ground loops II- The Two Amp Rig

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tdbajus
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ground loops II- The Two Amp Rig

Post by tdbajus » Tue Apr 20, 2010 7:05 am

  • I just finished building a tweed deluxe-ish copy, which I would like to use for recording in conjunction with my trusty blackface Deluxe (I like 6V6s.)

    However, previous attempts to run more than one amp at a time have been met with horrific amounts of noise, presumably from ground loops.

    For those who noticed, I was finally able to get a nice sounding DI out of my peterson strobostomp mkI when I found, through some helpful guidance, to the internal DIP switch that lifted the ground.

    I have a couple of questions, now:
    • How do people ordinarily run two amps at the same time, without using the 3prong->2prong adapter? I mean in parallel- not connecting the 2nd input jack from the first amp to the second.

      Could I make a ground lift by installing 2 jacks in a plastic box, and only connecting the tips, while insulating the sleeves?
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Re: ground loops II- The Two Amp Rig

Post by Nick Sevilla » Tue Apr 20, 2010 8:06 am

tdbajus wrote:
  • I just finished building a tweed deluxe-ish copy, which I would like to use for recording in conjunction with my trusty blackface Deluxe (I like 6V6s.)

    However, previous attempts to run more than one amp at a time have been met with horrific amounts of noise, presumably from ground loops.

    For those who noticed, I was finally able to get a nice sounding DI out of my peterson strobostomp mkI when I found, through some helpful guidance, to the internal DIP switch that lifted the ground.

    I have a couple of questions, now:
    • How do people ordinarily run two amps at the same time, without using the 3prong->2prong adapter? I mean in parallel- not connecting the 2nd input jack from the first amp to the second.

      Could I make a ground lift by installing 2 jacks in a plastic box, and only connecting the tips, while insulating the sleeves?
Usually, when I need to run a recording / live rig with one guitar going to multiple amplifiers, I tend to rent a Radial box, the Injector :

http://www.sweetwater.com/store/detail/JD7/

They now have cheaper alternatives like the JDV mk3, which has two inputs, for two guitars, and 4 outputs for different amps plus recording direct.

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tdbajus
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Post by tdbajus » Tue Apr 20, 2010 9:04 am

That thing looks very cool, but it seems perhaps a bit much for just me and my project studio.

In the interests of saving some money for a michael joly mod,

has anyone used any of these:

passive- http://www.sweetwater.com/store/detail/BigShotABY
active, solid state- http://www.sweetwater.com/store/detail/TwinCityABY
active, tube- http://www.sweetwater.com/store/detail/Switchbone
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Post by roscoenyc » Tue Apr 20, 2010 11:38 am

Ground one amp (3 prong)
lift the rest (2 prong) including pedalboard if it is AC powered.

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Post by swafford » Tue Apr 20, 2010 1:31 pm

I've used the Radial ABY, Kendrick ABC and currently run stereo off a Fulltone TTE and have never had an issue with noise on any of the 7 or 8 amps I own. Some of the older ones are not grounded, but I never have a need for a ground lift.

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Post by roygbiv » Tue Apr 20, 2010 2:00 pm

also, try to run both amps and all pedals off the same power-strip/extension cord.
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Post by ashcat_lt » Tue Apr 20, 2010 3:34 pm

roscoenyc wrote:Ground one amp (3 prong)
lift the rest (2 prong) including pedalboard if it is AC powered.
As I said in the other thread:
ashcat_lt wrote:DO NOT DEFEAT THE SAFETY GROUND ON ANY PIECE OF EQUIPMENT!!! It's called a "safety ground" for a reason. Those little adapter things you can buy are not "ground lift" plugs. They are adapters meant so you can plug a 3-prong plug into a 2-prong hole. There is always a screw tab on these things. The screw in the middle of the outlet goes through this, connects to the metal box, which connects to ground. If that screw is not in place, or (worse yet) the outlet box is not connected to ground, this adapter is no safer than just snipping off the third prong.

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Re: ground loops II- The Two Amp Rig

Post by Andy Peters » Tue Apr 20, 2010 10:13 pm

tdbajus wrote:
  • I just finished building a tweed deluxe-ish copy, which I would like to use for recording in conjunction with my trusty blackface Deluxe (I like 6V6s.)
So describe exactly how the power-supply transformer and the mains power is wired.

The mains ground MUST connect to the amp chassis.
The mains hot goes through a fuse and one pole of the power switch to one side of the power transformer primary.
The mains neutral goes to the other side of the power transformer primary. (More recent TUV requirements indicate that a double-pole switch be used, switching both hot and neutral, and fusing both.)
There should be NO capacitor to ground through a "ground switch" to either hot or neutral. If it's there, REMOVE IT.

One terminal of the power transformer secondary should tie to chassis as the circuit ground return. The other side goes to the plates and such. Obviously the heaters are fed from the heater winding.

Wired correctly -- and vintage amps most certainly are not -- you will have no trouble using multiple amps in parallel without having to defeat the safety ground.

If you have to defeat the safety ground to get the gear quiet, the gear is BROKEN.

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Re: ground loops II- The Two Amp Rig

Post by Darlington Pair » Wed Apr 21, 2010 10:05 am

tdbajus wrote:
  • I just finished building a tweed deluxe-ish copy, which I would like to use for recording in conjunction with my trusty blackface Deluxe (I like 6V6s.)

    However, previous attempts to run more than one amp at a time have been met with horrific amounts of noise, presumably from ground loops.

    For those who noticed, I was finally able to get a nice sounding DI out of my peterson strobostomp mkI when I found, through some helpful guidance, to the internal DIP switch that lifted the ground.

    I have a couple of questions, now:
    • How do people ordinarily run two amps at the same time, without using the 3prong->2prong adapter? I mean in parallel- not connecting the 2nd input jack from the first amp to the second.

      Could I make a ground lift by installing 2 jacks in a plastic box, and only connecting the tips, while insulating the sleeves?
DO NOT pay attention to the guy that told you to lift grounds! I wish people would keep dangerous advice to themselves.

Build one of these, it works quite well. http://www.geofex.com/FX_images/humfree2.gif

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Re: ground loops II- The Two Amp Rig

Post by tdbajus » Wed Apr 21, 2010 10:10 am

wavley wrote: Build one of these, it works quite well. http://www.geofex.com/FX_images/humfree2.gif

I have been looking for a schematic from something like that. I wonder if there are different options re:transformers.
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Re: ground loops II- The Two Amp Rig

Post by Darlington Pair » Wed Apr 21, 2010 10:46 am

tdbajus wrote:
wavley wrote: Build one of these, it works quite well. http://www.geofex.com/FX_images/humfree2.gif

I have been looking for a schematic from something like that. I wonder if there are different options re:transformers.
I used Triad transformers in mine, got them from mouser, they're a little more expensive than the ones in the schem (like $3 for his $4 for the triad) it seems that any 10K 10K or 15K 15K 1:1 transformers should work fine. Or if you wanna go for the Jensen or something higher quality if you want to drop the dough. RG is a great guy, that website is wonderful and he's always giving great advice at diystompboxes.com

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Post by Marc Alan Goodman » Wed Apr 21, 2010 11:02 am

True, it's a better solution. But most of the time you'll be find lifting grounds. It's the 0.01% of the time when the power situation is totally fucked and you grab the microphone with your right hand while holding the strings with your left that it becomes a serious issue. Very serious, very fast.

Personally I always keep a clown nose in my guitar bag and throw it on any venue microphone. Not only does it keep my from frying myself but it keeps germs and the smell of the last dudes breath out of my face. Extremely worthy investment. You can get a bag of black and flesh colored ones so you don't have this giant red thing in front of your face the whole set.

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Post by Darlington Pair » Wed Apr 21, 2010 11:36 am

Marc Alan Goodman wrote:True, it's a better solution. But most of the time you'll be find lifting grounds. It's the 0.01% of the time when the power situation is totally fucked and you grab the microphone with your right hand while holding the strings with your left that it becomes a serious issue. Very serious, very fast.

Personally I always keep a clown nose in my guitar bag and throw it on any venue microphone. Not only does it keep my from frying myself but it keeps germs and the smell of the last dudes breath out of my face. Extremely worthy investment. You can get a bag of black and flesh colored ones so you don't have this giant red thing in front of your face the whole set.
This is why I have transformer isolation between me and my amps, bring my own mic, and since I run an svc-350 vocoder with it's own mic pre I give the house guy a di so I'm transformer isolated there... no shocks, less noise, and grounded equipment.

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Post by roscoenyc » Wed Apr 21, 2010 9:05 pm

roscoenyc wrote:Ground one amp (3 prong)
lift the rest (2 prong) including pedalboard if it is AC powered.
You know guys,
as a guy who used multiple amps for many (25+) years
the above is what I used to do.
I never got a shock from that setup because of the way the ground lifts handle polarity.

but.

I haven't had any of the ground problems in quite some time using 2 amps and a pedalboard that uses an AC power supply.

I do have an Isolated Ground Transformer setup that I take out with my larger rig

but

I haven't had trouble lately grounding the small local (2 Pro Jr's and a pedalboard) gig rig either.

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Post by Andy Peters » Wed Apr 21, 2010 9:10 pm

Marc Alan Goodman wrote:Personally I always keep a clown nose in my guitar bag and throw it on any venue microphone. Not only does it keep my from frying myself...
Until it gets a bit wet from the usual spit and such, at which point it becomes conductive ...

-a
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