Hiss Issue with miniDSP HTx and Hypex Amps - Gain Mismatch or Defective Unit?

[Oscar21]

I’m having the same issue with the minidsp flex trs and a Hypex nc400 power amplifier connected to KEF R3 speakers. There’s audible background noise regardless of the volume when listening from over 2 metres away.

Would a -10dB XLR attenuator be the solution?

 

[lodex]

I'm facing the exact same issue with a Flex HTx and Hypex NC400 monoblocks connected to Nubert NuLine 334 speakers. I'm still in contact with miniDSP support, they have not been able to explain the issue and did not reply for some time now, so I don't expect to ever hear from them again. For now, I ended up using adjustable attenuators (https://www.jts-europe.com/products/microphones-and-wireless-systems/accessories/ma-123/). At -10dB the hiss is reduced to an acceptable level at listening distance, with -20dB being somewhere near the level I get when connecting a Topping D70 Pro Sabre (in DAC mode mind you) to the NC400s.

 

[jmdesignz2]

Sent miniDSP another email, and I guess they’re just ignoring me now for some reason. Kind of terrible tech support—ask me questions, I answer them with lots of detail, and then they ghost me. Or maybe something is happening behind the scenes with their company, but either way, they were of no help at all.

The retailer is sending me a warranty return authorization. Not sure if we’re talking about a return and refund or return and wait around for a repair (contingent on it actually being out of spec or not functioning correctly).

I still think it’s probably something to do with the gain. I bought a Sescom -5dB XLR attenuator. It cut down on the hiss, but not enough to be inaudible at my listening position (I guess I would need the -10dB). But almost everyone, the retailer, people on this forum, other people I’ve asked for advice, are insisting I return the HTx.


Bought some 10k resistors from Amazon; hopefully I can try them before shipping off the HTx.

What fixed your issue? Please update us?

 

[thcdru2k]

Do you have another amp you could test ? It sounds like Hypex gain is amplifying the source noise more than your system needs. I would also temporarily reduce any channel's output gain . If the hiss drops, it is generated earlier in the chain. If the hiss remains it is after the digital gain stage.

 

[pderousse]

I'm facing the exact same issue with a Flex HTx and Hypex NC400 monoblocks connected to Nubert NuLine 334 speakers. I'm still in contact with miniDSP support, they have not been able to explain the issue and did not reply for some time now, so I don't expect to ever hear from them again. For now, I ended up using adjustable attenuators (https://www.jts-europe.com/products/microphones-and-wireless-systems/accessories/ma-123/). At -10dB the hiss is reduced to an acceptable level at listening distance, with -20dB being somewhere near the level I get when connecting a Topping D70 Pro Sabre (in DAC mode mind you) to the NC400s.

You should not have to settle for a bandaid. Those are all highly compatible, high quality components. I suspect something is faulty.

 

[Matias]

Flex HTx + Hypex NCMP running flawlessly here fwiw.

 

[lodex]

You should not have to settle for a bandaid. Those are all highly compatible, high quality components. I suspect something is faulty.

Yeah, I'm not really satisfied with this "solution" either. However, I simply don't have the slightest idea what to do anymore. It seems to be an issue with the Flex and the NC400s specifically. Any other combination of DAC oder PA I tried works without issue. I can 100% confirm the issue OP is facing, meaning the hiss coming from the Flex itself, regardless of master volume, input or output gain setting or any other (or none at all) devices upstream. As soon as the Flex is muted, the hiss is gone.

It can't be an issue in my house either, since I carried the entire signal chain over to my parents house, where the issue remained. My father is an electrical engineer and hooked the Flex up to an audio analyzer. He found nothing specific that could explain the issue, the only surprising thing of note is that the unbalanced outputs measured about 10dB better when it comes to noise floor level.

 

[lodex]

I'm still in contact with miniDSP support, while another user posted on the miniDSP forums with the exact same issue in the thread I started originally: https://www.minidsp.com/community/t...noise-with-balanced-outputs.24317/#post-79346

@Matias: Do your NCMPs have a gain switch?

 

[Matias]

None have, they are fixed.