Voltage regulation on F5 power supply?


2010-02-20 11:57 am
My experience with audio electronics has not extended to building audio power amplifiers. I would like to try building a relatively simple design, and the Nelson Pass F5 looks very appealing as a first effort. The designs of Mr. Pass enjoy the highest reputation and I hope to end up with an excellent-sounding amplifier.

I have one question about the design. The schematic for the power supply does not show any voltage regulation. Most, if not all, of the audio circuits with which I have worked have included regulation. I assume if voltage regulation was needed on the F5, Mr. Pass would have designed it in. I would appreciate it if someone could explain why it is not needed, and if it is likely that any improvements could be had with it.

Thanks to all who respond.
Most power amps will gain little in performance by adding a properly integrated regulated PSU.
If the cost of the regulation is taken from the amplifier assembly cost, one is almost guaranteed a lesser sound quality for the money expended.

If you are asking if you can add a regulated supply, then I'd suggest you are not skilled enough to troubleshoot the problems that the combined PSU+AMP will give in addition to the problems that a simple non regulated supply will bring.

Power amps don't need regulation.
Power amps supply line modulation can and does affect the quality of supply sent to other parts of the circuit. These other low current circuits can benefit from a low current regulated supply simply because their dedicated supply is cleaner.

The F5 does not have other circuits that could benefit.
The two stages of the F5 must be fed from the SAME PSU.
In general, AndrewT has given you excellent advice.
The F5 is relatively insensitive to power supplies. There are other Power amps that can benifit more from regulation.

In the PassDIY site, there is a paper on power supplies.
Pass Labs: Technical articles Title "Power Supplies" 2001

Also, I know that 2 of the Zen power amplifiers were regulated.
If I recall correctly, the Zen 5 was one of the two.
The Zen series of designs is an excellent tutorial on Class A power amp design and would be well worth your time to read.




2010-02-20 11:57 am
Thanks to AndrewT and DougL for your comments.

If I build the F5, my preference would be to build it without a regulated supply for the sake of simplicity and convenience. My question was concerned more with the why and the wherefore of regulation or non-regulation as applied to the F5 circuit. It seems to me that with the complex load of a loudspeaker the circuit could benefit from a regulated PSU, but again I am approaching the subject from an inexperienced point of view, so I welcome explanations to the contrary.

I have visited the Pass websites and have found much of interest there, including the power supply article. Mr Pass is both informative and amusing, a winning combination.