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[SOLVED] Left and right audio into vertical and horizontal inputs...

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Advanced Member level 2
Jan 29, 2004
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Hi, good day.
What to consider to display stereo music patterns (lissajous?) on a very old tube type single channel oscilloscope with vertical and horizontal inputs with not much other use for it, is there any circuitry to add ?

To obtain ---->

That is the exact oscilloscope I have available to give it an use, and its schematic is :

When the music stops then there is a bright dot that burns the screen. My old scope was used to display music patterns and now it has a low brightness spot in its center.
The intensity control has a very high voltage on it and it will be difficult to change it when the music stops.


For "esthetic" lissajous figures you need to use artificial "audio signals".
True audio signals don't give nice nor stable figures.

Let's say you want to draw a circle you need two sinewaves, samevfrequency, same amplitude, but 90° phase shifted.
For an "8" you need one sine ... and another sine, twice the frequency, half the amplitude, and at zero of the lower frequency there needs to be a zero of the higher frequency.

Simple analog mixers use a panorama pot to "place" an instrument somewhere between right and left speakers.
They don't use phase shift/delay, thus you just get a straight line. 45° when the instrument is centered, horizontal line when most left, vertical line when most right.


Thank you, Klaus. True non-aesthetic audio is what am after. Sold my receiver that had a built-in oscilloscope to display several functions and thought to rescue this old instrument from the spider webs and put it to work. So any suggestion to obtain the "horizontal line when most left, vertical line when most right" will be appreciated.

To get lissajous figures (X-Y mode) on my ancient Tektronix 504 oscilloscope...
I turn the sweep dial to its first (lowest) position, marked "Horiz. amplifier only".

Adjust vertical beam movement the usual way. Adjust gain so that signal travel covers a good portion of the screen.

Horizontal beam travel has an attenuation knob. It's not amplified (on my scope). Incoming amplitude must be 5 volts peak-to-peak in order for it to travel from extreme left to extreme right. ('Your mileage may vary'.)

Horizontal position knob works as usual. By adjusting it you can offset a small amount of DC component.
Ahaaaa ! That should be the trick, I get not enough amplification on the horizontal input ! Time to try feeding a higher level to it. Thank you.:D
--- Updated ---

That did it. Overcompensating the H input weak gain by simple balancing the signal, displays properly. Success !

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