MOTM-700, variable PS volt drop, and VCO detuning?

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Overand
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MOTM-700, variable PS volt drop, and VCO detuning?

Post by Overand » Wed Mar 25, 2020 12:44 pm

So, here’s an odd one for you!

I have an MOTM setup, two 10U racks, with an MOTM-900 power supply in one and a 950 in the other.

My left rack has my 2xMOTM-300 & 1x310 VCOs, MOTM-650 MIDI-to-CV, assorted modules, and MOTM-950 (+/-15, +5V) power supply.

Here’s what’s odd. I was using my MOTM-700 (VC router/switch) - as I sometimes do - as a visual indicator of a gate pulse. I noticed, after some confusion, that my VCO tuning was shifting with that gate pulse. So, I did some experimentation!

(I may have drop/raise reversed here, going by memory). My VCOs drop in pitch a tiny bit when the MOTM-700 lights are green / when it’s routing B->X and/or D->Y. (Moreso if both are green).

Digging around a bit showed me that my power supply voltages drop JUST measurably on my Fluke 77 IV meter, so, dropping from 15.01 to 15.00. (I can’t remember if it was on +15 or -15). I’ll try to get a recording soonish, but, huh!

It’s not VERY noticeable, I imagine, but it’s also one of VERY few times I can recall my MOTM setup behaving unexpectedly!

I’m considering moving my modules around to rebalance the power consumption, but that might be overkill? I measured the consumption, and I was around 60% capacity on that left rack? I’ll have links to my two separate racks in a message soon! (And actual consumption numbers, if I can find them).

I’m wondering if other folks have noticed anything like this.

They’re analog oscillators, so, it’s not wacky for them to vary with power supply voltage I’m sure! But maybe my power supplies are getting tired?
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Overand
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Re: MOTM-700, variable PS volt drop, and VCO detuning?

Post by Overand » Wed Mar 25, 2020 12:48 pm

Left rack case (the one In question, with MOTM-950 PS)
Right rack

I couldn’t find my actual power usage notes, unfortunately. I recall them being a tad lower than specified!
Sites: overand.com | SoundCloud | YouTube ModularGrid: MOTM | Euro
WTB: MOTM Case, Euro VCAs, Sequencers, Env Followers & Interfaces.
Building the modular since ~2003

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Re: MOTM-700, variable PS volt drop, and VCO detuning?

Post by sduck » Wed Mar 25, 2020 5:42 pm

The power consumption numbers in that modulargrid page is way off. You've only got one module pulling anything from the 5v line, there's no way it would be more than the +15v usage combined. Otherwise, I don't think you're close to rated capacity of the 950 though, but maybe you're close enough that the switching circuit in the 700 (and associated led) is pulling it down just a bit. If it's really an issue for you, maybe you could swap some stuff and put the 300/310s over in the other case?
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JRamella
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Re: MOTM-700, variable PS volt drop, and VCO detuning?

Post by JRamella » Thu Mar 26, 2020 7:54 am

I know when I had droops similar to what you are experiencing I went back to the Modular Grid power requirements vs what Paul has listed in his manual and some were way off. For instance... 310 is listed as 31ma at MG... manual states 45ma. I reconfigured my case/power supplies based on the manuals and the droop was gone.

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Re: MOTM-700, variable PS volt drop, and VCO detuning?

Post by Overand » Fri Mar 27, 2020 10:59 am

https://synthtech.com/motm/650/ - the documentation on this module specifies 575mA on +5V

I’ll update the modulargrid pages if they’re wrong, but, I did an actual measurement and the consumption number totals were lower than modulargrid, if I recall. I’ll probably redo this. (It might even be worth me making a little dongle for testing power consumption of modules.)
Sites: overand.com | SoundCloud | YouTube ModularGrid: MOTM | Euro
WTB: MOTM Case, Euro VCAs, Sequencers, Env Followers & Interfaces.
Building the modular since ~2003

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Re: MOTM-700, variable PS volt drop, and VCO detuning?

Post by sduck » Fri Mar 27, 2020 11:03 am

Overand wrote:
Fri Mar 27, 2020 10:59 am
https://synthtech.com/motm/650/ - the documentation on this module specifies 575mA on +5V

I’ll update the modulargrid pages if they’re wrong, but, I did an actual measurement and the consumption number totals were lower than modulargrid, if I recall. I’ll probably redo this. (It might even be worth me making a little dongle for testing power consumption of modules.)
That's just the 5v rail. It's the other ones that are off, and the ones that will make a difference.
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