Hi folks!
Sorry for intruding! Just registered on the forum to ask a potentially strange question.
I was turning on my vintage Aiwa 3070 Cassette Receiver not noticing that the speaker is disconnected and speaker wires are lying on the ground shorted. (I normally listen in mono, single speaker connected).
After turning it on in FM mode, as I increased the volume, I could very faintly hear distorted music playing from the wires (?!) and could make out some lyrics before noticing that the speaker is not even connected. I listened for a few seconds and carefully separated the shorted wires, the faint distorted music stopped.
To be honest, I only assume so and I'm not certain that the sound was coming from the wires and not from inside of the receiver or..?
I don't want to repeat the experiment on purpose. Nothing burned and the receiver is still working fine.
That got me curious. Could someone please explain what might have happened, and why the audio was (barely) playing from the wire without any speaker connected? How is that possible?
Many thanks!
Sorry for intruding! Just registered on the forum to ask a potentially strange question.
I was turning on my vintage Aiwa 3070 Cassette Receiver not noticing that the speaker is disconnected and speaker wires are lying on the ground shorted. (I normally listen in mono, single speaker connected).
After turning it on in FM mode, as I increased the volume, I could very faintly hear distorted music playing from the wires (?!) and could make out some lyrics before noticing that the speaker is not even connected. I listened for a few seconds and carefully separated the shorted wires, the faint distorted music stopped.
To be honest, I only assume so and I'm not certain that the sound was coming from the wires and not from inside of the receiver or..?
I don't want to repeat the experiment on purpose. Nothing burned and the receiver is still working fine.
That got me curious. Could someone please explain what might have happened, and why the audio was (barely) playing from the wire without any speaker connected? How is that possible?
Many thanks!
You'll perhaps get many different answers on this but it is a fact that transistors themselves can make audible noise when operating under the conditions you describe. Also 'wound' components such as coils do the same. I've experienced this many times in years gone by when building/testing and abusing circuitry.
Definitely do not repeat the experiment though. You were lucky and no harm was done.
Definitely do not repeat the experiment though. You were lucky and no harm was done.
There is a way of safely doing the same experiment.
Wire a dummy load equal to the lowest speaker impedance for the amplifier using two lengths of hook up wire.
Run the wires across a thin steel sheet with a wide spacing and turn the amp up.
You will be able to vary the sound a bit by resting your fingers on the steel sheet.
If you look in the amp it is likely that the internal wires run close to a steel part of the chassis.
It is how very old moving iron speakers used to work.
Wire a dummy load equal to the lowest speaker impedance for the amplifier using two lengths of hook up wire.
Run the wires across a thin steel sheet with a wide spacing and turn the amp up.
You will be able to vary the sound a bit by resting your fingers on the steel sheet.
If you look in the amp it is likely that the internal wires run close to a steel part of the chassis.
It is how very old moving iron speakers used to work.
The wire IS a (1 turn) voice coil.
If it´s near a strong magnetic field it may vibrate somewhat producing very faint sound.
Both wires need to be spread apart, of course, if still parallel 1 mm away from each other that coil internal surface amounts to practically zero, and own magnetic fields cancel.
That IF sound actually comes from wire; as mentioned above there are other amp parts which can "sing", happened to me all the time from TO3 metallic case transistors and of course, from transformers.
I was testing some amp connected to a load resistor and customers asked : "hey!!! where´s that sound coming from? 😉 "
First case was from some kind of Piezo effect, second from Magnetostriction..
If it´s near a strong magnetic field it may vibrate somewhat producing very faint sound.
Both wires need to be spread apart, of course, if still parallel 1 mm away from each other that coil internal surface amounts to practically zero, and own magnetic fields cancel.
That IF sound actually comes from wire; as mentioned above there are other amp parts which can "sing", happened to me all the time from TO3 metallic case transistors and of course, from transformers.
I was testing some amp connected to a load resistor and customers asked : "hey!!! where´s that sound coming from? 😉 "
First case was from some kind of Piezo effect, second from Magnetostriction..
When I rebuilt my HK Cit II and adjusted the AC ballance control I used a 1KHZ sinewave input instead of the 60Hz signal supplied.
I used a 15 ohm (measured) toaster as a 16 ohm load and you could clearly hear that the sound was comming from the amplifier,
and not the toaster or the wires.
But that is a tube amp.
I used a 15 ohm (measured) toaster as a 16 ohm load and you could clearly hear that the sound was comming from the amplifier,
and not the toaster or the wires.
But that is a tube amp.
Thank you all for responses. Very interesting fenomenon and the first time I learn about this! I'll explore this more with a dummy load to see what comes out.
I don't think it's the wire indeed as it wasn't close to anything that could have a substantial enough magnetic field.
I don't think it's the wire indeed as it wasn't close to anything that could have a substantial enough magnetic field.
The 1 turn coil could very well have been making noise. So could any number of components inside the amplifier. The most likely suspect is the capacitor in the zobel network. Ceramic types are piezoelectric, and film types microphonic. When the short circuit protection activates in the amp, it produces a lot of spikes and harmonic content - making the cap sing. Clipping an amp with no load produces the same sound from the cap for the same reason.
Large Toroidal transformers can get LOUD when the amp is under heavy load too. But it’s a buzz that goes up and down with the music, and other than that does not resemble the music like the capacitor currents can.
Large Toroidal transformers can get LOUD when the amp is under heavy load too. But it’s a buzz that goes up and down with the music, and other than that does not resemble the music like the capacitor currents can.