Troubleshooting weird rumble - Topping MX3s

[Flup]

Hello! I have a weird issue when using Topping MX3s in my audio chain. So the full setup looks like this:
Record player - Technics Sl-1710MK2 with Ortofon M2 Red -> phono preamplifier Project Phono Box S -> amplifier Topping MX3s -> speakers Polk ES20.

The issue is that the speakers play some sort of low frequency rumble on this configuration. Non continuously, and not at low volumes. See the attached video for demonstration.

The issue disappears when Topping is replaced with another amplifier, so I believe it is the culprit.

The issue is also not present with a digital source, i.e. raspberry Pi over USB, or when built-in Bluetooth is used.

Any ideas and suggestions as to what might be happening here?

 

[Count Arthur]

Hello! I have a weird issue when using Topping MX3s in my audio chain. So the full setup looks like this:
Record player - Technics Sl-1710MK2 with Ortofon M2 Red -> phono preamplifier Project Phono Box S -> amplifier Topping MX3s -> speakers Polk ES20.

The issue is that the speakers play some sort of low frequency rumble on this configuration. Non continuously, and not at low volumes. See the attached video for demonstration.

The issue disappears when Topping is replaced with another amplifier, so I believe it is the culprit.

The issue is also not present with a digital source, i.e. raspberry Pi over USB, or when built-in Bluetooth is used.

Any ideas and suggestions as to what might be happening here?

What is the other amplifier that you have?

I couldn't open whatever it was in your zip, it doesn't have a file type, but it could be that the Topping's frequency response extends well down into the subsonic frequencies, whereas your other amp may be rolled off, so it kind of acts like a rumble filter.

Also, are your speakers and turntable on the same surface?

 

[Flup]

What is the other amplifier that you have?

I couldn't open whatever it was in your zip, it doesn't have a file type, but it could be that the Topping's frequency response extends well down into the subsonic frequencies, whereas your other amp may be rolled off, so it kind of acts like a rumble filter.

Also, are your speakers and turntable on the same surface?

Hi! Thanks for your answer. I've re-uploaded the file - please see if it works now, it should be an MP4.
The speakers are on stands and do not touch the shelf with the turntable, so I don't think it's a mechanical feedback.
The other amplifier is Denon DRA-F109.

 

[RandomEar]

Holy moly A spectrum from the audio track looks like this:

The biggest peaks are 104 Hz and going left: 52 Hz and a much lower 29 Hz. So the highest ones look like the mains frequency in most of the world + first harmonic. So, a ground loop, maybe? It appears that both, the MX3s PSU and the Denon use two-prong plugs, so no safety ground connection. Do you use a ground wire from your record player to your phono pre? Did you try it with and without this additional ground wire?

 

[Count Arthur]

What happens if you turn the bass all the way down?:

Does the problem persist?

 

[staticV3]

@Flup did you enable the Project's infrasonic filter?

 

[Flup]

Holy moly A spectrum from the audio track looks like this:

View attachment 422332

The biggest peaks are 104 Hz and going left: 52 Hz and a much lower 29 Hz. So the highest ones look like the mains frequency in most of the world + first harmonic. So, a ground loop, maybe? It appears that both, the MX3s PSU and the Denon use two-prong plugs, so no safety ground connection. Do you use a ground wire from your record player to your phono pre? Did you try it with and without this additional ground wire?

Hi! Thanks for the FFT, that looks interesting. I am using the grounding wire between record player and pre. Perhaps I should try to remove it?

 

[Flup]

@Flup did you enable the Project's infrasonic filter?

Yes, did not seem to make a difference.

 

[Flup]

What happens if you turn the bass all the way down?:

View attachment 422338

Does the problem persist?

I'll check, thank you for the idea to test.

 

[Flup]

I'll check, thank you for the idea to test.

Decreasing bass in EQ makes the rumbling quieter, but does not eliminate it even at -10 level unfortunately.

 

[Flup]

Hi! Thanks for the FFT, that looks interesting. I am using the grounding wire between record player and pre. Perhaps I should try to remove it?

I have tried with and without grounding wire, and both options result in the same rumbling.

 

[Flup]

I have done some more testing, and narrowed down the exact scario when rumble happens. These are the conditions:

1. The phono preamplifier is plugged in Topping MX3s and turned on.
2. The record player is connected to the phono preamplifier.

That's it. As soon as 2 happens while 1, rumble starts. It doesn't matter if the record player is turned on or off, if it plays a record or doesn't or even if it is connected to the electrical outlet or not.
Connecting phono pre-amplifier to the record player with additional grounding cable makes no difference.
Decreasing volume or bass on Topping decreases, but doesn't eliminate the rumble completely, unless at very low volume.
Enabling phono preamplifier infrasonic filter doesn't make a difference.
And, the rumble doesn't happen when Topping is replaced with another amplifier.

So I think I am even more confused as to what might be causing it.

 

[staticV3]

I have done some more testing, and narrowed down the exact scario when rumble happens. These are the conditions:

1. The phono preamplifier is plugged in Topping MX3s and turned on.
2. The record player is connected to the phono preamplifier.

That's it. As soon as 2 happens while 1, rumble starts. It doesn't matter if the record player is turned on or off, if it plays a record or doesn't or even if it is disconnected from the power.
Connecting phono pre-amplifier to the record player with additional grounding cable makes no difference.
Decreasing volume or bass on Topping decreases, but doesn't eliminate the rumble completely, unless at very low volume.
Enabling phone preamplifier infrasonic filter doesn't make a difference.
And, the rumble doesn't happen when Topping is replaced with another amplifiers.

So I think I am even more confused as to what might be causing it.

Sounds like a typical ground loop.

Have you tried grounding the MX3s to the other components?

You can attach a ground wire to one of the two screws at the rear.

 

[Flup]

Not yet, I will try that next. But would it make sense for this to be a ground loop, when the record player is disconnected from the electrical network?

 

[staticV3]

Not yet, I will try that next. But would it make sense for this to be a ground loop, when the record player is disconnected from the electrical network?

The phono pre likely isn't though

 

[Flup]

The phono pre likely isn't though

Yes, that is true, but the phono stage is not directly causing it. Or, in other words, phono stage can be turned on and connected to Topping, but unless the record player is connected to the phono stage, the rumble doesn't happen. Is it seems that plugging in the record player in the phono stage is somehow the trigger.
I might be of course misunderstanding something here, so aby clarification is welcome.

 

[AnalogSteph]

The speakers are on stands and do not touch the shelf with the turntable, so I don't think it's a mechanical feedback.

It sure looks an awful lot like it though. Can you reproduce the issue when plugging headphones into the MX3s instead of using the speakers?

Plan B: I noticed that the MX3s (switch-mode) power brick appears to have a 2-prong mains cable, and your entire system wouldn't seem to have an explicit ground/earth connection. Do you happen to have a nice grounded PC (or similar) that you could connect to the MX3s via USB? It doesn't have to be on or anything, just plugged into the mains. You could also use the ground terminal on the phonopre, but I'd rather want to divert leakage currents right at the Topping.

 

[Flup]

It sure looks an awful lot like it though. Can you reproduce the issue when plugging headphones into the MX3s instead of using the speakers?

Plan B: I noticed that the MX3s (switch-mode) power brick appears to have a 2-prong mains cable, and your entire system wouldn't seem to have an explicit ground/earth connection. Do you happen to have a nice grounded PC (or similar) that you could connect to the MX3s via USB? It doesn't have to be on or anything, just plugged into the mains. You could also use the ground terminal on the phonopre, but I'd rather want to divert leakage currents right at the Topping.

Thanks for your feedback, but this can't be mechanical resonance. The issue occurs even when the record player is not on, or even connected to electrical outlet. I went as far as removing the Ortofon cartridge, and this did not change anything.

As for the grounding, I have tried various combinations of groundg record player to phone preamp and to topping, or breaking any of the two connections or both at the same time - no dice, still the same issue.

But you are tight, the whole system is electrically floating as none of the three devices is grounded via power cables to the network.

 

[restorer-john]

It's got nothing to do with a ground loop.

There is instability. Could be DC from the phono pre causing a servo to work overtime or just a disastrously inept design from Topping when it comes to the real world. We've seen plenty of that.

 

[Flup]

It's got nothing to do with a ground loop.

There is instability. Could be DC from the phono pre causing a servo to work overtime or just a disastrously inept design from Topping when it comes to the real world. We've seen plenty of that.

Thanks for your input! Could you clarify the bit about "servo to work overtime"? I don't think I get that