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Forum Home > Layout Gallery - GuitarPCB Build Documents, Mods and Tips > Paramix by Tomann

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This is an Advanced Build with many uses and capabilities.

Standard usage is to mix the effect with the dry signal.

The phase switch ensures that both signals at the mix are in phase with each other.

If the effect is a delay or echo, you can use the “Kill Switch”feature to cut off the signal to the delay or echo and still preserve the “tails”or “repeats”at the mix stage.

A new feature of the ParaMix is the Insert jacks it the dry signal path. With nothing plugged into the IO (Insert Out) and II (Insert In) jacks, the dry signal passes directly to the mixing stage, IC1B. When an effects pedal is plugged into the IO and II jacks the dry signal passes through the effect before reaching the mixing stage.

It allows you to decide exactly how much wet and dry signal you want. No Ratios. This is a great way to Mix full-blown distortion with the gritty attack of your dry sound for added clarity. Or, just inject a little shimmer to your tone by adding in just the right amount of chorus or phase.

The Kill switch is a footswitch that is normally in the ON state i.e. it sends a signal to the input of the effects in the loop.


The type of footswitch you use depends more on your playing style than anything else.


If you want to kill the signal going to the effect input for a long time (how many bars is a long time ?) then a normal DPST footswitch (or you can use the more common DPDT footswitch as in the wiring instructions) is recommended. Using this type of switch means you don't have to stand at the pedal - switch the signal going to the effect off, leap around the stage and then come back and switch the signal on again. The status LED is wired in the build instructions so that the LED is on when the footswitch is on i.e sending a signal to the effect - if you want the LED to light when the switch is in "Kill Mode" i.e. not sending a signal to the effect input you would solder the orange wire to the bottom right hand lug instead of the top right hand lug.

If your intention is to kill the signal going to the effect for a short time (two, four, eight bars) a momentary switch would probably be a better idea as it is faster to operate. The momentary switch must be a "normally ON" footswitch i.e. stepping on the switch disconnects the signal going to the effect. It is possible to use a momentary footswitch that is "normally OFF" - this would require a slight modification to the wiring. Since you would be standing on the footswitch to operate it, the status LED is not really needed - save a few pennies on R17 and D3. If you are not installing the status LED then you could use a STST momentary footswitch.


Set your delay pedal to 100% wet - you only want the repeats and not the intial signal at the output of the delay pedal. Kill footswitch is ON (sending a signal to the delay pedal), the output of the ParaMix will give you a clean initial signal plus the repeats from the delay pedal. Switching the footswitch to OFF (disconnecting the input signal to the delay pedal) still leaves the repeats connected to the mixing stage of the ParaMix leaving you free to mix in a new clean signal.

The correct type of jack must be used for the Retun and Send Jacks these are mono jacks with a contact switch.

For C1 through C9 capacitors we list 220n or .22uF however anything from 220n to 820n would be fine.

It is more a matter of what you have most of in your parts drawer in this particular case.

Probably my favorite is to use a delay and fuzz/distortion in the loop. This will thicken the sound. The possibilities are limited only by your imagination though.

Bass Players can use this with any DIY or Commercial Pedal and not have to worry about Modding it for Bass! Mix in as much Dry Tone as needed for Bottom end and Rock out with the bass on any pedal you like!

Set a small time delay (10mS to 30mS) and no repeats, and the effect will “sit behind”your clean signal.

How about plugging your Ipod into the return jack and mixing your Jam Tracks with your Guitar for the perfect practicing tool!

Finished Build Thread for reference.

Board Dimensions (W x H) 2.1” x 1.75” ca.53.4mm x 44.5mm

Paramix Build Instructions

IC Chip is a TL074.

Courtesy of Tonmann a description/manual of usage ideas.

The ParaMix has six jacks:

  • IN - Input
  • OUT - Output
  • SND - Send
  • RTN - Return
  • IO - Insert Out
  • II - Insert In.

The input and output jacks should be obvious, connect your guitar to the input jack and connect the output jack to your amplifier.

For the SND / RTN part of the circuit you plug a cable from the SND jack to the IN jack of the effect and another cable from the OUT jack of the effect to the RTN jack on the ParaMix.  What you are doing is SENDING a clean signal (that's the signal from the input of the ParaMix) to the effect and RETURNING the effects signal to the ParaMix.

It should be obvious that if you don't attach one of the cables you won't get an effects signal back to the ParaMix.

The IO / II part of the circuit is very similar to the SND / RTN part of the circuit except that when no cable is plugged into the IO or the II jacks the clean signal from the input of the ParaMix appears at the output of the ParaMix.

If you plug a cable into either the IO or II jack (or both), the clean signal between the input and ouput of the ParaMix is disconnected.

The most basic configuration for the ParaMix is having a cable from your guitar to the input and a cable from the output to your amplifier.  This will give you just the clean signal at the output of the ParaMix.

Rather than writing lots of text, some diagrams might be helpful.  Please remember these are just examples, the effects that you use or find useful are a matter of personal choice.

Very basic, very useful (especially for bass players) as this will add a bit of clean signal to a fuzz / distortion effect (or a bit of fuzz / distortion to a clean signal).

Another basic that is a favorite. It is important to turn down the initial signal in the delay effect so that you are only left with the repeats otherwise the initial signal will be twice as loud as it should be.  Adding the Kill Switch option and setting the delay to infinite repeat will allow you to play over the tails of the delay signal.

Of course you are not limited to one pedal in the effects chain.

This time instead of having a clean plus fuzz signal mixed at the output of the ParaMix, the clean signal is routed through a compressor.

Like the SND / RTN loop, you are not limited to one effect in the IO / II part of the circuit.  Here you have a fuzz signal mixed with a compressed chorus signal - change the order of the chorus and compressor and you would have a clean compressed signal that has been "chorused".

These are the basic ideas behind the ParaMix, there are other uses plus a full lesson on bypass switching individual effects.

Let's look at some other applications.

As much as I or other people would like to think that the ParaMIx is some fantastically wonderful circuit, it is nothing more than a Buffer / Splitter / Mixer circuit (OK with a few bells and whistles thrown in).

It buffers the input signal - grabs as much signal as it can at the input and delivers as much signal as it can to the output which is split into two audio paths.  The two audio paths are then loaded with the effects pedal(s) of your choice and then mixed back together to give a single output signal.

So if the Buffer / Splitter provides two audio signals, what can I do with these (apart from that described in my last post) ?

I can feed two amplifiers !!

The above diagram shows the basics, one amplifier with a fuzzed signal (remember you can use any effect or effects you want) and one with a clean signal.

With this configuration I can:

Provide both amplifiers with a clean signal by removing the fuzz pedal from the circuit either by using the fuzz pedal bypass switch or connect the SND jack directly to the amp input jack via a cable.

Mute the fuzz amplifier by using the Kill Switch

Change the clean channel to an effects channel by inserting a pedal in the IO / II loop, or by inserting the pedal between the ParaMIx output jack and the amplifier input.  You can then choose between clean and effects signal by using the effects bypass switch.

The above diagram is almost identical to the previous diagram.  The main difference is that you can't use the IO / II loop and would have to insert your pedal(s) between the IO jack and the amplifier input.

The only advantage is that you are not using the mixing op amp in the ParaMix which would remove the theoretical mixing stage op amp noise (if any) from the input to the amplifier.

One main problem associated with using two amplifiers is that of ground loops, or hum in the guitar amplifiers themselves.  This is usually down to the amplifiers and not the effects, if you are using  two amplifiers I would strongly suggest at least one if not two DI boxes between the last effect output and the guitar amplifier input.

Let's now look at the mixing stage.

The diagram above shows that it is easy to mix two independent signals together and arrive at a single output.

The "Source" input connected to the RTN jack can be another guitar with or without an effects pedal chain - either you are using two guitars in a live playing situation or you are jamming with a friend.  It could equally be an audio signal from your computer, iphone, boogie box, record player, gramophone record player etc to enable practice play-along.

You are not limited to clean signal plus source signal, add your effects chain to the IO / II part of the circuit for an effects plus source mix..

For the even more adventurous, here is my last offering for the ParaMix:

You now have a three channel mixer;  IN / OUT or IO / II from ParaMix I plus IO / II from ParaMix 2 plus SND / RTN from ParaMIx 2 with up to five different places where you can insert an effects chain.

Here is the build thread for the above shot:

Here is a very cool combo build thread:

If you want to add a 100% Wet switch it is called the T-Diddy Boost Mod

Courtesy of Tonmann:

You can make this mod by using a DPDT footswitch- which prevents you from bending down !!!

If you are using something like a BB enclosure it's worth thinking about whether the footswitch will fit on the enclosure - either a larger enclosure or a separate dedicated ParaMix pedal for this function (a man can't have too many ParaMixers).

Since a picture is worth a thousand words:

When the switch is in the Up position the pads on the board are connected to lugs 2 of their respective pots - the circuit behaves as normal.  In the Down position, the dry signal is connected to ground and the signal doesn't reach the mixing stage. For the wet signal the pad is disconnected from lug 2 of the pot and connected to lug 3 of the pot - as if the wet pot is turned up fully.

If you want LED status switching, you would need a 3PDT switch.

The only problem I can foresee is popping when you switch - shouldn't happen, but it might.

Some additional Troubleshooting points if needed Courtesy of Tonmann:

Voltage measurements will tell you where the problem is or isn't, unless you are good at electronics they won't tell you which component is causing the problem.  The second part of fault finding is measuring resistances to find short circuits, open circuits and correct resistor values.

There are a few points to bear in mind before you start to measure resistances:

Phyiscally remove the power supply / battery from the circuit and wait a few minutes to allow any large capacitors to drain to ground.  Never measure resistances in the circuit with power applied, you will more than likely destroy your DMM at worst or have to replace a fuse at best.

Remove all active components (ICs, transistors and diodes) before you start measuring.  Your DMM uses an internal voltage when measuring resistances, this voltage could turn on transistors and diodes which will give you a false resistance reading.

Knowing what resistance value to expect between two points in a circuit is not very difficult, the hardest part is if you have more than one path running between two points in the circuit - instead of simple resistances in series we now have resistances in parallel which takes a small amount of maths to calculate.

An easy method to get things right is one I have used ever since I started electronics:

  • Print a copy of the schematic
  • Erase the active component symbols from the schematic (you have removed the components from the board)
  • Erase all capacitors from the circuit - DC voltage won't "pass" through capacitors so for all intents and purposes they act as a break (open circuit) in the path.
  • Look for multiple paths between two points in the circuit - use a pencil to mark the paths between two points

Here's my "resistance" schematic for the ParaMix.  As all circuits are different there is no actual one method to follow so I will just run through how I would measure the resistances for this circuit.

Check VB supply:  Measure from the top of R13 to the bottom of R14 - which is ground (I can do this on pins 4 & 11 of the IC).

Expected value is R13 + R14

Pin 10 to VB - I can use any VB on the circuit; the top (layout) lead of R13, pin 3 or pin 5.

Expected value is R2

Pin 9 to Pin 8 - connected together.

Expected value is 0Ω

Pin 10 to Pins 9 / 8 & 11 - checking for solder bridge (short circuit)

Expected value is infinite Ohms (open circuit) for pins 9 /8 and R2 + R14 for pin 11

Pins 3 & 5 to VB - between the top (layout) of R13 and both pins.

Expected value is 0Ω

Pin 2 to Pin 1 - depends on rotation of the pot

Expected value is either R5 + P1 or just R5

Pin 3 to Pins 2 & 4 - checking for solder bridge

Expected value is infinite Ohms for pin 2 and R13 for pin 4

Pin 5 to Pins 4 & 6 - checking for solder bridge

Expected value is R13 for pin 4 and infinite Ohms for pin 6

Pin 6 to Pin 7

Expected value is R11

Pin 7 to Pin 8 - checking for solder bridge

Expected value is infinite Ohms

Pin 12 to VB - depends on the setting of SW1

Expected value is R6 in up position and 0Ω in down position

Pin 12 to Pin 13 - depends on the setting of SW1

Expected value is R7 in up position and R6 + R7 in down position

Pin 12 to Pin 11 - checking for solder bridge

Expected value is R6 + R14 with SW1 in up position and R14 with SW1 in down position

Pin 13 to Pin 14

Expected value is R8

October 30, 2012 at 2:21 PM Flag Quote & Reply

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