The earliest Crimson preamps were run from +/- 15V. This was via a lead with 2x 2mm plugs at each from the power amp outlet. The power amp had a discrete internal regulator and it own rectifier etc. Also the same regulator was available in a power supply box called CRIPS and the lead was 3 x 2mm plugs at each end. The PCB (below) was called REG1.
The 610 preamp was fed from a very good isolated supply consisting of two dry cell PP9s (9V each). Sometimes NiCads were fitted fed via a switched charger. Preamps with batteries are totally free of hum or switching noise but not always that convenient.
In 2024 what is a good choice for a preamp psu? The old school stick with 50Hz transformers which are easy to use but have a couple of drawbacks. They often radiate loads of stray field which is very difficult to keep out of MC input stages. They are also becoming rare and more expensive than the SMPS type. However, SMPS can have a lot of switching noise which needs filtering. a lot of the simple regulators do not do a good job of eliminating the 50kHz or higher noise.Most designers choose split rail preamps because the coupling caps can often be eliminated. But PSUs are always single supplies. So if using a single ended SMPS you need two things. A good HF filter, followed by a series regulator and then a rail splitter if the load is asymmetric. If the preamp load is only slightly asymmetric the rail voltage can be equalised by adding parallel resistors. When decoupling is added across these resistors a good balanced PSU will result.
Below is a draft circuit for a preamp supply derived from a 24V SMPS input.