I had reconfigured some F/X in my rack yesterday, pulled some stuff
out and installed some newer stuff, moved some units around in the
order in the rack, etc.

When I got done, I noticed that I had this subtle hum on the stereo
bus....so I mute everything and I do mean EVERYTHING....and it's still
there. It gets a little louder when I unmute stuff but it's still
there.

I start checking cables, troubleshooting, etc. and finally I figured
out that it was coming from an F/X unit.

That makes sense but here is the weird part....

It was an Intellifex I had borrowed from a friend of mine; after using
it a few times I figured out it's not for me, it's "OK" but nothing
special.

Well the thing is EVEN WHEN I TURNED THE UNIT OFF the hum was still
there...it only went away when I disconnected the wall wart external
power supply from the back of the unit.

I know it was NOT bleeding into the unit below (TC M2000) because I
could solo that unit and it sounded fine, it was the Intellifex and it
still made my system hum turned on or turned off, muted or unmuted.
Disconnecting the power supply made it stop...strangely enough I would
leave the PS still hooked up (but not connected to the rack unit) and
it was ok.

I guess some kind of grounding issue or something with the Intellifex
but between the hum and the sound of the thing I have to say I was
less than impressed.

Took out the Intellifex, replaced it with another lowball unit
(Digitech TSR-24) and now it's nice an quiet...the TSR-24 does use an
internal PS tho...

I'm going to hook up the Intellifex to my "B Rig" to see if it still
hums on that system, maybe they all do this or something, that's why
they have that Hush noise reduction g

Analogeezer

In article , says...
Analogeezer wrote:

Well the thing is EVEN WHEN I TURNED THE UNIT OFF the hum was still
there...it only went away when I disconnected the wall wart external
power supply from the back of the unit.

Now you see why people hate wall warts so much. Was there anything with
an audio transformer in it anywhere near the wall wart? They produce a
lot of magnetic trash because of the crappy transformers, as well as RF
hash and heat.
--scott


I had a similar problem with the wall wart power supply for the Lexicon
JamMan in my stage rack. I have to plug the wall wart into an extension
cord and physically separate it from the power strip.

Art Cohen wrote in message .com...
In article , says...
Analogeezer wrote:

Well the thing is EVEN WHEN I TURNED THE UNIT OFF the hum was still
there...it only went away when I disconnected the wall wart external
power supply from the back of the unit.

Now you see why people hate wall warts so much. Was there anything with
an audio transformer in it anywhere near the wall wart? They produce a
lot of magnetic trash because of the crappy transformers, as well as RF
hash and heat.
--scott


I had a similar problem with the wall wart power supply for the Lexicon
JamMan in my stage rack. I have to plug the wall wart into an extension
cord and physically separate it from the power strip.


Actually I did this very thing and there was no improvement. If I
disconnected the PS from the rack unit then the noise went away.

JamMans are cool, too bad you have to do that. FWIW I have a Vortex
(same basic package and PS as the JamMan) in this same rack and no
probs with it.

Analogeezer

In rec.audio.pro, (Analogeezer) wrote:

Art Cohen wrote in message .com...
In article , says...
Analogeezer wrote:

Well the thing is EVEN WHEN I TURNED THE UNIT OFF the hum was still
there...it only went away when I disconnected the wall wart external
power supply from the back of the unit.

Now you see why people hate wall warts so much.
Was there anything with
an audio transformer in it anywhere near the wall wart? They produce a
lot of magnetic trash because of the crappy transformers, as well as RF
hash and heat.
--scott


I had a similar problem with the wall wart power supply for the Lexicon
JamMan in my stage rack. I have to plug the wall wart into an extension
cord and physically separate it from the power strip.


Actually I did this very thing and there was no improvement. If I
disconnected the PS from the rack unit then the noise went away.

In that case, it isn't the wall-wart's magnetic field that is being
picked up and causing a problem, but rather it's putting leakage
current into whatever it's powering. This can be cause by any power
transformer, not just wall-warts.
The wall-wart is 'leaking electricity - the primary is resistively
and/or capacitively coupled to the secondary. (capacitive coupling is
normal, and a small amount of current will always be there). This goes
into the power circuit and ground of whatever it's powering, and out
that ground into the rest of your system, and then something (maybe
the same piece of equipment, or something else) is sensitive to ground
current (amplifies it as if it were a signal) and is picking it up.
Read AN003 and AN004 from this page: I think they explain the
situation very well. One you understand it, it's easier to fix:
http://www.jensen-transformers.com/apps_wp.html

For a quick fix, you can try 'reversing' the wall-wart (if it's
plugged into the wall rightside up, unplug it and plug it in upside
down) to see if it decreases the hum. If one blade of the plug is
larger than the other (it is on most (all?) power plugs made in recent
years), it might be illegal or something to grind the larger one down
so that it would fit either way, so I won't suggest you do that... Or
you could try a different wall-wart with the same voltage and the
same-or-greater current rating. Digikey has a range of wall-warts.


JamMans are cool, too bad you have to do that. FWIW I have a Vortex
(same basic package and PS as the JamMan) in this same rack and no
probs with it.

Analogeezer

Well the thing is EVEN WHEN I TURNED THE UNIT OFF the hum was still there...it only went away when I disconnected the wall wart external power supply from the back of the unit.


One thing to try if you haven't already is to electrically isolate the
unit from the rack rails with some shoulder washers or some of that
rubber isolator strip some music supply houses sell. I have some very
large fx racks and after doing this in all the racks, I never
encounter this anymore. I usually chech to make sure the chassis of
the units in question aren't contacting the rails with a dmm.