Amplifier with no speakers making sound

[Max Headroom]

The Sound Of Aluminium....

Some heatsink fins ring/sing along with the audio even when no speaker or load connected.....gets louder with dummy load resistor connected.
Some amplifiers have rubber bungs between the fins to keep them quiet....motorcycle cylinder heads and barrels do likewise.

Dan.

 

[JMFahey]

I've never heard of Transistors "singing" due to the piezo effect. I'm not saying that speculation is wrong, I'd have thought it was something a bit bigger than a tiny silicon chip making the noise.

It's tiny but still big enough.
You won't hear chest thumping bass , of course , not even mids, but something comparable to what an unmounted piezo disk does on its own.
The piezo in your wristwatch is not much larger , say 10/15mm diameter compared to a 2N3055 class chip: 3.5 x 3.5mm or so.
And larger transistors (MJ15003/MJL21194/2N3773) have roughly 6 x 6 mm chips.

 

[PetruV]

This is so intresting,but i cant test myself since i only have gainclone amps,but im building a solid state amp so i will try it out

 

[Miles Prower]

Ok heres the deal. When i turn of the speakers in both my Luxman l30 and new Marantz pm5004, and when i turn it up real loud (full way) while music is still playing through it i can actually hear the music from inside the amplifier. why is this?
Thanks in advance for your input

There are a couple of possibilities. One is magnetostriction in the core of an OPT. With light loads (or no load: dangerous!) the core will change dimensions under the influence of core magnetization, producing sound. Even with the full load (e.g. 8R resistor) you can find some frequency where the core will "sing" at its natural resonant frequency. (Usually ~1000Hz). Sometimes, this can also be caused by turns that are too loose in an inductor or xfmr.

You also see this with Royer oscillators, as these depend on core saturation to set their frequency. Core type doesn't matter: ferrite or stacked steel lamms, these can be damned noisy.

Another possibility is piezoelectric effects from capacitor dielectrics. Some dielectrics, especially the high permittivity dielectrics that make for big capacitances in small packages are, more or less, piezoelectric.

 

[jcx]

old metal can TO-3 transistors could "oil can" due to thermal stress - from differing TCE of the materials - not strictly speaking piezoelectric - can happen at audio frequency - a cause of fatigue failure in the chip bond to the case

cap's electrodes can also move with the forces from changing electric field - would give 2nd harmonic if not polarized - with a bias V you can get fundamental too - famous in mylar rolled film caps in ancient 'scope switching supplies running at audible frequency

 

[Korrah]

I have the same issue with a tube amplifier, my Stax SRM-T1. The tubes really "sing" quite a bit when I turn up the volume, now I'm just wondering whether its supposed to do this or do I have an actual problem. The amp itself sounds fine.

The amp is DC coupled and its definitely the tubes which are vibrating.