dbx 286a causing hum, can't eliminate

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celtics23

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I have the current setup that I just put together for a new recording location:

EV RE20 => XLR/XLR cable => DBX 286a voice processor => 1/4" out to XLR => mackie mixer

I noticed a hum when monitoring the headphone output of the mackie mixer. i disconnected the mic from the dbx, and the hum remained, which told me that the problem is in the connection between the dbx and the mackie, ie the problem is the dbx. i tried changing the settings on the dbx. nothing changes the hum, except if i increase either preamp or output gains, the hum gets worse. also, if i "process bypass" the dbx, the hum gets way worse.

if i "skip" the dbx and connect my mic directly to the mackie, no hum, which is more confirmation that the problem is the dbx. i also added a ground lifter to the plug for the dbx. it made the hum just *slightly* better, but not much.

does anyone have some ideas for what i might try to resolve this hum?
 
celtics23 said:
i also added a ground lifter to the plug for the dbx. it made the hum just *slightly* better, but not much.
Click to expand...

You should never do this, but now that you have it reinforces the diagnosis that it's a grounding issue in the cabling between the dbx and the Mackie. As suggested, your cable may be unbalanced TS to balanced XLR. There's more than one way to wire a cable like that and not all ways work with all equipment.

Rather than go from your dbx line output to another mic preamp, use a TRS-TRS cable from the dbx to a line input on the Mackie. It would help to know exactly which Mackie product you're using so I can suggest a specific input.
 
celtics23 said:
I have the current setup that I just put together for a new recording location:

EV RE20 => XLR/XLR cable => DBX 286a voice processor => 1/4" out to XLR => mackie mixer

I noticed a hum when monitoring the headphone output of the mackie mixer. i disconnected the mic from the dbx, and the hum remained, which told me that the problem is in the connection between the dbx and the mackie, ie the problem is the dbx. i tried changing the settings on the dbx. nothing changes the hum, except if i increase either preamp or output gains, the hum gets worse. also, if i "process bypass" the dbx, the hum gets way worse.

if i "skip" the dbx and connect my mic directly to the mackie, no hum, which is more confirmation that the problem is the dbx. i also added a ground lifter to the plug for the dbx. it made the hum just *slightly* better, but not much.

does anyone have some ideas for what i might try to resolve this hum?
Click to expand...

Do you happen to have it racked up along side (on top or underneath it) a power amp or maybe an AC cable rubbing up against a patch cord ???
 
bouldersoundguy said:
You should never do this, but now that you have it reinforces the diagnosis that it's a grounding issue in the cabling between the dbx and the Mackie. As suggested, your cable may be unbalanced TS to balanced XLR. There's more than one way to wire a cable like that and not all ways work with all equipment.

Rather than go from your dbx line output to another mic preamp, use a TRS-TRS cable from the dbx to a line input on the Mackie. It would help to know exactly which Mackie product you're using so I can suggest a specific input.
Click to expand...

it's a mackie 820-vlz3.
 
TASCAM MAN said:
Do you happen to have it racked up along side (on top or underneath it) a power amp or maybe an AC cable rubbing up against a patch cord ???
Click to expand...

not really, things seem pretty well separated
 
bouldersoundguy said:
You should never do this, but now that you have it reinforces the diagnosis that it's a grounding issue in the cabling between the dbx and the Mackie. As suggested, your cable may be unbalanced TS to balanced XLR. There's more than one way to wire a cable like that and not all ways work with all equipment.

Rather than go from your dbx line output to another mic preamp, use a TRS-TRS cable from the dbx to a line input on the Mackie. It would help to know exactly which Mackie product you're using so I can suggest a specific input.
Click to expand...

ok, i tried going TRS-TRS from my DBX output into the mackie "line" input. i didn't notice much of a difference in the hum, maybe slightly better. i did notice that the volume level for the mic was way lower when i switched to the 1/4". is this normal? should i be remedying this by increasing the level INTO the mixer, or increasing the gain on the mixer into my recording device?
 
arcaxis said:
On the DBX about where do you have the Gain control (left knob) set when using the mic (0 to +60) and is this setting getting the Level LED's up to the yellow *0*? Where is the Output Gain control set (-30 to +10)? I have the 286S (newer silver face) and as left when last used Input gain is about +45 (with a condenser mic) and the Output gain was at about 0 (zero). You may need more gain on the input with a dynamic mic, but you should be just lighting the yellow LED.
Kind of wondering if you're setting the Output low and trying to make up the gain with the mixer and bringing up the hum with a lot of gain.
Click to expand...

interestingly enough that you mention it because with multiple different RE20's and dbx286a's that i use on my multi-mic production, over the years i have had both issues with preamp and output gain, and this is identical with various mics and various voice processors

1) preamp gain never lights up more than the first light or two, UNLESS i turn it to the max, at which point it distorts/clips, so i end up leaving it 3 clicks shy of max
2) output gain at 0, or anything more than barely all the way down distorts into the next device, so i keep it just above the lowest it goes

you'd think it was a faulty mic or processor, but i have 2 EV re20's and 4 dbx 286a's, and it 's always the same. suggestions on that?
 
Any fluorescent light fixtures on the same circuit, or CFL bulbs in close proximity? I have two 286As, one of which I cannot rack near my Furman conditioner. I discovered a hum in one of mine and had to un-rack it and set it on the desk, isolated, to discover the proximity incompatibility.
 
Have you tried lifting the earth (shield) on the XLR plugging into the Mackie?

Alan.
 
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