F3 - Small humming noise, how to get rid of it - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st March 2010, 10:21 PM   #1
diyAudio Member
 
Join Date: Sep 2006
Default F3 - Small humming noise, how to get rid of it

The left channel of the F3 has a light humming. When the F3 runs without any RCA / input connected, it is dead silent on both channels. If I connect the active crossover, the left channel has a light humming. The right has none, dead silent. The active crossover allows to switch on / off the channel. If I switch off the channel where the F3 is connected, the humming disappears. If i swap the left and right input on the F3, the humming remains on the left. I also changed the cable thinking it was the culprit, but not. The crossover output voltage specs are 2.5v / 50ohms with a minimum load impedance of 600ohms. Would any of you be kind to advise me in which direction i could look. Many thanks
  Reply With Quote
Old 21st March 2010, 10:27 PM   #2
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
As usual, I have to ask the question - is this a commercial F3
or a DIY version?

  Reply With Quote
Old 23rd March 2010, 03:58 PM   #3
diyAudio Member
 
Join Date: Sep 2006
Default F3

It is #547, built by the master (i.e you)
[Best
  Reply With Quote
Old 23rd March 2010, 07:38 PM   #4
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
In that case, it is very likely a ground loop with the RCA
input connectors, since the commercial version has a
regulated supply.

I would start by checking the noise for each channel with
only a shorting plug on the input, which will eliminate an
external loop.

  Reply With Quote
Old 26th March 2010, 12:17 AM   #5
diyAudio Member
 
Join Date: Sep 2006
Default Humming - what tests were done

Thanks for the advise, this is exactly what I did
-the left channel has a slightly more audible humming than the right
- if I unplug the left RCA from the left input there is almost no humming, comparable to the right side
- if a shorten the left input the humming becomes slightly more audible than when not shortened
- i connected the left input channel into the right output channel of the xover the noise on the left channel is exactly the same (i suspected it could be the xover)
- i changes the connecting cable suspecting one could be faulty, but nothing
-whenever i connect / disconnect a RCA on the left channel there is a smal 'clac' in the loudspeaker, phenonenon which is not present if i do the same operation on the right channel. Nothing that would risk damaging the driver.
When everthing is silent, at night, i can here the light humming on the left channel. I've been trying to find out where it comes. Of couse i could easily putr an lpad on the left amp, about 4-5db

Regards
  Reply With Quote
Old 26th March 2010, 03:05 AM   #6
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
My records indicate that you have had this amp for about
3.51 years. Has it always done this, or is this a new noise?

  Reply With Quote
Old 26th March 2010, 08:35 AM   #7
diyAudio Member
 
Join Date: Sep 2006
You're right. It had it from the beginning, but I thought it was normal and since the driver is a 106db you proposed me to address it with a lpad, which worked fine. Now with the arrival of the J2 :-) and the F5 :-) and your upgraded F2J i revisited the whole set up. I wanted to see how far I could lower the value of the Lpad. And this is how it came that the left channed was making slightly more noise than the right. And I started wondering why.... I can perfectly carry on with a lpad, although i would rather before see if there are other was to address it. Thanks.
  Reply With Quote
Old 26th March 2010, 07:40 PM   #8
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
The noise figures when they leave my bench are about
100 uV, and it is not unusual for one channel to have more
noise than the other, as the transformer field radiation is
somewhat random.

That said, 100 uV is still a very low noise figure. 105 dB
drivers will certainly bring that out. We could lower the
gain of the amp, easily done by inserting resistance in series
with the positive input. I would try 4.7K to 10K values,
which your tests indicate will take the noise down further.

Another option would be to isolate the grounds of the two inputs
by driving the input with an line level isolation transformer.

  Reply With Quote
Old 27th March 2010, 09:10 AM   #9
diyAudio Member
 
Join Date: Sep 2006
Default F3 - light humming, solutions

Thanks, i guess I'll try first the resistance in serie with the left input. I guess i'll try with a variable one in order to determine the minimal value.

Since I'm by far not a knowledgeable in this field, i would need a bit more explanation for "Another option would be to isolate the grounds of the two inputs by driving the input with an line level isolation transformer."
Would that mean on the left input line a transformer would need to be inserted between the RCA input and the print ? Are there specifications for this line level isolation transformer ?

From a specifications perspective what would be the most prefered approach ?

Thanks
  Reply With Quote
Old 31st March 2010, 10:27 AM   #10
larryho is offline larryho  United States
diyAudio Member
 
Join Date: Nov 2009
Location: Folsom
Hi, Nicola,

Just want you to know, although my F3 doesn't have the hum problem, My speaker is 104db. Install a new pair line level input transformer actually brings a sonic improvement. You can even do the balance input and totally noise free.

FYI.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Humming Noise in my amplifier??? lock dogg Chip Amps 29 23rd February 2006 12:33 PM
Get Rid of the Small SMD Capacitors on CDROM for Better Sound rickronn Digital Source 18 8th October 2005 10:39 AM
Small humming, but want's to get rid of it ! 2Bak Chip Amps 6 7th March 2004 07:42 AM
Trying to figure out how to get rid of noise, help is welcome! Jean Solid State 41 26th June 2003 05:02 AM


New To Site? Need Help?

All times are GMT. The time now is 06:01 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2