Ticking Transformer
 

Hi there - I have been building a simple LM3875 based kit using an old EI transformer. The transformer has varios output points including three I am using for 24-0-24 output. When I wired it up to the rectifier board I got a decent 33.7 v output and everything seemed perfect.

However, I've added the two channels to the mix and soldered on the input sockets and now when I plug it in and switch on the transformer makes a ticking noise.

Can anyone tell me what this is? Is this the "hum" lots of other people have mentioned? Why didn't the transformer make this noise before?

Thanks for any tips.

Is this ticking noise more of what you would call a buzz?

Each "tick" is detectable and it's approx 120 bpm...

Moving the various bits and pieces around doesn't affect the sound.

Hmmm, odd. Could it be the xfmr rapidly heating and expanding?

Whether so or not, it may be best to sweep your circuit with your dmm. A long shot, sweep the circuit with a cro?

I had a transformer make the same noises. It was melting (too much current draw). Is it getting hot to the touch?

Eeerrk!
Not that I've noticed (I did try to see, but didn't want to leave it plugged in too long - no detectable heat for the 10 seconds or so I leave it on for).

As I said, it didn't make this sound before I wired up the actually amplifiers and the inputs. Is it worth me doing some tests with the ol multimeter?
Sorry - I'm fairly new - what sort of thing should I be checking? (and what do you mean by cro?).

Thanks for helping me out.

Um. I mean an Oscilloscope (cathode ray oscilloscope). I figured you would first check that the circuit is performing as expected with your dmm. The oscilloscope could help track down an oscillation which may cause a large current draw. These can be hard to detect in other ways.

I'm guessing that the transformer is saturating during the short current pulses to charge the caps. It's possible that your amp is oscillating and drawing a lot of current even without an input signal and the transformer is just not up to the task. How big is it?

The first time I read this as 120 bps (i.e. 120Hz.) I wondered how you could discerned 120 ticks per second... But, you really said something like 2 ticks per second. So can I change my guess? ;)

Ok, I don't have a real good guess. Might be picking up something external like a cell phone....

if u r using those 25A or 35A rectifier in a square can, that could be the problem. There seems to be alot of faulty ones everywhere in the market. I had them too...I remember the transformer giving out a buzz...think it was saturating!