When you’re on stage, the true bypass simply turns your pedal on and off. Quite useful for a system!
So we’ll see how a true bypass works, its design, the different technologies and, how it is installed!
If you are reading this article because you are making a FX teacher kit, you can go directly to the realization step and then come back to the theory another time. But hey, you might miss something!
For the kit with 3PDT click here.
For the kit with relays click here.
what we expect from a true bypass
- When the pedal is bypassed, it means that you don’t go through the effect. To achieve this, the guitar signal passes through the input jack and then enters the switch, then the signal is routed directly to the output jack and thus the next amp or pedal.
- Conversely, when the pedal is turned on, the switch takes the signal from the input jack and sends it to the effect input. As for the effect output, it is redirected to the output jack. At the same time the switch also lights the LED by letting it pass current.
so on the electronic side, how’s it going?
Here is our favorite true bypass schematic, there are other variants but it is for us the one that works the most efficiently:
The little subtlety in this setup is that the output jack always has a DC level close to 0 thanks to the resistance of 1M Ohms. This is called a “pull down” resistor. And when the pedal is off, the effect input is also grounded.
By balancing the levels in this way we avoid a large number of pops when switching on! And yes! Pops are mainly due to phase problems or a DC level that changes suddenly.
what is not true bypass and why
The technical solution that opposes true bypass is the buffered bypass. It can be found on some Boss pedals and other brands.
What differentiates buffered bypass from true bypass is that the signal always passes through an active circuit, whether the effect is on or not. He will therefore be subject to processing that may be good or bad.
Without going into too much details, the input signal will pass no matter what happens through:
- Input buffer
- Pre-emphasis filter
- De-emphasis filter
In parallel the sound enters the other blocks but it will be processed independently.
The JFET switching block will simply serve as a memory cell when we will hit the footswitch. When the pedal is to be activated, it will “turn on” JFET Q9, which will let the signal from the WET branch pass through to the output summing unit.
So in bypass we have DRY that goes through a lot of op amps and transistors. When the effect is activated, we have the DRY signal + the WET.
If we only had one pedal like that on the pedalboard, I think it’s better than a true bypass. But this is never the case.
The problem is that the active components amplify signals, have thermal noise, affect the bandwidth, create harmonics…
When you accumulate several pedals in a row you will amplify your background noise! So your SNR, the ratio between noise and useful signal will drop.
is true bypass the best?
True bypass allows you to have a “simple” cable when you are in bypass mode. This is very advantageous since there are not expected to be any signal alterations. If all pedals are true bypass, the signal only sees a long cable to the amp.
Simple and efficient!
Unfortunately, the guitar signal is not designed to go through very long cables!
If you only use true bypass pedals and with a little cable length, you have a physical model equivalent to a very long cable (between 10m and 50m depending on the quality of the pedals and the size of the pedalboard). This is due to the characteristic of these environments, in fact we go from a cable jack, to a connector jack, then to a soldered wire, a truebypass… This creates parasitic resistances and capacities.
The only way to avoid losses in this case is to buffer the input of the audio circuits. Thus, the input impedance is so high that the current drawn will be low and the resistive loss negligible.
Well, we’re not moving forward! What’s the solution?
find a good compromise!
Our good friend Pete Cornish advises to place a buffer pedal before and after all of his pedals, and I also think it’s the best solution! By the way, if you also find that this is the best solution, we offer you a great homemade buffer.
I would even add that if you are equipped with good overdrive, you can dispense with the output buffer. Because, when properly designed, the input and output stages are perfectly designed to solve these problems. So I always recommend a Savage always ON at the end of the drive chain. It colors the tone just the right amount and offers plenty of dynamics and headroom! It’ll save you a buffer.
Well, come on, I’ll stop selling my products ( you have to when it works, right?) and I’ll summarize the situation:
- An excellent buffer with high input impedance and low output impedance at the very beginning of the pedalboard.
- Only true bypasses between the buffers.
- The same buffer at the output OR a good quality buffer bypass pedal OR an always ON quality overdrive
set up a true bypass
We will see together the 2 most widespread and effective solutions. The one with a 3PDT and then the most recent one with a relay and a pushbutton!
the 3pdt footswitch
what is it?
The 3PDT is a mechanical component that will integrate the true bypass. When you press this push button, brushes will switch from one side to the other. The 3 poles are used to build the true bypass. This method has been used for decades, it is just necessary to find good suppliers for the switch if you want it to last over time. It’s just a good old-fashioned mechanic! You can find dozens of them on our shop, right here.
how it works?
To understand how it is inside; There are actually 3 switches in the same box, each of these switches has a midpoint and a flip-flop. This switch will go up or down depending on how many times you press the switch. Thus a contact is made with the pins middle + top OR middle + bottom.
You can go back to the true bypass schematic, where you can see that the 3 switches have different functions, but move at the same time and serve the same thing, the signal path !
Here you know everything about the famous 3PDT and how to use it to make a true bypass. He has no secrets for you now!
pros and cons
- It’s a simple switch with 3 poles! They can be found everywhere and for a better price than other bypassing solutions.
- It is easy and quick to install because it does not contain any electronics. We remind you that it is very interesting if you want to transform a buffered bypass pedal into a true bypass.
- Unfortunately it is a fragile component with a random lifetime. On the one hand, 95% of them are made in Asia, and they get their heads hit all day long. With vigor in addition! Rough life of a boost pedal….
- Finally, it is not compatible with MIDI, which allows you to control the activation of the pedal remotely. You need a foot to activate it, the electronics can’t do anything for it!
prepare the 3pdt by hand
To prepare a 3PDT wired it will take patience and a good cable management because it can go in spaghetti mode very quickly!
The 3PDT wired method is rarely recommended because it often causes quite a few problems. Indeed, to cite a few examples, pins are sensitive to heat and an unequal heating can damage them, the wires will have to be well positioned to avoid signal coupling.
However, you have to know this solution if you can’t do otherwise!
- With my third hand, I come to clamp the top of the footswitch to hold it vertically but reversed.
- I insert my wires into the legs of the 3PDT from the inside to the outside. The cable assembly diagram is shown above.
- I set my solder iron between the pin and the wire and let it heat up for a few moments. Be careful the red paste that holds the pins melts quickly, I do not heat too long to prevent it from tearing off but enough to avoid a cold junction.
- Then I put the tin in until the pin is full and then I remove it.
- Finally I remove the iron by sliding it along the wire’s leg.
- Not to mention cutting off the excess wire!
prepare the 3pdt on pcb
To avoid you to wire the schematic at the beginning of the article we created a small PCB in which you insert the 3PDT. Then it’s ready! Now we just have to put this PCB in pins on the motherboard. You solder and it works!
The kit is available right here.
- First we will identify how to place the footswitch on the PCB. We push it on the opposite side to the writings (FX_I, GND…). Its pins are elongated and must be horizontal.
- We make sure that the footswitch is pushed as far as possible into the PCB, and that we can see the pins coming out as shown in the picture.
- Then the third hand is used to stabilize the whole thing and the pins are generously soldered to the pads. It’s the same technique as for the jacks, you already master it! Be careful to put tin to fill the pad which is wider than usual without overflowing. It is necessary to heat enough so that the solder is not cold but not to stay too long either as it would risk blowing up the pins of the crimping. Anyway, that’s why there’s a video!
- Last step, don’t forget the resistance to solder right by it. As usual it is placed on the writing side, for the soldering exceptionally I find it more practical to solder it on this side too.
the micro-controlled relay
what is it?
The relay is an electromechanical component that allows us to create the true bypass. The difference with a 3PDT is that it is activated by an electronic system and the push button is a simple contact that is used to activate it remotely. The push-button does not integrate the true bypass but sends a simple data to the system. It is the most expensive solution but the one with the longest lifetime! It also allows with a micro controller to offer many possibilities like a remote MIDI control.
how it works?
When we say relay bypass, we cannot illustrate as with a 3PDT where the contacts move when the foot is pressed on the footswitch. There is a part of electronics to control the relay. This is illustrated by the following block diagram:
When the footswitch is pressed, the current reaches the “trigger” pin of the memory. Logic level 1 is detected at its input (voltage that exceeds a threshold set by another pin of the integrated circuit) and the memory will transmit this logic state 1 to the relay driver. The driver supplies the necessary power to the relay coil so that it switches its contacts and activates the pedal circuit without damaging the memory by asking it for too much power.
After releasing the footswitch, the high logic state is no longer brought to the memory trigger pin. But it continues to send a high logical state to the driver, and the effect is still active. That’s what you expect from a memory!
Finally, when the footswitch is pressed again, the memory receives the new high logic state and switches the logic state of its output. The driver is no longer powered and the effect is bypassed! Not that complicated after all!
On the electronic side
The memory block is built on our pedals with a NE555 which is not a memory! It is basically an oscillator, but it is perfectly suited for this use. Amazing!
Then, the driver is a simple bipolar transistor that will receive on its base a logical level and then draw the current from the 9V power supply to feed the coil of the relay.
pros and cons
- Pedals that use a 3PDT for true bypass are the most returned to the after-sales service for dysfunction. This is due to the lifetime of the 3PDTs, which rarely exceeds 10,000 cycles. Very random rate are noticed within the same production. The relays have a lifetime of more than 10 million cycles and the manufacturers are very serious!
- The footswitch itself is a simple SPST, it is a contact that touches a stop. So you can go, you won’t risk shortening the life of your switch if you strike when you activate your effect!
- When using a relay, you need other components to surround it. An integrated memory circuit is necessary, you have to drive the relay, power all that…. It therefore requires a slightly higher level of knowledge to integrate it.
- And as a result, cost and space requirements increase.
- Another interesting aspect of the relays is that we can replace the memory (for us a NE555) with a microcontroller! Thus you can control your pedals remotely thanks to MIDI in particular. This then requires a little more knowledge since it is necessary to develop a few lines of code. But hey… we’re here to do some hacking, right?
There’s no doubt about it, if you can equip your pedals with relays, go for it! It’ll be much safer for your pedal in the long-term. This is why, since several months, all Anasounds pedals are equipped with relays. On the other hand this system will cost you more and take up a lot of space in the box so get started when you’re ready.
prepare the bypass relay kit on pcb
The kit is available directly on our shop.
As for the 3PDT version, we have a small PCB that will fit on on the motherboard. The difference is that there are a few more components to mount and a switch to wire on.
The BOM for this kit:
|1||3k||R5||1/4W metal film resistor|
The different solutions at fingertips:
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