Possibly Dumb Question re:Battery as a power supply

millercarbon: Never misunderestimate the ability of the forum to overthink even the simplest things. Full disclosure: I converted AC to DC battery, did none of that, and it was audibly quite a bit better. Just not that hard. Unless you make it so.

Truer words were never written. If the Clearaudio table uses a DC motor, it is not driven directly from the wall wart power supply. At 33 RPM, it is most likely driven by 3-4VDC and from an internal controller which not only regulates the voltage but has active current feedback (negative output impedance) to compensate for the motor’s negative-slope torque/speed curve, without which, the motor will slow under load.

Regulating an AC-to-DC supply is done to remove any AC ripple from the output. The turntable should work just fine from an unregulated battery supply as there will be no AC ripple present. Regulating a battery supply in this case would do nothing other than complicate the application and waste heat and power. The rest of this discussion is just noise.

FYI, MC7812 regulators have a dropout voltage between 2.1 and 2.4V, depending on the device, so you would need 14.4VDC or greater for proper regulation. LDO regulators (Low Drop Out) exist with dropout voltages as low as 200-300mV, but they can become unstable and oscillate without careful layout and compensation.

Advice to the OP: As millercarbon alluded to, don’t over think it.

Thank you, @imhififan  for new information. This shows that a 12V battery should be fine. Still, I would never recommend connecting an expensive component to an unfused battery. And while doing that, why not protect the battery too? I mean, diodes don't cost much.

But then again, I wouldn't want to be accused of overthinking the OP's investment.

Phoenix, from the MC7812 data sheet:
ELECTRICAL CHARACTERISTICS (Vin = 19 V, IO = 500 mA, TJ = Tlow to 125°C (Note 17), unless otherwise noted)

One last thing: different battery technologies have different noise levels. It's probably not an issue; but if that Clearaudio pack uses NiCds, maybe it's for a reason, and $1200 for NiCds is not excessive.

@lubachl 
I actually have an Amazon Model One - it's a superb motor unit - I think that is a great buy because the Amazon motor is actually not your usual DC motor - I think the UK importer at the time advised me it was from a nautical clock. It is exceptionally smooth and quiet.
@kingharold - why more people don't rug up a car battery is beyond me - they can easily be tucked away. Lithium Ion is particularly good as the voltage drop is very consistent. Be careful though not to discharge them too much as they become unstable and in fact volatile. I know all of this from Radio Control car racing. Not all lithium ions are created equally and I am more than happy to recommend those used in RC racing that are of a good quality. 

@terry9-

ELECTRICAL CHARACTERISTICS (Vin = 19 V, IO = 500 mA, TJ = Tlow to 125°C (Note 17), unless otherwise noted)

That is the standard disclaimer at the top of the chart of parameters. It is the operating point used in all of the measurements below it. One of those parameters is DROP OUT VOLTAGE which was listed as 2.0VDC (assuming 500mA load) on the datasheet I found on-line. The disclaimer does not mean the device has to be operated at those parameters, only that the published specifications were measured at that operating point.

Agree with your point about noise not being an issue. I don’t know that I’ve ever seen a measurement for this on a battery, but the internal resistance of a fully charged battery is extremely low so the equivalent noise resistance should be microscopic.

I would think a Sealed Lead Acid battery would be better (and cheaper) than a NiCad. SLAs tend to last longer and don’t suffer from memory effect if they are not fully cycled between charge and discharge as NiCads do. YMMV.

Phoenix, agree with what you say, but let me add that 19VDC is the voltage at which the part is known to meet spec. With obvious consequences - which, to an engineer such as yourself, pose no issues.

Battery noise was measured by someone in Germany some years back. I think they were looking at powering phono stages. He found that all technologies made a fair bit of noise, except NiCd, which measured at the noise floor of his HP instrumentation.

Anyway, I'm in the process of designing a new phono power supply based on NiCd's for listening and a linear PS for warming, and the unexpected issue is charging. Seems that no-one does it right - i.e. warning at 1.1VDC per cell to avoid memory effect and separate current source for each cell.

Expect to start building in a couple of weeks, will let you know if it makes a perceptible improvement over alkaline with LC filter.