DC power through Var. AC Xformer -> Wart

[ArtemisGoldfish]

The title is sort of vague, so I'll specify: Will a wall wart still produce a stable, usable voltage if it's plugged into a variable AC transformer? I've noticed that if I put 60VAC into the wart, it outputs half of it's rated voltage output. Is this power source still relatively clean?

And another question, if anyone can help me with this one: What is a practical purpose of using a Buffer chip? Is it merely useful as a replacement to a row of diodes in certain computer applications? (A ZX81 I assembled used a row of diodes in series with the keyboard connection.)

Thanks muchly, everyone!

 

[Sceadwian]

Buffers are basically seperators from high impedance signals to low impedance ones. A good opamp circuit can eliminate any loading effects on the sampled signal used as a drive, they can also easily filter.
Yes the power source is still relativly clean so long as the supplied waveform is still a sine wave. If your variable AC transformer is something like an auto transformer, you're fine.

 

[ArtemisGoldfish]

Buffers are basically seperators from high impedance signals to low impedance ones. A good opamp circuit can eliminate any loading effects on the sampled signal used as a drive, they can also easily filter.
Yes the power source is still relativly clean so long as the supplied waveform is still a sine wave. If your variable AC transformer is something like an auto transformer, you're fine.

Well, if it helps any, it looks like a Superior Electric Co. PowerStat, and I can feel it buzzing when I turn it on. It's kind of old, since the plug on it is ungrounded.

 

[Sceadwian]

Sounds like something every hobbyist should have, I've seen a few but they're all a bit expensive. Do keep in mind though that you're introducing high frequency noise (in relation to the normal 50-60hz mains frequency) from the contact bounce when you adjust it so you may get odd happenings on any circuit you have plugged into it if you don't add some bypass capacitors to bleed off the noise, wallwarts were meant to filter 50-60hz ripple. You could always check the output on a scope and see what the noise really was, but it shouldn't be too big of an issue.