Question about Voltages from my sequencer

[EricK]

Friends,
Im using a dotcom q119 quite frequently to sequence everything from the Voyager, the T3, to the delay time and all kinds of things.
It has a setting for -5/+5 or 0/5.

Now what I am thinking is that this makes the pots for a particular stage bipolar or not.

Do I need to be aware of this switch when patching to something like the 101 filter cutoff frequency?

There have been times where I have patched some low voltages to something and I hear a sound like an electrical hum through the speakers.

Basically I want to know if I risk frying my Moog stuff with the q119.


Thanks to anyone who may reply.


Eric

[EMwhite]

I don't have an answer for you but have a different question (pertains to voltage levels and safety so not quite off topic).

I picked up a Walking Stick from Psionic; stained to match my whitewash Old School beautifully and has all the bells and whistles that Joe's been asked for over the years (two axis w/attenuators, a momentary gate with 'pressure' sensitivity toggle) and a new feature... an external power supply.

As each of the Moog's CV inputs (like Filter Cutoff, for instance) send 5V, Joe's Sticks have, in the past been passive very much like an expression pedal which meant that he could only return some fraction of the 5V based on position of the finger along the ribbon. Voltor has one of the early models, I believe.

In order to make mine adaptable, Joe included an 12V/600mA power supply which is of course too hot for something wanting 5V... or is it?

What I've found is that the range @ 5V (I measured this on a voltmeter and then marked the attenuator knobs accordingly) only do push onboard Voyager pots about 120 degrees (similar to an expression pedal). If I roll the dice and boost the voltage a bit on the Stick's attenuator, it gives more range. [so the question is... is this bad?] It would seem that it's still within range of what the Cutoff knob will do?

Which brings to question, situations where you can actually go out of range using the Voyager (speaking from my VOS's perspective)... If you set the wave of a VCO up towards narrow Pulse width, then set a mod bus to Pressure with Wave as destination, you quickly find that you're at the top end of what appears to be the allowable range and the OSC will simply go offline {dead quiet... eerie dead quiet... again, the ghost of theremin past comes to mind}.

So the second question is... does the Voyager have built in protection so that the SUM of incoming CV and knob position will cut off if the voltage is at max?

[glide]

Eric,

I bet Moog stuff is well protected, but I still would check everytime, use a voltmeter and keep everything documented and handy. Perhaps you could incorporate a voltmeter in your rack. Whenever you go negative with, say your 101, you will be stressing which material is there to protect. It may resist a lot of times, but perhaps not forever.

g

[Kevin Lightner]

Whenever you go negative with, say your 101, you will be stressing which material is there to protect. It may resist a lot of times, but perhaps not forever.

Sorry, but there's no technical reason to believe this.
It's all up to how something is designed and which parts are used.
Protection can be designed in to limit voltages and the parts won't wear out.
Bad design is bad design tho.
If something is designed poorly, parts can fail whether it's positive or negative.

Generally speaking, one shouldn't exceed the voltage that a device itself is running on.
Since most synths use opamps powered by +15 and -15, inputting a voltage higher than 15 (or actually a bit lower usually) can cause problems.
But most opamps are protected for things like this.
They simply can't amplify a signal greater than they're supplied with.
And many opamps are protected on their outputs.
Even the ancient 741 opamp can have it's output shorted all day and not care.

CV inputs usually don't add any protection for inputs.
If one was to, say, add a diode to protect against negative voltages, it would also rectify audio waveforms with very audible results.
Designers usually expect control voltages to hit 10 volts max because that's 10 octaves and covers the normal hearing range.
But many circuits can handle more voltage, while other circuits can't handle negative voltages well at all.
Again, it's all up to the design, parts chosen, etc.

I think it's safe to say that it's rare for most modular gear to generate signals hot enough to do any damage to other modules of the same type.
This is kind of an inherent design thing: the same power supply generating voltages is the same one processing those voltages.
Therefore, a synth usually can't generate a voltage hotter than it can handle.
One might well distort something to shreds, but it likely won't do any real damage unless very poorly designed.
Of course, plugging an audio amp's speaker output into a pedal or modular will usually deliver way more voltage than expected and *can* fry things quite quickly.

Fwiw, not all synths expect negative voltages. Strange things can happen, but usually not damaging.
One might get an opamp "locked up" for example, where it stays at a voltage and won't change unless powered down again.
Also, sometimes people feed in voltages so high, their vcos are playing, but they're at a frequency higher than normal human hearing.
That's common to see on synths that don't limit things to defined musical ranges (like modulars, for example.)
The vco is working fine, but the player's ears or tweeters aren't. (and after about 50 years of age, expect your high end hearing to diminish.)

One thing not defined well is gate voltages.
Most are positive and 15 volts or under, but there's no standard as to the minimum voltage required for gating.
Stranger, many envelope generators will derive their maximum attack and sustain levels from their input gate voltage.
So a low gate voltage may produce a low envelope output voltage and vice-versa.
Many Arps are like this. Moogs, not so much.
It's a cool thing too because controlled correctly, one can achieve voltage controlled envs to some degree- very good for velocity sensitivity for example.
Few envs will trigger given negative voltages (unless they're expecting an S-trig perhaps.)

Fwiw, it's possible to mod many sequencers that puts out -5 to +5 into one that outputs 0 to 10 volts instead.
With some designs, it's as easy as adding just one resistor.

[glide]

Hi,

Kevin I read your post carefully and I found little, if any, content directly related with my remark.
Perhaps I did not explain my example correctly.
MF-101 has a 9V supply voltage. Once you connect a jack to its CV input with a -5V signal, you are outside 101's power supply range by 56%. Sure the op-amp should have current limitation (although for some like the 3140 a sudden death would occur).
"the parts won't wear out" under this kind of stress? Sure they do, even if they are aerospace quality. They are not eternal, and repeated stress diminishes their life. So it is a question of time. How much time? A bench test would have to be conducted under the relevant conditions. Maybe you would gladly offer your unit for such test.
Based on experience, I wouldn't.

Better safe than sorry.

Best,

g

[EricK]

Okay,

Should I operate my sequencer on 0/5 or -5/5 mode all the time?

THe only things I am sequencing are Moogerfoogers and other modern Moog products.

[latigid on]

Hi,

Kevin I read your post carefully and I found little, if any, content directly related with my remark.
Perhaps I did not explain my example correctly.
MF-101 has a 9V supply voltage. Once you connect a jack to its CV input with a -5V signal, you are outside 101's power supply range by 56%. Sure the op-amp should have current limitation (although for some like the 3140 a sudden death would occur).
"the parts won't wear out" under this kind of stress? Sure they do, even if they are aerospace quality. They are not eternal, and repeated stress diminishes their life. So it is a question of time. How much time? A bench test would have to be conducted under the relevant conditions. Maybe you would gladly offer your unit for such test.
Based on experience, I wouldn't.

Better safe than sorry.

Best,




g

A quick look at the MF101, 102 and 103 boards show they each have a 7662 charge pump located near the power rails. Thus the safe range for input CV is likely to be -9 to +9 V; this would also be necessary for OAs requiring a bipolar supply. I couldn't say for certain without looking closer at the board or schematic, but the components are there.

[Kevin Lightner]

Latigid on basically explained things correctly.

Just because a device runs on a single supply voltage doesn't mean it doesn't have a DC-DC converter or other method of producing higher voltages and/or bi-polar ones.

I myself have a test VCO box I built with a CEM3340 VCO chip and it tracks wonderfully over a 10 octave range.
That chip runs on +/-15 volts as well the opamps amplifying its signals.
But inside? There's a single 9 volt battery powering it all.
This might confuse some people with only a rudimentary understanding of electronics, but it's the way some things are designed and how they work.
There are lots of guitar stomp boxes that do stuff like this because it's uncommon to find bi-polar DC wall warts, but usually desirable to have them powered from a 9v battery too.

[glide]

[
A quick look at the MF101, 102 and 103 boards show they each have a 7662 charge pump located near the power rails. Thus the safe range for input CV is likely to be -9 to +9 V; this would also be necessary for OAs requiring a bipolar supply. I couldn't say for certain without looking closer at the board or schematic, but the components are there.

Latigid on, thank you for your elegant answer. That is good news! It is most probably safe to use ±5V then.
Happy New Year everyone!

g

[DeFrag]

& thanks to Kevin for his info as well.

[EricK]

The reason I was prompted to ask this question is because whenb sending the filter cutoff of the 101 some low voltages, I was getting a whining sound that I didn't think was a good sound.

I was attempting to make some very low bass drum sounds, and what I got was a high pitched whine that didn't change from stage to stage. I had to bump up the voltages in those stages to eliminate that whine.

I thought that I might be risking damage if I continued.


Eric

[latigid on]

Maybe it would be best to look through each manual to find out which parameters accept a negative voltage. My guess is the 102 Freq might, and I remember the 107 freq can. Voyager KB CV does -- how about the Theremin?

Because the CV input will sum with the knob position, a voltage lower than zero could create interesting effects. I would be wary of going over 5V though. For example, you can get a Phaser amount greater than the "Kill" setting, which sounds pretty nasty, but is not recommended by the Moog crew.

Eric, perhaps it's best to stick with 0-5 unless you are working with oscillators.

[Kevin Lightner]

I don't think you'll do too much damage with the setup you're using, but there's all kinds of devices and instruments that act strangely once they go past their "expected" range of operation.

For example, the early Arp filter (4012, I think that's the #) would break into ungodly noise and harsh feedback if given too much CV.
The original Oberheim Minisequencers have a "bug" where they'll lock up if you control the tempo using the sequencer stages for tempo control and already are running a very fast using the tempo pot.

While not related, even the Minimoog model D has several quirks people don't expect: Attack stage overshoot, a delay upon powering up before the noise source will sound (noise sources can sometimes take up to 5 or more seconds before they produce noise), modwheel bleedthru, etc.
It's normal for the coveted 904A lowpass filter to make a fairly loud pop when switching its range control too.

If you're hearing whines, hums or clicks tho, you might take some time to check out the grounding and power distribution of your setup.
Sometimes the craziest things can cause unwanted sounds.
Here's an example some of you may find amusing: http://www.studioelectronics.biz/Scrapb ... ul-13.html

[Brian G]

GREAT story.

Reminds me of an interference problem I had in the late 80's with a brand new video switcher. Some RF chokes. Filers, clamped on the power cables as they went into the switchers main frame, the sync generator and the central timing box solved the problem Took a few weeks to figure it out though, Thanks again Lee .

Eric have fun with the Q119.