I would refine or modify the circuit so that it triggers the heating immediately, and delays the onset of B+ by a couple of seconds. After the input signal ceases, it could break the B+ with a couple of seconds time constant, and break the heating after 1 minute or so.
No I get what you're saying, I managed to remove touch induced noise, but I don't get why do I need to biaa the opamp. The ground (0V) is the threshold, and the signal passes through it.
Yes. I guess you also don't get why using an opamp without feedback is unwise.
I assume you are happy with circuit operation depending on exactly which opamp sample you put in or what the temperature is? Also depends on the frequency of the music.
It is up to you. If you are happy with unreliable operation then fine by me.
An op amp without feedback won't do you any good when amplifying a signal linearly. For my purpose I just want any signal above 5-10mV, to slam the output from rail to rail, so the highest possible gain is desirable. Every datasheet has an open loop gain/temperature graph, and you can always read off of it, how affected will your circuit be. Maybe I can have an op amp amplify the signal linearly 10-15 times, and then run it through an OpAmp based Schmitt Trigger, with two threshold levels. This might somewhat improve the stability.
An externally hosted image should be here but it was not working when we last tested it.
How about now? The circuit will only enable with an input signal of 20mV and above, and anything below 20mV will not activate it, and everything equal and above, will hit the output from rail to rail.
An externally hosted image should be here but it was not working when we last tested it.
Mistake noticed - R19 should be 1Mohm
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