So what exactly does True Bypass mean?

[Rpschultz13]

I'm developing a tuner pedal, and trying to give the option of True Bypass or Buffered Bypass. The JFET splitter/buffer I'm copying from AMZ (PPCB uses similar). I've always understood that TB means the signal doesn't go through any IC's, chips, or anything that is powered. But can go through switches/resistance, etc.

In the below example for TB mode, the signal goes through SW1 and the relay but nothing powered. But the signal ALSO goes through Q1 to the tuner. I think the buffer creates a sufficiently high impedance such that it doesn't affect the parallel signal going through the TB leg, but I'm not sure.

Thoughts?
Thanks!

 

[bean]

True bypass means your signal passes from guitar input to output with no connection to the circuit. What you've drawn above is not true bypass because the input is always connected to the circuit input. Only the output is being switched. Also, the circuit is always powered, regardless of the switching state or method.

In order to make it true bypass, you'll want a DPDT switch that lifts the circuit inputs and outputs in addition to your 3pdt footswitch. The DPDT can be an internal slide switch or external one if you want that option.

Actually, you may not want true bypass after all if you want to have the tuner out always on.

 

[Rpschultz13]

So then like this, using the other side of the relay. Monitor mode bypasses that side of the relay but requires a buffer.

 

[bean]

I think there's a much simpler solution here. You shouldn't need to buffer your tuner output in most cases, unless it's a really so super old or cheapy one that loads down its input. Most modern tuners have true bypass and likely a high input impedance when on. This means you should be able to just split the input jack to a direct out for the tuner. Your circuit won't be completely true bypass, but I doubt you would have much or any signal loading from this method (esp. not when your buffer is on).



But, I think it's a matter of doing a couple test cases on the breadboard. Try your method and the one I suggested and see if you can hear a difference between them when everything is bypassed.

 

[Rpschultz13]

Just to clarify, when I say TUNER, it isn't a stand alone tuner that you buy. We are designing a tuner pedal using a CYD (Cheap Yellow Display) with an onboard esp32 MCU. So it doesn't have any impedance other than what I give it.

Last night I tested this using 2 J201's I had. It worked. C1 goes to the CYD-esp32. Although it popped when I tripped the relay, so I need an RPD before C6. Previously I tested it only with Q2 and the tuner didn't work, so I suspect both legs need a buffer.



CYD mounted to PCB. The breadboard has the additional buffers from true bypass mode.