How to get rid of transformer hum?

Cleaning up the sine wave certainly won't hurt anything, but oddly enough it may not help. Magnetostriction is related to volt/seconds. The transformer stores up energy during each half cycle. If you begin to push the storage capacity to its limit it begins to saturate and hum. Since you are stuck with 60 hz only the volts are available to change. It is the area under the curve and not the shape of the curve that counts for volt/seconds.

It would be interesting to know what your line voltage is. Use an RMS reading voltmeter if you can, rat shack sells them along with some nice speaker cable (opps getting off the subject :-) if you don't have one of those a regular volt meter will work OK. If the line voltage is high then the following option might help.

There are ferroresonant transformers you can buy for probably 3 to 5 hundred bucks that clean up the waveform and stabilize the voltage. They also provide tremendous surge protection. The problems are that they are (at least the ones I have seen) very noisy. This is because they deliberately run them in saturation. So, you would have to locate the transformer somewhere away from your listening area. They also waste alot of power. Something like a third of their rating. So it is best to disconnect them when not using your system.

A step down transformer would be cheaper. It can be an autoformer, since you are not looking for isolation. An autoformer has no secondary. This makes them smaller and therefore cheaper.

Try four or five more of those diode pairs. If they don't help you are not out much. Try the cheapest stuff first.

Steve

I have decaded 20A lines to each amp and voltage reads a solid 119 plus change on each one. Do you think any of the power conditioners will fix this problem? Do I put the second set of diodes across the first set? Thanks Tommy

Geeez, Tommy, it just doesn't make sense that they are humming at only 120 volts. If it weren't for the fact that both are doing the same thing I would think it was something mechanical.

I don't know much about the audiophile line conditioners. I did look up a couple of brands on the internect in response to a post someone had made. It said something like "No capacitors, no inductors, no transformers to interfer with the purity of the sound!". It cost 6 or 7 hundred dollars and they were advertising that there was nothing useful in the box?! The ferroresonant transformer I mentioned won't help because the line voltage is not too high.

The diodes are like little valves. One is pointed in each direction because AC needs to go both ways. It takes .6 volts to open the valve. ten pairs would give you a 6 volt drop. So, you just make some more pairs and put them in series with the one you have. They can be soldered to the one you have. They can go anywhere in either leg and will work the same, just not in parallel with each other. You could just temporalily cobble it all together with alligator leads to see if it helps before taking the time to do it right.

I'm not familiar with the amps. Is the manufacturer available for advice?

I have in the past used a vpi brick (currently on top of my Ls7 pre) and it brought the hum down a lot. It may not do what you want on a electical basis but it is the cheap fix you may be looking for.

A Shakti Stone electromagnetic stabilizer may be a useful fix for this application (at least one for each amp)