NEWS: monolith amp with Hypex amplification!

[Mistar Muffin]

Really sounds like there is something wrong with the internal interconnections/wiring such as ribbon cables. If there is a bad batch modules or just random bad modules or another other components, the probability with channels 2,4,6,8 would be extremely low. This being the 2nd unit, did Monolith say anything about what was the problem with the 1st one. Did the first 1 one hum the same way and also the 2,4,6,8 channels?

The behavior was identical between the two units. Even-numbered channels have a lot of noise and odd channels do not. Monoprice support didn't really say anything other than agreeing I had done all necessary troubleshooting before issuing the RMA. This morning I asked if anyone involved in engineering this device was available and I basically heard crickets on the other end of the line.

 

[GXAlan]

If I was on the other side of this, I would agree with @GXAlan that the most likely explanation would be operator error. My hope that by testing with only power and a single speaker I have eliminated any possibility of that. For the curious here was my testing methodology.

Agree 100% with your test methodology.

1) What happens if you have two or three speakers connected?
2) Is there a way to short the input? What if you connect a cable to a
DAC that isn’t playing anything at all.

When I tested my amp, I had both channels wired. Let me try the way you are doing it.

 

[Krusty09]

actually looking at those pictures of the inside you could do something easy to see if its all the boards and not just one corrupting others. you could just disconnect the white clip from each board power input and only connect one at a time and move through them that way. one board somehow and i'm not sure could possibly be the culprit. its a little different then the test you did with moving the speakers as all the boards were still powered. please if you don't feel comfortable do not play with it just pack it up and send it back. btw if you do go ahead with the test each time you power down let the amp sit a few minutes and discharge a bit before plugging in other stuff. this is just a suggestion move about the cabin at your own risk.

 

[Mistar Muffin]

Agree 100% with your test methodology.

1) What happens if you have two or three speakers connected?
2) Is there a way to short the input? What if you connect a cable to a
DAC that isn’t playing anything at all.

When I tested my amp, I had both channels wired. Let me try the way you are doing it.

1) No change. Initially noticed the issue with multiple speakers attached and ripped out all connections to narrow down the cause.
2) Will this work if I only have RCA DAC source? I am using Monoprice RCA to XLR.

 

[GXAlan]

@Mistar Muffin . I am able to somewhat reproduce your results. What is missing from my earlier set of images is that the even channel IS worse than the odd channels which is easier to see when I go through a few different experiments.

More to follow.

 

[saxlylong]

@Mistar Muffin . I am able to somewhat reproduce your results. What is missing from my earlier set of images is that the even channel IS worse than the odd channels which is easier to see when I go through a few different experiments.

More to follow.

I will also check with mine and see if I can reproduce something on my 8125x. I only checked that the hum/noise was there for several speakers, not that some were worse than others. It will be late tonight or tomorrow before i can report back.

 

[GXAlan]

Note that the even harmonics drop on both channels but the odd harmonics are reduced on the ODD channel but not the EVEN channel

1) I will need to play with grounding tests to see if there is a way I can get the even channel to improve. I actually am going to hit my return deadline soon as well.
2) I have swapped the speaker connectors and the hum stays with the amp channel, showing that my E1DA/non-inductive resistors/speaker wire is not the problem.
3) Running low-level 1 kHz test tones instead of silence still gives me

The data from the previous post still applies but the fact that one channel had worse power supply harmonics was missed.

@amirm -- is this just a ground loop that is more 'prone' on the EVEN channels? Or is this something else? If you go back 2-3 pages in the thread, you will see @Mistar Muffin has audible hum with his Klipsch speakers on odd even channels x 2 physical amps (so he has had 8 modules showing this issue).

 

[Mistar Muffin]

I will also check with mine and see if I can reproduce something on my 8125x. I only checked that the hum/noise was there for several speakers, not that some were worse than others. It will be late tonight or tomorrow before i can report back.

A tip for those looking to reproduce my results:

I have a single HDMI device, a computer, that generates a LOT of noise through this amp. The HDMI device manages to pass this noise through an HDFury, my Marantz AVR, and then over the RCA -> XLR cables to the amp. When the HDMI cable from the PC is connected to the chain, I get noise on *all* channels, but it is noticeably worse/louder on the even channels. If you have a ground loop issue or device like this adding noise to the chain it could be hiding the fact that half of the channels are worse. My advice would be to try the amp with no inputs connected, as I did.

As soon as I unplug this HDMI cable from the PC the noise from the amp drops to only the even channels. I have basically sidelined troubleshooting this PC HDMI issue in favor of figuring out why the amp is noisy with no inputs connected.

 

[Mistar Muffin]

These units have a 5 year warranty, so if they keep sending you units that do not work, that's on them for 5 years.

If it's a design flaw or systemic issue I'm not swapping these indefinitely. I would want my money back so I can give it to Dylan. Which is starting to look like what I should have done in the first place. I don't care if it's been over 30 days. They will make it right or Visa will.

 

[Mistar Muffin]

Thank you for running these tests. It's nice to be validated!

@amirm -- is this just a ground loop that is more 'prone' on the EVEN channels? Or is this something else? If you go back 2-3 pages in the thread, you will see @Mistar Muffin has audible hum with his Klipsch speakers on odd channels x 2 physical amps (so he has had 8 modules showing this issue).

Small correction: Issue identified on even channels, not odd. You referenced even several times earlier so I assume this is just a typo. Wanted to make sure @amirm got the right info, though.

 

[Buckeye Amps]

While the Monoprice doesn't have Auto Sense, it does have an MCU for muted on and fault code recognition (correct me if I am wrong).
It could be possible (just spit balling here since I do not have a schematic to go by) that part of the MCU pathway for, say, faults only looks at one channel of each model and there is a slight issue with this pathway introducing the distortion leading to the one channel per module issue.

I say this as during early prototype testing of my Purifi boards, there was an issue found with the Auto Sense circuit causing distortion in just one channel (the channel it was connected to on the PCB). Was an easy fix luckily.

 

[GXAlan]

To add to this.

I attached the Studio 530 to the amp. As @Mistar Muffin described, there is an audible buzz from even channels.

I attached XLR cables to the amp/preamp (CX-A5100). There is no AC buzz noise. Even turning up the preamp to +16.5 dB, I just hear normal random noise with no audible buzz at all. This takes out the laptop/HDMI/E1DA from the loop.

My I-am-only-a-hobbyist conclusion:
The even channels generate more buzz at idle with nothing attached to the connectors.
The even channels are more susceptible to ground loops somehow.
In a simulated real-world environment with XLR to XLR cables, the even channels are quiet.

I haven’t had a chance to try the XLR to RCA adapter.

 

[Mistar Muffin]

I tried discussing this issue with Monoprice tech support but it was clear it was a higher-level conversation than they were prepared for. I don't feel like they can help beyond continuous RMA. In an effort to draw some of that high-level attention I sent an email over to Hobie Sechrest ( @MonolithGuy ) at Monoprice. I'd really like to keep the amp so I am motivated in getting this figured out.

 

[PJ 1]

I tried discussing this issue with Monoprice tech support but it was clear it was a higher-level conversation than they were prepared for. I don't feel like they can help beyond continuous RMA. In an effort to draw some of that high-level attention I sent an email over to Hobie Sechrest ( @MonolithGuy ) at Monoprice. I'd really like to keep the amp so I am motivated in getting this figured out.

Bit dated, but this article solved many a ground loop problem of mine:

Ground Loops - Eliminating System Hum and Buzz

Got an annoying hum or buzz in your audio system? You likely have a ground loop. This article helps you diagnose the problem so it can be eliminated. Don't put up with hum. Read this article!

www.audioholics.com

 

[Mistar Muffin]

Bit dated, but this article solved many a ground loop problem of mine:

Ground Loops - Eliminating System Hum and Buzz

Got an annoying hum or buzz in your audio system? You likely have a ground loop. This article helps you diagnose the problem so it can be eliminated. Don't put up with hum. Read this article!

www.audioholics.com

It's not a ground loop issue.

 

[PJ 1]

It's not a ground loop issue.

RCA to XLR adapters? Good luck. Mine works great. No issues. No hums. No noise except what I feed it. Ground loops can occur in even the most expensive gear. I've been recording and engineering music for 20 years. I've had amps with no issues plugged into the same outlets as amps with issues. Come to find out, it was the OTA RF antenna that we all watched on breaks because the studio was too cheap for cable tv.

 

[Mistar Muffin]

RCA to XLR adapters? Good luck. Mine works great. No issues. No hums. No noise except what I feed it. Ground loops can occur in even the most expensive gear. I've been recording and engineering music for 20 years. I've had amps with no issues plugged into the same outlets as amps with issues. Come to find out, it was the OTA RF antenna that we all watched on breaks because the studio was too cheap for cable tv.

Thank you for providing your credentials. If you read the last few pages I think you will see what I'm talking about.

 

[MonolithGuy]

I appreciate @Mistar Muffin for sending me an email and bringing this to my attention!

We are investigating and will resolve it.

 

[GXAlan]

@MonolithGuy
That is awesome customer service!

 

[Mistar Muffin]

@MonolithGuy
That is awesome customer service!

Fingers crossed.