Note that the peak power to a speaker is already 48W in that mode. ^ the right ch pot and lots of other right ch components are thus unnecessary, but I list minimum changes, not minimum components.ĮDIT: Given some more time to figure out some more numbers, I believe the 2x24W at 14.4V (to 4 ohm) is continous sine wave power, which is consistent with the voltage limit, thus you cant get more power from that voltage by bridging the outputs (you could drive a load with less ohms, but that is unnecessary for me). Or will it just blow itself up from some internal channel mismatch? (Pete-O? :P) do not populate C12^, and bridge left and right channel from JP13, and connect speaker to both left and right ch (connect OUT1 and OUT3 to one side and OUT2 and OUT4 to other). Hi, has anyone tested whether bridging the STA540 into a single channel configuration would work? Eg. I used a separate switching PSU for the 5V, it is very clean, but now I have to be smart about tying the grounds together for the "mute" feature. This one was a quick demo, but if it catches up I will need to improve and make it a real product.įyi, I've been using a switching PSU, salvaged from a PC, and it was OK for the amps (+12V) but not OK for the Linux boards (+5V). Looks great, and I am looking forward to reading more I'd like to stay in touch with you for future projects. I control the amps with Linux boards and I use a GPIO from the CPU to control the amps mute Idle noise is suppressed using the "mute" signal. It is fed at a constant rate from the power supply through a L, containing the current spikes within each board The idea is that the large cap (15mF) near each amplifier board provides for the current spikes. I experimented with LC filters and found a good one. It seems that our projects have some similarities.Ĭrosstalk was carried on the +12V wires, not the ground. Try one or two large (10,000uF 25V or 35V) caps across the power supply to see if that helps. However the SparkFun board does have a separate input op-amp that may be re-configurable as a differential amplifier.Īs far as the noise, the STA540 has about -50db of power supply rejection at 300Hz and higher frequencies so you may hear power supply noise on the output. It uses a clever internal configuration that may make this technique hard to implement. I don't yet know how to do this for the STA540. To see details, go to and search for "ground trick". My DIY house-wide audio system uses two LM3886 amplifiers for each room and uses this technique with good success. This only works if the sources (preamps) are fairly close to the amps. The solution I used is to isolate the input signal ground of each amplifier (input connector, input network, feedback return) from the output grounds (speaker and power supply returns) and connect them only at a single point, back at the audio sources. The brute force solution is to use differential inputs or transformers on each amplifier input. Typically if you use multiple amps operating from a single supply, the crosstalk is about -40 to -50dB, which you can hear in the quiet rooms. I have spice simulated both the cause of and a solution to this problem. This appears as input signal and gets multiplied by the amplifier gain (26dB) and so, crosstalk. Whenever you use multiple amplifiers from a single power supply, each amplifier's large ground return current causes a small audio voltage to appear on every other amplifier's input ground. :(Ĭrosstalk can be from a number of sources, but I suspect yours is from grounding. It's insanely loud, even driving 8ohm speakers from only a ~12-13V supply, I have to keep the volume knobs at about 1/4 in order not to feel like a bad neighbour (although I sometimes see the 'peak' light flicker for very brief moments, even at this level - but only so much that can be done with using a 12V supply to drive 8ohm speakers).įinally time to decommission my dad's old 1970s Kenwood. Other than the couple of small design issues, this amp is great and was really fun to build. would have been nice instead of an extra volume knob. Also added a pair of 0.1♟ mylar caps on the input lines to remove some of the excessive bass (since I live in an apartment). I added another 10000♟ (probably overkill) just before the power-in to the board (with a Schottky diode on the battery side) and now everything is running great. The onboard 1000♟ bypass capacitor on the power input is really totally insufficient for this amplifier to remain stable. I thought there was no way it could be due to a noisy power supply since I'm running it straight off of a car battery (charged by solar panels). I was having the same problem as everyone else: the ~5Hz thumping sound.
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