I finisced my first board whit SMR-4 filter.
It was a very teaching experience, vary satisfactory, I enjoed myselt a lot.
Only trouble I found was at first the tuning of oscillator. The sine tone was fading quickly and, as is it told in the forum, I presume it was a problem of over heating. Before digging it, I lowered voltage in and I found that at 7,5V the Shruthy sounded well. I tuned it perfectly whit the tubeohm utility and checked later with a scope.
Responsible of over heating was 7805; with 9-12V in, it was untouchable.
Changed it presuming a defective unit. Nothing changed.
Checking the power section I mesure:
Volt in 7,45
pin 5: -6,18V
pin 8: +6,69V same tension than after diode
7805 out: +4,89
7905 out: -4,94
Same voltages on + - rails.
Feeding 9V change nothing, heathing a part.
With note C4 sine wave is around 3V pp.
My explanation is: if 1054 must output -5V and +5V the 7805 works too much and heats. But why 7905 not?
Electromistery to me.
As soon as possible I’ll replace 1054. May be I wave it half fried with a power supply too “hot”.
Anyway, at 7,5V the instrument sounds sweet. Waves dance on scope graciously and now I can play the oscillator over 9 octaves.
I believe that every machine has is own voice. Maybe the regulator is gone, but mine has found is own regulation.
Is it a Voltage Controlled Synth? VCS
All the best to all
Gengisthecan, 56, Roma, Italy