![]() And with a 10x probe to bring the DC into the scope's 50v tolerance, we fear we've attenuated the wiggles to nothing. BUT: We are uncertain if the AC-coupling in our wee DSO-112A pocket oscilloscope is cutting off all the low-frequencies we wanna see. So we're like ok cool - bring on AC coupling. But here is the problem: The power supply inside the amp is 400 volts by the time it touches anything. We want to probe around & find the oscillations in the circuit. We just got ourselves a wee pocket oscilloscope. We suspect something like the mains rectification diodes. ![]() Thus we suspect power supply in the amp and we suspect it is _after_ signal-amplification somewhere. When we turn the gain up & down on the amplifier, the wiggles/oscillations remain at constant amplitude. We're seeing sub and super-harmonics of 50hz, and at around 4hz its -84dBFS. We are seeing these wiggles when simply recording silence on the PC (we know its not the audio interface, that goes past -120dB). My buddy and I (noob #1 and noob #2) are trying to figure out how to fix this awful noise floor of this audio tube amplifier: There is low frequency oscillation of the signal all by itself when nothing's plugged in.
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