Yusynth CV standards

Funky40

Hello Yves,

I'd like to build the CV standards, a really important project. Boards are allready here,
But:

What Equipment do i need to measure the voltages accurate enough.
My DMM is definitly not good enough.

Yves, do you have some recommendations for a good DVM ?
Whats the pricerange one must think of ?

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

As a matter of fact one needs a 1mV accuracy for the octave switch and a 0.1mV (or better 0.01mV) accuracy for the semi-tone switch.
As such a 4000/5000 pts DVM will do (let you measure up to 4volts with a 1mV accuracy), personnally I have 50000pts DVM which provides me with a high resolution (let you measure up to 40 volts with a 1mV accuracy).
Obviously the cost of a 20000/50000pts DVM is not the same as that of a 4000pts one.

I bought mine at conrad's some seven years ago and this model is no longer sold but a good one would be (at conrad.ch):
EXTECH EX-510 (6000pts, 175 CHF)
or even better the
Voltcraft VC-860 (40000 pts, 190 CHF ! )

Funky40 · Posted: Wed Aug 27, 2008 1:36 am Post subject:

Thank you Yves.
so it seems all about the points.
when i looked at Mouser they speak from digits. 5 1/2 for example.
ok, i check some places. ( i found nothing at Reichelt yesterday )

Jaba · Joined: Feb 27, 2009 Posts: 48 Location: Genova, Italy

Hello,

I am building your Yusynth CV Standards module, on a PCB I bought from Bridechamber (a great PCB! Smile

), but I want to be sure about some details

Confused

I just don't understand the "IMPORTANT NOTE" on the project page: why must R7 be 156k ? shouldn't the two voltage dividers be symmetrical ? (I mean the positive semitones CV divider made by R5, T11, T12, T13, T14, T15, R6 and the negative semitones CV divider made by R7, T20, T19, T18, T17, T16, R8 ) ; 156k seems a little low too, IMHO

Question

and then why did you choose for +5 and -5 semitones ? this way one note in the octave is left out; I would add a +6 (or a -6), using the last position of the switch and one more trimmer

and last: the parts list says "R7,R22 15k" which seems wrong to me

thank you for these great modules and for the time you spend answering these questions Very Happy

P

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Hi Jaba

numbertalk · Posted: Mon Dec 07, 2009 6:48 pm Post subject:

Hi Yves,

Just finished your cv standards module and everything is great except I can't calibrate the -5 semitone setting. It's off by quite a bit (the closest I can get it is -.4223). I noticed while I had this on my bench it was really wanting more than +/-15VDC in order to calibrate everything correctly. For instance, in order to get a -.4166 I need to have my power supply set a bit higher than -15V. Which I could do, but it was a little high and I really don't want to have to recalibrate all my VCOs by changing the voltages of the supply Is there any other way around this - a resistor on the board I could tweak the value of?

EDIT - I just read the above post and I do have the 1.2M resistor in parallel with the 180K resistor. Should I try a different value other than 1.2M here?

Thanks!

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

numbertalk · Posted: Tue Dec 08, 2009 7:35 am Post subject:

I haven't tried it with just 180K yet. I just went by your website so put the 1.2M in parallel when I built, then I just read this thread last night. I will try just 180K, though it seems like I need to go with a lower resistance. Is there a don't-go-lower-than value for this resistor?

Thanks.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

numbertalk · Posted: Tue Dec 08, 2009 9:03 am Post subject:

Great thanks!!

numbertalk · Posted: Tue Dec 08, 2009 7:44 pm Post subject:

Ok, got it!

One more question, though - I don't seem to have a stable 5VDC source I can use for calibrating the "external cv" trimmers, so I used the highest output of my CV keyboard, since it's very stable - it's 3.903VDC - is this ok or does it really need to be 5V?

Thanks!

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

numbertalk · Posted: Wed Dec 09, 2009 8:23 am Post subject:

Thanks Yves, that's what I thought but wanted to make sure you hadn't picked 5V for some reason I wasn't seeing.

I think the reason that voltage from my keyboard is as far off from 4V as it is is that the highest note is a B, not a C, so it's just under 4 octaves. Still it's not quite perfect and this has made me realize it could use some calibration, so I'll need to figure that out at some point.

A few notes for anyone else building this - I upgraded the op amps to LT1014s for greater stability and accuracy - the pin out is a perfect match for the TL074. Also you should calibrate this module with it connected to your synth's power supply, not your bench supply. If the voltages differ even by a small amount between your bench supply and your synth supply the calibrations will be off. Also as already noted you might need to play around with the value of R7 if you're having trouble particularly trimming the -5 semitone setting. Also if you have any trouble trimming any of the higher or lower values of the octave or semitone settings make sure your supply is calibrated to give +/-15V and not a little under (or else I guess you'll need to tweak the resistors a bit as already noted to compensate for the tolerance values of the trimmers).

I'm very excited to have this module, Yves, thank you so much for this project! Not as glamorous as your filter series but incredibly useful - not to be overlooked! Even aside from the tuning capabilities it offers, having a buffered multiple for reliably distributing critical control voltages to multiple VCOs/modules is a must in any system I think.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France