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I have this old Soviet low frequency sine and square pulse generator "G3-36A".

enter image description here

I ran into an interesting problem.

When I try to generate square pulse under 100Hz I get a distorted wave. Like in the image:

enter image description here

When I increase frequency to 100Hz this is what I get:

enter image description here

At 1kHz it looks more like a square:

enter image description here

Does anyone know what is causing the distortion and how can I fix it?

Schematic of the signal generator:

enter image description here

The KT603B transistors circled with red color are the ones that generate square wave. The blue ones are amplifiers.

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    \$\begingroup\$ Is your scope set to AC coupling? This is what an AC-coupled square wave looks like. \$\endgroup\$
    – Hearth
    Commented May 4, 2022 at 14:15
  • \$\begingroup\$ so its about scope, and nothing to do with generator, kinda fell stupid rn ngl \$\endgroup\$ Commented May 4, 2022 at 14:26
  • \$\begingroup\$ Well it's the scope if your scope is set to AC coupled. \$\endgroup\$
    – Hearth
    Commented May 4, 2022 at 14:27
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    \$\begingroup\$ well guess i have to check that tomorrow and come back with results \$\endgroup\$ Commented May 4, 2022 at 14:32
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    \$\begingroup\$ The generator has a coupling capacitor feeding the output transistors and another coupling capacitor at its output. A good squarewave needs DC coupling. \$\endgroup\$
    – Audioguru
    Commented May 4, 2022 at 18:28

1 Answer 1

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This most likely isn't a problem with your waveform generator, but with the oscilloscope you're measuring it with. I'm not familiar with Owon scopes, but I assume that this ~ symbol here: enter image description here refers to AC coupling.

When a scope is AC coupled, it's applying a high-pass filter to everything it displays to filter out the DC component. A square wave under a high-pass filter looks like this:

enter image description here

(image source)

Note how it looks different depending on the frequency, just like your square wave.

The other possibility is that something in the waveform generator itself is applying a high-pass filter to its output, either intentionally or due to a fault. This seems significantly less likely to me, however.

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  • \$\begingroup\$ i was just reading about this, once i change to dc will let you know. i was thinking that either transistor or capacitor next to it was faulty but they seemed to work properly so i guess it's me being stupid not using scope properly xD, thanks again really helped out \$\endgroup\$ Commented May 4, 2022 at 14:50
  • \$\begingroup\$ ill post update \$\endgroup\$ Commented May 6, 2022 at 12:36

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