[sdiy] 7815 / 7915, "vintage sound", and modern replacements

[cheater cheater]

(this email seems to have been eaten by gmail... so I have to type it
all out from memory)



INTRO / BACKGROUND

Hi all,

I'm looking further into my project to modify rack devices to run on
DC rather than AC. Looks like most of them use a 7815/7915 combo with
a full-wave rectifier. Pretty much like the first circuit here:

https://www.eleccircuit.com/power-supply-regulator-15v-15v-1a-by-ic-7815-7915/



So the idea is to put a 4P2T switch (V, -V, phantom, 0V) or some
jumpers, right after the rectifier but before the regulators, in order
to either power the regulators from the internal power supply, or from
the remote DC supply. I would feed DC in, and let the rack unit do its
final volt or so regulation itself, to prevent sag and voltage rail
based crosstalk from other rack devices (10-20 units) that live on the
same DC distribution bus.

It seems like most of those racks are below the 10W mark, meaning at
30V, we're talking about less than 0.5A being delivered by the
regulators total.



VOLTAGE REGULATOR QUESTIONS

I've had a couple questions:

1. What is the best DC voltage to run to the 7815 / 7915 so they
create the least dissipation, have the best regulation, and produce
the least noise?

2. Are there any better modern replacement linear regulators for
audio? (I'm assuming linear regulators are still what's recommended)
Something with considerably better noise and regulation performance,
no more than say $5 a pop, though that's not a fixed price. I'll be
happy with something that's cents too if that's the go-to part. I
don't need an exact pin for pin replacement, but being able to use
something that doesn't require a massive amount of modification to the
existing circuit would be nice. Although I might just bypass the
existing internal power supplies completely, and build new ones, so
feel free to suggest anything. Noise performance and ripple rejection
are the most important thing here. I'm specifically not looking for
any sort of "vintage sound".


I would appreciate any info on the questions above. Thanks.



P.S. "VINTAGE" SOUND

I've also noticed something interesting when looking at 7815
datasheets. Specifically the output impedance, which I found plotted
in an older datasheet, on page 6 in the top left corner here:

https://www.alldatasheet.com/datasheet-pdf/view/9046/NSC/7815.html

The output impedance goes from 0.008 Ohm at 1 kHz to 0.03-0.04 Ohm at
20 kHz, even if bypassed with 1uF tantalum caps as the plot indicates.

It's common to find that older synths sound darker and modern ones
sound very bright (meaning older synths have lowered high frequency
reproduction). I wonder if between this nature of the most popular
linear regulators, and caps that were never good enough to bypass
those frequencies when they were new (let alone after decades), that
could explain some of that. Simply power supply sag in the higher
registers, creating a compounding loss of gain. What do you guys
think? I assume earlier voltage regulators were even worse than that
plot.