12V vs. 15V on VCOs

[Funky40]

Hi,

this is meant as a disscusion, and i post it here at DIY as the People with electronic Knowledge are here.



I just recongnized that my Plan B model 15 VCO in my Doepfer System pick up the Frequenzis from the LFOs.


And i just Recognized that all my other VCOs are running on my Dotcom PSU, also the curetronic VCO which is placed into my Doepfer Rack and built in 3HE ofcourse.

_________________________________________________________________-

the Point:

Once Matthias from curetronic told me that also when i like to built his VCO in 3HE euro Format, i should run it with 15V.
The VCO itself is running with 12V, and the incoming 15V are droped down to 12V.

He told me that it seems that this Process seems to filtering out the "noises" coming from LFOs.
He told me that there was a Case somebody had this Problem when running the VCO with 12V.

and now i recognized the same Problem on the Plan B VCO.


_______________________________________________________________-

this brings me to the final question:

should VCOs generally run with 15 V ?


( interesting is the Question in cases as the Zero from Cynthia . I allready decided for me soem time ago, that if i ever would get a Zero, i will not take it in doepfer format )

( btw.: my DIY Cabinet what is mostly finished and is held in 3HE Euroformat has also a 15V PSU )

[Mikmo]

My DIY modular http://www.mikmo.dk/synthstate.html is running on a homebuild 12 Volt powersupply, and i have no problems with the LFO's "bleeding" into the other modules, or any other crosstalk problems.

I believe that it has nothing to do with 12 versus 15 volts.

The problem has been discussed in the SDIY mailing list and if i remember right, i think the conclusion over there was that it is the way you distribute power to the modules and the way you implement bypass / decoupling capacitors that is central to the problem.

power should be distributed in a "star" pattern so each module is getting it's power from as close as possible to the power supply.

My system is made with little power distribution boards each connected directly to the power supply, and each feeding about 6 modules, kind of like a "star of stars". I think this is pretty close to the way the MOTM modules power distribution works.

[fonik]

[mono-poly]

With 15 volt you got less crosstalk.

[Coriolis]

[Funky40]

thanks mikmo, thats interesting.
And aslong my Powerbus thingy in my DIY cabinet is not really done i will maybe change some things.
yeah, star to star was also my plan, but with bigger Busboards ( ca. 12 connecttors )
i think i will ad a third 12V PSU. It was anyway short ( and funds are now better ... )


decoupling:
yeah, i put also caps to every IC + some near the Power


@mono-poly
yeah, please some more words.
Your experience ?

btw.: my 15V modules are running with the little Dotcom PSU.
I think this is a star concept, while my doepfer has 1 PSU for 4 Racks.All in series !!!
So this might be really a point too in my case.

[mono-poly]

I talked with my technican about it last week.
With 15 volt you got much more gain and less crosstalk.
More Power in short words.
Don't ask my to much technical stuff about it.

[zipzap]

I´m using +-12v, star connection of power lines (and ground!) and cabs like said above. Normally don´t have any problems.
It´s kind of a star of stars, i try to connect "switching" modules like adsr, lfo, sequencer independent from "sounding" modules like vcf, vca.
The thing about less crosstalk propably is because if your system is running at a fixed signal level of +-5v, a higher supply voltage is having it easier to supply the current needed with each swing of a signal. on the other hand, current in a modular is normaly quite low, so it´s no such big deal.
VCOs can be critical, since tuning may vary when the supply voltage is shakeing. To make them mostly independant from the main psu it can be a good idea to run the system on 15v and use a 12v regulator for each vco. Could work the same with 12v and a 9v regulator.
As i said, in my case it never mattered.
I´m using a 80va 15v transformer and 78/7912 regulators. each can give about 1A. Since my system is drawing less and i have all this cabs in the right places my supply voltage seems to be quite stable.

[Mikmo]

I think that if a system has more than one power supply, they should share ground right ?

One thing i have also avoided is to use the frontpanel as the only grounding for pots and jacks. In my system all panelmounted pots and jacks have a wired ground back to the board.

[mono-poly]

BTW my model 15 vco's pick up signal from each other to

[zipzap]

are u sure you have the bypass cabs installed correctly? try connecting the vcos seperately, directly to the psu.
do you use shielded cables? i don´t since 10v is a strong signal and it avoids ground loops.

[mono-poly]

Peter Grenader did built them in a custom panel.
So i guess he did his job right.

[funkyfarm]

[etaoin]

[fonik]