whit3rd wrote:


3{a}. Square wave output for checking tone circuits and amplifier stability.

Or, maybe a white-noise output?


** Worse than your other mad ideas.

A/B switch, headphones, attenuator; it's not hard to check uncalibrated tone
controls that way. Or, with a math-equipped DSO, it can be quick to measure.

** So you never tested a tone control or stack using a square wave and a scope ?

It is a VERY quick, easy and unambiguous way of seeing if all the controls do what they are supposed to.


A real square wave has lots of bandwidth, beyond the important, audible, spectrum.

** But a guitar amp does not - plus the amplitude of all harmonics fall in proportion to their frequency.

Square waves contain only the odd numbered harmonics, predominately 3rd, 5th and 7th with amplitudes 1/3, 1/5 and 1/7 of the fundamental.

With guitar amps, I use a 250Hz square wave and firstly try to set the controls so the output looks square on a scope. Next, I turn each control through is full range and then back to the "flat" position.

Treble boost causes overshoots to appear at the leading edges of the square wave, treble cut rounds them. Mid and bass controls cause the horizontal parts of the square wave to tilt sharply uphill and down. At the same time, you can see if the controls are working smoothly, free of noise and intermittent operation.



..... Phil