Excessive noise on MAX9744

[KAEZ]

Hi, I am using the 9744 with an iPOD nano driving it. The output has a very high noise floor. I am using a 12 volt 5 amp power supply and have installed the capacitor that came with the unit. There is audio, but the noise makes it unlistenable. Is there a way to eliminate the noise?

Thanks!

Bruce

[adafruit_support_mike]

Post a photo of your hardware and connections and we'll take a look.

[adafruit2]

it sounds like a ground loop - try running it off batteries, and with a battery powered ipod or something, as a test!

[KAEZ]

Speakers not shown in photo.

Max.jpg (413.11 KiB) Viewed 583 times

Speakers not shown in photo.

Max.jpg (413.11 KiB) Viewed 583 times

I disconnected the speakers. They were ADS 200C's. I tried to tie the AGnd and the Gnd together but it made no difference. Batteries are not an option.

Thanks,

Bruce

[adafruit_support_mike]

The suggestion to use batteries was for testing purposes.

If you still hear the noise when the iPod and amp are running from separate power supplies, it means there's a problem with the amp. If using separate power supplies makes the noise go away, it means there's a problem in the signal or ground paths.

[KAEZ]

The iPod has it's own battery so there are two separate power supplies. What shall I do next? Can you repair the amp?

[adafruit_support_mike]

If you're getting noise while running from separate power supplies, it can't be a ground loop.

That limits the problems to a bad amp, a noisy power supply, overdriven speakers, or physically damaged speakers.

The last two are pretty easy to check. If it's overdrive, the noise will cut in and out at a certain volume threshold. If the noise is continuous or is there when no sound is playing, it isn't overdrive. If the speakers are damaged, they'll buzz no matter what source is connected to them, and connecting the amp to other speakers will make the noise go away.

A noisy supply is an outside chance, but is worth checking just in case. Try another power source and see if it makes any difference.

[KAEZ]

Mystery! Tested it with a 12Volt battery and it worked fine. Then went back to the Original power supply and it works fine there as well. I will test for several days to see if it's intermittent. Thanks for your help.

[adafruit_support_mike]

That does sound like you had a marginal power connection. There might have been some oxidation on the terminals that got scraped clear when you unplugged and replugged.

As long as it works, it's a win though. ;-)

[eliseoriana]

I am having the same problem, but we have changed the power supply (both wall, bench supply, and battery), different speakers (just some hanging out about the lab), and we are still getting a bunch of noise on two of the amplifiers. Both are having the same problems. We hooked one of them up to a scope, and this is what we got with a sine wave input @ 500Hz at 10 Vpp, with a 3.4 Ohm load, and here is what we got. The one that doesn't look like crazy noise is the input (ch1) and the output (ch2) with the amp unpowered. The second one is who knows what.

So, I guess my question is--how do we get rid of the noise? So far, nothing has worked.

[adafruit_support_mike]

For starters, your signal is clipping badly. Try dropping it to 5vpp, 2vpp, and 1vpp and see if that keeps the output from saturating.

You'll need to filter the output if you want to see anything other than 360kHz hash. A 1k/10nF RC filter will at least smooth things out enough that you'll be able to see the output waveform.