Hum with two amp set-up

Randy Cook · Post by **Randy Cook** » 9 Dec 2004 5:13 am

I have two peavey amps, both of which are really very quiet when played by themselves. When I try to use a two-amp set up the Nashville 400 develops a somewhat loud hum. This happens when I jump a cord from one amp to the other or when I try two feeds from my volume pedal. How do I eliminate the hum? What is the best way to wire the two amp set up?

Jack Dougherty · Post by **Jack Dougherty** » 9 Dec 2004 5:24 am

Randy..

Try using a grey adaptor plug on one of the amps only...Two prong...The two amps when used from the same power source cause a cycle hum...The adaptor eliminates one of the amps grounding wires and the hum should go away...I used this system for years... Hope this helps..

JD[This message was edited by Jack Dougherty on 09 December 2004 at 05:26 AM.]

Darvin Willhoite · Post by **Darvin Willhoite** » 9 Dec 2004 6:12 am

Jack is exactly right. I use a bass amp driven with the crossover output of my Session 500 and I use the two prong adapter on the bass amp. That eliminates the problem.

PLEASE DISREGARD THIS POST AND READ MY LATER POST ON DOWN THE LIST. DLW

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Darvin Willhoite
Riva Ridge Recording

[This message was edited by Darvin Willhoite on 15 December 2004 at 05:54 AM.]

Mike Brown · Post by **Mike Brown** » 9 Dec 2004 8:51 am

This "symptom" will not occur when always using two amps though. A ground lift plug such as you described will help in solving the buzz problem most of the time. I carry two or three with me to every gig.

Brad Sarno · Post by **Brad Sarno** » 9 Dec 2004 1:01 pm

When there are two amps that are grounded and connected together, the ground wires in the power cords and audio cords create an actual loop. That loop is an inductor and the 60Hz in the air actually induces current in the ground conductor of the audio cables that connect the two amps. It's all based on the area of the loop. If you could theoretically reduce the area of that loop to zero, the hum would go away. That's not real practical, so lifting the ground of one amp, usually fixes it. Never lift both grounds. They call it "safety ground" for a reason.

Lift grounds at your own risk!!!

Brad Sarno[This message was edited by Brad Sarno on 09 December 2004 at 10:51 PM.]

Paul Matthews · Post by **Paul Matthews** » 9 Dec 2004 1:29 pm

NEVER EVER LIFT THE GROUND ON A POWER CONNECTOR.

Sorry about shouting like that, but the grounds are there for safety and kind of important.

Are both amps connected to the same power source? If not plug them into the same power circuit.

Then check ever signal lead carefully. If any are old or tatty, try a different lead.

Paul.

Paddy Long · Post by **Paddy Long** » 9 Dec 2004 1:57 pm

Same issue for a rack ? -- if you have all the units in the rack EG: DPC750/profexII/Tuner initially going to a plug board, then to the power source, do you need to lift the ground on everything, except the power amp ?? Just asking from a safety point of view, because sometimes I do get quite a bit of hum through the Nash E115's.

Ken Fox · Post by **Ken Fox** » 9 Dec 2004 3:23 pm

Use a Hum-x by Ebtech on the line cord of one amp. I just got one and it works great.

This thing eliminated the hum and still has the amp grounded. I am an electrician by trade, I do know the dangers of lifting a ground! I did it for years on a two amp setp, but no more!

Here is a link: http://www.musiciansfriend.com/srs7/g=home/search/detail/base_id/113645

Paul Matthews · Post by **Paul Matthews** » 10 Dec 2004 12:26 am

Paddy, lifting the *power* ground on ANYTHING is very risky. The ground is an important safety facility.

Please bear in mind that we often turn up at places and rarely do any checking of the power. If we lift the ground on power and someone else gets electrocuted we have major problems. Albeit not as great as the poor sod we just killed...

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Absolute beginner!
Bennet Freshman E9 3+3

David L. Donald · Post by **David L. Donald** » 10 Dec 2004 1:03 am

If you are getting a LOUD obnoxious hum, it is because the grounds are interacting,
lifting one ground will be generally safe,
because the other will still be in use,
and the same connection that created the hum, will be now grounding the ungrounded amp.

You have switched where the ground is being attached. if you do this though,

put BOTH amps on the same bus bar or multi plug extentsion,

thus all their hot leads and the ground will be from the exact same sourcres.

Never run an extention to another wall plug and then lif a ground ....

This is best with similar make amps. Some amps won't work with other makes well, because of differenig designs.
But two Peaveys shouldn't be an issue.

The grounding connect through the guitar chord will not be as strong as the lifted AC plug ground was, so these precautions are needed.

Always try flicking the BACK of your hand, very quickly past a PA mic, while touching the instrument also with the back of the hand.

Why the back.?
Because IF there is a high amperage or voltage connection from a bad ground scheme,
the electrcity will naturally make you hand muscles constrict, or grab,
and then you can let go... vewrt bad, that..

The back of the hand brushing by will constrict even after a zap, but not grab anything,
and the momentum of your arm will allow the connection to be broken.
NEVER test it with your moist mouth.. E GADS, no.
[This message was edited by David L. Donald on 10 December 2004 at 01:14 AM.]

Mike Wheeler · Post by **Mike Wheeler** » 10 Dec 2004 5:51 am

About lifting a ground on a two amp setup...I NEVER lift any grounds on ANY AC device. In a two amp setup, for instance, lifting one of the amp grounds makes the ground connection for that amp the ground wire in the interconnected audio cable. I've seen that audio cable melt when a serious AC fault occured.

So, what to do? Lift the ground on ONE end of the interconnected audio cable at the point where it is connected INSIDE the audio connector. This way, there isn't any signal wire exposed and it eliminates the 60 cycle loop hum.

The whole idea is to ground each amp, but eliminate any other SHARED grounds. This breaks the "loop", but preserves the safety ground. Learned this when I used to build recording studios, and such, back in the days.

David L. Donald · Post by **David L. Donald** » 10 Dec 2004 6:36 am

Never seen a connecting wire melt in 40 years,
but this other method also can work.
It may be safer, but it also doesn't always work in some set ups.

I think when you did have the amp connector cable melt,
it was because of one of those incompatible amp types I mentioned before. Or separate circuits.

Were both amps connected to the same buss bar,
or to separete wall circuits?...
the most likely cause for this extreme phenonminon.

James Quackenbush · Post by **James Quackenbush** » 10 Dec 2004 6:53 am

Another thing to be aware of is if you have a bunch of stuff running off of one circuit in your home, THIS will cause hum, and also check for dimmer switches ( major culprit) and also flouresant lights wreak havoc .... A good balanced power conditioner is another good thing to have..
Expensive ? Yes......Worth having ?....If you want CLEAN, SAFE, power that will also keep the line voltage right and save whatever you have plugged into it , then it's WELL worth it ...I keep line conditioners on ALL my gear ....How much is your gear worth to you ?.....How much is a clean, safe, and quiet tone worth to you ?......It's your call.....Jim

Bill Terry · Post by **Bill Terry** » 10 Dec 2004 7:16 am

I agree with Mike Wheeler. I've also seen the interconnecting cable become a 'fuse', albeit a poor one. If the ungrounded amp has some sort of catastrophic failure and high voltage goes to ground there, it goes right through the cable to ground on the other amp.

Mike Bowles · Post by **Mike Bowles** » 14 Dec 2004 1:23 pm

This is for Ken fox will this eliminate the hum of a tele when I remove my hand from the guitar I would appreciate any help from anyone Thanks

Paddy Long · Post by **Paddy Long** » 14 Dec 2004 8:03 pm

If for example in my rack, the power amp is grounded but the Profex/tuner are not, but they are all plugged into the same plug board - then go to the one power source is everything safely grounded ?? The plug board has the earth wire properly connected.

Darvin Willhoite · Post by **Darvin Willhoite** » 15 Dec 2004 5:53 am

Well of course, I should have known you can lift the ground on one of the cables from the pedal and have a much safer setup; or in my case the cable between the Session 500 crossover output and the bass amp. Please dis-regard my first post for safety reasons. I think I'll make some cables with the ground connected to one end only and paint the plug red or something so I'll know what its for. You guys may have saved me a very shocking experience.

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Darvin Willhoite
Riva Ridge Recording

[This message was edited by Darvin Willhoite on 15 December 2004 at 05:56 AM.]

Ken Fox · Post by **Ken Fox** » 15 Dec 2004 10:02 am

Mike I do not think it will help a Tele much! I went to Bill Lawrence pickups in my new Tele with a Bigsby (routed for a Strat middle after I bought it!). My 1997 American Deluxe Plus has vintage noiseless. My 1983 still hums (Tele neck, Strat middle and a Seymour Duncan lead).

Mike Bowles · Post by **Mike Bowles** » 15 Dec 2004 12:32 pm

Thanks a lot Ken my tele doesnt do this all the time just some places

basilh · Post by **basilh** » 16 Dec 2004 3:50 pm

Whatever draws the most current has the least resistive path to earth (ground).

If you only ground (earth) one of the amps, make sure to mark the other as earth lifted, to avoid accidents..

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Steel players do it without fretting

http://www.waikiki-islanders.com

Al Terhune · Post by **Al Terhune** » 16 Dec 2004 6:47 pm

Okay, I'm confused. Does lifting a ground mean using one of those two-prong adaptors, and this is what you're all saying not to do?

basilh · Post by **basilh** » 17 Dec 2004 8:02 pm

Al it's like I said .. only earth one item in the chain, and that should be the one that draws the most current...usually the most powerful amp.
Baz

John Bechtel · Post by **John Bechtel** » 17 Dec 2004 9:28 pm

Smetimes, if you are running through (2)-Amps, using (2)-cords from your Volume-Pedal you can get a slight Hum if you allow the (2)-Guitar-Cords to X! Sometimes it helps to keep the (2)-cords Parallel to one another as opposed to crossing at right-angles. Especially of you're not using ‘top-quality’ cords! (Just my 1¼ cents)

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“Big John” Bechtel
’49/’50 Fender T–8 Custom
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Eric West · Post by **Eric West** » 18 Dec 2004 11:35 am

Again, quickly.

Never plug a "ground prong" into a three prong plug unless you KNOW that it is a ground, and NOT just a connection to the neutral.

Lots of "homes" have them tied together in outlet box, many more tie them in anywhere along the line, and an equal number aren't even tied to anything. They just look that way to pacify "inspectors".

It HAS to be an isolated connection that comes together NOWHERE before it reaches the GROUND. Otherwise you have constant "bleed" from other devices' neutral lines. Basically, the current the appliance is using in a fraction of where you "tie into" it before IT reaches Ground. Multiplied by how wet your hands and feet/butt, or other ground connection are.

Clubs?

Lots of them are wired to fire.

I haven't plugged into a ground hole with an amp for more than ten years.I'm still marginally healthy.

I hope the hundreds of steel players that died from using these dreaded little "gray plugs" will forgive me.

A small "Outlet/Ground" tester is a good idea, and better yet, a "Ground Fault" interrupter.

I suppose a guy could make an extension box with one, but I don't know how they'd work in a source that isn't properly grounded.

Electricity. More is known about what it does than what it is.

EJL

Bobby Lee · Post by **Bobby Lee** » 18 Dec 2004 12:34 pm

I carry a two prong adapter in my gig bag, and use it whenever I need to. You know, if a ground is bad, sometimes a piece of equipment will bite you a little bit, so you fix it. The high voltages that can hurt you are inside the amp. I've never had anything but a minor shock from instruments, amps or wires. Certainly nothing life-threatening.

I think that shock hazard claims, on the level of equipment that I use, anyway, are vastly exagerrated.

I know that some of you professionals have very different opinions about this, and I'll probably be roasted for it, but that's my opinion. 110V house current doesn't send me trembling in fear. I've been bit by it before. No big threat, IMHO.

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<img align=right src="http://b0b.com/Hotb0b.gif" width="96 height="96">Bobby Lee - email: quasar@b0b.com - gigs - CDs, Open Hearts
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