Tube Amps / Music Electronics
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|10/26/2000 8:13 PM|
||Is ground switch unnecessary?|
Someone here said recently that a ground switch is completely unnecessary if you have a 3-conductor power cable and connect the ground wire to the chassis. I'd like to hear other persons' opinions on this. If it's true, then the hole would make a nice location for an OP impedance switch.
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|10/26/2000 8:53 PM|
Yes - with a properly wired 3-prong input the ground switch is not needed.
Oddly, I've seen ground switches (A-off-B) on some 3-prong amps (Fender TR-ii and a couple of boogies).
|10/26/2000 9:20 PM|
Not needed and also potentially dangerous...If that cap shorts, there is a 50/50 chance of having line voltage on the chassis. All Silver Face amps with 3 prong plugs also have a ground switch, as do some Marshalls (certain years, US export I think). It is sort of funny, the reissue Fenders have a ground switch, but it is disconnected.
|10/26/2000 9:46 PM|
Yes, some RI-Fenders have a cosmetically-only ground switch. That's pretty strange. I've got some pre-CBS dust and cobwebs I could sell to Fender to put in the back of their amps, for authenticity sake, of course.
On my amps, I install a ground switch and a ground lift switch. The ground switch is a 3-position with a center-off, no connection, and the lift switch disconnects the green wire, which is the round pin on the AC plug, from ground. I don't use these features all the time but there have been a few sessions that enabled me to get my rig much quieter than would have otherwise been possible.
For a recording amp, I like 'em in there but if you have a 3-prong power cord on your amp (and you should) then, you should also have a center-off position on that ground switch. This is just the other side of the argument. In England, they're called the 'Death Switch'.
|10/26/2000 10:19 PM|
||Re: Another take on this...|
In the Dave Funk tube amp workbook, there is a section on leaving the ground switch in line. He uses the original 2 position switch. Is this dangerous? I just got done wiring my BMR this way and I want to know if I should change it. - Jeremy
|10/26/2000 10:20 PM|
||Re: Is ground switch unnecessary?|
Thanks guys, it sounds like for gigging & practice that space would be better used for an impedance switch. I don't think I need all the ground options Bob is using, though it's interesting info.
I think most amps made in the 70s had 3-prong plugs and a ground switch. My SF Twin does, my Musicman HD130 did, and I think my SF Princeton Reverb did. I guess old habits die hard.
|10/27/2000 1:11 PM|
I play through old Fenders. Bruce is always changing them over to 3 prong and I'm always a little bummed when he does that. I don't like the way that looks on an old amp and also, I like to be able to quiet the hum by flicking the ground switch on my old Fenders.
But for gigging, the 3 prong will keep you from getting electrocuted. At home or in the studio, I much prefer a ground switch that works! Ussually, I can just use a two prong adapter and the ground switch will work again. I think if you have a vintage amp that originally came with a two prong AC plug and you're not going to gig with it you should leave it that way.
Also, I like to play in stereo and to eliminate ground loops, I have to eliminate the third prong on one of my amps, even tho they're both plugged into the same power strip. Ussually an adapter will accomplish this. Sometimes I file down the oversize plug so I can turn the plug around in the wall and reverse the ground.
So, IMO, I prefer a ground switch that works if I'm at home or in the studio. And it's nice to be able to reverse the ground on gigs too...BUT the 3 prong is safer, just like all the experts say. Lew
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