Signal injector 2

139

01:58:38

Can someone explain why this circuit worked for a while then without alteration inexplicably stopped.? At the o/p there should be a wave of varying frequency and amplitude. 

published 5 years ago

faceblast

5 years ago

it's oscillating at 0.3Hz, shift the simulation timescale up

guzgog

5 years ago

Yep did that already. Not what should be happening. It's supposed to ( and I'm pretty certain it did for 10 minutes or so) produce audio range frequencies.

BillyT

5 years ago

With the capacitor and resistor values as shown, there is no way of obtaining audio frequencies from this circuit. Also with a transistor gain of 100, to make this type of circuit to start self oscillations in an easy fashion the base resistor needs to be roughly 105 x the emitter resistor.

BillyT

5 years ago

See http://everycircuit.com/circuit/4798657399095296

guzgog

5 years ago

Thanks for the comments. I see what you're saying regarding the base/emitter resistor ratios. Tbh all I did was copy an already published schematic which as I said seemed to work initially. I think maybe what happened is the already noted shortcomings of the EveryCircuit program itself came into play. It appears to be quite a 'hit and miss' affair at the best of times.

BillyT

5 years ago

These oscillators rely on the basis that the transistor is biased to the point where they are just ready to turn fully on or fully off. The simulator just can't allow for the fact that most transistors have a wide gain that changes, depending on the devices load stability. Most small transistors gain can be between 100 to 800. And when the current flowing thru the transistor changes, the gain changes, ie trans- resistor

guzgog

5 years ago

Thanks for the info. Much appreciated. It had been a cause on confusion as to why seemingly key transistor parameters had been omitted. This goes a great way to explaining why. Again thank you.

guzgog

5 years ago

Update: Made this as is on a bread board. It does indeed work as intended. Not sure how with the indicated 0.3Hz but as an audio injection for linear amplifier signal tracing it works perfectly.

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