Inaudible Hum - Ignore or Not?

[watchnerd]

So I got my new integrated amp and my .2mV MC cartridge is right at the borderline of usability with the .3mV MC input sens.

It sounds fine when an LP is playing and at the gain I'm using (volume knob about half way up, seems to be about -20 dB), I don't hear any hum.

However, even though inaudible, if I touch the woofer I can lightly feel hum when nothing is playing.

Should I try to address this?

SUT would be an obvious potential solution, but those can introduce hum, too. I guess I could explore exotica like cheater plugs or get more obsessive about the pre-out cabling to the subwoofer (likely culprit just based on trouble-shooting).

Or is it just moot given the noise floor of LPs?

 

[abdo123]

my Cambridge audio duo shows a -60 dBFS hum with my cartidage (and that's the best phono stage measured on this forum) So i really think it's kind of inevitable with the copious amounts of gain cartridges require.

Phono stage on, needle off the record.

With groove noise (a quiet passage on a track).

As you can see it's borderline submerged under the noise floor of the groove, but just about. feel free to draw your own conclusions.

 

[antcollinet]

Inaudible?

Why would you spend any effort or money solving a problem that doesn't exist?

 

[watchnerd]

my Cambridge audio duo shows a -60 dBFS hum with my cartidage (and that's the best phono stage measured on this forum) So i really think it's kind of inevitable with the copious amounts of gain cartridges require.

Phono stage on, needle off the record.

With groove noise (a quiet passage on a track).

As you can see it's borderline submerged under the noise floor of the groove, but just about. feel free to draw your own conclusions.

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?

 

[abdo123]

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?

the output of my cart is 2.5mv (Amir used 10mv for his measurement) and the gain is set on 40 dB like he measured.

 

[watchnerd]

Inaudible?

Why would you spend any effort or money solving a problem that doesn't exist?

Why do ASR members obsess over inaudible SINAD differences?

 

[watchnerd]

the output of my cart is 2.5mv (Amir used 10mv for his measurement) and the gain is set on 40 dB like he measured.

Huh, that seems unusually high. I don't know of any cart that goes that high.

At 2.5mV that must be for an MM cart.

 

[abdo123]

Huh, that seems unusually high. I don't know of any cart that goes that high.

At 2.5mV that must be for an MM cart.

the phono stage was hum limited and since he doesn't do A-weighting he wanted to highlight it's low noise and low distortion by pumping up the input a bit.

At least that's my interpretation of things. it's honestly a phenomenal phono stage nonetheless.

 

[antcollinet]

Why do ASR members obsess over inaudible SINAD differences?

I don't think many do. I certainly don't: it's why I still use my "poorly" measuring Soundblaster as a DAC.

 

[DVDdoug]

Welcome to analog! And be VERY thankful it's not audible...

There's always SOME noise and since phono cartridges put-out a very-low level signal that has to be amplified by about 100 (at mid-band), getting a good signal-to-noise ratio can be a challenge.

 

[watchnerd]

I don't think many do. I certainly don't: it's why I still use my "poorly" measuring Soundblaster as a DAC.

Well, if I cranked the gain higher than I listen to it, it would be audible with no LP playing.

 

[MakeMineVinyl]

SUT would be an obvious potential solution, but those can introduce hum, too.

That might be obvious if I knew what an SUT is. Is it the same thing as a QUR?

 

[watchnerd]

That might be obvious if I knew what an SUT is. Is it the same thing as a QUR?

Step Up Transformer.

I don't know what a QUR is, so we're even.

 

[antcollinet]

Step Up Transformer.

I don't know what a QUR is, so we're even.

Depending on source - you might just step up the hum also. But then also increase output impedance from transformer into Preamp.

 

[Blumlein 88]

Have you physically moved components near the phono stage or moved the phono stage to see if this changes the level of hum? Another trick is to take a metal plate which you ground and place on different sides to see if it blocks or diminishes the hum in the vicinity of the phono stage itself. For instance this could be a piece of aluminum foil taped to cardboard and connected by jumper clips to ground.

 

[antcollinet]

Well, if I cranked the gain higher than I listen to it, it would be audible with no LP playing.

I think I get that if I crank up the Amp volume when fed from my MM cartridge/preamp. Hang on....

Yes - but I have to crank up the volume at least 20-30dB from my normal/high listening level for it to be audible at listening distance. I'd not be able to hear it with music playing because I'd either kill my speakers, or my ears.

I'm going to fail to worry about it.

 

[Bob from Florida]

So I got my new integrated amp and my .2mV MC cartridge is right at the borderline of usability with the .3mV MC input sens.

It sounds fine when an LP is playing and at the gain I'm using (volume knob about half way up, seems to be about -20 dB), I don't hear any hum.

However, even though inaudible, if I touch the woofer I can lightly feel hum when nothing is playing.

Should I try to address this?

SUT would be an obvious potential solution, but those can introduce hum, too. I guess I could explore exotica like cheater plugs or get more obsessive about the pre-out cabling to the subwoofer (likely culprit just based on trouble-shooting).

Or is it just moot given the noise floor of LPs?

Don’t worry about it if you are satisfied with the sound. Keep in mind total gain in the MC position is 56 db which is low for a .2 mv cartridge. If you are unsatisfied - then go with an external phono preamp. The ifi Zen phono has 72db available for cartridges such as yours. Get the adapter cable for the balanced output to one of your balanced inputs and you are all set.

 

[watchnerd]

Have you physically moved components near the phono stage or moved the phono stage to see if this changes the level of hum? Another trick is to take a metal plate which you ground and place on different sides to see if it blocks or diminishes the hum in the vicinity of the phono stage itself. For instance this could be a piece of aluminum foil taped to cardboard and connected by jumper clips to ground.

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.

 

[Blumlein 88]

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.

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.

 

[JRS]

Why do ASR members obsess over inaudible SINAD differences?

Maybe worried about intermodulation? Or that maybe it is sign that something catastrophic could happen. It's a bit differet then handwringing over 112 vs 125 dB noise floor. But agreed we do tend to worry for nothing some times.