Inaudible Hum - Ignore or Not?

[0bs3rv3r]

I say don't worry. Here's another example to not worry about, just for further perspective. I have this lovely BIG old Rek-o-kut turntable. I have adjusted cleaned renewed until it's in close to peak condition, but there is a tiny tiny amount of vibration that can only be heard as rumble on the quitest of vinyl, between tracks. Most normal surface noise on a record is louder and masks it. So, yep, I do not worry about "fixing" the turntable any further.

 

[watchnerd]

If you connect a voltmeter between ground of the pre out and the input ground of the subwoofers (while they aren't connected) do you read some higher than usual stray AC voltage values? Maybe you need to plug the subs into the same outlet as the integrated.

Tricky -- the distance from the pre-out to sub in put is about 9' on each side

 

[watchnerd]

I say don't worry. Here's another example to not worry about, just for further perspective. I have this lovely BIG old Rek-o-kut turntable. I have adjusted cleaned renewed until it's in close to peak condition, but there is a tiny tiny amount of vibration that can only be heard as rumble on the quitest of vinyl, between tracks. Most normal surface noise on a record is louder and masks it. So, yep, I do not worry about "fixing" the turntable any further.

I checked to see if I could feel the hum when the record is playing the lead-out groove of an LP.

Nope.

I don't know if it's because the surface noise of the lead out groove swamps the hum, or there is something about having the stylus in the groove of a playing record that makes the hum better.

 

[antcollinet]

Sounds like you have a ground loop issue between amp and sub (Mains to amp to sub and back to mains via sub power cable). Or around the amp to sub 1 amp to sub 2 and two subs back to earth.

Not sure how you can eliminate that with all three devices so far apart, other than switching to balanced audio.

 

[Holmz]

At first, the 50 Hz threw me, but then realized you're in Belgium.

And, yes, I see your point about the groove noise. How much gain are you using and what's the output of your cart?

What 50 Hz?
I would have expected a narrow 50 Hz, unless the FFT size was massive.
And there is no 100 and 200 Hz components.

But I guess it is found?

The phono stage is inside the integrated amp, so I can't move it.

I know the culprit -- it's the pre-out to the 2 subwoofers. If I disconnect it entirely, even the inaudible hum goes away.

 

[Bob from Florida]

The phono stage is inside the integrated amp, so I can't move it.

I know the culprit -- it's the pre-out to the 2 subwoofers. If I disconnect it entirely, even the inaudible hum goes away.

This is odd. If your Luxman is like mine the chassis is double insulated - no ground pin in the IEC jack. This would normally preclude any ground loops. Two subs being involved - does it happen when the subs are turned off while connected?

 

[raindance]

Does it go away if you just disconnect the power from ONE of the subs?

 

[watchnerd]

Sounds like you have a ground loop issue between amp and sub (Mains to amp to sub and back to mains via sub power cable). Or around the amp to sub 1 amp to sub 2 and two subs back to earth.

Not sure how you can eliminate that with all three devices so far apart, other than switching to balanced audio.

Unfortunately, balanced isn't an option with these subs and this amp.

However, the subs do have an option for wireless.

There is an optional wireless transmission module that I don't have that can be plugged into the pre-outs.

 

[Juhazi]

First thing to do is to set Sample size in Audacity higher, to get more resolution at low freq.

If it is 50Hz exactly, then try suggested hum reduction/elimination tricks. If can't hear it but you feel the woofer moving, freq is much lower and stresses your amp and speakers anyway. Especially if noise is lower freq than bass-reflex tuning

If it is mechanical resonance, you should use a separate phono pre-amp with highpass, rumble filter.

Filtering the Vinyl Signal between a Phono Preamp & Digitizer?

Filtering the Vinyl Signal between a Phono Preamp & Digitizer?

hydrogenaud.io

 

[antcollinet]

Unfortunately, balanced isn't an option with these subs and this amp.

However, the subs do have an option for wireless.

There is an optional wireless transmission module that I don't have that can be plugged into the pre-outs.

Wireless would eliminate the ground loops. Do you have the possibility to try-before-you-buy?

 

[DonH56]

There are a myriad of line-level ground isolators on places like Amazon, Monoprice, Parts Express, etc. that could go between preamp and subs to eliminate a ground loop. I would get one (or two) and see if that fixes it.

 

[abdo123]

What 50 Hz?
I would have expected a narrow 50 Hz, unless the FFT size was massive.
And there is no 100 and 200 Hz components.

all the components are there at 100Hz and 150Hz (you can see cliffs emerging there that are smaller in magnitude). The FFT size is in the picture as well.

I don't really appreciate the conjecture when all the evidence is obvious, i have no reason to lie.

The reason why it looks odd is because of RIAA equalization.

 

[antcollinet]

Wireless would eliminate the ground loops. Do you have the possibility to try-before-you-buy?

Having said that - if the hum is inaudible. I'd not be spending any money on fixing it which is back to where I started .

 

[Holmz]

all the components are there at 100Hz and 150Hz (you can see cliffs emerging there that are smaller in magnitude). The FFT size is in the picture as well.

I don't really appreciate the conjecture when all the evidence is obvious, i have no reason to lie.

The reason why it looks odd is because of RIAA equalization.

Easy there… I was not accusing you of lying… I was only trying to understand it.

I see, ”4096”. Doing it again at a larger FFT size might be worthwhile?

And I am not sure how the RIAA can spread the spectrum out to remove sharp peaks which I assume would be at 50 Hz. How does that work?

 

[abdo123]

And I am not sure how the RIAA can spread the spectrum out to remove sharp peaks which I assume would be at 50 Hz. How does that work?

RIAA adds 20 dB of gain at the sub-bass, so with my FFT window the 50Hz peak would almost drown the 100Hz and 150Hz harmonics.

 

[abdo123]

Btw I ordered a new ADC with a S/N of 115 dB, so i should provide even higher resolution measurements before the year ends.

 

[Holmz]

RIAA adds 20 dB of gain at the sub-bass, so with my FFT window the 50Hz peak would almost drown the 100Hz and 150Hz harmonics.

It was the width of the “50Hz tone” that confuses me.

 

[Blumlein 88]

Btw I ordered a new ADC with a S/N of 115 dB, so i should provide even higher resolution measurements before the year ends.

What are you getting?

 

[Blumlein 88]

It was the width of the “50Hz tone” that confuses me.

50 hz and 60 hz tone both at - 6 db.
4096 FFT.

Same with 16k FFT.

Same with 64K FFT.

If we use 48 khz it has a 24 khz bandwidth for the FFT. A 4096 FFT will divide it up into 2048 equal bins 11.72 hz wide. Both tones fall into the same bin. At the other end with a 64k FFT it will divide it up into 32,768 equal bins .732 hz wide. Easily able to separate the two tones. Windowing means the FFT responds slightly to energy in the adjacent bins still the basic idea of width of the bins holds for how much resolution you have. It is more important at the low end where we might hear tones a few hz different as different tones while less important at high frequencies where tones a few hertz apart sound the same to us.

 

[Chrispy]

TLDR for the most part just curious why would you want to ignore hum or not consider it an audible issue?