This is a printed circuit board for a low noise dual 15V power supply (eg. +15V, 0V, -15V output).
I designed it specifically to work with the K1450 Preamps, but it is equally suitable for any audio or analog project that needs dual low current supplies at 15V, or other voltages from +/- 65V to +/-24 V if different regulator ICs and capacitors etc. are used as appropriate.
Both the circuit and PCB design design are Copyright © 2020 Robert Jenkins.
A lot of thought went into this design, both the overall circuit and the specific components used an given in the parts list.
The main electrolytic capacitors are deliberately over-specified, each is a Panasonic part 1500uF at 50V - as these have exceptionally low internal resistance (ESR), less than 0.025 Ohms.
They are also rated at over three amps ripple current, with is vastly more than required, again for a good reason: Under-running electrolytic capacitors vastly increases their life expectancy and reduces loss of performance. The basic datasheet lifetime of these parts if run at all maximal values is 5000 hours; the predicted life with loading in this design is in excess of one million hours.
For optimum quality and minimal noise, the board has options for R-C snubber networks across the AC inputs and also across each rectifier diode.Or it can be run from a battery source to give total isolation from AC power systems and any possible source noise or ripple.
The voltage regulator ICs are "low drop out" (LDO) type which can maintain the correct output voltage with a little as 0.5V higher input voltage.
The circuit board can be assembled with anything from an absolute minimal configuration with a single input and output capacitor for each rail, plus rectifiers for AC input. to a fully suppressed system with multi-stage filtering.
The three input reservoir / smoothing capacitors in each regulator circuit can be split with an appropriate low value resistor between the first and second capacitors, which drastically reduces the AC ripple present at the regulator input. Or a link can be used in place of the resistor, if not needed.
The regulator inputs and outputs also have positions for polyester film capacitors, to bypass any high frequency noise.
There is also provision for up to two electrolytic capacitors on each regulator output.
Power input can be AC from an appropriate centre tapped transformer, with onboard rectifiers, or DC for a battery source to dedicated inputs that bypass the rectifiers. Those DC connection points may also be used to take a rectified unregulated output for other devices when the board is used with an AC supply.
Two "20V" power tool battery packs, or a single 40V pack containing two 20V sections, work very well for a DC supply to the board and it was designed with that power source in mind.
The boards have two sets of outputs with provision for Polyswitch style PTC fuses if required, separate 0V connections for each and another 0V for system ground connection if needed.
A full topside ground plane is also used to give the lowest possible ground impedance and minimise noise, as with the preamp PCBs.
Note that the final version of these boards has provision for an additional resistor and capacitor following each voltage regulator. These were added as a precaution, as apparently some LDO regulators may not be stable with large, low ESR capacitor loads. I've never seen any such problem with any of these or other LDO regulator designs I've built, but the addition preempts any such possible problem. The components in the photo are to highlight teh locations; values would typically be 0.18 or 0.22 Ohms and 39uF.
See the final photo below for the additional component locations.
Bare PCBs are £9.99 each plus postage (£2.99 presently, for one or two PSU PCBs sent to an address in the UK; no additional charge for a PSU PCB ordered with one or two preamp PCBs).
A package deal for two preamp boards and one PSU board is 29.00 including UK postage.
A full parts list with suggested sources will be included with each purchase.
For order enquiries or postage / shipping costs, email audioparts (at) robertjenkins.co.uk
Photos - a bare PCB and some built to both maximum specification and a minimal build version:
Fully built with all reservoir / smoothing and snubber circuits:
A minimal build version:
Optional component positions to prevent instability in regulator ICs that do not work well with large capacitive loads.
Probably never needed, but Murphy's Law states they would be required if the components could not be fitted!