[sdiy] 2 multimeters showing different voltages

[Scott]

I did check with a scope.  I have 2 psu's.. both power one, one 1amp and
one 3amp, and I did find a problem on the smaller of the two.  One of
its caps must be bad, as I get some oscillations on the negative rail.
(I don't hear it in my synth, tho.  I have had bad PSU's that gave a hum
in the synth) The other PSU looks to be fine.  Both gave the same
readings for voltage with both meters.  (one meter 15, the other 17.5)
My scope is very old and uncalibrated, so it's really only useful for
viewing the waveforms, and not for measuring anything.

I couldn't find a fresh battery anywhere in my house.  I'll go out later
and get a couple of 9v batteries to do another test, just to be sure.  

-----Original Message-----
From: JH. [mailto:jhaible at debitel.net] 
Sent: Tuesday, August 07, 2007 1:50 PM
To: Scott; synth-diy
Subject: Re: [sdiy] 2 multimeters showing different voltages

Have you checked with a scope?
My first guess is the regulator is oscillating, and the two meters react
to 
the HF in a different way.

JH.


----- Original Message ----- 
From: "Scott" <Scott at scottwick.com>
To: "synth-diy" <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, August 07, 2007 6:07 PM
Subject: [sdiy] 2 multimeters showing different voltages


I've got two multimeters, and each is showing a different voltage.  One
shows my synth to be at a solid 15 volts, and the other shows it at
17.5.

I tested my computer PSU to try to figure out which one is correct, and
I still don't know!  One shows the PSU 12v output at 11.05, and the
other shows it at 12.62.

Both meters are less than 3 years old, and have little use.  One is a
radio shack, the other is a Velleman.
I'm starting to think that the one that shows 17.5v (and 12.6 on the
computer PSU) is correct.  However, that would mean my synth PSU came
calibrated incorrectly.  (which is possible.. its just a used power-one
supply)
Does anyone know how I can figure out which to trust?

Also, how much of a difference would those 2 volts make?  If my synth
PSU is putting out +/- 17.5v, would that explain some tuning issues I've
been having?

thanks!

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