Amplifier with no speakers making sound

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Quite interesting. What could be acting as transducer?
The output coil even though almost unloaded? (...except for the...)
The headphone-output voltage-divider?
The FL display picking up power supply 'noise'?

In my car the cabin airflow fan act as a speaker and 'plays' out the ignition-noise of the engine.
 

Mooly

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2007-09-15 8:14 am
Lorentz forces (i.e. normal electric motor action), magnetostriction, piezoelectricity - all methods by which electrical activity can produce sound.

If there is no output load then currents will be low so my guess is piezoelectricity.

Maybe. Its an effect I noted when I first started playing around with amps and semiconductors. A pair of T03 devices can be surprisingly loud.
 
Maybe. Its an effect I noted when I first started playing around with amps and semiconductors. A pair of T03 devices can be surprisingly loud.

I first noticed it on a high-voltage amp with bipolar transistors in the input stage and PL519 valves in the output stage. The PL519s seemed to produce the sound. I didn't dare to put my ear close to the PL519s, that was a bit too dangerous with 1100 V anode bias voltage.
 

Mooly

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Paid Member
2007-09-15 8:14 am
I first noticed it on a high-voltage amp with bipolar transistors in the input stage and PL519 valves in the output stage. The PL519s seemed to produce the sound. I didn't dare to put my ear close to the PL519s, that was a bit too dangerous with 1100 V anode bias voltage.

I remember those as TV line output valves :D You could draw quite an arc from the top cap of those with a (well insulated) screwdriver.
 
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