Deepdark

Acceptable hum level in tube gear
« on: May 05, 2016, 03:52:09 PM »
Hi

Just for fun, I'm curious to know what is an acceptable level of hum for you guys. I mean, in real life, not only in term of specs and numbers, but in term of use. ie, if you can't ear any hum in normal tracking/mixing level, but to hear a tiny bit of it you have to crank your headphones/speakers at max, do you consider it like an acceptable result?  I know there is a pletora of tricks to kill hum like using aluminium chassis, encasing power transformer into an steel box, external psu, dc heaters, trying an infinite numbers of tube and put on the cleanest one at V1, mu-metal sheet/can around power transformer, etc. but the goal is not to speak of all the possible maner to extinct hum, or to start an war over the hi-fi guys but in general use, what is your acceptable level of hum?

 :)
"I'm givin' you that money so I don't have to kill your ass."


ruffrecords

Re: Acceptable hum level in tube gear
« Reply #1 on: May 05, 2016, 04:47:02 PM »
In this thread:

http://groupdiy.com/index.php?topic=62094.msg786765#msg786765

I have been exploring just how low the hum can be made when using ac heaters. From this work, two things are clear;

1. An external power supply providing dc heaters entirely eliminates hum.

2. Even with ac heaters, the measured noise levels are very similar and under normal operating circumstances it is completely inaudible. To put this into context, using ac heaters , a condenser mic and 70dB of gain and listening on phones with the gain turned up full, you cannot hear the hum because it is swamped by the acoustic background noise. You can measure the hum but you cannot hear it.

Cheers

Ian

buildafriend

Re: Acceptable hum level in tube gear
« Reply #2 on: May 05, 2016, 08:01:51 PM »
What Ian said.

Also for the literal numbers, they are nice to look at and know but in practice for me it's what I can or can not hear when compressed through a "clean" compressor.

Deepdark

Re: Acceptable hum level in tube gear
« Reply #3 on: May 06, 2016, 08:09:15 AM »
Thanks guys.

Ian, it's a good testing method you just tell us. Basically, if ambiant noise cover the hum, in that sense where hum is no more audible, then this shoudl means hum is enought low for general purpose use, right? And the same could probably apply to, ie, compressors such as Vari-mu or LA2A, by strapping it across our converters, with max gain, internal and input noise should cover the hum, right?

buildafriend, yeah I know what you mean :)

One thing I noticed is how critical Heaters wiring is, just like Ian tested in his thread relative to the very best we can do with ac heaters. And the right choice of tubes at V1 (first preamp tube). The gap between a Noisy one and an clean one can be quiet huge. And the order you wired the tubes, ending by V1 to ensure less a possible EMI. Unfortunatly, it does not always run to the most direct path, depending upon the layout, and we are more pronned to pollute other elements around
"I'm givin' you that money so I don't have to kill your ass."

abbey road d enfer

Re: Acceptable hum level in tube gear
« Reply #4 on: May 06, 2016, 11:22:53 AM »
Hi

Just for fun, I'm curious to know what is an acceptable level of hum for you guys. I mean, in real life, not only in term of specs and numbers, but in term of use. ie, if you can't ear any hum in normal tracking/mixing level, but to hear a tiny bit of it you have to crank your headphones/speakers at max, do you consider it like an acceptable result?  I know there is a pletora of tricks to kill hum like using aluminium chassis, encasing power transformer into an steel box, external psu, dc heaters, trying an infinite numbers of tube and put on the cleanest one at V1, mu-metal sheet/can around power transformer, etc. but the goal is not to speak of all the possible maner to extinct hum, or to start an war over the hi-fi guys but in general use, what is your acceptable level of hum?

 :)
I understand your reluctance regarding hard figures, knowing we'll thay don't tell all, but at some point, someone has to design a product, and needs objective performance targets. You can't tell a designer "make it sound good and quiet", because his acceptance of good and quiet will be different than yours.
Then the actual perceived hum is dependant on the program and the signal chain. A mic pre that seems nice and clean on trumpet may be too noisey for dulcimer, or even for vocals if a lot of compression is applied.
As to what is "acceptable", it depends on personal preferences and circumstances. One tends to forgive a Hammond B3 for being noisy, because it's just the way they are, but everybody hates guitar players with noisy rigs.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
"The important thing is not to convince, but to give pause for thought." (B. Werber)
Star ground is for electricians.