Transformer humming

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I realised that my active crossover transformer is humming physically. I can feel the minute vibration on the chassis and is faintly audible.

Done few reads including the one here:, but would be keen to know if anyone has had similiar experience and what can be done to rectify this.

It is a simple E Transformer 15-0-15 150mA with a rectifier and 1000uF capacitors and is used to suppy 6 TL072 op-amps. It's running rather warm so I'm also wondering whether it's under rated for the load.
It should have enough current capacity to run those op-amps no problem but it might be worth checking with an ammeter exactly how much is being used in case there is a fault somewhere or the op-amps are being excessively loaded.

Smaller transformers are often poorly made and loose windings may be the culprit here. With the higher magnetic flux of E-core transformers is it possible the radiation is making panels vibrate, amplifying the buzz? Check all panels are highly secure.
These tiny (4.5VA) EI transformers are very inefficient.
The cheap ones always run hot due to the wasted power they consume.
The max continuous DC current from this transformer is 75mA and it will run very hot at that.
It will run cooler at 30 to 40mAdc but due to the poor efficiency it will never run cool nor warm.
Just had a silly thought, Are you using 7815 regulators?
Not too sure exactely how the 7815's work internaly but:

The 7815 has a maximum input of 23V, if you are using a 15V transformer then the regulator is getting 21.2V (getting close to limits), so it is dropping 6.2V. Is it possible that this voltage drop is causing the 7815 to draw more current? thus putting your transformer under unexpected load?

The reason I wondered this was because I read your other thread about the active XO's and realised you are running an almost identical XO to myself (only without the hum). From what I can tell the only difference is that I am running the 12-0-12 transformer which supplies the regulator with 17V (16.9V). Even though the regulator requires 17.7V to regulate properly, the load is not demanding enough that it is quite happy at 17V.

Hope this helps.
Sorry for late reply as I was hunting yet another hum on my quad channel gainclone ... not transformer but rather 'normal' hum :mad: strange when I put only the first pair all are quiet, but when the second pair is connected the hum appears. It's also not the "hmmmm" hum but a rather "rattly" hum. I wonder whether using separate rectifiers for the second pair would help (currently the rail voltage is simply taken from the 1st pair)

Back to the topic, my active crossover does not use regulators. It's simply smoothen by a pair of caps and is about 18 on the rail. I feed these to the opamps with no problems.

I tend to agree now that it is down to the quality/capacity of the transformer. I shall try to get a much bigger one let's say 3A ones with 12-0-12 volts as suggested.

I hate hums :smash: ... especially on a dead-quiet night like tonight :whazzat:
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