could be a new challenge, though?

Marco.

[Marco]

The other thing too, and this is aimed at Simon...

If there wasn't any mileage in making a more highly specified off-board PSU for the M-DAC, then why is John Westlake giving advice on this thread on pfm, as to how best to do precisely that:

http://www.pinkfishmedia.net/forum/s...d.php?t=120306


...with people building stuff like this, in order to gain a sonic improvement:





Surely if there was no sonic benefit to be had, like Simon suggests, the manufacturer (who, after all, knows best) would say so, and wouldn't be wasting people's time guiding them through building a DIY PSU?

Marco.

[sq225917]

Like I said they are all bypassing the internal AC/DC psu and providing regulated DC directly to the internal regs, not just replacing the external AC supply with a 'bigger transformer'.

[Marco]

Sure, I don't really care what the method is - it's the end result that matters!

Clearly, there are potential sonic benefits to be had by using a good DC (as opoosed to AC) power supply, to power the M-DAC, which means that the supplied AC one is a compromise, just as I originally suspected

Marco.

[anthonyTD]

Looking at the picture of the outboard power supply, it would seem that this is only the bare AC part, ie; the DC rectification and regulators are actualy inside the unit its powering, if this is correct then as long as the transformer is rated well for the load its intended to supply,[good basic regulation] then the rest is mostly up to how good the rectification, and regulator circuits perform inside the unit.
On another note, some people think that having banks of huge value capacitors is all that is needed for a good stiff power supply, unfortunately capacitors do not have a linear impedance with frequency, hence the need for well designed active regulators that have ultra low impedance way beyond the audio frequency bandwidth.
There are many people here who are well aware of what is needed to make such power supplies, so there is no need to teach people how to suck eggs.
A...

[Paul Hynes]

Hi Marco,

In principal any power supply can be improved with a little thought and attention to detail.

Firstly, quoting noise levels of –120 dB to –150 dB means little without qualifying the measurement spectrum and operating conditions for both the regulation and the load. All regulators have a limited bandwidth and it’s just a question of where their regulation ability starts reducing due to bandwidth limitations. Once the gain of the regulator error amplifier starts to roll off with increased frequency, the regulation capability reduces, as does the supply line rejection. Whilst the cascaded regulation used in the Mdac may well measure –120 dB to –150 dB at audio frequencies it can be an entirely different matter at 1 MHz, 10 MHz and 100 MHz. The cascaded low noise regulation combined with the SR7 used on your SL1210 easily achieves supply line rejection exceeding this well past 100 KHz, and does not run out of regulation capability until it gets well past 100 MHz. Upgrading the mains transformer is clearly audible even with this power supply as you are well aware.

Most regulators are virtually ineffective above 10 MHz. I should point out that the clock, used in the Mdac for timing the Sabre DAC chip, is likely to be clocking at frequencies in excess of 80 MHz. Anthony is quite right, capacitor banks have their limitations and regulators have to be designed with exceptionally wide bandwidth to have any effect at these signal processing frequencies, and they must be damn fast to allow stable signal processing whilst keeping supply reaction low. This is why I use 5,000 volts per microsecond regulator error amplifiers, with a 1 GHz gain bandwidth product, for the regulator kits I make for the Buffalo DAC, Eastern Electric Minimax DAC etc. which use the Sabre Dac chip, to keep regulation and supply line rejection going to the highest frequencies I can. My regulator kit for the Buffalo Dac, etc is internationally regarded as the best regulation available for the Sabre Dac chip.

I do not have information about the specification of the Mdac external supply but if anyone can provide the specification It is easy enough to design a custom high performance supply to replace it. This will prove the point one way or the other.

Regards
Paul

[sq225917]

Here the internal psu board schematic



and the pin out for the external trasformer

[Marco]

Hi Paul and Anthony,

Many thanks for your input. Anthony:

On another note, some people think that having banks of huge value capacitors is all that is needed for a good stiff power supply, unfortunately capacitors do not have a linear impedance with frequency, hence the need for well designed active regulators that have ultra low impedance way beyond the audio frequency bandwidth.

Interesting... Basically, it goes back to the tried and tested practice of keeping circuits as simple as possible and reducing the component count, wherever one can, in order to minimise unwanted interactions, thus potentially maximising the sonic effectiveness of the circuit. The best component, after all, is NO component. However, if one must be used, then use the best possible option for that specific application.

Paul, even though I'm not a technical person, I understand what you mean by this:

Firstly, quoting noise levels of –120 dB to –150 dB means little without qualifying the measurement spectrum and operating conditions for both the regulation and the load.

Which is why that judging equipment solely by 'the numbers' (measurements), without looking at the bigger picture, as it were, doesn't tell the FULL story! Simon, are you paying attention?

This is why it's completely pointless buying (or judging) equipment, solely on technical specifications, unless said specifications fully explain their relevance to the design(s) in question - and you *really* understand what the information given means. The fact is, the vast majority of end users of products will not have the required technical knowledge to make proper sense of the 'numbers'.

Therefore, that's why anyone without the level of technical knowledge, of the likes of Anthony or Paul, should ignore the spec, or at least don't treat it as an 'absolute', and always use their ears as the final arbiter, or otherwise be prepared to arrive at erroneous conclusions, based on only being in possession of part of the story. As they say, a little knowledge is dangerous...!

The cascaded low noise regulation combined with the SR7 used on your SL1210 easily achieves supply line rejection exceeding this well past 100 KHz, and does not run out of regulation capability until it gets well past 100 MHz. Upgrading the mains transformer is clearly audible even with this power supply as you are well aware.

Indeed. Even before your regulator mods were fitted to my T/T, upgrading from the SR5, to the SR7, with its massively bigger mains transformer, caused a notable improvement in sound quality, which proves that, with linear PSUs, one can never have too big a transformer (or transformers), providing of course that they are also of the requisite quality. That last bit is very important, as in that respect, not all transformers are equal.

In my experience, the better the mains transformer is to start with in a PSU, the better the end result will be, regardless of how good the regs are.

This would therefore suggest that even though, superficially, the M-DAC, due to its specific design, should not benefit from being fed by a bigger, better quality mains transformer, that it would not necessarily be the case if it were put into practice...

I do not have information about the specification of the Mdac external supply but if anyone can provide the specification It is easy enough to design a custom high performance supply to replace it. This will prove the point one way or the other.

Well, now that Simon has provided the circuit diagram, why not give it a go? In my opinion, it would be a valuable addition to your product range and would also prove to people that the PSU arrangement inside (and outside) of the M-DAC, good though it may be, is not yet the definitive article

Marco.

[realysm42]

Not long until I receive this to demo now; expect pictures and full write up...

[bobbasrah]

Not long until I receive this to demo now; expect pictures and full write up...

Excellent Martin, some facts are much appreciated...