[Rashiki]

I bought two 5V 1.A linear power supplies to try out with my squeezeboxes -- one for experimenting and another as a backup in case I break the first one. The supplies came from Hosfelt, and these have been discussed on several other threads.

After cutting the old plug and soldering on a new one, I plugged in the supply and noticed a faint hum coming it. I also tried the unaltered supply and heard the exact same hum. The hum is coming directly from the power supply and it doesn't matter if my squeezebox is connected to it or not. Connecting it to my voltmeter shows a steady 5.03 volts.

Is this because I have noisy power in my home, or could both of the power supplied been damaged in shipping? I've read that having a small amount of DC on your AC line can cause transformers to hum. What else causes hum in a transformer?

Is there any way to tell if I have DC on my AC line? I'm sure I could measure it with an oscilloscope, but I don't have easy access to one. Are there any DIY ways to eliminate DC?

Thanks,
-Rob

[EDS_]

I bought two 5V 1.A linear power supplies to try out with my squeezeboxes -- one for experimenting and another as a backup in case I break the first one. The supplies came from Hosfelt, and these have been discussed on several other threads.

After cutting the old plug and soldering on a new one, I plugged in the supply and noticed a faint hum coming it. I also tried the unaltered supply and heard the exact same hum. The hum is coming directly from the power supply and it doesn't matter if my squeezebox i ...

Sounds like DC offset may be the culprit. Do you have a plasma TV?

[ctviggen]

you should be able to put your multimeter into an AC outlet, set the multimeter for DC, and measure DC.  If it's zero, there shouldn't be DC.

[Dan Banquer]

If it is DC or a low freqency oscillation on the AC line than the only effective way that I know of is to encase the transformer in potting compound which will help absorb the mechanical vibrations.  For those folks who may be using Toroids, Plitron transformers come with a potted center which is helpful in reducing the mechanical hum.
        Are we having fun yet?
                      d.b.

[gpkoo]

Hi

I've noticed a bit of transformer hum as well from my Almarro A318B amplifier, which I assume is DC related. Is encasing the transformers in potting compound the only way to go? Sounds messy!

But the other thing I've noticed, espcially at night, when I put my ear to my speakers with no signal from the source, is the faint sound of a radio station. I assume that's RF, but what's picking it up? Where is it coming from and what can I do about it?

Thanks

Gary

[Karsten]

Adding a 2 microfarad (approx) mylar or polypropylene capasitor over the phase-null input mains wire (hot and neutral wire, leave the ground alone) may help to elliminate hum from the transformer. This will alter the power correction factor.

Disclamer: Cap should be adequately rated for the AC line voltage involved and don't kill yourself with a stupid approach to this

Karsten