Triple Parallel Mixer...EHX inspired

[MAO]

02/17 UpdateThe layout dated 01/10 is verified with some changes noted below. But I would suggest building the newer untested layout dated 02/15/2020.

01/10 Update Updated layout, moved the tone controls after the return stage for improved performance. Added another column to help minimize the spaghetti wiring.

01/06 Update Have it built, but need to tweak a couple things with the layout. If anyone else is considering building this, hold off until my next update

01/05 Update Moved some components around and added another cut plus another optional ground connection in case I need to change the Master Volume to a voltage divider like the Clean Volume. As it is right now, the Master Volume can only boost, not cut. Unfortunately as the layout is, if a master boost/cut is desired, this will require a standing resistor, but can be easily done if needed. I'll report back once built.  

01/04 Update: As I started to build this today, I realized I hadn't designed in a way to reduce the Clean signal. So I added in a 15db boost for the Clean signal and a voltage divider pot for the Clean Volume control. And I found one of the ground links was misplaced.  I also got rid of all the double links.

01/03
This is not a trace, just my take on the EHX Tri Parallel Mixer as seen here, without the crafty switching.

edit 01/10
My "version" is essentially a quad buffer/4-way splitter/boost (send Level +15db), each return feeds a phase switcher that has a built in boost(+6db) with additional boost capability (Return Level +11db) which feeds a modified big muff style tone control (flat response at noon, signal loss -6db), which then feeds the mixer that has a master volume with up to +14db gain. The Clean signal is also boosted +15db, which can be attenuated with the Clean Volume control.

The Phase switching is designed to keep the output levels the same with both the inverted and non-inverted signal paths.

Turning the Send and Return level controls full CCW should be unity gain. (The Send/Return level controls can only boost the signals)

11 pots, 9 jacks, 3 toggles(or rotaries), 4 stomp switches, it's going to be an experience wiring this thing up.





 

[andrea83]

Very interesting! Thanks

[MAO]

Thanks, hope it works out.
I just added updated the layout again.

[MAO]

I have it built, but need to tweak a couple things with the layout. If anyone else is considering building this, hold off until my next layout update.

[MAO]

I ended up moving the tone control stages after the phase switches, and made a few minor changes which has improved the output level matching for the inverted and non inverted signals (via the Phase Switches).

So now the signal path is Input > Buffer/4-way Splitter > Send Levels (Boost) > Send.  Then, Return > Phase Switch > Return Levels (Boost) > Tone Control > Mixer > Master Volume > Out.  

The Clean signal is Input > Buffer/4-way Splitter > Boost > Clean Volume Control > Mixer > Master Volume > Out.

Still haven't decided on how to bypass/mute the channels, most likely just a DPDT to interrupt (or ground) the return signal, or a 3PDT to interrupt (or ground) both the Send and Return signals. Will figure that out once I have it boxed up.  

All the tips on the send and return jacks will be grounded when nothing is plugged into them.    

I'll post some pictures once I have it all wired and boxed up.

 

 

 

[highsolstice]

Awesome job!  Following this thread to see this thing progress!  I'd definitely like to build my own so keep us posted!

[MAO]

Thank you!
I should be back on it this weekend.
Added a couple more switching options too...stay tuned.

[MAO]

Ok, finally have all the hardware. Built a new board while waiting as I kinda hacked the original one up a bit trying out a few things.

Hope to have it wired up tomorrow.

[mercury6]

amazing job. these parrell mixers can be quite amazing for so manythings. I was trying to tell people about them years ago when I bought the badger schism. and for one that's trying to get there own custom guitar synth sounds  these are amazing for that. was wondering if youd ever do the nady td-1 tube distortion which is also the Westbury w-20. its even smoother and more liquidy than a big muff

[MAO]

So the original layout dated 01/10/2020 is verified, although I did add an addition 2u2 cap to lug 3 of the Clean Level control as the pot was noisy being tied directly to pin 7, which was an oversight on my part.  

I also changed some component values, the feedback resistors are now 56k and the Return Level pots are 200k.

The original layout can be modified to version 2, but if I would suggest building the untested version dated 02/15/2020 that I'll be posting shortly.

The simplest option would be to just hang an additional 2u2 cap between the Clean Level pot lug 3 and the wire connection to the board. This is how I did it. Also make the component value changes as noted above.  

If you don't want to add the "flying" capacitor, you can modify the board as follows: the only tricky part of the conversion would be adding the new link under the IC where there has already been a cut. You would need to place the link through the original cut and then bend it over to solder to the adjacent pad.

Of course soldering the 2u2 to lug 3 of the pot would be much easier, but here is version 2 of the "original" layout if you do want to modify it. All changes are circled in white.

[MAO]

Here is the recommended newer, untested layout.

Layout changes were made to add some additional switching options and to somewhat help with the offboard wiring. But it is essentially the same circuit with additional switching options.

I have added these switching options to my original build and recommend them for convenience amd additional versatility.  

(all 5 switches are 4P3T rotary switches)

Phase Switches (x3) 
Position 1 inverts that channel's signal
Position 2 is non-inverting
Position 3 (new) bypasses that channel's Return and Tone controls for the most transparent tone, and is non-inverting.

Serial Parallel Switches (x2) - With both of these switches in position 2, all channels are in parallel as in the original. Having one or both switches in positions 1 or 3 gives a variety of series and parallel combinations as follows:  

There are 9 Serial/Parallel Switching Modes. (See Layout for corresponding switch positions)

1. Channel 1 in series with Channel 2 in series with Channel 3
2. Channel 1 in series with Channel 2, which are in parallel with Channel 3
3. Channels 1 in parallel with Channel 3, which are in series with Channel 2
4. Channel 2 in series with Channel 3, which are in parallel with Channel 1
5. Channel 1 in parallel with Channel 2 in parallel with Channel 3 (the original design)
6. Channel 3 in series with Channel 2, which are in parallel with Channel 1
7. Channel 2 in series with Channels 1 and 3 which are in parallel
8. Channel 2 in series with Channel 1, which are in parallel with Channel 3
9. Channel 3 in series with Channel 2 in series with Channel 1

Note, these 2 switches are more of a convenience as the same series/parallel combinations (and more) can be achieved by relocating the effect patch cables.

When using any of the Series Modes, the Return and Tone controls of the preceding series effect(s) are bypassed. Also, only the 1st Send Level Control of the series is active.  
And when in series mode, muting any of the channels that are in the series mutes the entire series chain. You could however bypass a channel in series by using that effect pedal's bypass.  

The series/parallel switching combinations does not include Channel 1 in parallel with Channel 2, then in series with Channel 3 (or visa versa). So place the effects you want in parallel in Channels 2 and 3.


When turned up, the Clean Channel's non-inverted signal is added in parallel.

Channel Mute Switches (3PDT stomp switches x3)
Both the send and return jacks are grounded in the Mute position. I used stomp switches with built in bicolor LEDs, blue for active, red for mute.

Master Bypass Switch is the typical 3PDT wiring.

A couple other uses for this design other than combining effects in series/parallel:
A super buffer and/or booster by jumping 1 or more channels
A splitter by running any or all of the channel's send jacks (or the effects out jacks) to a separate amplifier
A mute for an amplifier by feeding the amp from a send jack. Muting that channel grounds the input jack of the amp.
Coloring the Clean signal by jumping 1 of the channels and using it's EQ control.
And I'm sure more
   


Waiting on some more white knobs and so far only one of the stomp switches wired up with the LEDs.

[andrea83]

wow great! as soon as I got time to do it, I'll give it a try!
thanks for the work!