• JPS70
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Topic: Running ADI-2 DAC from my power supply?

I have an old Musical Fidelity X-PSU and I'd like to use it to power the ADI-2 DAC. I need to be able to cut the power without turning off every other connection in the room. I've tried using it but the ADI-2 DAC is stuck on the red circle and won't boot. I'm not very good with electronics so I'm not sure if there is a mismatch somewhere that's causing the problem. Everything obviously works with the standard RME cables. https://www.musicalfidelity.com/uploads … h/xpsu.pdf

2 Reply by lewis71980 (edited by lewis71980 2023-05-30 20:00:53)

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Re: Running ADI-2 DAC from my power supply?

Hi there looking at the manual it says the output of that PSU Four @ 12V AC 20VA and the ADI-2 DAC requires 9-15v DC. So that's why it isn't working.

AC = Alternating Current
DC = Direct Current

  • KaiS
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Re: Running ADI-2 DAC from my power supply?

In general it’s a bad habit to plug random PSUs in devices.

The ADI-2 has some protections against over voltage and reversed polarity, but their effect is limited.
There’s even an internal, non-user-replaceable fuse inside.
If it breaks, you have to send ADI-2 in for repair.

If ADI-2 boots with it’s dedicated PSU nothing bad has happen at this point.

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  • weme
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Re: Running ADI-2 DAC from my power supply?

Interesting test:
But it would probably have been carried out by some other people as well. I asked about it. The reason given was the design of the X-PSU.

In the ADI-2 DAC, a negative voltage is blocked by a diode. The ADI-2 DAC was therefore operated with a pulsating DC voltage: approx. 18 V max. with a frequency of 25 or 30 Hz (1/2 of mains frequency).

JPS70 wrote:

I have an old Musical Fidelity X-PSU and I'd like to use it to power the ADI-2 DAC.

An X-PSU (only toroidal transformer) could drive an ADI-2 DAC via an AC-DC linear regulator (output approx. 10V).


By the way, you can laugh with us here - a toroidal transformer (X-PSU) is said to be able to "do magic":
"... the midrange becomes more warm and clear, and timbre improves overall. There is a much greater sense of space, and the sound at both the low and high frequency extremes is even more detailed and exciting. The listener is able to hear the "sting" of cymbals and the precision of drum rolls better. ..."
http://listeninn.com/Website/Used-Other … U-Info.htm

5 Reply by KaiS (edited by KaiS 2023-06-04 14:28:38)

  • KaiS
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Re: Running ADI-2 DAC from my power supply?

weme wrote:

Interesting test:
But it would probably have been carried out by some other people as well. I asked about it. The reason given was the design of the X-PSU.

In the ADI-2 DAC, a negative voltage is blocked by a diode. The ADI-2 DAC was therefore operated with a pulsating DC voltage: approx. 18 V max. with a frequency of 25 or 30 Hz (1/2 of mains frequency).

This is not exactly true.
There’s no series diode in ADI-2’s power supply input.

For reverse polarity protection, it’s a shunting diode that quasi short-circuits the negative halfwave of the X-PSU’s AC voltage.

The only reason that nothing broke is that the X-PSU luckily is too weak to either kill the diode or itself.

JPS70 wrote:

I have an old Musical Fidelity X-PSU and I'd like to use it to power the ADI-2 DAC.

weme wrote:

An X-PSU (only toroidal transformer) could drive an ADI-2 DAC via an AC-DC linear regulator (output approx. 10V).

Would mean building a full-fletched DC PSU:

Transformer (e.g. X-PSU) - full wave rectifier - load capacitor - Linear Regulator like an L78S12 or better.
Can be done if you are an electronics guy, but what for (see below)?

If you handle mains voltage you must be educated for this (not by Youtube-video!), or you will kill yourself or others, with all legal consequences.
This starts when you open the case of the X-PSU:
No user serviceable parts inside!


Remark regarding toroidal transformers,
compared to e.g. EI-Core-transformers:

Toroidals are indeed beneficial for Speaker Power Amplifiers with unregulated PSUs, as they deliver more stable voltage under high load, like strong bass pulses.

This can’t be generalized for (low power) regulated PSU’s like needed for ADI-2, as the voltage regulation decouples the transformer and it’s effects from the load.

Toroidal transformer based PSU’s even have there downsides, like producing more diode switching noise in the mains.

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6 Reply by MC

  • MC
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Re: Running ADI-2 DAC from my power supply?

KaiS wrote:
weme wrote:

In the ADI-2 DAC, a negative voltage is blocked by a diode. The ADI-2 DAC was therefore operated with a pulsating DC voltage: approx. 18 V max. with a frequency of 25 or 30 Hz (1/2 of mains frequency).

This is not exactly true.
There’s no series diode in ADI-2’s power supply input.

This is not exactly true wink

The diode serves as overvoltage protection. The polarity protection follows in form of a MOSFET.

BTW, a half wave rectifier (one diode) produces the original frequency, 50 or 60 Hz.

Regards
Matthias Carstens
RME

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  • weme
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Re: Running ADI-2 DAC from my power supply?

@MC
Thank you for kindly clarifying my silly comment (astonishing performance), the incorrectness of which could have been easily clarified via two different considerations!

And also for the explanation of the protection circuit from the DC input.

@KaiS
A combination of shunt diode with fuse to protect against polarity reversal would not be a suitable protection option for a professional device, as the fuse would be immediately defective after a polarity reversal.

An AC-DC linear regulator (output approx. 10V) does not have to be installed in the housing of the X-PSU.

8 Reply by KaiS (edited by KaiS 2023-06-05 09:28:52)

  • KaiS
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Re: Running ADI-2 DAC from my power supply?

weme wrote:

A combination of shunt diode with fuse to protect against polarity reversal would not be a suitable protection option for a professional device, as the fuse would be immediately defective after a polarity reversal.

I don‘t know the exact order of protection stages, but a blow-out-fuse is placed as last resort.

At least the design is robust enough that I don’t recall failures mentioned here. RME’s design takes care of such stuff.


We had that discussed some time ago.
Over the time RME seems to have used variations of the protections, even a self-resetting fuse variant exists, if I recall correctly.


The general problem with protections:
You don‘t want them to cause voltage drop, as this would decrease energy-efficiency and generate heat.
Therefore a shunt-based solution, from this point of view, is preferable.

weme wrote:

An AC-DC linear regulator (output approx. 10V) does not have to be installed in the housing of the X-PSU.

Externally would indeed be the best, safest way for a layman’s DIY-project.

Higher voltage - 12 V instead of 10 V - would be more energy efficient, as ADI-2 uses an SMPS internally to condition the supply.
Higher voltage does proportionally reduce current draw.

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