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Topic: Soldered grounds, star grounds - but monkey-bar grounds? |
Jim Sliff
From:
Lawndale California, USA
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Posted 3 Feb 2010 7:20 am |
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One of my buddies brought this custom-build from '66 or so over for service. Pretty much an AA165 Pro Reverb front end, Twin-type SS rectifier, and multi-section can filters (and wired in such a painfully secure way that will make it a 2-hour replacement job...each!). PT codes are 18P154A 606620; nothing at all on the OT or speakers and I haven't pulled a pot yet (my inspection mirrors just can't get in there, and removing one...well, check out the ground "wire" behind the pots - it violates just about every tech rulebook regarding separation of preamp and power amp grounds - but this sucker, even with NO service performed (except a suspect resistor or two based on a visual inspection) has zero hum.
Pretty cool amp - he told me one of the Fender employees built it for his own use - made his own cab and silkscreened a normal Fender BF panel with "Custom Reverb Amp" script.
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No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Bill A. Moore
From:
Silver City, New Mexico, USA
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Posted 3 Feb 2010 8:21 am
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Jim, I used a similar grounding scheme with my "Twin" clone, and it's quiet for a Twin.
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Blake Hawkins
From:
Florida
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Posted 3 Feb 2010 8:59 pm
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Jim, I'm surprised you have not encountered that technique before.
It was very common in audio equipment of the '30's to the 60's. Used a lot in professional mixing
consoles.
The bus bar is grounded only at one end and the component connections are connedted with short leads.
From your picture, the fellow who wired that was
very familiar with that style of grounding.
Probably learned his electronics way back when I learned mine. 
I'll poke around my library and see if I can find
a text reference.
Blake |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 4 Feb 2010 1:40 am
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| Yup, a busbar connection is pretty common - http://en.wikipedia.org/wiki/Busbar - and are still commonly used in building wiring. Done properly, I think it's a good technique. |
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Ben Jones
From:
Seattle, Washington, USA
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Posted 4 Feb 2010 6:52 am
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I am guessing Jim has seen bus wire ground before. Just never one that was not soldered to the pot backs (marshall style)..is that right Jim?
Ive seen a couple "monkey bar" ground assemblies not on the pot backs. saw one attatched top the to of the board once. saw one under the board once. people do all sorts of stuff...and often it works fine. |
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Rich Hlaves
From:
Wildomar, California, USA
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Posted 4 Feb 2010 12:53 pm
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| I used a buss bar ground on my last build and it work out very well. Quiet as a church mouse. I started the buss at the normal channel inputs (DR AB763) and continued all the way across the control pannel and terminated at a connector I mounted at a PT bolt. From there I continued across the rear pannel ending up at the reverb RCAs. Ultimately all the chassis grounds are connected so I felt this might help keep the beast quiet. It worked out great and I am not relying on any mechanical only connections with dissimilar metals, a source of hum in Fender guitars and amp for years. |
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Bill A. Moore
From:
Silver City, New Mexico, USA
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Posted 4 Feb 2010 2:25 pm
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I can't give the scientific reason for using that type ground in my "Twin" build, other than making every ground the same potential, all the way back to the green AC wire.
In the automotive field, we're always chasing a poor ground connection to make some system work,(it's especially bad with the modern cars with ma current draws). |
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