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Originally posted by tangent
If the battery voltage sags 3V when you start to pull power from them, they're probably about to die, or you're pulling way too much current from them.
Batteries drop in voltage over time, so it's perfectly reasonable that your batteries happen to be at 15V at the moment, not that they jump back to 18V when the power is removed. Alkaline batteries are useful down to about 0.9V per cell; there are 6 cells in a 9V battery, so around 5V. |
All I know is where the trace is on my oscilloscope, which was given to me a couple weeks ago.
I might have screwed up something before, so I'll do it again right now.
First I measure it up there at 18V (actually, closer to 19V now as I check it again). When I put them into the amp, it's down to... okay, now 16.5V. I switched scales to get the 16.5 reading though, so maybe that affected the accuracy.
If I check both on the bigger scale, it looks like it's going from 18V down to 17V. OK, so maybe switching scales wasn't a good idea.
So it looks like they drop by about 1V when being powered by the amp. And then if I rotate the volume control up, there is another dip in voltage when I pass a certain point. That make sense?
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Regarding your Radio Shack power supply, it will either be an unregulated supply or a switching-regulated supply. Neither is ideal for audio; you may get some additional noise with the supply relative to batteries.
Make sure you didn't get an AC-AC supply! I seem to recall that there is a 15VAC output unit at Radio Shack. |
Definitely not an AC-AC supply.
There was actually an 18V of that kind there. Here's what is on the box is "Output: Regulated 15VDC, 1000mA" So what sort of supply would you suggest for me? (yeah I could probably find that in a quick search.. I'll do that now.
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EDIT: more information on the power supply -- if I hook it up to the o-scope, I have to pretty much go to the lowest scale to see any variation in voltage. (this is with no load ... or max load ... what is it called if the only circuit is through a huge resistance?) It looks like about a 300Hz (1cycle/0.003ms) fluctuation, with an amplitude of 1-2 mV. DC voltage was right on at 15V, though. I don't know if this matters to anyone, but I gathered the data, and I want to put it down somewhere.