[2526] Fet Bypass Distortion

Date: March 6th, 2019 | Comments : [1] | Categories: DIY.
fet bypass distortion

While getting acquainted with my new audio distortion analyzer, I decided to do a quick test to compare a true bypass pedal with another that used jfet bypass switching.

Since there was a new Boss SD-1 in a box next to my workbench, that is the pedal that I chose for the fet bypass test. The true bypass test was actually performed twice using a prototype of the Mosfet Boost module pedal and a similar mosfet boost pedal that I made using through-hole parts, but there was no difference in the results when the pedals were bypassed.

The bottom line is that jfet switching with buffers, as used in the Boss pedals, results in 135 times more distortion! It also has a signal loss of 0.81dBV while true bypass has no loss.

True bypass did not introduce any distortion and the THD shown in the listing is the residual distortion from the sine wave generator. It was the same with the true bypass switch as with a straight loopback without the pedal.

I will post a more complete article when I have had time to run further tests and optimize the settings on the test equipment.

Update: Further tests on bypass switching were conducted and the article is now in the Lab Notebook. Enjoy!

 

One Response to “Fet Bypass Distortion”

[786265] admin Says: 9:23 am, March 6th, 2019

Let’s be clear… 0.0824% is still a very low distortion figure, and 0.81dBV loss is small, but they will definitely add up when you put several fet bypassed pedals in series on your board.

On the other hand, true bypass still has the issue with long cables that can cause high frequency loss.

I plan on also testing some buffers without the jfet bypass switches to see how they react.


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