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Today i made second attempt to make HH, opt 1. This time i made it. It is working. Just finished, hour ago. Still early to establish opinion. I made suggested coil (0,4mm, 30 wind. on 20cm diamm.)
Frequency can be adjusted from 890Hz to 2kHz.
Fet is cool all the time. No issues there. Every trimmer reacts and make some change. Detection is quite descent even now when nothing really adjusted.
But...only one thing bugs me right now. First i used ordinary 8 ohms speaker and after 3-4 minutes of producing weak sound, Q11 burned!? Than i replaced Q11 and put telephone speaker (250 ohms). Cool! Loud audio and Q11 is cool after 20 minutes.
Still there is background weak whistle under main audio. Turning freq. trimmer also whistle is changing pitch? So there is main frequency also audible in speaker?
How? What should be a problem?
Noise on pcb? Bad S/N ratio? I doubt that.
Except that whistle issue, everything else seems very good.
To be continued...
Frequency can be adjusted from 890Hz to 2kHz.
Fet is cool all the time. No issues there. Every trimmer reacts and make some change. Detection is quite descent even now when nothing really adjusted.
But...only one thing bugs me right now. First i used ordinary 8 ohms speaker and after 3-4 minutes of producing weak sound, Q11 burned!? Than i replaced Q11 and put telephone speaker (250 ohms). Cool! Loud audio and Q11 is cool after 20 minutes.
Still there is background weak whistle under main audio. Turning freq. trimmer also whistle is changing pitch? So there is main frequency also audible in speaker?
How? What should be a problem?
Noise on pcb? Bad S/N ratio? I doubt that.
Except that whistle issue, everything else seems very good.
To be continued...