Audio amplifer is voltage amplifier not current amplifier you don't need to
connect a load to measure the output voltage.
C.H.Ling
----- Original Message -----
From: "James King" <jking@xxxxxxxxxxxxxx>
> #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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