Control Voltage in to EXP inputs? Is it safe?

[Embo20910]

Hey,

 

Does anyone know if it is officially safe to plug a control voltage into the EXP inputs on the Helix?  I haven't found anything in the manual that would answer this.  It seems to assume that you would just be using a passive controller like an expression pedal.  But some devices will also accept a voltage source.  Just not sure if the Helix is designed to do that, and I don't feel like frying it just to see what would happen.

 

Thanks in advance!

 

[PeterHamm]

Man, I would NOT try it.

[jbuhajla]

An expression pedal is a resistive device (potentiometer). You probably do not want to inject any external voltage into that EXP circuit.

 

What are you trying to achieve?

[Embo20910]

I want to use CV outs on my theremin to control a variety of parameters while I’m playing guitar. I move a lot while I play anyway, might as welll turn that into some dynamic sound modulation, lol.

 

Most TRS expression pedals receive a reference CV on the ring, divide it down with the pot, and return that lowered voltage on the tip. So it is effectively a CV even though the pedal is passive. I think that’s why many products will accept either a passive pedal or a CV as input. But Line6 just uses TS for expression. So I’m not sure it would work, or worse could damage something.

[DunedinDragon]

I'd put my odds on it causing damage myself.  But I may be erring on the side of caution given it's a $1500 piece of equipment and damage from that likely wouldn't be covered under warranty.

[jbuhajla]

I want to use CV outs on my theremin to control a variety of parameters while I’m playing guitar. I move a lot while I play anyway, might as welll turn that into some dynamic sound modulation, lol.

 

Most TRS expression pedals receive a reference CV on the ring, divide it down with the pot, and return that lowered voltage on the tip. So it is effectively a CV even though the pedal is passive. I think that’s why many products will accept either a passive pedal or a CV as input. But Line6 just uses TS for expression. So I’m not sure it would work, or worse could damage something.

You could measure the voltage at the EXP port to see what is going on there, but that may not tell you enough. Rig up a 10k pot to a 1/4" jack so you can easily measure what's happening with a mulitmeter. 

 

However, things get wonky when you have the Helix reference voltage and whatever control voltage you intend to send it marry up. I wouldn't recommend experimentation. 

[tedulrich]

I run a tip/sleeve CV signal into my EXP3 port all the time and have zero issues.  I just measured it, and I get +3.23V open, 8mV closed, positive lead at the tip, negative lead at the sleeve.  This is coming from an Electro Harmonix 8-Step Program, with the depth set to 5 for Helix compatibility.   If the 8-Step is set wrong, and puts out the whole 5V signal, all that happens is that the parameter being controlled resets to minimum once the 3V threshold is exceeded and you need to sweep the control voltage to reset it.  There are no ill effects that I've found. 

 

I also have a Korg SQ-1, but I don't bother with that as it sends 1V, 2V, 5V, or 8V depending on setting, none of which are really convenient for parameter control on the Helix.

 

You'd need to see if your theremin has settings for maximum control voltage, and limit it to 3V to make it work properly.  Otherwise you'd need some kind of external voltage limiter, or to simply stay outside of the range to the theremin where the CV would exceed 3V. 

[DannyMcO]

On 1/5/2018 at 4:39 PM, tedulrich said:

I run a tip/sleeve CV signal into my EXP3 port all the time and have zero issues.  I just measured it, and I get +3.23V open, 8mV closed, positive lead at the tip, negative lead at the sleeve.  This is coming from an Electro Harmonix 8-Step Program, with the depth set to 5 for Helix compatibility.   If the 8-Step is set wrong, and puts out the whole 5V signal, all that happens is that the parameter being controlled resets to minimum once the 3V threshold is exceeded and you need to sweep the control voltage to reset it.  There are no ill effects that I've found. 

 

I also have a Korg SQ-1, but I don't bother with that as it sends 1V, 2V, 5V, or 8V depending on setting, none of which are really convenient for parameter control on the Helix.

 

You'd need to see if your theremin has settings for maximum control voltage, and limit it to 3V to make it work properly.  Otherwise you'd need some kind of external voltage limiter, or to simply stay outside of the range to the theremin where the CV would exceed 3V. 

 

@tedulrich - sorry to bug you on this, but you seem to be one of the only people who knows about CV with Helix.
is that 8mV closed measurement the theoretical minimum?

I'm trying to connect a Moog MP201 to Helix to get its LFO (and other) properties to work within Helix; it's capable of producing (in default unipolar mode) 0v to 5v or (in bipolar mode) -5v to +5v.  I don't know if there are any advantages to unipolar vs bipolar.

I can also connect it via MIDI, but I typically lack the patience to program.

Appreciate any insight you can provide; thanks

 

DMcO

[tedulrich]

It’s been a while since I tried, I don’t think the 8mV low end is the problem, but once it exceeds 3V, the parameter will set to minimum and stay there until the next sweep.  I haven’t tested ANY of this under Helix Core, though I’d venture to say that since it’s a hardware function it wouldn’t be affected.  

 

MIDI is probably your best bet, it should be easy enough to assign with the “learn” function.