Quote:
Originally Posted by Pete240885
I studied amplifier design in the seccond and third years of my degree, this does not agree what i've been taught.
If the power is not being fed to the speaker then it is being dissapated inside your amp, therefore an impedance missmatch, be it too high or too low, is bad.
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This seems to be a bit of a grey area. This is my understanfing:
Amp type and Class bias are effected slightly differently by load mismatch.
In a Class A biased amplifier mismatched load does not cause power dissapation problems.
Power dissipation is maximum in Class A when the amp is idling. A change in load simply rotates the load line either way and does not cause additional power dissipation. With a signal applied a lower load (assuming it's not a large mismatch) will not cause any problems but may noticably affect the frequency resposne. A higher load may cause higher than expected signal voltage peaks which, if above the limits of the valve/transistor or OT (if present), could cause problems. Power delivered to the load will be reduced.
In Class AB a load mismatch is more serious. A lower load is never a good idea in Class AB as you will most likely cause excessive power dissipation in both the valves/transistors and OT (if present). It effectivley rotates the load line right above the max dissipation level. A higher load may also cause problems with excessive signal voltage peaks.
However most good amps are desined with valves/transistors and OTs (if present) that are rated well above the max voltages expected and a higher load (again within reason) can usually be tolerated but will cause reduced power and changed frequency response.
In short, a higher load is ok but not ideal in both Class A and AB.
A lower load is ok with Class A but definitley not in Class AB and solid state amps are designed to drive multiple different loads ( 4, 8 or 16ohm) but will put out maximum power to a certain specified load.
This is based on my reading so far from sites like The Valve Wizrd, Electronic Circuit Theory text books, RCA manuals and a Designing Solid State Amplifiers pdf book that I downloaded.
However I may have interpereted some of this info incorrectly, does anyone have a definitive answer on this?