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meanwell and noise
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author meanwell and noise
a.b.o.z.
Hi all,

I've got this interesting issue with my rig. I have two racks each with two 104hp rows. I'm powering all from two meanwell RS-100-12 wired together to get +/-12V. When connected to external mixer I get high pitched noise coming out from both racks but lower rack has it slightly more. Interesting stuff happens when I disconnect one rack from PSU, that noise just goes away. It is with both racks. If I disconnect upper rack from PSU lower rack stops noising and vice versa.
What to do?
LED-man
Can you post a Schemata please ?
Maybe it’s a failure in ground/earth wiring
a.b.o.z.
V+ of PSU1 is V+
V- of PSU1 goes to V+ terminal of PSU2 and this link is GND
V- of PSU2 is V-
Mains eartn is tied to each ground connection on PSU1 and PSU2 and also to busboard GND
clorax hurd
So you are powering two racks from one set of power supplies?
So is your PSU kind of external?
This is quite important as what you describe could be caused by bad ground/power distribution.
Perhaps connecting the busboard "grounds" (they are 0V references really, just abused for shielding too) of the two rack by with some really thick wire.

Also how exactly are you connecting modular into the mixing desk?
Eurorack is unbalanced and doesn't have a chasis ground. Your mixer probably has chasis ground and accepts balanced connections, except on instrument inputs - if it has such, try connecting there.
Or making special cables for connecting from modular into mixing desk could help too as described in more of the ground/earth/eurorack-sucks threads here on muff.

Can't find it now, but if I remember correctly, it was about using cable with 2 leads + 1 shield
TS (mono) jack on modular side
TRS (stereo) jack on mixer side

Tip on modular to Tip on mixer using one wire
Sleeve on modular to Ring on mixer side using another wire
Sleeve on mixer side connected to cable shield and NOT connected to anything on modular side.
(somebody correct me please if i'm wrong)
a.b.o.z.
thanks for reply.
I am powering two racks with same PSU wich is external unit. I am connecting modular to mixer from two mixers in racks. One is Frames from MI and another is Hexinverters Hot Glue. I'm connecting to external mixer with mono cable (TS) and it is going into line in. Tommorrow I will try connecting with pair of DI boxes but will also try making this kind of cable.

Cheers!
clorax hurd
a.b.o.z. wrote:
thanks for reply.
I am powering two racks with same PSU wich is external unit. I am connecting modular to mixer from two mixers in racks. One is Frames from MI and another is Hexinverters Hot Glue. I'm connecting to external mixer with mono cable (TS) and it is going into line in. Tommorrow I will try connecting with pair of DI boxes but will also try making this kind of cable.

Cheers!


I'm not surprised you have problems, cause this is a very bad setup.
How do you connect the external PSU to the racks?
a.b.o.z.
eek! You mean because of cables or external PSU? I'm connecting PSU to racks via XLR connectors but stronger wires inside not microphone. What do you suggest?
clorax hurd
a.b.o.z. wrote:
:O You mean because of cables or external PSU? I'm connecting PSU to racks via XLR connectors but stronger wires inside not microphone. What do you suggest?


Well if you use short and very thick wires with very low resistance, then maybe it's not that bad... But eurorack is not ideal even with internal PSU and using external PSU is making it even bit worse...

Now re-reading i'm not sure - by "high pitched noise coming out from both racks" you mean high pitched noise coming from speakers when their channels in mixer were on... right? You don't mean sound going literally from the rack? (that would be strange, because I usually hear only transformers, but if don't have PSU inside those racks...)

If it's just from speakers, then have you maybe tried if it goes away after disconnecting all patch cables from one of them, while leaving the PSU connected to both?
a.b.o.z.
Noise is from speakers when channel fader is turned up. Even with fader turned down you can hear that same high pitched noise but very very faint. It is happening when fully patched and when all patch cables are disconnected.
kassu
If I understand correctly,
- You have two racks connected to the same PSU
- There is noise in the output when both racks are powered
- The noise goes away if either rack is powered off

Perhaps you are simply pulling too much current from the PSU? It sounds unlikely since it is specced to supply a massive 8.5A. However, even if the maximum current is not reached, the amount and spectrum of switching noise may change drastically depending on the load current, and you may just be hitting a bad spot.

In generally I would recommend multiple smaller PSUs rather than one massive high-power supply. More power often means more noise, and it also means a bigger bang when something is plugged in wrong.

When buying switching PSUs its also good to look for one with a switching frequency above audio range. For this model I cannot find a specified switching frequency.
a.b.o.z.
I also tried removing half of modules from each rack and same thing is happening. If DI box and cabling doesn't solve it I will have to go multiple linear supplies.
a.b.o.z.
ok, DI BOX removed noise, sort of. Signal is now way higher than it was on line level. I just turn down gain until I can't hear noise and apply modular signal and have clean strong signal with that same noise burried down under it all. Will try doing that TS-TRS cable and test once more.
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