[DavidMahler]

Can some transformers rattle slightly when they sing.  I've been noticing on my 307a that the transformers present a slight rattle at times.  It's not always apparent, but it's there about 50% of the time.  I did a little iPhone recording to demonstrate the rattle I am referring to.  This rattle I'm referring to is the very slight tambourine-like sound heard throughout this recording.  If this is something which some transformers do, would you please mind telling me what it is a result of.  If you consider yourself an expert in this are and have never run into this sound before please let me know.
 
This is an MP3 which I am referring to:
http://www.megaupload.com/?d=NI3X5WPA
 
The music itself is coming from a K1000, while the rattle is coming from the transformers.  The transformers were recorded from roughly 2 feet away.  Sorry the recording is so low in volume.
 
 
Thanks very much!
 
-Dave
 

 

[Kingrat]

correct me if im wrong, if it is the bobbin i wouldnt worry but it sounds to me kind of like the windings are vibrating against themselves? if so i would imagine that could be bad and could lead to them wearing through the enamel and shorting together...is it an EI lamination transformer? does it have an air gap? it could be coming from the laminations/air gap too which is no big deal just annoying, if it was mine i would give the SOB another dunk in some varnish and put it under vacuum

 

[DavidMahler]

Quote:

correct me if im wrong, if it is the bobbin i wouldnt worry but it sounds to me kind of like the windings are vibrating against themselves? if so i would imagine that could be bad and could lead to them wearing through the enamel and shorting together...is it an EI lamination transformer? does it have an air gap? it could be coming from the laminations/air gap too which is no big deal just annoying, if it was mine i would give the SOB another dunk in some varnish and put it under vacuum

This is helpful!
 
Any second opinions?

 

[nikongod]

I cant download the file  
 
Before the rest of this about audio transformers I should ask:
Are you sure it was the audio transformer? Many things on the power line can cause the mains transformer to make noise (for much the same reasons as audio transformers) at random times which is not as significant of a problem, and the fact that this changes from day to day dosnt tell you anything about the amp.
 
Anyways:
It is not uncommon of for gapped EI transformers to sing along with the music. I would say its pretty common, but very few people notice it above the din of their speakers
 
When you hear it, its normally ~3Khz and up. No bass, ever. VERY little mids - about the same as you get from playing just a crossed over tweeter.
 
What causes it:
It is caused by magnetic forces moving in and out of the iron bits of the transformer. The magnetic forces actually squeeze and stretch the iron and this microscopic motion results in sound. In extreme cases where something is loose it gets worse. The fact that the transformers sing along with the music is not an indicator of quality, or lack of quality as the case may be - very nice transformers can sing along. If you are sure its coming from the audio transformer, and it suddenly changes I would be worried. 
 
Regarding mains transformers:
Mains transformers can also make noises when certain problems are present on the power line. Any DC on the power line is known for causing this. One day the amp is dead quiet, the next it makes an audible humming sound coming directly from the amp but the speakers/headphones are still quiet, and the day after that all is right with the world again. Its very frustrating. Be happy that the 307A has an EI mains transformer - Toroidal transformers dont play nice with DC. If the noise is coming from the power transformer, and it goes away eventually, dont worry.