HX Effects control of amp switching, impedance considerations.

[bordonbert]

I have an enquiry on another forum from someone who is using a HX Effects unit in 4 cable mode with additional switching to control his Hughes & Kettner Tubemeister 18 amp  channel and boost settings.  As I understand it the Pedal/Ext Amp socket of the HX has been configured to switch channels in the amp by effectively emulating a plain old "FS2" type passive TRS stomp switch.  To their credit, in the Helix manual Line 6 does warn that this is not always fully compatible with all amp units but gives no further technical details which might help.

 

The owner found that the amp is not reliable in its switching when controlled by the HX, though it works perfectly with a mechanical switch of course.  The reason I know is that the HX is introducing some additional resistance to the H&K control line when it should be a dead short thus decreasing the switching current in the amp presumably to the very edge of reliability, and it also appears to be leaving a residual resistance in the line when it should be open circuit increasing the current which should be 0mA in that state.  This effectively runs the simple direct switching circuitry inside the H&K, a mixture of a simple relay and BJT+FET saturation switching units, over too narrow a band whereby not all switching elements activate/deactivate at either extreme.

 

Can anyone give me any info on the output impedance of the HX control circuitry in the On and Off states when it is used in this way?  I would guess it must be fairly significant seeing that it can also act as an input for an expression pedal in a different mode.

 

Would it help to approach Helix Tech Support direct rather than using the forum for such a specifically technical enquiry?   I'm not underestimating you members' technical ability, only the availability of the information outside of Line 6.

[zolko60]

I would get a Tech Support ticket for that. I have used it only once so far, but information was helpful and not published anywhere else.
By the way - if you think such info should be a part of Specification, please vote and add your comment.
https://line6.ideascale.com/a/dtd/Specifications-publishingof-I-O-imedances-FS-levels-etc/943915-23508#idea-tab-comments

[bordonbert]

Thanks for the reply Zolko.  I've done that as best I can.  It's lucky I'm a Line6 Variax guitar owner and I am already registered with Line6 for that.  It does seem you have to have registered a product to request info via a ticket which is logical I suppose.  I have raised a ticket but only as an advisory supporter of the original owner, best to be straight with them I find.  Whether they will talk to me or not is up for grabs.

 

If they will release info on the output impedances in the Open/Short states, or at least the general configuration of the circuitry on that socket, we could maybe get more amps working with it by trimming values in their own circuitry.

 

I'll let you know how I get on.

[zolko60]

You can also join the fb group and ask there. You never know who you can find there ;) 
https://www.facebook.com/groups/line6helixusergroup/?fref=nf