MOTM

Well, I just finished building my first modules, the 900, 120, 420 
and 320, and amazingly everything seems to work (and looks great 
too!)  What a sweet filter the 420 is!  (In just a few more days, my 
girl gets some flowers, and I get some sound sources - my 2nd order's 
in!)

I've run into a little problem, however.  When the 900 power supply 
is installed into a rack with the modules and is powered on, I begin 
to pick up some minor 60hz hum; not much, but enough to ruin the dark 
background - Bummer.  (FYI, the rack is wood frame with metal rails.  
A mixer is in a separate all-metal rack.  Everything is plugged into 
the same power strip.  Patch cords are shielded)  I pick up hum 
regardless of which jack/module I plug into.  I visually checked all 
coax solder joints and ground wires; everything looks ok.  Funny 
thing is that even when I disconnect all of the modules' power cables 
from the 900, I still pick up hum whenever the 900 is on.  There's no 
hum when the 900 is not in the rack, whether connected to and 
powering the modules or not.

Is appears the AC ground is part of the common ground with the 
modules when installed in a rack with metal rails.  This is by 
design, correct?  Is it possible that the mixer being in a separate 
rack is a problem?  If anyone on the list has some insight, that 
would be great.

Cheers,
George

----- Original Message ----- 

From: GeorgeK <george.kisslak@...>
To: <motm@yahoogroups.com>
Sent: Sunday, February 11, 2001 4:43 PM
Subject: [motm] Ground Loops


Well, I just finished building my first modules, the 900, 120, 420 
and 320, and amazingly everything seems to work (and looks great 
too!)  What a sweet filter the 420 is!  (In just a few more days, my 
girl gets some flowers, and I get some sound sources - my 2nd order's 
in!)

I've run into a little problem, however.  When the 900 power supply 
is installed into a rack with the modules and is powered on, I begin 
to pick up some minor 60hz hum; not much, but enough to ruin the dark 
background - Bummer.  (FYI, the rack is wood frame with metal rails.  
A mixer is in a separate all-metal rack.  Everything is plugged into 
the same power strip.  Patch cords are shielded)  I pick up hum 
regardless of which jack/module I plug into.  I visually checked all 
coax solder joints and ground wires; everything looks ok.  Funny 
thing is that even when I disconnect all of the modules' power cables 
from the 900, I still pick up hum whenever the 900 is on.  There's no 
hum when the 900 is not in the rack, whether connected to and 
powering the modules or not.

Is appears the AC ground is part of the common ground with the 
modules when installed in a rack with metal rails.  This is by 
design, correct?  Is it possible that the mixer being in a separate 
rack is a problem?  If anyone on the list has some insight, that 
would be great.

Cheers,
George

Try plugging the MOTM AC cord into a 2-wire adapter. I bet it's your house
wiring.

Paul S.

----- Original Message -----

From: "J. Larry Hendry" <jlarryh@...>
To: <motm@yahoogroups.com>
Sent: Sunday, February 11, 2001 6:14 PM
Subject: Re: [motm] Ground Loops


>
> ----- Original Message -----
> From: GeorgeK <george.kisslak@...>
> To: <motm@yahoogroups.com>
> Sent: Sunday, February 11, 2001 4:43 PM
> Subject: [motm] Ground Loops
>
>
> Well, I just finished building my first modules, the 900, 120, 420
> and 320, and amazingly everything seems to work (and looks great
> too!)  What a sweet filter the 420 is!  (In just a few more days, my
> girl gets some flowers, and I get some sound sources - my 2nd order's
> in!)
>
> I've run into a little problem, however.  When the 900 power supply
> is installed into a rack with the modules and is powered on, I begin
> to pick up some minor 60hz hum; not much, but enough to ruin the dark
> background - Bummer.  (FYI, the rack is wood frame with metal rails.
> A mixer is in a separate all-metal rack.  Everything is plugged into
> the same power strip.  Patch cords are shielded)  I pick up hum
> regardless of which jack/module I plug into.  I visually checked all
> coax solder joints and ground wires; everything looks ok.  Funny
> thing is that even when I disconnect all of the modules' power cables
> from the 900, I still pick up hum whenever the 900 is on.  There's no
> hum when the 900 is not in the rack, whether connected to and
> powering the modules or not.
>
> Is appears the AC ground is part of the common ground with the
> modules when installed in a rack with metal rails.  This is by
> design, correct?  Is it possible that the mixer being in a separate
> rack is a problem?  If anyone on the list has some insight, that
> would be great.
>
> Cheers,
> George
>
>
>
>
>
>
>
>
>
>
>

Paul, I live in a condo, so that's a safe bet!  Turns out a 2-wire 
adapter eliminates the hum, but now whenever I connect a jack from 
the out-board mixer to a module there is a good sized POP.  If I 
first zero the mixer's input level, this becomes just a slight 
"scratch" which is not too objectionable.  Once the mixer's plugged 
in, everything's pretty quiet.  I have to admit that I'm not 
satisfied with this non-std setup, though.  Now, if I were to have a 
nice black ON-board mixer with white lettering and switchcraft jacks, 
hmmm, this might cut the gordian knot... :)

George

--- In motm@y..., "Paul Schreiber" <synth1@a...> wrote:
> Try plugging the MOTM AC cord into a 2-wire adapter. I bet it's 
your house
> wiring.
> 
> Paul S.
> 
> ----- Original Message -----
> From: "J. Larry Hendry" <jlarryh@i...>
> To: <motm@y...>
> Sent: Sunday, February 11, 2001 6:14 PM
> Subject: Re: [motm] Ground Loops
> 
> 
> >
> > ----- Original Message -----
> > From: GeorgeK <george.kisslak@h...>
> > To: <motm@y...>
> > Sent: Sunday, February 11, 2001 4:43 PM
> > Subject: [motm] Ground Loops
> >
> >
> > Well, I just finished building my first modules, the 900, 120, 420
> > and 320, and amazingly everything seems to work (and looks great
> > too!)  What a sweet filter the 420 is!  (In just a few more days, 
my
> > girl gets some flowers, and I get some sound sources - my 2nd 
order's
> > in!)
> >
> > I've run into a little problem, however.  When the 900 power 
supply
> > is installed into a rack with the modules and is powered on, I 
begin
> > to pick up some minor 60hz hum; not much, but enough to ruin the 
dark
> > background - Bummer.  (FYI, the rack is wood frame with metal 
rails.
> > A mixer is in a separate all-metal rack.  Everything is plugged 
into
> > the same power strip.  Patch cords are shielded)  I pick up hum
> > regardless of which jack/module I plug into.  I visually checked 
all
> > coax solder joints and ground wires; everything looks ok.  Funny
> > thing is that even when I disconnect all of the modules' power 
cables
> > from the 900, I still pick up hum whenever the 900 is on.  
There's no
> > hum when the 900 is not in the rack, whether connected to and
> > powering the modules or not.
> >
> > Is appears the AC ground is part of the common ground with the
> > modules when installed in a rack with metal rails.  This is by
> > design, correct?  Is it possible that the mixer being in a 
separate

> > rack is a problem?  If anyone on the list has some insight, that
> > would be great.
> >
> > Cheers,
> > George
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >

> Paul, I live in a condo, so that's a safe bet!  Turns out a 2-wire
> adapter eliminates the hum, but now whenever I connect a jack from
> the out-board mixer to a module there is a good sized POP.  If I
> first zero the mixer's input level, this becomes just a slight
> "scratch" which is not too objectionable.  Once the mixer's plugged
> in, everything's pretty quiet.

The *only* way to fix this is to use isolation transformers. 1 on the mixer,
1 on the MOTM.
Allied carries these for about $50ea. I have a big-assed honkin' one on my
bench (it 'floats'
the whole test equipment setup).

Paul S.

Turns out if I plug any module directly into the amp (bypassing the 
mixer) the hum is completely eliminated.  (The mixer does not have a 
3-prong plug - time for an upgrade.)  JLH suggested the 900 makes the 
mixer hum; I agree.  I'll just bypass it for now.

Thanks for the info.
GK

--- In motm@y..., "Paul Schreiber" <synth1@a...> wrote:
> 
> 
> > Paul, I live in a condo, so that's a safe bet!  Turns out a 2-wire
> > adapter eliminates the hum, but now whenever I connect a jack from
> > the out-board mixer to a module there is a good sized POP.  If I
> > first zero the mixer's input level, this becomes just a slight
> > "scratch" which is not too objectionable.  Once the mixer's 
plugged
> > in, everything's pretty quiet.
> 
> The *only* way to fix this is to use isolation transformers. 1 on 
the mixer,
> 1 on the MOTM.
> Allied carries these for about $50ea. I have a big-assed honkin' 
one on my

> bench (it 'floats'
> the whole test equipment setup).
> 
> Paul S.

> The *only* way to fix this is to use isolation transformers. 1 on 
the mixer,
> 1 on the MOTM.
> Allied carries these for about $50ea. I have a big-assed honkin' 
one on my
> bench (it 'floats'
> the whole test equipment setup).

do you have a part number on this, paul?  

thanks,
alex

small ones

967-5861
967-2361

big-assed ones

704-2367

Paul S.


----- Original Message ----- 

From: <perpetual@...>
To: <motm@yahoogroups.com>
Sent: Tuesday, February 13, 2001 11:14 AM
Subject: [motm] Re: Ground Loops


> > The *only* way to fix this is to use isolation transformers. 1 on 
> the mixer,
> > 1 on the MOTM.
> > Allied carries these for about $50ea. I have a big-assed honkin' 
> one on my
> > bench (it 'floats'
> > the whole test equipment setup).
> 
> do you have a part number on this, paul?  
> 
> thanks,
> alex
> 
> 
> 
> 
>