TOPIC:

Hi folks,

I have a "problem" with my miniDSP SHD power supply. When the device is in Standby mode the power supply makes a high pitch noise almost all the time.
To hear it I have to stand besidey rack so it normaly doesn't bother me. But I don't like the fact it does this.

I had a DDRC24 before the SHD and changing the power supply to a linear psu really elevated the sound quailty so you could easily hear the difference.

Did anyone in the forum upgrade the power supply in the SHD?

I like to hear your opinions.

thanks
greetz Marcus

If anybody reads this later on here a few infos:

After a bit of research I found out minidsp implemented a pretty high standards (medical grade) meanwell SMPS (RPS-60-15) into the minidsp.
While it's an open frame design I don't know if putting a cage around it or maybe just a metal plate between the DSP board and the psu would bring any benefits.

But all in all it seems to me this is already a pretty good psu.

Power supply upgrade is definitely possible. I know of mean well supplies. The SMPS in my SHD is an open frame type, it's 24v not 15v. Current draw is about 500ma. After having a look under the hood, there are plenty of things that can be done to improve on the sound quality. I'm not being critical of the equipment, but this is not exactly high end audio gear, due in part to being a mass production type of equipment. I will be doing some A/B comparison of the existing smps vs battery-powered. 

Another interesting point, I believe the miniDSP website states the SHD has AK DACs. Mine has ESS ES9028Q2M DACs, opamps are OPA1612A, A/D converters are Burr Brown PCM4202. My pcb is ver 3.1 mfg 3-7-2022. Nichicon UES series bi-polar capacitors are also used.

These are nice units, and the DSP can make a huge improvement. I just cannot help myself from wanting to squeeze a little more out of any piece of audio gear! 

Cheers!
-Mike

Hi Mike,
what does the model number on your psu say?
Is it a RPS-60-24?

And well because of material shortages the last few years I can understand they used what they could get to produce as many devices as possible.

I don't want to solder anything on the Board. So probably not much for me to do on my device.

I disconnected the analog RCA output cables from the board because I don't use them. That's it

greetz
marcus

OhmegaMike wrote:

Another interesting point, I believe the miniDSP website states the SHD has AK DACs. Mine has ESS ES9028Q2M DACs,

That's interesting, and I'd guess a change that may have been forced by chip shortages?. You're right that the product listing refers to "32bit Audiophile converters: AK5574 / AK4490EQ". A quick Google suggests that the ESS chip is higher performance though.

How old is your SHD?

I will have to check on the PS. I didn't look at it too closely. I saw the SMPS, and immediately decided I want to experiment with an external supply. I will keep you updated...

I was happy to see the ESS DACs. I have a DAC I built myself which uses ESS DACs. My DAC has USB isolation, high quality crystal oscillators, very nice I/V circuit, and linear supplies. Along with 3 individual regulators for the dac chip itself. I bought the SHD in order to use my DAC. Sadly, I am downgrading my sampling rates, and losing DSD playback by the SPDIF output of the SHD. But, gaining the room correction abilities seem to be a wothwhile trade-off.

My SHD was purchased in December. The circuit board says Version 3.1 and made on March 07 2022...

Whoa. That’s a huge change! The performance might be identical, or better, but miniDSP should have said something. If not in a post here about the hardware update, at least in the spec sheet. They’ve cooperated with ASR in the past, but why not send one of these units in for testing and free publicity?

I took Pictures of the inside so I could have a look after closing it.

I have Version 2.0, Oct 2020
On my board are AKM chips.

That probably explains why Mike's SHD runs with a 24V PSU and mine with 15V.

Tonight, as I was wiring an external battery supply, I realized this is probably a waste of time... Here's why... The switching supply which provides a single DC voltage to the main board, is then fed into yet another mess of switching circuitry to provide the unit with pos and neg supplies for the op amps, 3.3-5v, and the 1.2v supply for the dac IC (AK or ESS doesn't really matter, power requirements are similar).

Regardless, I hooked up a pair of SLA AGM batteries, a relay, and did some listening tests. I used a smart plug for wireless switching between power sources. Maybe a very small change in the sound? Nothing to get excited about. So subtle, it may be all in my head! I'm running the SHD directly into tube high voltage amplifiers, direct 5kv OTL monoblocks driving electrostatic speakers. The system is very revealing.

It's relatively easy to substitute the SMPS for an external linear supply, but don't expect anything great... In order to improve on the power supply, will require some fairly serious hacking of the unit. There are other areas for improvement that will likely bring better results, but for now, I'm going to connect my homebuilt DAC to the SHD, and put the power supply mods on the back burner... Still, it was a fun little experiment! I'm sure I will be tempted to go back into the SHD for more mods down the road, I've only had it for a month....

 I have a "problem" with my miniDSP SHD power supply. When the device is in Standby mode the power supply makes a high pitch noise almost all the time.
To hear it I have to stand besidey rack so it normaly doesn't bother me. But I don't like the fact it does this

I have exactly the same issue, it’s like the squealing from a switch mode transformer that isn’t properly held down and resonates.  Mine goes away as soon as I start up.  I loath having switch mode power supplies onboard.  I wish it could be replaced with a linear supply.  

Im hoping MiniDSP will release some higher end quality units with some attention to the power supply and analogue circuits.  

I’ve also dispensed with the Roon section of the unit and I feed the RCA SPDIF input with my Aries unit, it made quite a difference.  

Has anyone done a replacement with a linear supply?

Bear in mind that linear power supplies aren't guaranteed to be silent when a unit is in standby mode either. My SHD makes the noise described above in standby but it's only audible close up and so doesn't bother me. Right next to it I have a DAC with a linear power supply that has a lower frequency hum when in its standby mode - it sounds about as loud as the SHD just at a lower frequency.

It’s not really the noise in standby that’s worrying me, it more the question of what the switch mode supply is doing during operation.  I went to some lengths to get rid of all my switch mode wall warts on the audio circuit.  I’m considering getting rid of the SHD and going to a Flex.  I don’t like the Roon part of the SHD anyway and the only advantage of the SHD that remains is the DAC.  I think I’ll sell the SHD.  On the Flex I can use a linear supply.  I have found when I leave out the SHD from the chain and just connect the Aries to the DAC there’s quite an improvement in sound quality but I wanted to integrate my subs.  I ended up selling my MSB DAC due to its latency so I’m hoping the MiniDSP of some sort ends up working out.

Im waiting on new speakers and I’ll decide after I’ve used the SHD with them.

Note that a Flex running Dirac Live uses a 48 kHz internal sample rate vs 96 kHz on the SHD series. Personally I'd look more at the external DAC route with your SHD if you wanted to upgrade, just not one with a high latency.

Is your SHD power supply noisy when not it standby? I'd thought from your* first post that you'd only noticed this when in standby mode? This is the case for me.

*Edit - actually I realise the first post wasn't by yourself @rortmanns but you'd quoted it and said you had the same issue.

Oh, and just to add that if you have a Neo3 SHD one other advantage over a Flex is the option to use a Microsoft Surface Dial as a volume control, which may or may not appeal.