screening a phono cable - Page 2

woodturner-fran · 24th August 2007, 12:26 AM

Yep.

What I need to do is pull out the rack (

) unplug everything and then add them back in one by one and see what I get.

What a right royal PITA.

Fran

SY · 24th August 2007, 12:28 AM

If the hum is 100Hz, then Arnold is right, you've got to get your preamp in order. Does the hum go away when the cables are disconnected from the input? If you put shorting plugs on the input, is there still hum?

Assuming "yes" and "no," you really are picking up hum externally. As to your preamp...

Quote:

...you need either a balanced preamp or an input transformer (I use the latter).

If the preamp hums with open or shorted inputs, you've got to clean up its grounding. Grounding is ultra-critical for low-level circuits with lots of bass boost.

woodturner-fran · 24th August 2007, 01:27 AM

Ok,

disconnecting even one of the input cables into the phonostage makes the hum dissappear. I think the hum is 50Hz (my mains frequency) but being new at this means I'm not 100% sure.

I think I'll investigate the whole grounding in my system. Perhaps theres some kind of ground loop between components thats somehow being magnified by the high gain of the phonostage and thats why I'm seeing it there.

Really annoying this is!

Fran

SY · 24th August 2007, 03:08 AM

Classic hum loop, which is nice because the fixes are well-known. Going balanced is the surest, highest performance, and most difficult way. Does that preamp use an input transformer? If so, balanced will be easy.

Do you have your arm grounded to the turntable and the turntable ground connected to the preamp chassis?

woodturner-fran · 25th August 2007, 02:00 PM

OK the good news: this problem is sorted. Yes SY it was a hum loop - got it sorted out - and I'll post some details over in the Phonoclone thread soon.

As for input transformer - SY, have you got a glass of malt in your hand? Are you sitting down...

Its a SS amp using opamps...

Please forgive me for straying form the true path of tubes...

yours (humbly bowing)

Fran

SY · 25th August 2007, 02:24 PM

He weighs the same as a duck! He's a witch! Burn him!

woodturner-fran · 25th August 2007, 03:31 PM

tell you what - it must be some duck - supply a cities worth of chinese restaurants that duck would!!!

fran

arnoldc · 26th August 2007, 08:25 AM

Glad the problem has been solved.

I'm currently auditioning a Tango phono stage from Acoustic Signature, and this one is good!

It does not need a ground wire when used with my Clearaudio 'table, but requires one when use my JVC or Technics.

24th August 2007, 03:08 AM	#14
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Classic hum loop, which is nice because the fixes are well-known. Going balanced is the surest, highest performance, and most difficult way. Does that preamp use an input transformer? If so, balanced will be easy. Do you have your arm grounded to the turntable and the turntable ground connected to the preamp chassis? __________________ “There are no greater liars in the world than quacks, except for their patients.” - Benjamin Franklin

25th August 2007, 02:24 PM	#16
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	He weighs the same as a duck! He's a witch! Burn him! __________________ “There are no greater liars in the world than quacks, except for their patients.” - Benjamin Franklin

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24th August 2007, 12:26 AM	#11
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	Yep. What I need to do is pull out the rack ( ) unplug everything and then add them back in one by one and see what I get. What a right royal PITA. Fran

24th August 2007, 01:27 AM	#13
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	Ok, disconnecting even one of the input cables into the phonostage makes the hum dissappear. I think the hum is 50Hz (my mains frequency) but being new at this means I'm not 100% sure. I think I'll investigate the whole grounding in my system. Perhaps theres some kind of ground loop between components thats somehow being magnified by the high gain of the phonostage and thats why I'm seeing it there. Really annoying this is! Fran

25th August 2007, 02:00 PM	#15
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	OK the good news: this problem is sorted. Yes SY it was a hum loop - got it sorted out - and I'll post some details over in the Phonoclone thread soon. As for input transformer - SY, have you got a glass of malt in your hand? Are you sitting down... Its a SS amp using opamps... Please forgive me for straying form the true path of tubes... yours (humbly bowing) Fran

25th August 2007, 03:31 PM	#17
woodturner-fran diyAudio Member Join Date: Jan 2006 Location: Ireland	tell you what - it must be some duck - supply a cities worth of chinese restaurants that duck would!!! fran

26th August 2007, 08:25 AM	#18
arnoldc diyAudio Member Join Date: Apr 2003 Location: Makati	Glad the problem has been solved. I'm currently auditioning a Tango phono stage from Acoustic Signature, and this one is good! It does not need a ground wire when used with my Clearaudio 'table, but requires one when use my JVC or Technics.

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