cv vs. expression pedal input

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polytoxicommander
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cv vs. expression pedal input

Post by polytoxicommander » Mon Mar 11, 2013 3:16 pm

hi,
got a subdecay starlight dlx today.
Neat pedal...
But what i´m interested in for now, is to feed the expression pedal input via CV.
There is a warning sign on the bottom of the pedal, that says: "Using a mono plug will damage the pedal. Use TRS plug only."

So my intention is to solder a cable for this use ...

What is unclear to me:
Do i have to send CV to the Tip (constant +5V) and the Ring (0-5V) of the plug, or would it be sufficient to send only to the Tip of the plug and vary this value( 0-5V)?

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BugBrand
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Post by BugBrand » Mon Mar 11, 2013 4:49 pm

Sounds like Ring connection is your CV input - 0 to +5v range.
(does it say in the manual whether voltages outside those ranges are OK/useable/dangerous? Could be any of those three.. depends)
Make a special adaptor plug / cable - should be simple.
I *think* that pedals are sometimes/?more?often? wired with the CV to tip, voltage bias to ring and ground to sleeve..

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Post by EMwhite » Mon Mar 11, 2013 9:54 pm

The Moog EP-2 pedal and MoogerFoogers inferred, use a reference voltage of 5 or 5.1v DC on the ring and the pedals return voltage to the tip. Sleeve is GND.

Some Moog products (MP-201 Multipedal) send voltages using TS cables only. MoogerFoogers don't seem to mind, not sure why the SubDecay would but I'm no engineer.

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polytoxicommander
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Post by polytoxicommander » Tue Mar 12, 2013 10:44 am

At first, thx for the answers.

The Manual doesnt mention anything about the signal that is compatible with the expression pedal input ... I guess its max. 5V.

In the following link it is discribed very detailed, how to simulate an expression/(volume?) pedal for the same proposal, using a Vca in addition.

http://www.analogindustries.com/blog/en ... 9321991586

I thought that maybe there is a possibility to do the trick without having to use a Vca channel from my modular.

The Cv source/s that im willing to use are provided without exception from the Expert sleepers es-3 eurorackmodule which generates steady offsets as well as changing voltages and can be limited to 5V.
Therefore there is no risk to damage the pedal because of too high voltages.
I´m rellay confused by now, but would it be an option to send a CV to the tip and dont send anything to the ring of the plug, so that there would be only the connection of the ring for the Expression pedal input so that the (voltage bias?) doesnt run dry on the plug?

Thats the only info by "subdecay" related to the control input of the unit.
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Post by wxyz » Wed Mar 20, 2013 10:03 pm

Works with Eventide, but don't know about this pedsl

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Post by Rex Coil 7 » Fri Apr 12, 2013 2:44 pm

Why not use a VCA as a "CV'd expression pedal"? Seems much safer.
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Post by mrcharles » Fri Apr 12, 2013 3:46 pm

FYI... I just bought a Red Panda Particle effects pedal and they specify a max of 3.3v (quotes below from Red Panda re. their pedal...)

ie:
tip: 0-3.3V specifying the expression pedal position
ring: 3.3V output for expression pedal
sleeve: ground
and...
Most guitar pedals designed for CV inputs take a 0-5V range. The Particle was not specifically designed for CVs, and uses 0-3.3V instead. There is no over/under voltage protection so, for example, driving it with -5V or +5V for extended periods could damage the pedal.
So, you may wish to write to your pedal manufacturer and double check on the specifications before risking damaging it.

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Post by Rex Coil 7 » Fri Apr 12, 2013 5:29 pm

Again, why not use a VCA as the expression pedal. That way all you're doing is using the voltage that the stomp box is actually sending to a standard expression pedal to do the modulating. The stompbox won't know the difference, it will just think it is connected to an expression pedal instead of an incoming CV.

Just modulate the VCA with CV, then use the VCA's controls to use with the expression pedal input.

That way you're in no danger of shoving too much voltage into the expression pedal port, because you're using the VCA in exactly the same way that you're using an expression pedal, by using the CV that the stompbox sends out to the expression pedal to be attenuated. It's 100% safe with no chance of screwing up the polarity or over-volting the expression pedal circuitry in the stompbox.

This has been well documented in other threads as well as in other forums other than Muffwigglers. Here's another reference thread with the same method only described better than I have done here ....

viewtopic.php?t=41228&highlight=

Scroll down to the FOURTH post by Cat-a-tonic and the discussion about how to use a VCA begins there.

:)
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Post by Overand » Sun Jul 14, 2013 9:34 am

A little thread-digging-up.

I have had weird and unexpected successes and failures with this, probably due to the whole thing working differently than I expected - on an Eventide Space.

Doing the "multiple" patch, i.e. patching VCA In, VCA Out, and 1/4" TS (mono) to the Expression Pedal input of the Space.

This 'worked' - though not as expected. Oddly, doing things like this would cause the pedal to 'glitch' if the CV went over a certain level.

Oddly, doing what *I* thought would work - using TRS ("stereo") from the expression pedal jack, you get a ~3 V reading between tip and ground on the TRS cable. Sending Tip to VCA In, and sending VCA Out to Ring.... doesn't work.

I threw a meter across the output, and scaling the CV in to the VCA caused it to slide from 0V to about 5V - but the pedal didn't register anything.

All in all, the experience was mostly-just-frustrating, and I may end up following the Eventide-employee advice I read on a website's comment thead that just said "Send it CV, just try to keep it in 0-3.3V, though -5 to 5 shouldn't break anything"

"EatYourGuitar" had an explanation on IRC last night:
EatYourGuitar wrote: 00:52 <@eatyourguitar> it works because of pullups and or pulldowns
00:53 <@eatyourguitar> if there is a protection resistor in the eventide it will be sending and recieving on one wire
00:53 <@eatyourguitar> something they put in there to protect from pops when you plugin the cable
00:55 <@eatyourguitar> your VCA output will sink current as it goes down
00:55 <@eatyourguitar> but the eventide resistor that is pulled up will create the DC bias at the input of the VCA when it is not sinking current
01:01 <@eatyourguitar> thats why you get perfect range patching it like that
01:01 <@eatyourguitar> cause your vca is at 3.3v wide open
01:02 <@eatyourguitar> but you could just attenuate CV and use a mono TS cable instead of a y cable
01:02 <@eatyourguitar> I dont like the idea of patching a VCA output to input
Note that at the time, I didn't catch the 'perfect range matching' that doesn't seem to match my experience - oddly.
Last edited by Overand on Sun Jul 14, 2013 7:46 pm, edited 1 time in total.
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Post by Rex Coil 7 » Sun Jul 14, 2013 6:36 pm

Hmm .. well .. I suppose we can't expect all of this stuff to work with all of our stuffs. Very solid info you've submitted here though, (member Overand).

From what it seems like, it comes down to a matter of "try and see" with a heavy measure of caution thrown in. Too bad a very simple "control standard" couldn't be adopted/agreed upon by the various makers when it comes to the expression port so that a VCA or ~any~ Ernie Ball type control scheme could be used, especially in the present day situation where outboard control is so highly adopted by so many users.

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Post by PrimateSynthesis » Mon Jul 15, 2013 7:00 am

Rex Coil 7 wrote: Too bad a very simple "control standard" couldn't be adopted/agreed upon by the various makers when it comes to the expression port so that a VCA or ~any~ Ernie Ball type control scheme could be used, especially in the present day situation where outboard control is so highly adopted by so many users.

... and I continue to dream on ... my perfect world fades to black.
There might not be a standard but it's not that bad!

Afaik, the Ernie Ball is a volume pedal, not an expression pedal. I'm not sure why you would want to use a VCA either. It would need to be able to pass DC, and if it had gain, might return an output voltage higher than the input voltage.

Almost all expression pedals and volume pedals are potentiometers wired as voltage dividers. I've heard of pedals wired as rheostats, but I don't know of any specific examples. The difference between a volume pedal and an expression pedal is the connector. A volume pedal has two jacks, one in and one out. An expression pedal has a TRS plug. Regardless the sleeves are all ground.

You don't need to build a special cable. All you need is an insert cable ("stereo to dual mono") that has a TRS on one end and two TS on the other end. Stick the TRS in your effects box.

If you are using a volume pedal, stick each TS into the in and out jacks. You're done. Enjoy your logarithmic foot control. :nana:

If you are using CV, get a voltmeter. Measure the voltage across each TS plug from tip to sleeve. One will have a constant voltage. That's the maximum control voltage you want to send your effect. Most boxes are 5V. You might want to wrap tape around it so it doesn't accidentally put a voltage on the sleeve of a metal plug somewhere.

The other plug should measure around 0V. Stick that into your CV controller. You're done. Enjoy your voltage control. :party:

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Post by Overand » Mon Jul 15, 2013 7:41 am

Incidentally, some volume pedals *are* VCAs and not just potentiometers. (DOD FX-17, I believe, works this way).

And regarding the VCA I used, it *does* pass DC, in my case, but for some reason still doesn't work when used in the TRS fashion, but does when used in the 'mult' fashion. Very odd.

Wiring as you described, however, would work. Weirdly, sending a CV into a TS cable works fine too - even though when using TRS, the Tip is the part that's sending DC out of the pedal. (See the quoted reply from "eatyourguitar" for some thoughts on that).
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Post by Rex Coil 7 » Mon Jul 15, 2013 1:17 pm

PrimateSynthesis wrote: Afaik, the Ernie Ball is a volume pedal, not an expression pedal. I'm not sure why you would want to use a VCA either. It would need to be able to pass DC, and if it had gain, might return an output voltage higher than the input voltage.
The use of a VCA makes sure the expression circuit is only sent back what it sends out. It also opens the door to CVMod.

As far as I know, many (most?) VCAs can be used to atttenuate CV, in fact it seems like that is what what many people use them for.

The only reason I said "Ernie Ball" is because they're a super common scheme, and a very easily upkept and repaired mechanical design. Many many stomp boxes can use an Ernie Ball type scheme to operate their expression circuits. After all, maybe the pedal you're thinking about is a "volume pedal", but then again, isn;t that what we use VCAs for as well? In the end, aren't they both just attenuators?

I've posted the how-to link in this thread three of four times already (I think). It's easy to do and makes for a safer setup, especially if one is unaware of how much tolerance the circuit we're trying to modulate has for feeding it too much of anything.

It's just some ideas, no need to pick nits :) If it doesn't work for you, just don't do it. Easy peasy.
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Post by PrimateSynthesis » Mon Jul 15, 2013 3:26 pm

Overand wrote:Incidentally, some volume pedals *are* VCAs and not just potentiometers. (DOD FX-17, I believe, works this way).
I thought active volume pedals were just amplifier circuits with treadle pots for volume. Anyway, that wouldn't work.
Overand wrote: And regarding the VCA I used, it *does* pass DC, in my case, but for some reason still doesn't work when used in the TRS fashion, but does when used in the 'mult' fashion. Very odd.
I'm not sure what you mean by TRS vs. mult fashion...

Overand wrote:Wiring as you described, however, would work. Weirdly, sending a CV into a TS cable works fine too - even though when using TRS, the Tip is the part that's sending DC out of the pedal. (See the quoted reply from "eatyourguitar" for some thoughts on that).
If the tip is sending the control voltage out of the pedal, the the ring is sending the constant voltage out of effects box. So using a TS would short the ring to sleeve, which one would hope the effects box would be able to do safely. Then again, there is that warning label above. Which is something I've never seen before.

Or if you mean the other way, and it's based on sinking current? That seems like a rather odd design. Although the low output impedance of most synth modules would probably pull it down.

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Re:

Post by avandelay » Sat Mar 14, 2020 12:40 pm

PrimateSynthesis wrote:
Mon Jul 15, 2013 7:00 am

You don't need to build a special cable. All you need is an insert cable ("stereo to dual mono") that has a TRS on one end and two TS on the other end. Stick the TRS in your effects box.

If you are using a volume pedal, stick each TS into the in and out jacks. You're done. Enjoy your logarithmic foot control. :nana:

If you are using CV, get a voltmeter. Measure the voltage across each TS plug from tip to sleeve. One will have a constant voltage. That's the maximum control voltage you want to send your effect. Most boxes are 5V. You might want to wrap tape around it so it doesn't accidentally put a voltage on the sleeve of a metal plug somewhere.

The other plug should measure around 0V. Stick that into your CV controller. You're done. Enjoy your voltage control. :party:
Thanks for the practical advice! I took this idea a little further. Bought a TRS male->Dual TS Female adapter which is just about six inches long. Figured out which ts end worked with my pedal and snipped the other one off. Now instead of having a specific longer cable Ive got a small custom CV adapter that stays with the pedal. Works great!

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