Most of our customers are buying our kits with the power supplies/regulators that we have designed for the kit. However, there are also some who say: “I have 1N4XXX diodes and some 3-pin regulators in my surplus box, so I will make the power supply/regulator myself” Good idea to make them yourself, but by all means, NOT with 3-pin regs. Must admit that we have also used the 317/337 regs for our lineamps many years ago, however, it became painfully clear that those regs are not suitable for high performance audio circuits. The most critical case is the MC phono preamp, with a very low noise, high gain pre-pre. You can’t even do a proper noise measurement on these, when you are using the 3-pin regs, let alone listening to them with a low-output pick-up.
A good power supply starts with soft/fast recovery rectifier diodes, which have a major influence on the sound of the amp. The best diodes we have found are the BYV-type diodes for low-power applications, the 8A HFA-type HEXFRED diodes from International Rectifier for medium power applications and the 25A HFA HEXFRED, and the 25/50A FRED diodes from Infineon, for high power applications. They reduce noise and improve the dynamics in your amp.
The next stage in the power supply is the filter cap. Electrolytics are usually specified with ESR (Equivalent Series Resistance). It is important to use caps with low ESR. For low and medium power applications we are using ELNA CERAFINE and Nichicon caps, which have been designed for high performance audio, or ROE/Frolyt caps, which have been designed for switch-mode power supplies. The Panasonic FC electrolytics are also very much used in this power range. The electrolytic caps show increasing impedance at high frequencies (usually above 10kHz), so it is a good practice to parallel the electrolytic with film caps. There are a number of good big electrolytic caps on the market for power amps. We prefer the RIFA, CDE, and the BHC/AEROVOX caps for the power amp. Use them as big as possible, preferably not less than 47000uF.
The final stage in the PS/reg chain is the regulator itself. Walt Jung has done a super work on the regs, which was published in the Audio Amateur 1/95, 2/95. These are “must read” for all who attempt to build their regs. Basically, our amplifier circuits are getting faster and faster, i.e. their frequency range extends to many hundred kHz. The impedance of the power supply/regs must be very low at these frequencies, to make sure that it does not adversely affect the operation, especially the feedback of the amps. Additionally, they have to produce very low noise.
As I mentioned before the 317/337 type 3-pin regs are not up to the noise and bandwidth requirements of high performance audio. We are therefore recommending our off-board regulators, which are using wide-band opamps (AD797, AD743, etc) and MOSFETs as series elements. Extremely low noise and low output impedance are the important features of these regulators. They can be used for all low-level circuits (phono, line, DACs, crossover, etc.) in your amps.
When it comes to regulated supplies in power amps, I have never been able to prove that regulating the supply for the output stage really brings a sonic improvement. However, there is a clear indication that the driver circuits should use regulated supplies. Unfortunately the opamp-type regulators are limited in terms of voltage capability and you need to use a regulator with discrete semiconductors. The very minimum you should use is a MOSFET follower with a zener-reference. (These types of regulators are also very useful as pre-regulators for the opamp-type ones.) The more elaborate types are “high-voltage opamps” designed with discrete components, and “integrated” with the driver circuit on the same PCB. We are using these in all our ALL-FET power amps.
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