Question-what's the output impedence of the CV output?

[doughadfield]

Hi, I can't find anywhere the specification of the CV control voltage output on the Helix - specifically what's the output impedance - in other words, how much current can it drive?

 

I'm intending to use the CV output as another amp switching output (my amp has three remotely switchable functions that I want to automate with Helix) so I'm keen to know whether I can drive a relay coil directly from the CV output, or whether I need to buffer it with a custom-built transistor stage.

 

Any indication would be nice (in fact, a "specifications" section at the back of the manual would be even nicer!! :-))

 

[davidb7170]

Ok, without knowing the answer specifically, until someone responds that does..... I would expect the CV output to be in need of a very high impedance load - i.e. not be able to drive much if any current at all, as the act of serving up current would actually drop the voltage -- change the Control Voltage, just like a volt meter needs to have a very high impedance several mega Ohms at least, so as not to materially change the quantity being measured. I'd think this would be necessary to not exceed the design limits of the Helix's internal power supply.... Remember they just moved the power supply internal -- hooks to outside AC, inside the box, turns it into DC...

 

Just thoughts of a this old electrical engineer... ;)

 

Dave

[davidb7170]

Also -- your question on a relay coil was not how I envisioned the CV. A relay coil is on or off (voltage or no voltage), where CV's are usually a variable voltage for analog fx devices.... A relay coil would not like a variable voltage.... It would lead to relay chatter, and yes would need some current to actuate... Doubting this is what you're after.

 

Dave

[doughadfield]

Hi Dave,

thanks for replying. I'm an old electronics engineer too ;-). I was planning to use the CV output like a switched output, by using simply 0v and "Max"v values - clearly you don't want to continuously vary the CV if you're trying to switch something on or off. As you rightly say, loading the CV output with a low impedance load such as a relay coil will change the voltage (depending of course on the output impedance of the CV) but the relay coil won't care what the precise output voltage is, as long as it's high enough to reliably switch the relay. This is what I'm trying to ascertain.

 

I can, of course, build an external buffer amp using a transistor to drive the relay coil, but I want to avoid that complexity if possible.

 

regards

Doug

[HonestOpinion]

Hi, I can't find anywhere the specification of the CV control voltage output on the Helix - specifically what's the output impedance - in other words, how much current can it drive?

 

I'm intending to use the CV output as another amp switching output (my amp has three remotely switchable functions that I want to automate with Helix) so I'm keen to know whether I can drive a relay coil directly from the CV output, or whether I need to buffer it with a custom-built transistor stage.

 

Any indication would be nice (in fact, a "specifications" section at the back of the manual would be even nicer!! :-))

 

 

Hi Dave,

thanks for replying. I'm an old electronics engineer too ;-). I was planning to use the CV output like a switched output, by using simply 0v and "Max"v values - clearly you don't want to continuously vary the CV if you're trying to switch something on or off. As you rightly say, loading the CV output with a low impedance load such as a relay coil will change the voltage (depending of course on the output impedance of the CV) but the relay coil won't care what the precise output voltage is, as long as it's high enough to reliably switch the relay. This is what I'm trying to ascertain.

 

I can, of course, build an external buffer amp using a transistor to drive the relay coil, but I want to avoid that complexity if possible.

 

regards

Doug

 

This looks like it is on the same track as an idea I put up on IdeaScale for using the CV output as a second External Amp control. Looks like there are a couple of electrical engineers on this topic.   Could this be enabled through a global setting in the firmware or even with the current available settings for the CV output?  Can this be done safely without any additional hardware and without damaging the Helix or the amp?

 

 

You can vote for it here:

http://line6.ideascale.com/a/dtd/Allow-CV-output-to-double-as-a-2nd-Ext-Amp-controller/790054-23508

[doughadfield]

Hi again, to answer the reply from HonestOpinion, you can't change the electrical characteristics of the CV output simply by changing firmware, as it's a hard-wired variable voltage output and not a relay contact. However, you can *easily* use it as an additional amp switching output simply by setting the CV value to switch between 0v and 10v in the "Command Centre" section of helix (using a switch or "instant location" setting; not an expression pedal!). The CV output voltage will then "switch" between 0 and +10v as you enter the patch or hit the stomp mode foot-switch. The issue is then how to drive your particular amp. It may be that the CV output can source (or actually, sink) enough current to engage the relay in the amp (typically around 20-30mA). If so, then happy days. If not, you'll need to add a transistor to act as an amplifier - the simplest would be simply to embed a single FET (2N7000 would be ideal - at around 8p each!) into the jack plug at the helix end - Gate to CV output, Source to ground and Drain to Amp relay input. The FET will then switch on when the CV voltage is above about 2v (10V will do it!) and pull the relay line to ground, switching on the relay in the same way that a foot-switch would.

 

So, back to my original question - Line6 guys, what's the output impedance (sink current capability) of the CV/Expression output?

 

Thanks

 

Doug

 

EDIT!! - the CV voltage output of the Helix is actually 0-5V, NOT 0-10v, as I'd incorrectly assumed above!

[HonestOpinion]

Hi again, to answer the reply from HonestOpinion, you can't change the electrical characteristics of the CV output simply by changing firmware, as it's a hard-wired variable voltage output and not a relay contact. However, you can *easily* use it as an additional amp switching output simply by setting the CV value to switch between 0v and 10v in the "Command Centre" section of helix (using a switch or "instant location" setting; not an expression pedal!). The CV output voltage will then "switch" between 0 and +10v as you enter the patch or hit the stomp mode foot-switch. The issue is then how to drive your particular amp. It may be that the CV output can source (or actually, sink) enough current to engage the relay in the amp (typically around 20-30mA). If so, then happy days. If not, you'll need to add a transistor to act as an amplifier - the simplest would be simply to embed a single FET (2N7000 would be ideal - at around 8p each!) into the jack plug at the helix end - Gate to CV output, Source to ground and Drain to Amp relay input. The FET will then switch on when the CV voltage is above about 2v (10V will do it!) and pull the relay line to ground, switching on the relay in the same way that a foot-switch would.

 

So, back to my original question - Line6 guys, what's the output impedance (sink current capability) of the CV/Expression output?

 

Thanks

 

Doug

 

Brilliant! Thank you for your response and this is great to know for players who have more than two controller jacks on the amp they would like to address with the Helix.

[doughadfield]

My rack unit should be arriving this weekend, so I'll measure the impedance of the CV output myself and let y'all know :-)

 

Doug

[Bangha]

My apologies for hijacking the thread but, Im wondering, could the amp switching output be used for other things like sending tap tempo to external pedals? I'm no engineer myself so I turn to the smart folks!

[doughadfield]

Helix CV Output Impedence Measured!! - My Helix arrived at the weekend and I've just got around to measuring the output impedence of the CV output..... and the answer is..... 695ohms (allowing for inaccuracies in the measurement process, assume between 600 and 700ohms). This is nowhere near enough to drive an external relay directly (it will source around 7mA into a short circuit - far too little for relay coils). I'm guessing the output circuit of the CV is an op-amp (output impedence around 100ohms) in series with a 560ohm resistor (nearest standard value to 600ohms) making around 660ohms.

 

Also, the CV output is 0-5V, not 0-10V, as I'd assumed!! (I was thinking of old lighting controllers, with their 0-10V signals).

 

So, now we know ;-)

 

Doug

 

PS - this output can still be used to drive the relay input of an external amplifier, simply by putting a FET into the jack plug body, as I mentioned above (I'm doing this now, with my own amp).