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Interactive Volume Hum Increase

2/1/2003 6:49 PM
Jason A
Interactive Volume Hum Increase
When using the "unused" volume as an interactive tone control, are you guys geting a large increase in hum? I was told that this should not happen when adjusting this control. I am using a star ground setup--1 ground for the AC cord ground, 1 for the PT CT's and output stage filtering and 1 for the preamp/PI stages and filtering. 3 seperate star grounds. I was advised to use Fender's original layout for the ground plate instead of using star grounds--and that this would eliminate the hum. Personally, I use star grounds in all of my other amps and really have no problem at all. The main reason I ask this question is because I don't want to undo the entire amp unless it is going to be worth it.  
2/2/2003 9:49 AM
Chris ( CMW amps )

In a 5E3 style amp I do use the same stargrounding but I also do use shielded wiring ( the so called RG174 cable ) in all my amps ...... no hum .  
good luck !  
2/3/2003 8:52 AM
Sean Kilback

I do seem to get some extra hum when turning the unused channel to MAX...but I never use it this way so it doesn't bother me.  
2/3/2003 10:13 PM

I get that as well in addition I get screeching when I turn volume up full, same with the tone.
2/8/2003 12:35 AM
Bruce J

When I turn the mic channel up my amp hums also. When I use either channel separately, no hum. Go figure?
2/8/2003 6:54 PM
Jason A
Any ideas on how to minimize this?
Yeah, either channel on it's own is fine. I measured approx 50 millivolts of hum/hiss on the speaker terminals with the tone control and bright volume up 1/2 way. When I activate the "unused" volume, it peaks at about 200 millivolts. It is fairly loud. In a band/practice situation, this is not a problem. However, if I were to use the amp for quiet passages in a recording situation, I woudl have to resort to a noise gate or filter. Yuck. I'd like to figure out how to minimize this hum on this circuit. I don't believe it is the tubes [I have swapped out many and have roughly the same measurements]. I am using the artificial CT [100R's from 6.3VAC secondary leg to ground]. There is no difference between connecting this to the 6V6 cathode [DC+] or ground. I was told to use the brass gound plane instead of the 3 point star ground setup. Any ideas/opinions?  
2/8/2003 8:06 PM
Bruce /Mission Amps

Is this a homebrew 5E3 or someone's kit Jason?  
Although 200mvac noise on the speaker output with everything dimed is not the end of the world, I don't think I've seen that much pure noise on one of these unless it was wired funny or there was a problem somewhere.  
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