Why do my amps hum so bad?? Help!!

Lee Baucum · Post by **Lee Baucum** » 26 Feb 2000 7:10 pm

Does your delay unit have a 3 prong electrical cord? If so, you will need to lift the ground on it and one of your amps.

Lee, from South Texas

Richard Sinkler · Post by **Richard Sinkler** » 26 Feb 2000 9:36 pm

Cuz they don't know the words? Seriously, it sounds like grounding problems. Try Lee's suggestion. You might need to lift the groung on one of the amps too.

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Carter D10 8p/10k
www.sinkler.com

db · Post by db » 26 Feb 2000 10:35 pm

This effect is called a "ground loop".
Where the difference in AC "potetial" between the two grounding point becomes induced into the signal path.

Cairo Zoots · Post by **Cairo Zoots** » 29 Feb 2000 10:30 pm

groung? potetial? Izzat anything like a cord of wook? Cheezoids!

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ree-oo-dee-doo

db · Post by db » 1 Mar 2000 8:40 pm

When I went to the the electrinics supply stock room clerk to ask for a "ground lifter" (that grey two prong thingy with three holes and a green ear), the clerk brought me back a child's plastic sand shovel.[This message was edited by db on 01 March 2000 at 08:40 PM.]

Rick Barber · Post by **Rick Barber** » 1 Mar 2000 11:34 pm

Ground loops are present. I run a lexicon effects mono input from steel and 2 channel out into 2 HI Z amp inputs. The easiest but not necessarily the safest solution to hum was to lift the ground on the Peavey Nashville 400.

There is a company called Whirlwind who have specialty isolation transformers including mic and line transformers that you can insert inline with your signals including ones that wont drop your signal much. 600 ohm to 600 ohm inline transformer. Check their products out on the web. Call companies like this ask to speak to an application engineer and tell them whats happening. I guess the beauty here is that its the signal lines (your coaxes) that sometimes need to be isolated by using these transformer products. Most of them have email or 1-800 numbers and I ask stuff all the time. I asked questions to Jensen transformer company , whirlwind, and lexicon and mackie and they had technical people calling me or writing me with advice.
My feeling is the music industry would be much better off if EVERYTHING was balanced in balanced out.

If you dont have a line level transformer to try but if you have a couple passive direct boxes with ground lift , you could try two of these in series, one running backwards to boost the signal back up. If your effect puts out line level you could put in a direct box 1/4 inch TS plug in unbalanced to XLR balanced mic out which will drop your signal usually by 20 to 40 dB . So then plug XLR out back into XLR of a second passive direct box and then take the 1/4 inch plug of this second box on over to one of your high Z amp inputs.
Lift ground switch on both direct boxes.

Of course I would eventually just use one Line transformer so you dont get low end rolloff and extra distortion. The dirct box idea was just something to try if thats all you have. They would have to be unpowered passive type so one you could run backwards.

By the way , look at the specs if you are going to use passive transformers or direct boxes. There would be more to it than just having the right connectors. Its not magic. All transformers distort, have a proper signal level range, transform impedance and voltage level, and have a frequency range. Cheap ones will give more harmonic distortion and will roll your low end. If you pay more you can get "broadcast quality " performance --- Check out the Whirlwind products. I'm going to buy some transformers myself but they are going to be high end ones.

Also the www.sweetwater.com as I recall has discussions and links all about solving ground loops on stage and in the studio. Sometimes you need the stuff and sometimes you dont. We recorded live on stage a month ago direct from a Mackie 1604VLZ PRO mixer direct to a MAC G3 hard disk and had a bit of hum once in a while by a stupid refridgerator kicking on next door.

Personally I would strive for solving ground loop probs with signal ground lift or isolation devices before I would defeat AC 3rd lead power ground on your AC plugs.

You can also work the other end with pricey AC power line conditioner products.

Rick Barber

c c johnson · Post by **c c johnson** » 2 Mar 2000 12:47 pm

could be they don't know the words. Sorry,I couldn't resist.

db · Post by db » 2 Mar 2000 10:36 pm

There is a company out there that makes an optical isolation box that may have better specs than the isolation signal transformers.

"Personally I would strive for solving ground loop probs with signal ground lift or isolation devices before I would defeat AC 3rd lead power ground on your AC plugs."

You should not eliminate all grounds, just limit it to one ground point for the whole system.

joeguitar · Post by **joeguitar** » 6 Mar 2000 7:18 pm

While not up on an ADA I wondered why you would connect the preamp out of one amp into the instrument input of a second amp? A more plausible choice for me would be guitar into one amp input, amp preamp out into the mono input of the ADA. Take the stereo out of the ADA into the power amp in or "return" on each amp. To eliminate the ADA, take the "preamp out" from the amp your guitar's plugged into to the "return" or power amp "in" of your second amp. I would never defeat the ground on any amp for any reason. Maybe in a pinch with a piezo pick-up on acoustic guitar, bass or fiddle but on a "steel" guitar? Never! Have a tech help you before defeating the ground. What you're trying to do can and will work but you'll need to sort out the signal path first and troubleshoot the equipment after that, if the problem persists.

CU, joe

db · Post by db » 9 Mar 2000 8:55 pm

The opto-isolator device is
the Ebtech hum Eliminator (2 channel).
http://www.musiciansfriend.com/cgi-bin/shop.dll/0002261827216207321959238231324?pid= 150450
[This message was edited by db on 09 March 2000 at 09:03 PM.]