It shouldn´t sound, but...

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Putte
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It shouldn´t sound, but...

Post by Putte » Sat Feb 15, 2020 10:29 am

My modular gave me some severe headache today. I couldn´t manage to include a photo, so in short it is six portable cabinet system with some 120 MU:s in front and six power modules on the back. I had just unpatched everything to start something new, and I noticed the problem when just a few cables were plugged, outputs from VCA:s to mixer and some including step sequencers. No sound patches (osc:s., filters or EG:s) were included at all. For some reason I turned main volume up on the mixer (MGP32X), and there was a sawtooth tone. A bunch of channels had to be muted to kill the sound, including the two coming from a Fantom G8. The rest were all modular channels. So, I unplugged all output cables coming from the modular, one or two at a time. I also switched them between the VCA:s. Still, there was sound.
Then I started detuning the oscillators, to locate the sound source. It turned out both my Dove audio WTF:s were guilty. The other knew to keep quite. I finally solved the problem by connecting both their outputs to a Q113 (It might have helped just to plug the outputs).
So, how is it that these two wonderful modules can transmit their tones into my mixer, without being patched at all?

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Re: It shouldn´t sound, but...

Post by KSS » Sat Feb 15, 2020 10:29 pm

Putte wrote:
Sat Feb 15, 2020 10:29 am
So, how is it that these two wonderful modules can transmit their tones into my mixer, without being patched at all?
Typically this will end up being power distribution related. Often becoming noticed with additions of digital modules to the sytsem. The problem may not be the digital modules themselves, but rather their impact on the other modules.

Please describe your power supply and distribution in detail. Including between cabinet distribution, and How the mains voltage is spread around your system, from wall outlet to each cabinet. And include any digital modules in your setup.

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Re: It shouldn´t sound, but...

Post by synthetic » Sun Feb 16, 2020 12:27 am

Better yet, what’s an ideal power distribution method to avoid issues like these?

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Re: It shouldn´t sound, but...

Post by KSS » Sun Feb 16, 2020 12:51 am

synthetic wrote:
Sun Feb 16, 2020 12:27 am
Better yet, what’s an ideal power distribution method to avoid issues like these?
Search the site for Graham Hinton's posts on Power and distribution. Even if you don't end up with his ideal aluminum buss bar setup, you will learn enough to make informed decisions about best practice for your own situation.

Graham isn't the only one making good additions to those threads, and you'll pick up over the breadth of what's said who else is making sense and who isn't.

It's a contentious subject. But extremely useful to investigate with more than casual glance.

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Re: It shouldn´t sound, but...

Post by steffengrondahl » Sun Feb 16, 2020 6:53 am

I don't get it putte. Please provide some more information, like answering these questions:
  • What is connected to the mixer. Just VCA out from your modular?
  • What is connected to the VCA input? Nothing?
  • What are the outputs from the WTF oscillators connected to? Nothing?
  • If the answer is yes, nothing and nothing, is seems like a bleed through from the WTF oscillators to the VCA. Power related? Perhaps (I don't know) :hmm: What are you powering with? QPS-something from dotcom?
  • What does the Q113 mixer do? You say it solves the problem to connect the WTF oscillators out to the Q113 input, but what are the Q113 output connected to? The VCAs? Nothing?
  • Hmm re-reading your initial post, it seems like just plugging a cable into the WTF out might solve the problem. Can you verify?
  • What kind of VCA's do you use? Are the open, perhaps by the initial gain not zero?

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Re: It shouldn´t sound, but...

Post by Putte » Sun Feb 16, 2020 8:42 am

You´re probably right, I´ve been a bit worried about the power supply for a while. Just goes to show it´s a lot more fun buying filters than pay to get enough power.

But first, Steffen, the only cables connected were the outputs for my mixer. Nothing else. And the Q113, i only used it to put the cables coming from the WTF:s somewhere. They were meant to go there later anyway.
Now, K55, it would be best to supply a photo of my system, I guess. They tend to be about an acre in size, I´m afraid. It seems they can be clicked on for a more useful size. I hope that works for you. There are six cabinets in my system, the two at the bottom having one QPS1 each. They supply their cabinet and the two on top of them. Power modules are on the back, two Q137 and four Q103.

That means now the left QPS1 supplies power for 60U, the right for 68U. i know I should´ve done the math on Modulargrid, but I haven´t yet. The two WTF being in the right part of the system would explain things, but today my M554 started acting weird, and it´s in the middle cabinet to the left. I´m guessing getting another QPS1 can´t be avoided anymore. Hell, I need two more simple envelope generators anyway, so it´s time to turn to Texas.
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Re: It shouldn´t sound, but...

Post by Putte » Sun Feb 16, 2020 10:24 am

Here´s what Modulargrid says, but there are some question marks. The Grove audio Dual LFO/VCA has incomplete power specifications, as well as the krisp1 Dual VCA has. The latter only goes for the one I have on the right power supply system, not the left!
The three cabinets to the right: 1413 mA +15V| 1038 mA -15V| 285 mA 5V
The three on the left: 1281 mA +15V| 843 mA -15V| 94 mA 5V

According to this, I should have margins this far on hte right side, I guess. There should be no need to worry about power for the left side, now. But, as you probably guees, those top cabinets are supposed to be filled with modules. No matter the situation now, I´ll have to get another QPS1.

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Re: It shouldn´t sound, but...

Post by steffengrondahl » Sun Feb 16, 2020 11:13 am

As a rule of thumb (not mine but some of the guys who knows about power) you should only draw up to around 75%. 1413 mA is 94% and 1281 mA is 85% :woah:

Perhaps some of the experts will chime in ...

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Re: It shouldn´t sound, but...

Post by Putte » Sun Feb 16, 2020 12:13 pm

Thanks/tack, Steffen! That was totally new information for me. I should perhaps also mention that there are quite a number of mschines around me that need power supply, 20 I think, so the electricity has to support a lot of things. I´m not sure if that is related to this issue, though.

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Re: It shouldn´t sound, but...

Post by burdij » Sun Feb 16, 2020 12:37 pm

The GMS-782 Dual LFO/VCA uses less than 50mA from the +15 and -15V supplies.

Have you checked to see if the voltages on your supplies are drooping. They should be within 50 millivolts of their rated voltages. With this supply, that will be the first indication of whether you are drawing too much current from the supply. There are also potentiometers on the supply to permit adjusting the voltages to the correct values. I wouldn't worry about the "rules of thumb" about derating supplies. This linear supply is designed to supply 1.5 Amps at 15 Volts day and night forever. When the current goes above 1.5 Amps, there is an overcurrent circuit that begins to lower the voltage to reduce the total power dissipated by the supply so that the output transistors don't overheat. When this happens, the internal impedance of the supply rises which allows more noise to appear on the output and also prevents the supply from shunting external noise on the power buses to ground through the operation of negative feedback of the internal servo that controls the voltage.

Out of curosity, do the WTF oscillators have a setting for the source of the internal +5V? I gather this MU compatible device is derived from a Eurorack predecessor? When I design modules for Eurorack, I usually provide a means to derive +5 either from the powersupply +5 rail or from an internal +5 regulator powered by the +12 or +15 V rails. If this exists in your module, the correct setting for the module should be to derive the +5 V from the power rail.
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Re: It shouldn´t sound, but...

Post by burdij » Sun Feb 16, 2020 12:57 pm

I have another question. What cabinet stack contains the Q113 you used that you plugged the oscillators and noticed that the noise went away? Its a bit hard to see in the photo included.
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Re: It shouldn´t sound, but...

Post by Putte » Sun Feb 16, 2020 2:29 pm

I know, Burdij. It used to be easier taking pictures of the system. Not so much anymore.
The Q113 I used then is just under the two WTF:s. They are in the middle right cabinet, the Q113 in the lower right.

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Re: It shouldn´t sound, but...

Post by Putte » Sun Feb 16, 2020 2:42 pm

Sorry, burdij, I didn´t see that first comment to begin with. I am, which should be obvious by now, not much of an electrician. It´s been years since I took a closer look at the QPS1:s, if I ever did. My cabinets open on the back, but their too close to the wall now. I have to remove them to work from behind, as the heaviest (with QPS1) naturally are at the bottom, or remove some modules to get thru. All that can be managed, but not my poor electricity knowledge.
I think you´re right about the WTF, but I´m not sure. I´m just happy to have them.

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Re: It shouldn´t sound, but...

Post by KSS » Sun Feb 16, 2020 9:02 pm

After a quick read of posts, feel the need to say that my reply was not meant to suggest that there was not enough power. But rather to suggest that the power sources and power users were influencing each other in negative ways. Usually because of too much resistance from source to user. As Graham has pointed out many times, the power distribution which might work in a small system is not necessarily the one you'd want for a large setup.

The dotcom power distribution is adequate for the modules and typical systems present when it wass designed. That was a long time ago, and the modular environment has changed dramatically. Digital modules, fitting more modules to a given supply as systems get larger than the small wires in the dotcom ditribution cables can handle (DIN6 to DIN6) "Handle" here meaning having a low enough resistance to minimize power supply interaction between modules.

Adding another PSU may help -probably will- but it's not because of overall draw. It would be due to shorter cabling, and fewer modules per PSU. It might also help you to isolate 'noisy' modules on different PSU than others -not necessarily meaning random/osc/noise sources. In this context, any module can be a bad actor.

Which brings up amother point Graham has made many times. It's obvious and sounds simple, but it may prove harder than it might first appear. That is to look at the whole of the modular system -taking into account goals and expectation for it- and not try to put temporary band-aids on problems.

The 75-80% suggestion is more cargo cult than actual fact. Although the actual fact miught be that it arose because power supply capability was spec'd inaccurately and unreasonably hopeful.

Short summary is that you could still have problems like this even if your supply had three times the ampacity your modules demanded. It not all about the total draw. It's about the resistances in all the pathways power, shield and GND take along the way.

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Re: It shouldn´t sound, but...

Post by KSS » Sun Feb 16, 2020 9:51 pm

Putte wrote:
Sun Feb 16, 2020 2:42 pm
as the heaviest (with QPS1) naturally are at the bottom
Having just written not to apply band-aids, one look at your setup and this comment you made suggests a couple. Right now you have oscillators at the farthest reach from the power supplies. Moving the power to the middle pair of cabinets means you can use shorter power cables between cabinets. These wires 'should' be much larger than what Dotcom uses. To get the best power isolation between cabinets and modules. If you or someone you know can shorten the ones you have, and better could make some up with heavier wiring, it will help.

If you purchase a third power supply, look at all the possible ways you could arrange them with the six cabinets to have the shortest cabling. For example, it might make sense to go three high with power and left to right from PSU's on left to 2nd,4th,and 6th cabinets on right. But if your cabinets are like the ones dotcom sells, you'd want to flip one or the other side so the cable is as short as it can be. If this is not practical, then it might be better to go to vertically paired PSU-cabinets. This way the destination is just above the source, times 3. Make that times two, with the third pair left to right. /edit

When you load modules onto your busboards, draw mental lines of the path the electricity is taking from the point on ther busboard where the power is input across the PCB to the module connector, then through that module's cable to the module itself. Put the modules with the heaviest draw closest to the busboard power entrance. Don't use overly long cables from busboard to module.

To say more will just be duplicating what Graham and others have already shared in prior threads. Here's one further thought.

Sometimes it can be helpful to a non-electrical person to think of the electricity as water, and then imagine your goal is to supply each modules all the 'water' it needs, avoiding the unpleasant effect of taking a hot shower when someone flushes the toilet in a poorly plumbed home. If you've ever experienced that, it's the same kind of problem as you'll find in power supplies and distribution. The toilet in this case is a cyclic user of large amount of water, and this sudden grab of water when it's flushed reduces what you have and need in the shower. If the toilet and shower both had direct lines -of large enough volume- to the water source, this wouldn't happen. One would not affect the other. Same thing in your synth.

In your synth the 'water' needs vary by module. Not only in total amount, but also in how evenly they draw this from the source.

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Re: It shouldn´t sound, but...

Post by Putte » Mon Feb 17, 2020 6:04 am

Lots of information to process there . Thank you, KSS.
The cabinets will have to be stacked in this way, in pairs and three in height. I have synths, a Hammond C3 and two Leslies all around me. There is only one flank left for the modular, and it´s not very wide. I will, however, have to find another table/bench to rely on. This thing is getting too heavy.

Thanks for adding the distance perspective. Hadn´t thought of that. I´ve never had any trouble with the modules in the top cabinets, though, farthest from the QPS1. Could it be that the problem has to do with the Q101:s in the middle, those receiving power, but also sending on to the top cabinets. I´m thinking that if the distance can be an issue, surely also the fact that electricity has to pass thru a module could have en effect. Anyway, the all together five oscillators on top of everything seems to work great. I have a lot more problem with the three Q106CRS in the bottom right cabinet. I think they are the oldest. They are incredible unstable, and sometimes I have to tune them after a few minutes. On the other hand, lately almost a week have passed and they have been in tune from the start (without any warming up). Could such a problem also be related to power supply?

I´m not sure of the length of the power cables I bought as cabinets 3 and 4 were built, but I remember choosing the longest as I added 5 and 6. They were the same price. Now that I´m adding another power supply, and if place two of them in the middle, I´ll get rid of the distance problem (especially with shorter cables).

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Re: It shouldn´t sound, but...

Post by burdij » Mon Feb 17, 2020 6:35 pm

Your problem is starting to sound less like a power capacity issue and more like a ground referencing problem. I think there are three areas to consider.

According to what I read in the Swedish electrical standard document (which for some reason is in English), the common electrical outlet (European type C or F) has an earth (safety) reference which contacts the power plug through one or two clips on the external circumference of the connector. It seems that this is a relatively recent addition so older power system installations may have outlets or wiring which don't support the ground wire connection. Depending on the age of your building, you may or may not have this earth connection. If it doesn't exist you could have a situation where your cabinets and mixer have no common earth ground reference. This can be a source of noise issues.

Secondly, the DOTCOM power cables for interconnecting cabinets don't contain a separate earth reference wire. Interconnected cabinets are only reference to the earth ground in the cabinet containing the power supply and the AC inlet module through the power ground wire in the power cables which is at best a number 22 or 24 gauge copper plated steel wire. This is not a good design practice when building a system for low noise performance. Lowest noise is achieved using a star ground path with the center of the star connected to the mains earth ground reference pin by a single wire. Multiple paths may cause ground loops which can pick up line hum as well as noise conducted through EMI (electro-magnetic interference). You can connect the separate wiring harnesses to each other and to the power supply common safety ground through external wires running from cabinet to cabinet. This may cause some ground loop issues but just go back and remove any that affect the newly introduced noise and leave the others. Start by connecting the two cabinet grounds in the cabinets with the power supplies.

The third problem that I have noticed with DOTCOM wiring harnesses is caused by the use of wire nuts to combine dozens of small diameter connections together by twisting them and using a wire nut to complete the connection. This problem is enhanced by the fact that the conductive part of the wire nut is made from aluminum so there is a possibility of failure due to dissimilar metals being used between the wire and the shell. I had a harness on a Box 11 cabinet with this problem in one of the power rails. This problem can be fixed by removing the wire nut, binding the individual strands together with bare copper wire wrapped in several turns around the bundle and then soldering the connection. Insulate the soldered bundle with shrinkable tubing or electrical tape. Soldering that many wires will be difficult. Use a high wattage iron or soldering gun.

Finally, depending on whether your mixer's power supply passes an earth reference through to the frame of the mixer, you can also need to connect the frame of the mixer to the star ground earth reference on your cabinets.
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Re: It shouldn´t sound, but...

Post by Putte » Tue Feb 18, 2020 3:18 am

It´s all very clear to me now, but I have suspected it for a long time. I should have stayed with the wooden flute! Electricity isn´t for me.
Thanks for that essay, Burdij. I suppose you´re more fond of electricity than me. Well, I am, when it works. I´ll have to read your explanations tonight, when I got time to do so without interruptions.
My spontaneous thoughts is to buy more modules and see what happens.
Oooh, where is my flute?

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Re: It shouldn´t sound, but...

Post by Putte » Tue Feb 18, 2020 2:47 pm

So, you went through information about swedish electricity standards, Burdij? That´s…. That´s commitment.

The building is old, some kind of former factory, but rebuilt with rehearsal rooms for bands. I have no idea when that happened. One concern is the number of wall contacts (4), which for me mean I have had to add four power strips. Could it be that the capacity not is enough for my gear? I mentioned 20 Before, but there are 24 instruments and other stuff coming from four wall contacts. But why then, doesn´t any of the others act weird?

I´m not sure about that last thing you mention, the MGP32X power supply I can´t find anything on it in the manual.

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Re: It shouldn´t sound, but...

Post by steffengrondahl » Tue Feb 18, 2020 5:38 pm

putte if you are overwhelmed by burdij (and kss) great posts, you're not alone :wink: Yet I have a master in physics (theoretical) my insight into electronic engineering is lacking. And what worries me is, I've got a setup not so different from yours:
  • I live in Denmark, so the same power outlets problems are probably also valid here (first point in burdij long post).
  • My modular synth is 4 cabinets, 1 big QSC44 in the bottom with a QPS3 power supply and on top of that 3 QSC22 cabinets. So the problems mentioned in the second paragraph in burdij long post could also be a valid for me?
That said I have not experienced any severe noise problems. Or maybe I had. When I had the Moon Modular 568 trigger sequencer, enabling steps on the sequencer and thus turning on the LED's, I got some very weak 2kHz noise even though the 568 wasn't connected to anything. I've also been bothered with noise from my WIFI router, but here the solution is simple: Turn the WIFI router off :)

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Re: It shouldn´t sound, but...

Post by burdij » Tue Feb 18, 2020 5:40 pm

Well, since I sell supplies and adapters for international use, I like to also supply a power cord which plugs directly into the outlets in the country I am delivering the equipment to. Knowing the electrical specifications is handy. With regard to the mixer, it appears that the inlet to the device uses an IEC style power connector so I am assuming that you were supplied a Euro plug to IEC cord with your mixer which also implies that the cord probably uses a connector with a safety ground terminal. Of course, it still won't do any good if the outlets don't have the safety or earth ground connection. Below and to the left of the AC connector, it appears there is a screw to attach a ground wire, though.

I checked a couple of stores in your area for socket testers which could be used to verify the AC connections safely. This one was on the Jula site: Socket tester.

After sticking my fingers in an extension cord when I was three (the only thing I remember from that time) while my mother was vacuuming, I haven't been quite right since.
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Re: It shouldn´t sound, but...

Post by Putte » Wed Feb 19, 2020 3:28 am

Nice to hear that even a physicist is having a hard time with this. Somehow, Steffen, I always think Norway when I read your posts. Your names sound more norwegian, but it´s Denmark. Okey, we´re both Scandinavians anyway!

I have masters in history and a bachelors degree in Earth science, which explains my poor understanding of electricity. I once, in my youth, had to choose between drums and synths, and obviously made the wrong choice. Then again, that was just before Simmons started coming out with their hexagonal drum pads. I might have had the same issues, whatever choice I hade made in the early 80s. As I mentioned before, where´s my flute?

I guess one idea is to actually read through your suggestions while I´m at the rehearsal studio, and not at home. i´m still thinking, though, that I should try the more aggressive approach. Bye another module, then another, and do so to see if the problem gets worse! Fight fire with matches?

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Re: It shouldn´t sound, but...

Post by KSS » Wed Feb 19, 2020 4:40 am

Putte wrote:
Wed Feb 19, 2020 3:28 am
i´m still thinking, though, that I should try the more aggressive approach. Bye another module, then another, and do so to see if the problem gets worse! Fight fire with matches?
It's generally best to fight fire with additional clear space. In this case, that would suggest removal of modules to see if it gets better. And to better define which modules are cause -if any- and which are effect.

And it never hurts to improve your power supply distribution.

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Re: It shouldn´t sound, but...

Post by Synthbuilder » Wed Feb 19, 2020 5:25 am

Personally, I'd have a power supply in each box. This simplifies the distribution and usually reduces any problems with unwanted return currents travelling down the screens of the patch cables.

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Re: It shouldn´t sound, but...

Post by Putte » Wed Feb 19, 2020 1:40 pm

Yeah I know, KSS, but my method seems so much funnier - until somethings really go wrong. I´ll pick out a few modules that will make a difference, some with a little more power consumtion than others. One thing, though, it´s not every time there is a problem, at least that I detect. When there is, I suppose I should try with less modules without turning the power of. That would mean deconnect one module after another with the power stiil on. I´m sure I´ve seen some manuals underlining that no such thing should be done while the modular is running (As with most electronics).

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