Help identifying noise

juszat · « **on:** 8 Oct 2017, 11:29 pm »

Voice 003.m4a
https://drive.google.com/file/d/0B-XZ3tUk7cMcLWJxMjZvS2U3d1k/view?usp=drivesdk

juszat · « **Reply #1 on:** 8 Oct 2017, 11:31 pm »

juszat · « **Reply #2 on:** 8 Oct 2017, 11:44 pm »

Hi . I would like to share the above to file with you . Its related to a noise coming out of my sapatial hologram M3 speakers . 4 ohm ,94 db sensitive . The system consist of an odyssey kismet stereo amp and a candela tube preamp
And a tube cd player .

When the amp connected to the speakers only there is a slight hiss emanating from the speakers and i assume that is the noise floor of my amp . However when i connect the preamp via blue jeans cable RCA as soon as the preamp operational ( protecting delay switch clicks) there is a considrable hiss /hum can be heard . Clearly audible from the listening position . I tried to rule out ground loop by using an ungrounded cheater plug and also a Jensen isomax line level isolation transformer which did not change anything . The noise is independent of the volume control . So my question if its possible that it is a tube rush type noise related to faulty tube . The candela uses two 12au7 vacume tubes current production JJ12au7. As you can see the frequency analisis show a peak of 120 hz . I am planning to get a replacent tube to check . What puzzles me is ny effort to deal with the potential ground loop (common outlet ,cheter plugs and line level Iso transformer did nothing to the noise .

Any thoughts are appreciated .

Tamas

FullRangeMan · « **Reply #3 on:** 9 Oct 2017, 12:17 am »

I suggest you remove this tube from the preamp and listen the noise again without the tube.
The preamp tube filament heater is AC or DC?

juszat · « **Reply #4 on:** 9 Oct 2017, 12:32 am »

I will do that . I assume if the tube is bad the noise should stop if i remove it . Honestly i cant answer if the heater is'ac or dc but i will find out . What difference would that mean to the noise ?

FullRangeMan · « **Reply #5 on:** 9 Oct 2017, 12:44 am »

Quote from: juszat on 9 Oct 2017, 12:32 am

I will do that . I assume if the tube is bad the noise should stop if i remove it . Honestly i cant answer if the heater is'ac or dc but i will find out . What difference would that mean to the noise ?

Correct.
Some tubes w/filaments or indirect heating have little space or distance between Cathode and filaments, this may generate Hum when the heater is AC.
This is other advantage from DC Heaters aside better sound.

juszat · « **Reply #6 on:** 9 Oct 2017, 01:08 am »

Is filament heating is a design principle ? Meaning changing the tube won't address the problem ?

FullRangeMan · « **Reply #7 on:** 9 Oct 2017, 01:16 am »

Quote from: juszat on 9 Oct 2017, 01:08 am

Is filament heating is a design principle ? Meaning changing the tube won't address the problem ?

Is need to heat the filament in some way to it heat the Cathode to it emit Electrons, the heater circuit may be AC or DC.
AC heater is a cheaper way to do it, as DC heater circuit need more some resistors etc and more solder work, time etc.
A tube with more distance between filament and the Cathode will be free from the 60Hz AC noise coming from the filament and solve your noise prob.

Edited for corrections.