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Moogerfooger CV question.

B

biggs1249

Jun 2, 2008
277
0
Philadelphia PA
www.myspace.com
#1
So I recently acquired a moogerfooger ringmod. While searching on the internet, I stumbled upon a neat fact from the guy who made Frostwave pedals. He said you can take a 9v battery and solder connections to a quarter inch plug and plug it into a volume pedal. This can be used as an expression pedal for anything that uses CV. I tried this. I wired the positive to the tip, and the negative were the ground would go. He said to use a volume pedal with a pot, but I used a Morley little alligator. It worked pretty well. (I tried it on a moog modular system which was AWESOME) I later read that moog recommends 5 volts of control voltage, and not 9. SO FINALLY HERE IS THE QUESTIONS:

does anyone see why this would be bad for the ring mod?
does it matter that i'm using a little alligator and not a passive volume pedal?
is there any way to attenuate the voltage so that I am using 6v max?
(right now the upper extreme of the exp. pedal is a little too extreme)

hopefully people smarter than me and shed light on these questions...
 
#2
biggs1249 said:
does anyone see why this would be bad for the ring mod?
does it matter that i'm using a little alligator and not a passive volume pedal?
is there any way to attenuate the voltage so that I am using 6v max?
Click to expand...
Moog don't seem to specify a maximum voltage, and I'm sure the circuit would be well protected. However, they do say that 5V will result in the maximum adjustment possible - so anything above that is wasted, meaning a portion of the sweep of your "expression pedal" is useless.

I was quite surprised the Morley worked, until I saw the schematic (freely available on their site). It looks to be ok, but there is a chance that you might damage the LDR's (light dependent resistors) in the Morley if, say, you accidentally shorted the output to ground and the full current available from the battery flowed through the LDR's. But, not knowing the specifications of the LDR's it's hard to say if this would be a problem.

A simple solution might be to use a flat battery - chances are the current the Moog requires is tiny so a flat battery might handle it. Otherwise, you could make a voltage divider, or perhaps put some diodes in series with the battery.

I would encourage you to search wikipedia for info on voltage dividers - just make the resistors very large values to avoid draining the battery too much. There's a small amount of maths involved, but nothing that's too difficult.

Series diodes would also work - they drop about 0.6-07V each, so you might use 6 in series to get down around 5V.
 
#3
how long does a 9V battery last? I guess quite long..
just a thought, but if you plan to use this expression pedal it might be cheaper in the long run to get a used passive one that uses the power supplied from the moogerfooger..
 
#4
I think the Moogerfoogers work with a passive expression pedal (like the Moog EP-2) as well as a CV source. If so it might be possible to wire up a regular passive volume pedal to work. Does anyone know if you can use a Y-cable with a TRS jack going to 2 mono jacks hooked up to the input and output of an Ernie Ball volume pedal to turn it into an expression pedal?
 
#5
niftydog said:
Moog don't seem to specify a maximum voltage, and I'm sure the circuit would be well protected. However, they do say that 5V will result in the maximum adjustment possible - so anything above that is wasted, meaning a portion of the sweep of your "expression pedal" is useless.
Click to expand...

Well thats not exactly right. 5v is just what the knobs do, not the maximum that the pedal can do. With this setup I was able to go way above the frequency rage on the frequency knob. It was so piercingly shrill and high though that it wasn't so useful. even on the "low" setting, toe down resulted in some pretty high frequencies. This was really cool, because you could sweep up from tremolo all the way up into ring modulation, which could be very useful.

Thanks for the info guys. Does anyone else think that this could damage the Morley?
 
#6
dubsymmetry said:
how long does a 9V battery last?
Click to expand...
In this application, a long time. The Moog's current draw should be quite small, and if the volume pedal is a 250k type then it won't waste much through the pot either.

dannybuoy said:
Does anyone know if you can use a Y-cable with a TRS jack going to 2 mono jacks hooked up to the input and output of an Ernie Ball volume pedal to turn it into an expression pedal?
Click to expand...
That should work as long as you get the Y end around the right way - 'ring' to the input and 'tip' to the output.

biggs1249 said:
Well thats not exactly right. 5v is just what the knobs do, not the maximum that the pedal can do.
Click to expand...
Sweet - that's good to know. They don't mention anything like that in the manual.
 
#9
Did you try it without the batteries as well? Get a cable with a stereo TRS jack on one end and 2 mono jacks on the other; plug the TRS into the Moog expression input and the other 2 into the input/output of the volume pedal. Not 100% sure it'll work, but it should do if the Moog accepts passive expression pedals (which I think it does) and the Morley volume pedal is just a passive potentiometer (like the Ernie Ball VP-Jr) rather than a powered/buffered circuit.
 
#12
biggs1249 said:
could anyone help me with figuring out what I need to do to rig up this voltage divider? I just need a few resistors? what values?
Click to expand...
You want high values (>50k ohms) so that the voltage divider doesn't waste too much power from the batteries. The equation is a simple ratio of the two resistors:

Voltage out = (voltage in x bottom resistor) / (top resistor + bottom resistor)

Code: 
voltage in
      |
     .-.
     | |
     | |
     '-'
      |
      o---voltage out
      |
     .-.
     | |
     | |
     '-'
      |
      |
     ===
     GND

dannybuoy said:
the Morley volume pedal is just a passive potentiometer...
Click to expand...
Well, it's not, but your idea should work anyway.

biggs1249 said:
I don't quite understand the premise of this idea. Why would you want the input and the output of the volume pedal going to the unit?
Click to expand...
The Moog actually provides a voltage on one of the pins of the CV jack. You can route this voltage to the input of a volume pedal by using an "insert cable". The same insert cable is capable of routing the controlled voltage from the volume pedals output back to the CV input.

biggs1249 said:
Is there any reason why I can't just throw a pot on there to control the maximum voltage from the batteries? what value should it be?
Click to expand...
A pot is essentially a variable voltage divider, so yeah, I guess so. But a pot is potentially unreliable and unstable, they're also a source of noise when used to control DC voltages.
 
#13
Ok, so i'm trying to make a box that has a stompswitch, a pot and a jack. This will go into a volume pedal to be a CV control. the switch will turn voltage on and off, so you can hit the switch and go from 0 to 10, or anywhere in between and/or sweep that value with the volume pedal.

I bought a very small enclosure but batteries wont fit. is it safe to use 9v DC like a one spot? I have a few standard DC jacks. Do I wire ground to the enclosure? I have always steered clear of using wall power for safety's sake.
 
#14
It is safe to use a wallwart, provided it is wired up correctly. There is absolutely nothing inherently unsafe about wallwarts - the mains power voltage is isolated from the low voltage side and they meet all relevant safety standards.

Ground doesn't necessarily have to go to the enclosure, but you'll probably find that wiring ground to the sleeve connection of a jack will result in the enclosure being grounded as well due to the mechanical connection provided by the jack socket itself.

Alternatively, you could use the power source provided at the moogerfooger jack as described in my previous post.
 
#15
So I made this diagram.
diagram.jpg


Am I on the right track? I didn't put in the ground wire, but I was going to run it right to the sleeve of the jack. Is it ok that the negative power and the ground are both running to the same point? I wasn't sure.

Also how do I know which contact is which on the DC jack? and how can the DC jack be grounded if the one spot adapter that plugs into it doesn't have a ground pin?

also I bought a bench power supply to test out stuff I'll be building but I dont know how to use it. Anyone? where do I hook up the negative wire to? the output that says "COM"? there looks like there is a connection in the back too? what is that?

thanks
 
#17
well this has many advantages over an normal expression pedal. You can use it without a volume pedal and set a CV value that you can stomp on and off. so you can make the mix go 5 to 10, or set two frequencies you like on the Ring mod and switch between them. or be able to turn the LFO on and off with your feet by going from 0 to whatever. also if you do use a volume pedal you can set the sweep with the knob. The EP 2 is more like 50 bucks and doesnt have an on/off stompswitch. also I like my morley volume pedal and think its much sturdier than most expression pedals.
 
#18
Ooooookaaaayyy... here we go.

Firstly, let me just clear up something that I think is confusing you. "Ground" is a completely arbitrary point in a circuit which is used as a reference point for measurements. "Earth" is what you find on the third pin of a mains outlet. Ground and earth are distinctly different. A wall wart power supply often doesn't have an earth pin, and that's fine. Earth and ground are sometimes connected, but not always.

Ground is usually at zero volts ie; the negative terminal of the power supply (but it doesn't necessarily have to be.) In this case lets go with that - call the negative of the supply ground and go from there. Connect the sleeve of the jack to ground. This will, by virtue of the mechanical mounting of the jack socket, connect the metal case to ground as well. Now the whole case is a ground connection point.

The best way to find the positive terminal of the DC jack (or for that matter the tip or sleeve of a jack socket) is with a multimeter. If you don't have one of these and you intend to continue with DIY electronics then I strongly recommend you get one. They are cheap and absolutely indispensable. Take a good look at how the jack is built and take a calculated guess as to which pins connect where.

"COM" refers to "common" which is an alternative term that represents the same thing as ground. It is the negative terminal of the power supply. Remember that electronic circuits are literally circuits - the current must flow out of the supply, through the parts in the circuit and return to the supply. The return path is most often the one labelled ground or common.

Now, the circuit. Personally I can't stand scrappy Paint circuit drawings - I reckon they lead to errors and confusion for beginners. It really is best to take the time to understand proper circuit notation - after all, that is the language that everybody uses to communicate electronic ideas.

I suggest you google for a program called ASCII Circuit. It can create stuff like this:

Code: 
              VCC
               +
               |
               |
              .-. pot  _/  switch       jack
              | |<---o/  o--------v  ||
              | |                    ||
              '-'              ______||
               |               |
               |               |
              ===             ===
              GND             GND

"VCC" is the positive of the power supply. "GND" is ground, or the negative of the power supply. This is a simplified circuit showing only the pot and switch. To include a LED indicator, or allow the use of an expression pedal as well you'll have to consider how to do that.
 
#19
niftydog said:
Ooooookaaaayyy... here we go.

Firstly, let me just clear up something that I think is confusing you. "Ground" is a completely arbitrary point in a circuit which is used as a reference point for measurements. "Earth" is what you find on the third pin of a mains outlet. Ground and earth are distinctly different. A wall wart power supply often doesn't have an earth pin, and that's fine. Earth and ground are sometimes connected, but not always.

Ground is usually at zero volts ie; the negative terminal of the power supply (but it doesn't necessarily have to be.) In this case lets go with that - call the negative of the supply ground and go from there. Connect the sleeve of the jack to ground. This will, by virtue of the mechanical mounting of the jack socket, connect the metal case to ground as well. Now the whole case is a ground connection point.

The best way to find the positive terminal of the DC jack (or for that matter the tip or sleeve of a jack socket) is with a multimeter. If you don't have one of these and you intend to continue with DIY electronics then I strongly recommend you get one. They are cheap and absolutely indispensable. Take a good look at how the jack is built and take a calculated guess as to which pins connect where.

"COM" refers to "common" which is an alternative term that represents the same thing as ground. It is the negative terminal of the power supply. Remember that electronic circuits are literally circuits - the current must flow out of the supply, through the parts in the circuit and return to the supply. The return path is most often the one labelled ground or common.

Now, the circuit. Personally I can't stand scrappy Paint circuit drawings - I reckon they lead to errors and confusion for beginners. It really is best to take the time to understand proper circuit notation - after all, that is the language that everybody uses to communicate electronic ideas.

I suggest you google for a program called ASCII Circuit. It can create stuff like this:

Code: 
              VCC
               +
               |
               |
              .-. pot  _/  switch       jack
              | |<---o/  o--------v  ||
              | |                    ||
              '-'              ______||
               |               |
               |               |
              ===             ===
              GND             GND

"VCC" is the positive of the power supply. "GND" is ground, or the negative of the power supply. This is a simplified circuit showing only the pot and switch. To include a LED indicator, or allow the use of an expression pedal as well you'll have to consider how to do that.
Click to expand...

Wow thanks. That is the type of response I always dream of receiving in an internet forum. Very helpful.
 

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