Harry Dalek wrote:Yes the pot part is a bit of problem...
I haven't studied the internals of the LM317/337 but I'm sure with some relatively simple rearrangement of the die it could be made such that if the pot goes open-circuit it shuts down - or at least resorts to the minimum output (1.25V) rather than almost the whole of the unregulated input. It's most unlikely that a re-design will ever be done as the current version is successful as is.
This flaw isn't the fault of the LM317/337 design but the inherent unreliability of the usually available (cheap) pots. A 'crackly' volume control is an annoyance, here it could spell disaster for attached circuitry. Sure, you can buy better quality pots, but the inherent weakness remains.
I think most would prefer an arrangement where you can slowly increase the voltage while keeping an eye on the current. Any faults, shorts, errors, whatever, should be obvious before frying any downstream components....especially if expensive.
This bench power supply does have a few fixed output voltages provided by the usual 78xx/79xx regulators in addition to these variable outputs. Once you're sure there are no major faults your creation can be transferred to those. - +3.3V, +5V, +12V, and -12V.
+/-15V is rarely used except in quality audio designs where the highest dynamic range is desired, sometimes +/-24V, usually a discrete design with no op-amps, or using specialist devices rated for that sort of voltage are specified...rare/expensive. (D. Self, a prolific audio designer in the 60s/70s, often used +/-24V supplies in his discrete designs. Much of his work was published in the UK 'Wireless World' magazine of that era.) Today, with the exception of the output voltage capability, there are op-amps that better those and similar older designs....there has been 50 years of development since then...
Steve A.