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Noise on LS1 and LP1 CV outputs
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Author Noise on LS1 and LP1 CV outputs
pugix
I noticed that my LED voltage monitor was indicating a slight negative voltage on the CV output of my LS1, when it is in any mode and the output should be zero volts. I put a scope on it and I see this. The vertical resolution is 1V per division on the screen. So the noise is about 1V in size.

[/img]

When the output voltage rises above about 0.5 volts, the noise is greatly attenuated, but it's still there.

I see this on the CV outputs of both LS1 and on all three CV outs (X,Y,Z) on the LP1.

The modules are in a 84 HP skiff with other manual controllers, and a BI1 Brainterface. I scoped the +12 and -12 power rails and they are clean. Power comes from a 4ms Row Power 40, which is way over the needs of this skiff. I see no noise on any other outputs in the skiff. The LP1 and LS1 gate outputs are clean.

This is a serious problem. If I patch one of the affected CV outputs to a VCO FM input, it makes the VCO wander a little. A DC voltmeter shows a small negative voltage that fluctuates. But it's actually the noise, averaging negative.

HAS ANYONE ELSE SEEN THIS? Is there a remedy? I cannot imagine that this is normal for these modules.

Thanks,
pugix
There's no problem with the modules!

I dug into this deeper. It turned out that the spiky noise signal appeared only when my voltmeter test lead was connected in parallel with the scope probe. I also found that just having the test lead -- unconnected to the meter -- on the circuit injected the noise. Must be acting like an antenna. I don't know where the noise originates, but it is external to the modular.

It can be tricky to know where a signal you're seeing on a scope comes from.

Sorry for the disturbance. Back to patching now.
pugix
I'm still seeing this, even with no test equipment hooked up. When I run the CV outputs to a CGS slope detector, all the lights are going crazy when the CV out is supposed to be zero. This is not good. I have no idea what to do about it.
dan_k
Hi Richard, I just tested with my two Light Strips and my Elby Slope detector and neither of the modules exhibit the behaviour that you're experiencing.

Without anything being generated from them the steady light is on as normal with nothing plugged in. Moving up and down the strip the slope detector tracks rising and falling accordingly as it should. Something weird is definitely up for you.

Sorry wish I had more to offer. Have you tried contacting soundmachines?

If there's anything else you'd like me to test please let me know.
pugix
dan_k wrote:
Hi Richard, I just tested with my two Light Strips and my Elby Slope detector and neither of the modules exhibit the behaviour that you're experiencing.

Without anything being generated from them the steady light is on as normal with nothing plugged in. Moving up and down the strip the slope detector tracks rising and falling accordingly as it should. Something weird is definitely up for you.

Sorry wish I had more to offer. Have you tried contacting soundmachines?

If there's anything else you'd like me to test please let me know.


Thanks for testing this. I'll have to do more testing myself. One test stood out. When in complete isolation (only one light strip on the power supply and connected to nothing but the scope), I was able to see the noise appearing when I just TOUCHED the output lead, or when I hooked the output also to a DC meter. So I thought that the noise was being injected externally. But why would this only occur on the LS1 and LP1? There is something going on with those outputs.
soundmachines
Hi there guys!
Just one hint about 'erratic' module behaviour with respect with what could be seen as a noise.
Normally those kind of problems are connected with bad ground paths (I mean hi impedance ground paths).
Just to give yo an example, I had an S&H behave completely random adn I discovered that the power cable was HALF inserted and I basically had NO ground return path. The module worked because I patched it with other modules and the ground was connected with the patch cord smile

Cheers, and let us know if situation evolves!

Davide
pugix
I have tested this more. I see the same problem with great regularity. If nothing but a scope is patched to the CV outs of the LP1 or LS1, zero volts output is clean. As soon as the output is patched to some CV input, the noise appears, just like on that picture in my original post. The noise greatly attenuates, but does not completely disappear, when the LP1 or LS1 output is at some positive value.

This is the same for all the LP1 and LS1 CV outputs. And it only happens on the Sound Machine modules. I have two Synthwerks FSR-1N and two Super Synthesis PH01 modules in the same skiff. The zero volt outputs from those modules is clean.

I have all the power supply grounds of the different power supplies in my modular cases connected together. However (and this is supposedly not correct) there are multiple points in which the AC earth ground is hooked to the DC common ground. I see no way to avoid this, because of how the 4ms Row Power 40 hooks AC earth to DC common. I am not aware of any other issue being caused by the grounding in my system. Given that this noise appears only on the Sound Machines modules, something must be different about them.

I am really at a loss what to do about it. I may decide to sell or trade, because this just isn't acceptable.
soundmachines
Hello,
Just for the sake of being cautious, I made some measurements with a pretty good Agilent scope on the output of different LS1.
I see an average -100mV as 'zero' with a 10/20mV noise. The outputs are configured as 0-5V.
This in a pretty crowded system with a couple of uZeus PSU.
I am pretty sure that this is the first time we have a report like this and LS1 and LP1 are our best selling products, going well beyond the thousand sold.

I may ask you to check the LS1 with the FMJ3 power supply? It's not requested to be inside of the case.

Let me know!!
pugix
soundmachines wrote:
Hello,
Just for the sake of being cautious, I made some measurements with a pretty good Agilent scope on the output of different LS1.
I see an average -100mV as 'zero' with a 10/20mV noise. The outputs are configured as 0-5V.
This in a pretty crowded system with a couple of uZeus PSU.
I am pretty sure that this is the first time we have a report like this and LS1 and LP1 are our best selling products, going well beyond the thousand sold.

I may ask you to check the LS1 with the FMJ3 power supply? It's not requested to be inside of the case.

Let me know!!


I did try the LS1 with the FMJ3 supply. That was one of my first tests. It had the same behavior. In that case my oscilloscope provided a second path to earth ground. (I used the same wall supply as with the 4ms, which is part PA-1900-24, made in China, recommended by 4ms.)

UPDATE: I went through the earth grounding in my whole studio. I discovered that none of my modular supplies internally tie 0V to earth. There are only two paths to earth: the 4ms supply AND my studio mixer. If I don't patch to the mixer, the noise on the LS1 almost (but not completely) disappears. So it's definitely an earth ground issue.

So now I need to look for an alternate wall supply that does NOT connect earth ground to the DC output. Unfortunately I don't have one of these to try at the moment. It needs to be 19V at about 5A. Any suggestions? (I've emailed 4ms about this, too.)

Thanks,
soundmachines
It's a quick and dirty hack that some time works:
Try, one at a time, to reverse the AC plugs ( starting from the one of your mixer). This could solve a dodgy earth system...
Let me know!
pugix
soundmachines wrote:
It's a quick and dirty hack that some time works:
Try, one at a time, to reverse the AC plugs ( starting from the one of your mixer). This could solve a dodgy earth system...
Let me know!


All of my equipment uses three prong plugs with earth grounding. I can't change how the mixers are wired internally.

I may be getting a 2-prong adapter for the 4ms Row Power 40, to isolate that from earth ground.
pugix
Another update.

The problem definitely has to do with earth (chassis) ground. By not connecting the ground prong on the power plug for the adapter that powers the 4ms Row Power 40, and not connecting earth ground to DC 0V anywhere in the system, the noise is gone.

But I still have a problem. When connecting between the modular TR outputs and the external mixer TRS inputs with a specially made cable that does not connect 0V to earth, the mixer imparts about 40K resistance between the ring and earth ground. (The TRS sleeve is earth grounded but is not connected on the TS side. The R from the TRS goes to the S of the TS plug.) With a stereo connection it becomes 20K. In this case the noise from the LS1/LP2 CV outputs at 0V out is reduced, but still not eliminated.

See this thread for more details on the grounding issue.
https://www.muffwiggler.com/forum/viewtopic.php?t=145512&highlight=

The only idea I have left is to put a hum/noise eliminator between the modular and the mixer. I'll have to order that.
pugix
This was bugging me so much, I had to do more testing.

For my test I removed one Lightstrip from the case and powered it alone, using the Sound Machines power supply. What I saw is baffling beyond belief. With the CV out connected only to my Fluke multimeter, it behaves well. The zero point is about -22mv DC out and there is no noise (measured by the AC reading).

As soon as the CV is patched to my 5U modular bay (power ground is connected by a separate cable), there is about 22mv AC of the noise. Here's the kicker: this happens when I patch into an unconnected multiple. The ground goes separately. That's right, just hooking it to a 1/4" multiple that has nothing but 4 jacks on it, open jacks that are connected only to each other, the weird noise appears. When patched to any CV input on the modular, the amplitude doubles to about 40mv.

I also tried simple loads on the CV output (not patched to the modular): 10K, 100K, and even a 0.47uf capacitor. Those didn't produce any noise.

This happens regardless of the earth grounding, which puts the lie to my previous conclusion.

So now I have tested and seen this noise issue in as many different setups as I could think of. And I am left no wiser than when I started. I am out of ideas and it seems this just has to be put under the WTF category. seriously, i just don't get it
soundmachines
Let's try to get out of the WTF category, we're scientists, for God's sake!
smile

I make a very silly question: are you powering the LS1 correctly?
With the jacks downward, the -12 is UP and not DOWN, as it is normally.
This seems a silly question but it's not looking at the power usage of the LS1.
Let me know!!!!!
pugix
soundmachines wrote:
Let's try to get out of the WTF category, we're scientists, for God's sake!
smile

I make a very silly question: are you powering the LS1 correctly?
With the jacks downward, the -12 is UP and not DOWN, as it is normally.
This seems a silly question but it's not looking at the power usage of the LS1.
Let me know!!!!!


Yes, it's powered correctly. I'm very careful to always align the red stripe with the -12 pins, as indicated on the PC board. Other than this weird noise when the output is below about 0.5V, everything works fine. I have it set on the 0-5V scale. Have not tried the 0-10V setting. Also, it's in the 'jacks up' position.

I'm wondering where the noise signal originates. It could come from the power supply or maybe from the clock of your microprocessor. It looked the same, regardless of which power supply was used.
Coetillion
bumping this older thread. i have the same issue where 0v outputs a little voltage. it's quite a bother to use it as a pitch controller because whenever i take my finger off the ls1, the osc will just drop down to a super low pitch. i can avoid this when using the hold mode, but not when trying to loop the movements :\
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