Thread: DacMagic Plus PSU

Has anyone tried to use another PSU for the new DacMagic Plus from Cambridge Audio? Any advice on this and candidate replacement PSU's welcome. Thanks!

Someone mentioned using "a lab power supply". If you're looking for a nice clean variable supply, then a lab supply would do quite well (and they've gotten quite cheap lately). You should recognize, however, that most lab supplies these days are switchers. If you want to try a 12v switcher, your cheapest option would be a 12v 4 amp power "brick" intended to run most LED computer monitors and such (you can get them on eBay for about $10). If you want a 12v linear power supply, you're going to have to specifically shop for one.

Likewise, you can get a 12V LiIon rechargeable battery with a charger on eBay for about $30 - they're intended for security cameras and such devices, but they work fine for anything that wants 12v (many LiIon packs put out 11.7 V or so, which is just right). You get a nice little plastic unit with a plug for the power wire, a switch, and a wall charger - all made up for you.

I would also like to mention that you should not confuse "quiet" with "low impedance". Batteries are very quiet because there's no AC involved in how they work (although some put out low level noise from the chemical processes themselves). However, the impedances of various batteries vary considerably. Specifically, lead-acid batteries (gel-cells) are very low impedance; LiIons are somewhat low impedance; (NiCds are low impedance if you can find them - although they have other issues); other batteries like NiHm and disposable alkalines are NOT especially low impedance. Larger capacity batteries also have lower impedances (so a D alkaline has a MUCH lower impedance than an AA alkaline.) So, for example, running a USB-to-S/PDif converter from a pack of AA Duracells will get you a low noise supply, but the impedance won't be very low at all - it won't be nearly as low as that of a reasonably well designed AC supply.

Using batteries, and then adding a regulator sort of defeats the point of using batteries since a well designed regulated supply running off of AC should work as well as batteries anyway.

Originally Posted by JonP

The 12.76 volts is unlikely to matter too much. If that were to cause issues then I would consider this to be very bad design on the part of Cambridge. When I used to own the original Musical Fidelity V-DAC I powered it directly from a 12 volt SLA battery without any regulation at all.

You would not be able to use a Belleson (or any other) regulator with just a 12 volt SLA battery, because the drop-out voltage at the required current draw is too high.

So in the case of the DAC Magic Plus, if it were me I would probably acquire 3 x 6 volt SLA batteries such as these:

12.0 Amp Hour 6 Volt Sealed Lead Acid Battery - Jaycar Electronics

and run them in series. According to Cambridge specs, the DAC Magic Plus requires a 2 amp input, so you would actually have to buy 2 of the Belleson high current 7812 series substitute regulators and run them in parallel (their older versions used to be 2 amps each, but they have changed the design and it is now 1 amp).

You would then need a fairly large heatsink as well due to the input-output voltage differential and the current draw.

All of that will be quite expensive (and more expensive again if you add buffering capacitance to the inputs and outputs of the twin regulators).

I'm currently building something very similar for my Heed phono amplifier - the batteries cost me $180 (6 x 6 volts), the two regulators about $150, the capacitors another $40 and other components, case, hardware etc about $40. So it isn't cheap unfortunately and I could probably get a commercial AC supply for much less than that (but it would not sound as good).

You could also consider writing to Mike at Rock Grotto and see if he can make a custom Little Pinkie for you specially for the Cambridge. It would not sound as good as the Belleson based supply mentioned above but it would be substantially cheaper and you won't have to muck around with electronics, circuit boards, soldering irons, batteries, etc. It would also benefit from a power cord upgrade down the track such as an entry-level Wireworld.

Playing Devil's advocate here....

Assuming that your AC supply is well designed and well filtered - in which case ALL of the line frequency and noise on the AC line will be removed by it - what, precisely, will enable "a better power cord" to "make it sound better"?

Assuming that your power supply delivers properly filtered, clean, low impedance DC, then what will changing the line cord do to change that? (Remember that we are still running off the same (presumably crappy) line voltage.) IF you can hear a difference with a different line cord, then doesn't that suggest that the power supply is NOT doing its job properly?

Thanks for the 12V LiIon battery tip. I am in need for a 15V battery solution. Do you have any creative suggestions? Couldn't find anything on Ebay. I am not much (at all) of an electronics guy, so plug-n-play would be my preferred option, like your suggested 12V battery packs.

Thanks & Cheers

Originally Posted by kLevkoff

Someone mentioned using "a lab power supply". If you're looking for a nice clean variable supply, then a lab supply would do quite well (and they've gotten quite cheap lately). You should recognize, however, that most lab supplies these days are switchers. If you want to try a 12v switcher, your cheapest option would be a 12v 4 amp power "brick" intended to run most LED computer monitors and such (you can get them on eBay for about $10). If you want a 12v linear power supply, you're going to have to specifically shop for one.

Likewise, you can get a 12V LiIon rechargeable battery with a charger on eBay for about $30 - they're intended for security cameras and such devices, but they work fine for anything that wants 12v (many LiIon packs put out 11.7 V or so, which is just right). You get a nice little plastic unit with a plug for the power wire, a switch, and a wall charger - all made up for you.

I would also like to mention that you should not confuse "quiet" with "low impedance". Batteries are very quiet because there's no AC involved in how they work (although some put out low level noise from the chemical processes themselves). However, the impedances of various batteries vary considerably. Specifically, lead-acid batteries (gel-cells) are very low impedance; LiIons are somewhat low impedance; (NiCds are low impedance if you can find them - although they have other issues); other batteries like NiHm and disposable alkalines are NOT especially low impedance. Larger capacity batteries also have lower impedances (so a D alkaline has a MUCH lower impedance than an AA alkaline.) So, for example, running a USB-to-S/PDif converter from a pack of AA Duracells will get you a low noise supply, but the impedance won't be very low at all - it won't be nearly as low as that of a reasonably well designed AC supply.

Using batteries, and then adding a regulator sort of defeats the point of using batteries since a well designed regulated supply running off of AC should work as well as batteries anyway.