Audio Amp questions/changes

moody07747 · Jun 24, 2006

OK so the wire is fairly good after all if not bent far which i never do.

it was my understanding that you needed 3 insulated conductor wire (in my case, white, red, and black) to wire a stereo plug.

now I'm thinking all I will ever need for mono or stereo is 2 insulated conductor wire, white, black...

or do I only need one insulated conductor for mono wires?

here's a drawing on how I think I have to wire a stereo now.

**broken link removed**

right now I have a 3 conductor wire,,,white goes to that long pin that also holds all the wires in place, black goes to the tip, and red goes to the middle ring....So am I supposed to be using 2 conductor wire and instead of attaching an insulated wire to the big pin, putting the drain wire on there instead?

audioguru · Jun 24, 2006

Your drawing is correct.

moody07747 · Jun 24, 2006

thanks for the info...ill start rewiring that right now

moody07747 · Jun 24, 2006

still humming...

im going to get down to the shack tomorrow to get some cable ends so I can run this with 2 inputs at the amp and use the L and R outputs on the mixer.

zevon8 · Jun 25, 2006

For some reason I was assuming ( slaps-self for that ) that you were using balanced lines. Therefore, as a test, you could have lifted the shield at one end to see if it stopped the ground loop.

If you still have a ground loop, even the most expensive cables with Neutrik connectors are not going to help.

Is the equipment mounted in a metal rack? It is possible that the mixer's chassis being electrically connected to the amp's chassis via the rack is causing the groupd loop. Physically isolate the mixer so that the only connection is by cable. If that stops it, then some nylon or similar plastic washers could be the solution. The exact opposite could also help, funnily enough. Try letting the chassis touch to electrically bond to the same potential.

audioguru · Jun 25, 2006

zevon8 said:
If you still have a ground loop, .....

Read what he said. He did not connect the cable's shield. No wonder it hums.
"when I hook my leads up to them all I remove the wrapper and grey wire and use the black, red, and white wires for each solder point on the stereo connectors.

should I be hooking the grey wire to the big ring/ground on the audio ends?"

moody07747 · Jun 25, 2006

well what I did this time was I cut out the red wire as its not needed anymore, removed a little bit of the foil shield, black and white went to the rip and ring, grey drain went to the big ground ring.

exactly as in my photo I drew.

I have to get to reading that ground look link and read what balanced / unbalaned cables are and how they're wired.

the mixer is on a plastic roll around storage unit and theres rubber feet under it as well.

Dr.EM · Jun 25, 2006

Yep, though I think the only balanced cables you can use with that mixer are the ones on the mic inputs. Didn't have any humming issues today using that mixer with a PA, and that was connected via long extensions to a very dodgy power outlet!

moody07747 · Jun 25, 2006

zevon8 said:
To me, the "buzz" , if it is power line frequency ( 60Hz in North America) , would make it appear like you have a ground loop. Two pieces of equipment that have grounded power cords, and are pluged into different outlets, or through various "power bars", etc, may end up creating a long enough connection betweem the chassis of each piece of gear that there is a slight differnce in what each "sees" as ground. This can cause enough current flowing along the ground of the interconnect cable to become part of the audio. Then you get hum.

In you case, removing the one piece of gear from the chain ( the mixer ) stops the hum, so either the amp or the mixer could be the problem. If everything else can be connected to the amp, and no hum, then blame the mixer, if the othe way around, blame the amp. Note that even when turned "off" the chassis will still be grounded anyways, so being turned off will not stop a ground loop.

Here is a link to ground loops:

https://www.soundonsound.com/sos/1994_articles/aug94/groundloops.html

The hiss could be digital noise generated by some of the input control / switching logic. It could also be self generated by the amp oscillating or having a noisy pre-amp circuit.

If it is digital noise, some bypass caps at each of the IC's DC power terminals may cure that for you. If it's in the power/pre-amp it may be due to its design or choice of components, and harder to fix.

Thats a great page with a bunch of information but they keep saying theres photos everywhere yet I have not seen them on the page at all...

Back to reading...

Nigel Goodwin · Jun 25, 2006

moody07747 said:
That a great page with tons of info but they keep saying thers photos everywhere yet I have not seen them on the page at all...

Back to reading...

Looks like it's the text only from a 12 year old magazine article?.

zevon8 · Jun 25, 2006

I did see how he had miss-wired, but then he posted a picture showing that he had figured out the correct way. Then he said he was going to rewire it correctly. In a post after that he said it was still humming. This is why I felt he may still have a ground loop, and posted further suggestions.

moody07747 · Jun 25, 2006

lol yea I didn't get much sleep...

my typing has been bad all day

moody07747 · Jun 25, 2006

I did rewire the wire like in the photo I drew....thats how its wired right now therefore the problem is still there.

**broken link removed**

moody07747 · Jun 30, 2006

I finally found the culprit (took long enough lol), another one of my DIY cables...well 2 actually

I have the main out L and R from my drum module going to the L and R input of channel 9/10 on the board. I just took those plugs out and the ground loop stopped so i'm going to attach that drain in both cables now and see how it goes.

now I can finally turn my amp up allot more, get some recordings done and do it all in half the time as I won't have to edit so much audio.

BTW I finally got done reading that page on ground loops, great read.

audioguru · Jun 30, 2006

moody07747 said:
i'm going to attach that drain in both cables now and see how it goes.

now I can finally turn my amp up allot more.

The drain wire in the cable is its connection to the foil shield of the cable.
The drain wires weren't connected? Then the cables weren't shielded.

moody07747 · Jun 30, 2006

audioguru said:
The drain wire in the cable is its connection to the foil shield of the cable.
The drain wires weren't connected? Then the cables weren't shielded.

yea in these mono cables i was using the black and white wires inside the shield and didnt know i had to attach that drain....i though it was there to give strength to the cable or something like that.

ill check back in a few minutes to let ya know how it goes.

moody07747 · Jun 30, 2006

ok now im just goin crazy here

i finished the cables and one checked out...the other didnt get past eh meter test so i have to get a new cable end for that....(old ones shot)

i plugged the good cable into the L main out of the module and into the L in channel on the mixer....and i get the good ol buzzing again.

i switch to the R channel and same thing.

so whats this mean?

its a ground loop somewhere between the drum module and the mixer board...

audioguru · Jul 1, 2006

A properly made shielded cable shouldn't cause buzzing when plugged into a mixer input when there is not anything except a connector at the far end. When you plug the cable into the output of the drum module and you get buzz, then either the drum module has power supply hum, it has poor internal shielding or you have a ground loop.

moody07747 · Jul 1, 2006

audioguru said:
A properly made shielded cable shouldn't cause buzzing when plugged into a mixer input when there is not anything except a connector at the far end. When you plug the cable into the output of the drum module and you get buzz, then either the drum module has power supply hum, it has poor internal shielding or you have a ground loop.

I just plugged the cable into the mixer without attaching the other end to anything.....no buzz but as soon as i plug into the module i get the buzz again. btw this is plugging into a module thats turned off...let me try it with it unplugged though

its possible it is the module...it has the computer type power cord setup where you plug it into the 3 prong outlet and the power transformer is inside the module.

Roland makes really great high quality units...i don't think its the problem with the power in there.

there has to be another ground loop somewhere that im just not seeing...

moody07747 · Jul 1, 2006

interest...with the power cord unplugged form the drum module the buzzing stopped even with the cables in but as soon as i put the cord in the unit the buzzing starts again, the module power switch was off for this test

so now what do I do?
i could snip the ground lead on the module but that's not safe

BTW, this module is mounted from a metal mount that i made which clips to the metal drum rack
the module bottom has a metal backing plate.

do you think this could be causing the buzz?

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