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Copied in below is Ed's excellent message 76038 about the 22xx singing power supply problem from 2012.
tom jobe...


Ed Breya
Apr 29, 2012
It depends on the perception level. If a "piercing whine" means it's unbearable to be near it, then there is probably a circuit failure such as the cracked core problem or other components. If it's a "perceptible" or irritating whistling - like the sound of the horizontal frequency of the old TV sets - it's then a matter of degree, and it depends on the hearing response of the listener.

This "singing power supply problem" (that was the official name) arose just as the 2230 was going into production. I investigated it and found that the true cause is the beat between the running frequencies (and harmonics) of the pre-regulator and the chopper stages, which are asynchronous and highly variable with line voltage, load, and temperature.

The main "speaker" is the pre-regulator power choke - the pot core, which emits from the surface but mostly from the center hole in the core. I used the old mechanic's trick of poking around the circuit with a plastic tube held to the ear - you can do the same for locating specific noise sources.

It turned out that this was an inherent characteristic of the 2200 series power supply topology, but the 2230, which used basically the same stuff, aggravated the tendency because it took a lot more power. Of course, it never happened during the entire design project, but in production the true variability of components, and the huge number of units ramping up started to expose the problem.

The best solution technically would have been to modify the design to synchronize the sections, but the simplest and most expedient was to minimize the transducer efficiency by plugging the pot core hole with silicone goop, and on the occasional one that was still too loud (I think one of the line workers with good hearing was assigned to judge them), to change the transformer or "factory select" one of the oscillator timing parts to move the frequency a bit. I think that later that became the norm for all of the 2200 series.

So, if you have a 2200 scope that "sings," you can look at the pot core and see if the hole is plugged. If not, you can likely quiet it down a bit by filling it with electrical grade silicone goop or almost any kind of inert, nonflammable material. Do not use anything magnetic or conductive - it is a gapped core with an intense magnetic field in the center that will burn the material or possibly upset or damage the circuit.

Ed