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RME User Forum → ADI-2 & 2/4 Pro series, ADI-2 DAC series → Question about PSU choice for ADI-2
I have here a linear PSU here with the correct V, current and phase pin-out I wanted to try. Its an old school design with no regulators and 1000uf of filtering after the rectifier. It does work on some other digital devices.
Does the ADI have any minimum amount of filtering capacitance needed for the ripple?
thanks in advance
I have here a linear PSU here with the correct V, current and phase pin-out I wanted to try. Its an old school design with no regulators and 1000uf of filtering after the rectifier. It does work on some other digital devices.
Does the ADI have any minimum amount of filtering capacitance needed for the ripple?
In short: Don’t!
In detail:
Be at least sure the unloaded voltage does not exceed ca. 15V.
At 18 V an ADI-2 internal (non user-replaceable) fuse blows, and you need to send the unit in for repair.
ADI-2 does condition the supply voltage by an internal switched mode PSU, the nominal lowest voltage is 9.5 V.
My guess is your LPS’s does not deliver stable enough ca. 1 A current, as the ripple with 1000 uF filtering will be 10 V, so the lowest part of the voltage curve falls below 9.5 V.
I wouldn’t even exclude that such a high ripple could damage elements of ADI-2’s DC filtering / preconditioning, short term or in the long run.
Well that's a good point. I think the digital device it was intended for had inrush resistors, so who knows if there is a spike above 12v that ADI is not prepared for.
For learning purposes, how much higher filter capacitance do you think most digital devices should have? Esp. unregulated LPS. It seems most SMPS have maybe a few thousand uF on the secondary.
For learning purposes, how much higher filter capacitance do you think most digital devices should have? Esp. unregulated LPS. It seems most SMPS have maybe a few thousand uF on the secondary.
In general I’d say, an unregulated PSU is not very well suited for an audio device with an SNR (Signal to Noise Ratio) at the edge of what’s technically possible.
A high ripple current causes a strong AC magnetic field, and no matter what you do as a designer, it will stray into the audio somewhere, finally even into the connected cables.
PSU building is based on a number of some relatively simple calculation.
But you need to know various parameters, like the transformer’s internal resistance or unloaded and loaded voltage, and the load’s demands.
Not even knowing the ADI-2 model (- DAC, - Pro, - 2/4 Pro SE), having different maximum power consumptions, I can only estimate.
If we look at the ripple voltage alone:
For the “DAC” a minimum charging capacitance of 10,000 uF, and for the “Pro”-models 22,000 uF, should keep ripple below ca. 1 V at normal use.
But, don’t just replace the existing PSU’s cap - the higher inrush current can kill it’s rectifier diodes, and a layman shouldn’t fumble inside a mains connected device anyway, if he doesn’t want to be electrocuted.
The expectable result is not worth to take this risk.
RME will release an LPS (Linear Power Supply) soon, have a look there if you like the idea.
By the way, what is this internal SMPS on ADI? It is the external SMPS PSU that comes with it. Am I missing something?
And the UFX has I think 1000+470+470 filtering on their internal XP Brand PSU. there are a few more 470uf aluminum electrolytics on each board right after, that's not close to your recommended 10k number.
By the way, what is this internal SMPS on ADI? It is the external SMPS PSU that comes with it. Am I missing something?
Yes, from 2/4 Pro SE’s manual page 9 (similar to DAC‘s manual page 10):
6. Power Supply
In order to make operating the ADI-2/4 Pro SE as flexible as possible, the unit has a universal DC input socket, accepting voltages from 9.5 Volts up to 15 Volts. An internal switching regulator of the latest technology with high efficiency (> 90%) prevents internal hum noise by operating above audible frequencies. Internally the switching regulator is followed by standard linear regulators, followed by super low-noise linear regulators. Therefore the ADI-2/4 Pro SE achieves its technical specs even with less optimal power supplies. Or in other words: the choice of power supply is not critical.
Still the unit includes a high-quality switching power supply, 12 V / 3,3 A, which not only accepts any mains voltage between 100 V and 240 V (usable world-wide), but is also fully regulated against voltage fluctuations and suppresses line noise. Additionally it only weights 150 g in spite of its high power of 40 Watts.
And the UFX has I think 1000+470+470 filtering on their internal XP Brand PSU. there are a few more 470uf aluminum electrolytics on each board right after, that's not close to your recommended 10k number.
If you double the operating frequency, you can halve the capacitor value.
From above „ ...by operating above audible frequencies.“
In this case the switching frequency is at least some 1,000 times higher than mains, so...
Additionally there are filter coils in play, etc. etc.
And don‘t forget:
I explicitly do NOT recommend using an unregulated and unfiltered power supply, no matter how high the charging capacitance is.
BTW: a single charging capacitor is NOT a filter.
You need at least one further step (coil or resistor + cap) to remove spiky ripple frequencies.
If you like, here’s a link to some basic info and an online calculator:
https://electronicbase.net/smoothing-ca … alculator/
RME User Forum → ADI-2 & 2/4 Pro series, ADI-2 DAC series → Question about PSU choice for ADI-2
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