Hi Stewart,
But I did see in the "feedback" section a couple of potential "issues":
The TL081 appears to be rated to only 36 volts, certainly not enough for a 30 volts output regulator if it uses a -6 volt rail.
So I would be looking for a "better" Op-Amp, ideally a single-rail type which would save a few components and (also) avoid the other (potential) issue of "unbalanced" transient supply voltages during switch-on or switch-off. Then the -rail could just be connected to 0v (using the same PCB).
Unfortunately, the TL081 data sheet does indicate that it may need around a -5 volt rail (relative to the lowest input signal). But it may be possible to find an Op-Amp with inputs that can be used much closer to the negative rail (if not actually zero volts). Then replace the 5v6 (D7) zener with a LED (but "pointing" in the opposite direction), which can make quite a good low voltage reference (and even a "free" pilot lamp for the front panel if you wish).
Cheers, Alan.
Yes, IMHO certainly the most appropriate of the three above.
But I did see in the "feedback" section a couple of potential "issues":
The TL081 appears to be rated to only 36 volts, certainly not enough for a 30 volts output regulator if it uses a -6 volt rail.
So I would be looking for a "better" Op-Amp, ideally a single-rail type which would save a few components and (also) avoid the other (potential) issue of "unbalanced" transient supply voltages during switch-on or switch-off. Then the -rail could just be connected to 0v (using the same PCB).
Unfortunately, the TL081 data sheet does indicate that it may need around a -5 volt rail (relative to the lowest input signal). But it may be possible to find an Op-Amp with inputs that can be used much closer to the negative rail (if not actually zero volts). Then replace the 5v6 (D7) zener with a LED (but "pointing" in the opposite direction), which can make quite a good low voltage reference (and even a "free" pilot lamp for the front panel if you wish).
Cheers, Alan.