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Using Helix to control both Channel A/B switching and Reverb on/off for JCM-900 Dual Reverb


sboggs71
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I have a '96 JCM 900 I am experimenting with. It came with a Marshall two-footswitch pedal, one footswitch for channel A/B switching, one for reverb on/off.

I can get my Helix floor unit to control channel A/B switching using a TRS "cable", but not the Reverb on/off. I have experimented assigning to two Helix footswitches for "Ext Amp", with one set to one to "(1) Tip), and the other to "(2) Sleeve", and "1 and 2".

The cable I am using is actually two TRS "Y" cables (one with twin male at one end, the other with twin female at one end) plugged together. I am not sure "Y" cable configuration is the problem.

 

Has anyone else had success getting the Helix to control both channel switching and reverb with the JCM-900? If so, perhaps my rigged, "multi-Y" cable is the issue.

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I did a search for info and it looks like a simple 2-button LATCHING switch.

You should be able to run a common stereo cable from the Helix Ext Amp jack to the Amp's FS jack, with one Helix FS set to "TIP" and the other set to "RING".

Your multi-y cable should work, just be sure you've got tip to tip and ring to ring. 

Basic troubleshooting if all else appears to be correct, get a proper stereo cable.

 

Get a multimeter/continuity tester. Check your Marshall FS to see what happens when you press the switches.

One switch should be TIP and the other "RING".

See if you can make Helix do the same.

I'm pretty sure that "1 and 2" will not be relevant and could even damage your amp.

Set the switches to LATCHING.

When the preset loads, the SAVED status of the switches determines if the assigned amp function will be activated or not. 

IOW - if the FS is assigned to TIP and that is the REVERB, then if the preset is SAVED with that FS ACTIVE (LIT) then REVERB will be activated.

 

 

 

 

 

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@rd2rkThanks for your answer. After reading it, and some testing, I see that least one set of the "Y" cables could not work - the twin female plugs are identical - so only two of the three conductors of the TRS plug at the other end terminate in the female plugs (!). I have ordered an actual 20' TRS cable, and expect it will work. I have high hopes of success now, and I'll post details later in the week after I test with the ordered cable.

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@rd2rkThanks - good catch! I was able to cancel the order.

 

Sounds like the cable I am looking for would be the same as a 1/4 male to 1/4 male headphone extension cable. UPDATE: I just got this to work using a male to male headphone extension! Channel switching is "(1)Tip" and Reverb switch is "(2) Sleeve".

 

Recalling how balanced XLR's work, I didn't realized that there were also TRS cables that work the same way. I have not needed to use any TRS cables for anything, and the "Y"s I've had for so long I don't know why I have them. Hence the now-fading fading ignorance.

 

Now to find a good 20' stereo TRS online so I don't have to use my headphone extension cable.

 

I appreciate your help with this!

 

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