#include <std_disclaimer.h>
#include <no_liability.h>
#include <your_millage_may_vary.h>
Amplifiers are current devices and they expect around an 8 ohm impedance
across their output terminals.
since V = IR 8 ohms is going to give a lot of current for a
particular voltage for even a small voltage across the load.
A multimeter, in measuring volts mode, is going to have an impedance of
40M ohms or more and this kind of load is going to draw almost no
current and therefore provide almost no voltage - it will look to the
amp like nothing is connected.
In current measuring mode the meter will have a very low impedance
<1ohm and this will draw too much current from the amp and blow
it/trigger the protection circuits. - you cant examine it this way. You
need to simulate a reasonable load and then measure that....
What you need is a dummy load or a pair of crappy speakers to test it out.
if you can get an 8ohm resistor of around 25+ watts and connect it to
the speaker terminals of the amp. Then you can simulate a very well
behaved speaker. Then connect the volt meter in parallel to the resistor
and put it in volts measuring mode.
Measure with the volume at minimum i.e. system noise should not be much
around 1mv or so
Beyond this its difficult to measure without a scope so that you can
"see the amp output"
You need a scope and a sine and square wave generator so you can "see"
what the amp is producing. (or a cd with known test signals or a pc
soundcard into the preamp and some software)
Either way you need a realistic 8 ohm load before you can do any
measurements.
Good luck
James
On 02/06/2010 21:13, Charles Geilfuss wrote:
> Given the vast experience of this group, I'm hoping one of you can answer
> a question for me. Sunday evening I was bike riding in my neighborhood.
> Since Monday is trash day people start putting things to the road for pick
> up. I noticed a pile of stereo gear at the curb and went to investigate.
> Picked up a Technics CD player and tape deck that work fine. There was also
> a Technics SE-A50 Amplifier in mint condition. It weighs as much as a Yugo
> but I managed to get it home. Alas, someone else had already taken the
> Preamp. This brings me to the question: when I power up the unit there is a
> brief pause then a click (seems normal so far). There are two small lights
> on the front; one for each channel. The left channel light glows but the
> right does not. If only the bulb is burned out then all is well and good.
> How could I simply test the unit to see if the right channel is working? Is
> it safe to put a multimeter across the speaker terminals on the back?
>
> Thanks,
> Charlie
>
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