I'm not sure if I should have put an inductor or voltage regulator between the analog and digital portions of my circuit. I have a feeling it will solve my problem, since the noise does go away when you power the amp and Mighty from separate power sources.Īnyway, as I mentioned above, here is the layout of my main PCB:Īnd here is the full schematic of my board: This is what the ground loop isolator my friend is picking up today has inside it. A standard 600 ohm 1:1 transformer should do the job. You can get these from the major component distributors. Add an audio transformer between the line output of the Mighty and the amp.Which indicates to me that the noise may be generated by the LED driver chip itself, and I have no control over its speed. Now that you mention it though, I seem to recall in testing that the sound went away when I set the LEDs to a 100% duty cycle. The noise doesn't seem to be some kind of 60hz hum though. I am only sending an update 60 times a second though. I am already sending data to the LED modules at 8mhz, it's impossible to send the data any faster. Increase the PWM frequency you are using for the LEDs to more than 20KHz.I don't know if you consider that sufficient or not. These were what were recommended in TI's datasheet. You also need good decoupling of the power to the LEDs, to decrease the amplitude of the LED switching current in the ground side of the power input.Įach LED module has a 10uf and. I have included my schematic and layout below. Both the Line-Out and LED grounds are connected to the ground on the main power connection which then goes to the battery ground via a 5V regulator. And the Line-Out connection has a ground pin as well. The ribbon cable connector for the LED modules has a ground pin to get ground to the LEd modules. There's a power connector on the board for 5V and ground in. If the Mighty has 3 ground pins, then use one for the power in, one for the LED grounds or LED driver grounds, and one for the audio out. So rather than the data or clock causing the issue, it may be the current draw.īut you need to be make sure they don't share a common ground wire with the output signal or power supply. I've been told disconnecting the 8ft one, or the board attached to that module with most of the leds on it makes the noise go away. One is around 6in long, the other is around 8ft long. The LEDs are driven by a couple of TLC5947 LED drivers on individual modules which are chained to the main board using a couple of 6 conductor ribbon cables. You haven't said how the LEDs are connected The sound goes away if you disconnect the ribbon cable going to the LED modules. The buzzing is presumably the PWM signal to the LEDs. So I don't know what I should actually be doing here. And their schematic seems to show an op amp whereas my output is from a dac. So if I connect a 5-20 ohm resistor between the Mighty ground and the ground pin on my RCA output.īut looking at my own schematic again, the ground pin on the line out goes directly to device ground. It appears though that Rgbk is actually connected between the ground of the device and the ground of the RCA output. Now that I look at the "Ground Loop Noise Reduction at an Output" section again though, that doesn't seem to match the schematic I got from the other site. I didn't have any 5 ohm resistors, so I tried the 100 ohm which I assume should work but might act as a filter for some of the signal I want to keep, but that didn't make a dent in the noise. And I found some suggestions elsewhere that a 10-100 ohm resistor there would work. and it seems to indicate that a 5 ohm resistor on the ground of the RCA cable should do the job. I found this document by TI with circuits for breaking ground loops: ti.com sloa143.pdf But I don't have a clue how to break said ground loop. These all seem like good suggestions for isolating noise from the circuit, but even if I succeed in removing the noise by adding shielding, seeing as the Mighty and Amp work fine together when they don't share the same power source, correcting the issue with more shielding somehow doesn't really seem like it's getting down to the root of the problem, which the evidence seems to be indicating is the result of a ground loop. Work backward from the speakers to inputs(audio and power). I'm aware I'm supposed to only ground the shield on one side, but I don't see how I can accomplish that with a standard RCA cable. How? Use shielded RCA cable? I've taken apart two RCA cables and only one had any kind of a braided shield, and that also functioned as the ground connection. Try it without the charger in the circuit.Ĭharger isn't in the circuit except when charging. But I'll make sure it's set up that way for future tests. Pull the Y cable out and plug your 'line out' cable directly into each side of your power amplifier input individually to isolate.
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