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....