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Topic: Sinusoidal noise when subwoofer amplifier is connected (Read 2750 times) previous topic - next topic
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Sinusoidal noise when subwoofer amplifier is connected

So I'm building a portable sound system consisting of two coaxial speakers for mids and highs and a subwoofer for bass. These are supposed to be driven by a maxamp20 and bassamp20 respectively.

While trying out my everything I discovered a problem. The maxamp20 works fine on it's own but when I split the incoming audio and hook up the bassamp a sinusoidal noise starts playing out of the maxamp. I would guess it's about 2khz and it dissapears as soon as the audio is disconnected from the bassamp.

I'm guessing that there's some sort of crosstalk between the two amps but I haven't got a clue what to do about it. Both amps were powered by the same power supply.

Re: Sinusoidal noise when subwoofer amplifier is connected

Reply #1 –
That's a strange problem.   What happens when you connect the bass amp by itself?  

How are you "splitting" the audio?    Is there an active crossover?    Are you shorting the left & right channels together to drive the bass amp?

Re: Sinusoidal noise when subwoofer amplifier is connected

Reply #2 –
Quote from: DVDdoug on
That's a strange problem.   What happens when you connect the bass amp by itself?  

How are you "splitting" the audio?    Is there an active crossover?    Are you shorting the left & right channels together to drive the bass amp?

I haven't tried just running the bass amp by it self. The input signal is split by simply soldering two wires for every channel on a 3.5mm jack and using one of them for every amp. The bass amp is stereo so I'm just running them as is.

Re: Sinusoidal noise when subwoofer amplifier is connected

Reply #3 –
Quote
The bass amp is stereo so I'm just running them as is
You said "a" subwoofer, so you're only using half of the bass amp, and you are only feeding it signal from one channel???    Sorry, but it's not clear how you're handling a 2-channel stereo signal into single subwoofer.   You can run only one channel into a single sub and it usually works because the bass on most recordings is mono (identical in both channels), but usually there's a (passive or active) mixing circuit so you can send bass from the left and  right channels combined to the sub.  

Something's probably wired wrong.    Connecting two or more inputs together shouldn't hurt anything.   However, connecting two or more outputs together can cause problems.    

Quote
II haven't tried just running the bass amp by it self.
think you should try it.  You  didn't say which amp was oscillating, or if it's all of them.  You can also try connecting the signal to all of the amps without powering-up the bass amp.   If connecting to the unpowered amp messes-up the signal, that's a clue that something's wired wrong, or maybe the bass amp Is defective.

Re: Sinusoidal noise when subwoofer amplifier is connected

Reply #4 –
Quote
Sorry, but it's not clear how you're handling a 2-channel stereo signal into single subwoofer.
The subwoofer is a dual coil so I just connected one output to each coil. Is this bad? My thinking was along the lines of what you wrote, that the signal should be the same on both since bass is mono.
Quote
You  didn't say which amp was oscillating, or if it's all of them.  You can also try connecting the signal to all of the amps without powering-up the bass amp.   If connecting to the unpowered amp messes-up the signal, that's a clue that something's wired wrong, or maybe the bass amp Is defective.
I'm only experiencing the noise in the regular amp although this might be because the frequency is to high to be played in the subwoofer.

I'll try just connecting the bass amp signal wire to see what happens.

Re: Sinusoidal noise when subwoofer amplifier is connected

Reply #6 –
Quote from: Hehepls on
So I'm building a portable sound system consisting of two coaxial speakers for mids and highs and a subwoofer for bass. These are supposed to be driven by a maxamp20 and bassamp20 respectively.

While trying out my everything I discovered a problem. The maxamp20 works fine on it's own but when I split the incoming audio and hook up the bassamp a sinusoidal noise starts playing out of the maxamp. I would guess it's about 2khz and it dissapears as soon as the audio is disconnected from the bassamp.

I'm guessing that there's some sort of crosstalk between the two amps but I haven't got a clue what to do about it. Both amps were powered by the same power supply.

Is there any chance that some of the speaker leads of the amps are shorted or connected together?