Dennis Detweiler
From:
Solon, Iowa, US
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Posted 1 Oct 2012 6:47 am |
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To Electronic Wizards:
I have two Session 400's (1970's) which are both very quiet. I have a Session 400 LImited (1980's) that has too much 60 cycle hum. All three amps have recently been upgraded and have new filter caps. Is there a method of quieting the Limited a little more? Adding more smaller filter caps in parallel to the existing filter caps? I live within 100yds of a power station, which is the real problem. I get the hum with nothing plugged into the input. How about preamp power supply? Ideas?
Thanks
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1976 Birdseye U-12 MSA with Telonics 427 pickup, 1975 Birdseye U-12 MSA with Telonics X-12 pickup, Revelation preamp, Carbon Copy Delay and Hall Of Fame Reverb, Crown XLS 1002, 2- 15" Eminence Wheelhouse speakers, ShoBud Pedal, Effects Pedals. 1949 Epiphone D-8. |
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Jerry Fleming
From:
Roanoke, Virginia, USA
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Posted 1 Oct 2012 8:36 am
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Hi Dennis,
One explanation or theory why the Session 400 Limited is more susceptible to the high intensity emissions might be, the Session 400 Limited has several more (leakage ports) with the effects loops and return amplifiers. Also the power supply routing for the OPAMPS is more complex and harder to decouple at 60 Hz than the older Session BJT circuitry. I would unplug the reverb cables and ground the input to see if the hum changes. If it does try better shielded coax for the reverb pan interface cabling. Another possibility is adding better shielding with aluminum tape on the top of the cabinet similar to what Fender did with screen mesh. Inductive coupling can be a difficult problem to solve. You could investigate the power quality of your service feed with an AM radio. See if it hums close to the ground connections. Being so close I doubt the power company is going to offer to help analyze the problem.
Good luck and best wishes, I hope this helps.
Jerry |
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