Two chip amps together make radio kind noise???

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I’m working on an active 2-way open baffle monitor style speaker. I'm using a Tang Band w3-871 3” fullrange driver from about 200Hz and up, and a GRS 10pf-8 10” woofer for bas. I’m using active filtering and two cheap stereo chip amps from ebay to power the speaker drivers. IMO the chip amps give amazing value for the money, as they sound good, with low noise floor and good overall performance and they are easy to use for only a few bucks. I am using a labtop power supply (20VDC) to power the amps, and some homemade active filters to do the x-over.
Here is the problem: When the two amps are on at the same time, they somehow interfere, which results in a fairly loud radio frequency kind of noise in the speaker drivers. It goes away as soon as I turn off just one of the amps! Bothe amps work fine individually, but as soon as they are turned on together, they become noisy!
Does anybody know what is going on, and if there is a solution to the problem? I have tried moving the one amp away from the other (about 20 cm) but with no change in result.

The amps I’m using are TPA3116D2 based amps:
For bas: DC 10V-25V TPA3116D2 HIFI Digital 2 Channel Stereo Amplifier Board Module 2x100W (8.50 USD)

For mid/treble: 2x50W TPA3116 D2 Subwoofer Stereo Audio Power Amplifier Board 100/200/240W Blue/Red (6 USD)


  • Bas modul.JPG
    Bas modul.JPG
    32.5 KB · Views: 118
  • fullrange modul.JPG
    fullrange modul.JPG
    38.6 KB · Views: 119
  • Rear.JPG
    195 KB · Views: 118
Basically the switching frequency on the output of one amp must not get into the input of the other, even at low levels, as the difference frequency between the two oscillators will get out to the speaker. The best approach is use a multichannel amp board with all oscillators synchronized, so no difference frequencies, failing that rigorous isolation/filtering and screening may help.
What you are getting is sum and difference frequencies of the two amps oscilators intermodulating to give audio frequencies.
Look up IRS2092 application notes and they have some good advice on reducing this.
Not sure what IC's your amp is using but IR give a good explanation.
The cure is make both osc same frequencies or so wildly different yo udfont get audio frequencies.
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.