Add second circuit into EHX Mel9

[lars-musik]

My Mel9 sound quite dull and is not loud enough for the backwardish sounds I play with it. At the moment I switch a bandpass-filter/boost to it. As I downgraded my pedalboard to a minimum, there’s no space for a loop-switcher - and so I’d like to integrate the bandpassfilter or some kind of tonestack into th Mel9 (there's still some space left in the enclosure). Unfortunately it is not a true bypass pedal and I can’t seem to make out any relays.
Could you advise me on how to place a second circuit board into the Mel9 so it is switched together with it? How would you go about it.
I took a lot of photos and traced/beeped the 3PDT.

Thanks a lot!

Lars

Overview
https://postimg.cc/gallery/29ibzwm62/























ICs details
https://postimg.cc/gallery/20yjf7diy/

























3PDT (from above)
https://postimg.cc/ftNgsnj1

[pinkjimiphoton]

hate to bear bad tidings, but this isn't a circuit you can likely clone too easily. probably cheaper to buy a second one and build a box to mix the signals with bro

[lars-musik]

Hi Jimmy,
thanks for answering! I guess the language barrier prevented me from being brief and clear… Let me try again: I don’t want to CLONE the Mel9, I merely want to understand the signal path so I can cut it at a place where I could insert a bandpass filter and a signal booster. There’s enough space in the enclosure to accommodate another PCB and on the surface for some knobs.

As it is not true bypass I don’t know where to start looking….


Like this maybe?

[pinkjimiphoton]

yeah bro, sorry for misunderstanding you! makes perfect sense now that i re-read it.

yes, you can likely do whatever it is you want as shown. should work fine. just figure out which pin is the "return" to the footswitch from the output of the board, and insert there and you should be good to go!

[ElectricDruid]

What makes you so sure it's not true bypass? I don't know the pedal all, but it seems a bit odd to put a 3PDT in it if it's *not* true bypass. If you were to do a DSP-based pedal like this and just feed the dry signal straight through for the "bypass" setting, you'd only need a momentary SPST.
So...I'm curious - what makes you say it isn't true bypass? And if not, do you know what else it does that might require a 3PDT?

Thanks,
Tom

[mth5044]

What makes you so sure it's not true bypass? I don't know the pedal all, but it seems a bit odd to put a 3PDT in it if it's *not* true bypass. If you were to do a DSP-based petallike this and just feed the dry signal straight through for the "bypass" setting, you'd only need a momentary SPST.
So...I'm curious - what makes you say it isn't true bypass? And if not, do you know what else it does that might require a 3PDT?

Thanks,
Tom

The manual states buffered bypass.

Might be a job for a signal tracer and googling up what all those IC’s and transistors are.

[lars-musik]

What makes you so sure it's not true bypass? And if not, do you know what else it does that might require a 3PDT?

Hi Tom,

I beeped input/output jacks vs the 3PDT and neither had a direct line, so I guessed it can't be true bypass. Secondly, two of  the three switching planes are hardwired (see my drawing above)... So at least a 2PDT would have sufficed, yet EHX put a 3PDT in there... So it is all a bit of a mystery to me.

Regards, Lars