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Hum and hiss after connecting miniDSP SHD

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Smidge

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Is the hum/hiss only audible when the unit is in Standby? If so, this is a known problem. Seems to be an issue with the power supply.

https://www.minidsp.com/forum/shd-series/18460-buzzing-hum-from-the-shd-when-in-standby?limitstart=0

Surprised you haven’t heard back from miniDSP support. I bought my unit in January 2021. I didn’t have this problem, but they sent me a new power supply “just in case”.
It’s both standby and when operational. I already updated to the latest firmware to eliminate the known issue you refer to.
 

Glasvegas

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It’s both standby and when operational. I already updated to the latest firmware to eliminate the known issue you refer to.

It’s disappointing that you haven’t had a response from miniDSP support. Even an acknowledgement would be the minimum I would expect.
 

q149

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That's what equally surprises me. At minidsp they should be perfectly able to know what SHD serial numbers are impacted by the humming power supply and take appropriate action. But apparently their official dealers aren't able to get decent feedback from minidsp in order to fix flawed units. Or may be there is yet another technical issue going on that we aren't aware of?
 
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It’s disappointing that you haven’t had a response from miniDSP support. Even an acknowledgement would be the minimum I would expect.
I did get a standard reply to provide more details on 8 April which I did that same day. But since then it had been silent.
 
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I got a reply from miniDSP support. They asked me to test 3 more things (connecting/disconnecting cables, impact of changing volume on the amp’s pre-amp), which I did. As expected, no positive impact. I’m now waiting for follow-up.
 
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Short update: miniDSP tech support asked me to take off the cover and send them some images of the power supply, which I did. Now waiting for their reply.

This whole process takes a long time because it takes 2 days minimum before they reply to any email. And we are now 5 emails further. Nevertheless, I’ll report back when it makes sense.
 

Glasvegas

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Short update: miniDSP tech support asked me to take off the cover and send them some images of the power supply, which I did. Now waiting for their reply.

This whole process takes a long time because it takes 2 days minimum before they reply to any email. And we are now 5 emails further. Nevertheless, I’ll report back when it makes sense.

At least you are making progress, if slowly.
 

Glasvegas

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Short update: miniDSP tech support asked me to take off the cover and send them some images of the power supply, which I did. Now waiting for their reply.

This whole process takes a long time because it takes 2 days minimum before they reply to any email. And we are now 5 emails further. Nevertheless, I’ll report back when it makes sense.

Any progress?
 
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Any progress?
Yes actually. I’m sending the unit back to HK for further inspection. We have been pinging back and forth and did various tests with regards to possible grounding issues but no meaningful lessons could be learned from that.
 

Pdxwayne

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Curious, did you get another SHD to compare?

I had a very bad hum noise a short while ago when using minidsp HD 2x4, connected to my DAC with no ground to my sub with ground. The hum went away if I connect to my other DAC with ground. Connectione were RCA.

Even without the loud hum using my DAC with ground, the minidsp added hiss to my speakers output when nothing is playing.
 
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Smidge

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Curious, did you get another SHD to compare?

I had a very bad hum noise a short while ago when using minidsp HD 2x4, connected to my DAC with no ground to my sub with ground. The hum went away if I connect to my other DAC with ground. Connectione were RCA.

Even without the loud hum using my DAC with ground, the minidsp added hiss to my speakers output when nothing is playing.
No I didn’t get another SHD to compare unfortunately. I did request it but it doesn’t fit within their internal policies.

I’m not sure I fully understand what you are trying to say with these scenarios you tested. I have an extra DAC laying around so if you have any suggestions to test before sending it back I’m all ears.
 

Pdxwayne

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No I didn’t get another SHD to compare unfortunately. I did request it but it doesn’t fit within their internal policies.

I’m not sure I fully understand what you are trying to say with these scenarios you tested. I have an extra DAC laying around so if you have any suggestions to test before sending it back I’m all ears.
I am thinking about getting a SHD myself. What you are describing is concerning to me.

I am sharing what I observed with my hd2x4. It doesn't like DAC with no gound. Also, it adds hiss. Just sharing experience and not suggesting any fix.

It seems like SHD is no better. Thus, I am hesitant to get one.....
 
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Smidge

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I am thinking about getting a SHD myself. What you are describing is concerning to me.

I am sharing what I observed with my hd2x4. It doesn't like DAC with no gound. Also, it adds hiss. Just sharing experience and not suggesting any fix.

It seems like SHD is no better. Thus, I am hesitant to get one.....
Okay, gotcha. I am still hoping I just have a faulty unit, or perhaps there is another explanation. In terms of features I really love it. And there are multiple satisfied SHD owners on ASR, although I do have the impression they are nearly all using the balanced outputs of the SHD.
 

Glasvegas

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Okay, gotcha. I am still hoping I just have a faulty unit, or perhaps there is another explanation. In terms of features I really love it. And there are multiple satisfied SHD owners on ASR, although I do have the impression they are nearly all using the balanced outputs of the SHD.

I must be in the minority. I’m using RCA.

Seems like a faulty unit.
 
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I got an update from miniDSP after they inspected my unit:

We indeed received the unit in early May and our engineers have been doing some tests with the unit. The report just came out and we were about to reach out to you. Attached are some reports done by the engineers regarding noise.

Here is the report from our engineers:

"Progress update for SHD return unit RA#70552:

- Returned unit works normal with expected performance, the measured noise level is quite close to our golden sample.

- After listening check, SHD (with max vol.) is connected to a power amp that max gain is 26.6x, little noise can be heard when ear is touching on tweeter. It became silent just after moving away from it.

- I guess the possible root cause is the loop ground issue and also a large voltage gain 75x on K3 power amp that amplify the noise in audible level.

- If the user wants to get back the SHD, he can try:
1. balanced input power amp
2. K3 as int. amp but fix the vol. control to near minimum (let's say 8 o'clock) as an signal attenuator, SHD set vol. to near maximum and use for vol. control.
3. We can provide an attenuator for RCA port, to decrease the max. signal level from 2V max to 0.44V for K3's bypass. (Not sure it works or not, may affect SNR and THD)"


It appears to us our engineers could not reproduce the exact same symptoms you mentioned in your initial ticket. However they have given some data and suggestions that you might want to take a look at. Please let us know what you think and get back to us once you have made a decision on your unit. Thank you very much again for your patience.

They didn’t respond to the hardware noise so I sent them a reply to inspect this as well.
 

abdo123

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I got an update from miniDSP after they inspected my unit:



They didn’t respond to the hardware noise so I sent them a reply to inspect this as well.

this is some royal treatment! glad that they're putting so much effort to fix this issue!

ground loops can be quite persistent, good luck!
 
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I got an update from miniDSP after they inspected my unit:



They didn’t respond to the hardware noise so I sent them a reply to inspect this as well.
this is some royal treatment! glad that they're putting so much effort to fix this issue!

ground loops can be quite persistent, good luck!
in the meanwhile I purchased a power amp with balanced inputs that should be delivered next week. So assuming their analysis is correct, this should resolve those issues. But the hardware noise is still a concern.
 
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And I now received an update regarding the hardware noise:
Regarding the hardware noise issue:

When the SHD is in stand-by mode, it is louder and that is as expected. It is because the SHD is consuming low current during stand-by mode, but that should only be the worst case scenario for a switch mode power supply using typical pulse skipping method to maintain the output voltage in low current mode. Therefore you can hear switching noise in different frequencies.
 
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So basically they're saying you are out of luck and just have to deal with it?
Well, that’s one way of looking at it. I would say we have eliminated SHD hardware defects, and we learned it has become more likely that switching to balanced outputs to the power amp might take away the audible issues.
 
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