| Re: Linear measurements in audio gear [message #99305 is a reply to message #98644] |
Mon, 23 March 2026 15:42  |
positron
Messages: 162
Registered: May 2020
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Master |
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I know of two different ways. I know most have never
used an oscilloscope before and I would like to help
if I may. I mean no harm to those who can.
I use a Tektronix 535A dual trace scope with
CA plug in, which I will describe use below as the first
way. The second way uses a volt meter.
1. First we want to compare the two channels at what ever test
frequency (ies) and signal levels.
A. Set switch to alternate. Next
B. Set one channel switch to "polarity" + and the other channel to
polarity -. Next
C. Set Voltage level of each channel to the same setting, example, 5 volts.
D. Connect the test input signal to both channels. They should match to zero,
resulting in a flat line across the screen. If the channels do not match,
the line will Not be straight.
E. Each channel has a variable gain control set at maximum. Adjust the
variable control of the higher gain channel until the wiggly line
flattens out. (Adjusting the wrong variable control will simply increase
the wiggly line. No harm done, just max it again and adjust the other
variable control for less gain, a straight line.) Check at different
signal levels and at frequency (ies).
If all is well, feed input to device under test and check. The amp
or preamplifier may or may not be linear vs different signal levels
or outputs. Not super accurate but probably within 5% or better.
2. A less precise method is to use a volt meter, again check at
different signal levels, and maybe frequencies. Since one is
simply checking for, say, does double input signal produce
double output, one should obtain a fairly reasonable conclusion.
Differences may vary with amplifier brand, model, and power output etc.
I hope this helps all. All the best.
pos
ps. 99 I found a gain vs phase shift graph. But it is not
down to the nearest degree.
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