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Topic: Session 400 Limited hum |
Peter Freiberger
From:
California, USA
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Posted 19 Nov 2014 6:22 pm |
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I have a Session 400 Limited. I like the tone but the basic noise level is a bit more than I'd like. I know nothing about electronics, but I can order parts and solder. I have successfully re-capped two older Session 400's according to Brad Sarno's Geek Page. They are quiet and sound great:
http://home.earthlink.net/~bradsarno/session_400page.html
I think what I should start with on the Limited is replacing the big black filter caps and put in .47uF film bypass caps Brad recpmmends. On the Limited the big caps are axial. How do I put in the bypass caps (if this is even the right thing to do)? Should I replace the other large blue and gray caps while I'm at it? Transistors, too?
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 19 Nov 2014 8:55 pm
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If you want the bypass caps you'll have to piggy-back them across the big black ones, since they're axial, not radial like Brad shows. They can't hurt! Make sure they're rated for at least as much as the big black ones (63V). The 8200uF/63V value looks great for the big ones.
The smaller ones will have less effect (unless there's something wrong with one)... have you done anything to the chips (op-amps)? This is a common place to throw money at for these amps IIRC. I certainly wouldn't worry about the big transistors until I went through most everything else.
_________________
New FB Page: Lap Steel Licks And Stuff: https://www.facebook.com/groups/195394851800329 |
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Peter Freiberger
From:
California, USA
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Posted 20 Nov 2014 6:37 am
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| Thanks, Stephen. By "piggy back" you mean I should run the bypass cap from front to back on each filter cap, I take it. |
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 20 Nov 2014 8:29 am
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| Peter Freiberger wrote: |
| Thanks, Stephen. By "piggy back" you mean I should run the bypass cap from front to back on each filter cap, I take it. |
That's correct... they'll have slightly more inductance, having more lead length... but the purpose here is to give the performance (as near as possible) to a 'perfect' capacitor... all capacitors (indeed, all components) have an inductance, resistance, and capacitance associated with them... the 'bypass' cap is trying to give the benefits of both big (lots of uF) and small (not much L) geometry capacitors. They certainly don't add much uF. Observe polarity, as always with electrolytic caps... same polarity as the one they're paralleled with.
_________________
New FB Page: Lap Steel Licks And Stuff: https://www.facebook.com/groups/195394851800329 |
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John Booth
From:
Columbus Ohio, USA
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Posted 20 Nov 2014 8:35 am
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Looks like someone sneezed on those caps 
_________________
Jb in Ohio
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GFI S10 Ultra, Telecaster, a Hound Dog, and an Annoyed Wife
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Peter Freiberger
From:
California, USA
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Posted 20 Nov 2014 9:07 am
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| The bigger caps are hot glued down, so they don't vibrate loose, I believe. |
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Ernie Renn
From:
Brainerd, Minnesota USA
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Posted 20 Nov 2014 11:37 am
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Peter;
As silly as this is, take your bar and smack it down on the top of the amp, (not so hard as to dent the cabinet, but flat on the top with the butt of the bar), and see if the hum stops.
I have an old LTD that about once a year it'd start humming. It turned out that some of the solder joints had loosened somehow. I'd go thru it and resolder most of the connections and it'd be fine. My electronic tech told me that the rap on the top would seat the connections temporarily.
I don't know if this is what's going on with your amp, but it only takes a few moments to see...
Best of luck taming the hum...
EDIT: Don't solder or disassemble the amp without unplugging it from the electrical outlet.
_________________
My best,
Ernie
www.BuddyEmmons.com
Last edited by Ernie Renn on 20 Nov 2014 7:55 pm; edited 1 time in total |
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John Booth
From:
Columbus Ohio, USA
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Posted 20 Nov 2014 12:55 pm
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| Ernie Renn wrote: |
Peter;
As silly as this is, take your bar and smack it down on the top of the amp, (not so hard as to dent the cabinet, but flat on the top with the butt of the bar), and see if the hum stops |
I second that. I have has several Peavey amps that get cold solder contacts and hum or even quit. If smacking it helps one of them is not making good contact.
_________________
Jb in Ohio
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GFI S10 Ultra, Telecaster, a Hound Dog, and an Annoyed Wife
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Peter Freiberger
From:
California, USA
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Posted 20 Nov 2014 1:08 pm
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| Interesting technique. I'll try it. I've used it on other appliances. Been tempted to use it on my kids, but haven't... so far. |
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Clyde Mattocks
From:
Kinston, North Carolina, USA
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Posted 20 Nov 2014 1:16 pm
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I have had success in reducing hum in Session 400's by simply rerouting wiring. However, you must be extra careful when working in there with the amp powered up. Simply move the wires around (you may have to clip some of the little plastic ties) and listen for a reductuon in hum. Of course, if the filter caps need replacing, this is not going to help.
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LeGrande II, Nash. 112, Fender Twin Tone Master, Session 400, Harlow Dobro, R.Q.Jones Dobro |
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