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EHX 9 Series Dry Mute Mod

Here’s a simple mod to make your early EHX 9 Series pedal operate correctly.

November 12th, 2019 | Technology | , , , , , , | Comments: 8

The 9 Series

I have a few EHX pedals from their 9 Series: the Mel9, C9, Key9, and Bass9.

They all basically function the same way — input an audio signal and the multi note pitch detection will trigger samples. It’s like having MIDI guitar without the hassle of setting up a MIDI-enabled guitar.


I use the Mel9 a lot. I set the attack slow and sustain long to supplement my acoustic guitar like a synth pad. It extends the perceived sustain of the guitar and is detached enough from the transients to make it seem like a completely separate instrument instead of just my acoustic triggering a sound.

As you can see from the photo below, there are two output jacks labeled DRY and EFFECT.

exterior look at output jacks of Mel9 pedal

Our beloved culprit

The DRY output acts like buffered pass through. This is a great feature especially when used in the manner I mentioned above as a way to generate a faux second instrument. I can separate the dry and wet signals and send them to the house as discrete channels, which can then be processed with EQ, compression, and board FX differently. On the wet pedal signal I like to roll off the highs and lows and add more reverb than I would for the dry acoustic signal.

A lot of players will just put this pedal in line with all their other pedals with the only output coming from the EFFECT output jack. In that case the DRY and EFFECT volume knobs can be used to create a blend of the 2 signals. I have used the pedal this way occasionally when I only get one mixer channel input. I set the DRY knob all the way up and blend in some of the EFFECT knob anywhere from 9 o’clock to noon. Then when I step on the footswitch it acts to toggle the wet signal on and off.

The Design Flaw

However, if you want to use the pedal in the way I first mentioned — as a dual output with the DRY channel being DRY only and the EFFECT channel being EFFECT only — the footswitch isn’t useful at all. When the footswitch is toggled off, it doesn’t just mute the effect as you would expect.

Instead, it mutes the EFFECT and sends the DRY signal out of the EFFECT output jack. So now you have your original signal being sent out of both outputs.

The pedal should have been designed to detect when a cable is plugged into the DRY output jack and then mute the DRY signal from going out of the EFFECT output jack.

This is a glaring oversight in design.

Modern audio jacks also acting as switches is very common (e.g. speakers muting when headphones are inserted). So really, this feature should have been included this series of pedals in the initial design specifications.

When searching for a way to disable the DRY signal on the EFFECT output I found the following forum post where EHX acknowledges their mistake: SYNTH 9 – MOD TO REMOVE DRY OUTPUT ON SYNTH OUTPUT SOCKET

screenshot of an EHX forum post


Needless to say, that response seemed very final and quite disheartening. I almost gave up hope of finding a solution.

A Quiet Switch

Then I saw a reply from EHX to a comment on a YouTube video for the Bass9 pedal.

screenshot of YouTube comment

What’s this?! A switch inside the case?!

Apparently, EHX changed their later revisions of some pedals and quietly added an internal dry mute switch to the base of the foot switch. I haven’t been able to find any info about this switch anywhere on the EHX site.

Long ago I had checked the inside of my Mel9 and didn’t see a switch. So I opened up my C9 (no switch) and Key9 (yay, a switch!).

interior look at PCB of Mel9 pedal

EHX Mel9 Rev C — no switch

interior look at PCB of C9 pedal

EHX C9 Rev D — no switch

interior look at PCB of Key9 pedal

EHX Key9 Rev F — Hey look! A switch!

Reverse Engineering the Switch

Comparing the K9 pedal that had a switch with the ones that didn’t I could see that the switch was simply shunting the DRY signal to ground via a single SPDT switch in between one of the lugs of the 3PDT foot switch and line 2 of the ribbon cable.

Back on my Mel9 I cut the PCB trace in the same spot and tested it. Sure enough, the dry signal was no longer present when the foot switch was turned off.

Completing the Mod

Now that I knew it was possible to disable the the dry signal, I contemplated the following options:

  1. Permanently soldering a cable between the lug and ground. Simple, but not easily changeable if I wanted to use the pedal with only a single output.
  2. Connecting up a small internal switch. A little harder, but still very easy. I could change it later if I wanted to, but I would have to unscrew the back to flip the switch.
  3. Wiring up a switch like above, but mounting it externally. It would be way more convenient if I wanted to change the setting, but I’d have to drill a hole through the chassis.
  4. Make the DRY output jack act as the switch, so the pedal would automatically change the setting depending on how I connected cables to it. This is how it should have been designed, but would take some real thinking to make it work that way.

Ultimately, I settled on the last and hardest option. And…it worked.


Here is a downloadable PDF of the mod: EHX 9 Series Dry Mute Mod.pdf

I’ve included all the options for modification so you decide your level of difficulty and expertise.

For the simplest mod, at minimum you will need:

  • a screwdriver – to take off the back plate
  • a sharp knife – to cut the trace
  • soldering irons and accessories – to connect things back up
  • 1 tiny length of signal wire
  • wire cutters
  • wire stripper

If you want to tackle the intermediate mod, you’ll need everything above plus:

  • a small SPDT switch
  • 2 more tiny lengths of signal wire
  • a drill & bit – if you want to mount the switch externally

For the advanced mod, you’ll need all of the above and:

  • sockets – 10mm (top row of pots), 7/16″ (for selector pot and jacks), 14mm (for footswitch), and a love for both metric and imperial systems
  • patience – to slowly cut away or drill out the switched lug on ring 1 of the DRY output jack
  • digital multimeter or continuity tester – to make sure you have electrically isolated the switch on ring 1 of the DRY output jack
  • glue – hot glue or CA glue to secure switched lug on jack after removing soldered connection

Once you have your tools, follow the diagrams in the PDF. It’s a fairly simple mod that will make your pedal way more useful.


If a cable is inserted or removed after the pedal is already on, the pedal might not recognize it. The internal brain box probably does a check when it toggles. A quick toggle of foot switch will make the circuit “see” the inserted cable (or lack thereof). After the toggle, the pedal will act exactly how you expect. This is a by-product of the pedal not really being designed this way from the start.

Don’t want to DIY?

If you really want this mod but are afraid to do it yourself, hit me up. I can do the mod for you (for a fee, obviously). We can work out shipping and all that.

Hope this helped you! Let me know in the comments!