Digital Amplifier Questions

Thanks for the info Bombaywalla and Kijanki.

I tried the test again using the AM radio. I couldn't even find an AM station that was tunable. There was too much buzzing on the whole range. I'm thinking this is caused by RF leakage from my 3 class D amps, all located within a 5ftx 2ft area.

I plugged the radio into an outlet in my adjacent dining room (less than 20ft away) and the buzzing (hash?) went away and I was able to tune in a station in the low AM band.

I then moved the radio as close to my amp rack as the cord would allow (about 10ft away) and there was no interference; the station continued to be clearly audible without hash/buzzing. I was thinking the interference would increase as I moved the radio closer to my amp rack (from about 20 feet to about 10 feet way) but it did not.

These somewhat mixed results have me a bit confounded. I think further testing is called for, perhaps with a better AM radio, before conclusions are drawn. My current thought is that at least one of my amps is producing RF interference but I don't know for certain at this point.

I'm going to get a better AM radio, plug it in in my dining room using a 20ft extension chord, tune in a station on the lower AM band and retest by walking toward my amp rack in the adjoining living room. I'll post again with results.

If anyone has a better idea, please let me know.

Thanks,
Tim

Hi Tim,

If you are going to get another AM radio, consider purchasing a portable one that is battery powered. Also, the test will be most sensitive if you tune to a frequency at which no station is present. If a station is present the radio's AGC (automatic gain control) circuit will reduce its sensitivity, especially if the station's signal is strong.

Best regards,
-- Al

Hi Tim, I recommend that you repeat test walking around with the radio as follows....

Amp 1 on, 2 and 3 off;
Amp 1 off, 2 on, 3 off;
Amp 1 and 2 off, 3 on;
Amp 1 and 2 on, 3 off;
Amp 1 on, 2 off, 3 on;
All three amps on.

G.

Guido and Al,

Both good ideas; I'll get a battery powered portable radio (I've been needing to buy a new hair dryer, anyways) and set the dial to a low frequency on the AM band that lacks a strong station signal. Next I'll test with the various amps on/off according to the permutations Guido listed.

This amateur RF interference technician will report back on results soon.

Thanks,
Tim

Tim, if you use a battery powered radio, and you find that one of the amps seems to leak, try sliding the radio along/around the amp case, and then along the power cord, the speaker wires, and the input ICs.... There is no telling from where the leak might originate... It might even come from a totally different device... Make no assumptions, as reasonable as they might seem.

G.