Audio struggle with stereo signal and mono amp

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Kharmeleon
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Audio struggle with stereo signal and mono amp

Post by Kharmeleon » Sat May 07, 2016 2:29 am

Hello wermy and other fellows! I am making my own definition of a Game Boy with a Raspberry Pi 3 inside. I am struggling with the audio right now. I've bought the Adafruit class D 2.5W mono amp and removed the RCA jack from the Pi-board. I don't know how to wire up the stereo signal correctly to the amp.

At first let me explain how i want it to be. I want the stereo signal to get into the mono amp and want to integrate an audio jack to the circuitry so that when i plug in the headphones to the jack the sound of the speaker turns off and i get stereo sound for the headphones. I want both output volumes to be controlled by the contrast poti of the Game Boy. Yes the contrast poti, not the audio one because there is the HDMI-Port at this point. I hope you get what i mean.

Thank you for your great tutorials and helping people out wermy! I appreciate it a lot!

Greetings from Germany

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Kharmeleon
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Re: Audio struggle with stereo signal and mono amp

Post by Kharmeleon » Sun May 08, 2016 7:41 am

Hello? Anybody? :shock:

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Re: Audio struggle with stereo signal and mono amp

Post by ktechelonbreak » Sun May 08, 2016 9:51 am

I'm a bit confused as to what you are trying to do? So you want stereo sound to the headphones while cutting sound to the speaker, and you want to control it all with a pot, but not the audio pot? You might need to get a stereo amplifier with a built in pot if that is your goal.

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Re: Audio struggle with stereo signal and mono amp

Post by Kharmeleon » Sun May 08, 2016 10:02 am

Thats kind of what i want to do, yes. Can i really only accomplish it with a stereo amp? The Mono amp has an installed poti too.. Would it be possible to get Mono Sound from the Headphones though? :/

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Re: Audio struggle with stereo signal and mono amp

Post by ktechelonbreak » Sun May 08, 2016 10:26 am

So I tried fiddling around with some configurations and some weird results. If I put the pot before the headphone jack then line out from jack to amp then amp to speaker, the pot would only control the volume for the jack and not the speakers. My assumption is that the amp negates any impedance the pot was making. This left me with 2 options for the mono amp:

1) Have the pot after the amp output. This will only give mono sound to both headphone jack and speaker.

2) Do it without the amp to get stereo sound jack and mono speaker. This is only possible if there is enough power going to the speaker. I was using USB DAC and 10 ohms 1W speaker and it was sufficiently loud so I omitted the amp but results may vary.

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Kharmeleon
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Re: Audio struggle with stereo signal and mono amp

Post by Kharmeleon » Sun May 08, 2016 11:14 am

Ok thanks for the research so far. I may say that i am using a pi 3 for my interpretation of the Game Boy Zero.

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Re: Audio struggle with stereo signal and mono amp

Post by crispy_tofu » Sun May 08, 2016 8:00 pm

Hi,
I don't think that you can pass a stereo signal through a mono amp and get a stereo output. The only methods that I can think of to achieve this is by not passing the headphone signal through the amp, or by getting two mono amps (which might be cumbersome).

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Re: Audio struggle with stereo signal and mono amp

Post by ktechelonbreak » Sun May 08, 2016 9:16 pm

You could probably pass stereo to pot then pot to headphone jack as stereo, then pass R chan to amp. When I tried that though, the speaker volume was not affected by the pot so I'm not sure if there's another way?

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Re: Audio struggle with stereo signal and mono amp

Post by wermy » Mon May 09, 2016 7:04 am

ktechelonbreak wrote: 1) Have the pot after the amp output. This will only give mono sound to both headphone jack and speaker.
Yep, this is what I did. You only get mono in headphones, but I never wind up using that so I didn't mind. The pot controls the volume on both headphone jack and speaker.

You can still get stereo out when plugged into HDMI, though.
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Re: Audio struggle with stereo signal and mono amp

Post by Kharmeleon » Mon May 23, 2016 12:08 pm

wermy wrote:
ktechelonbreak wrote: 1) Have the pot after the amp output. This will only give mono sound to both headphone jack and speaker.
Yep, this is what I did. You only get mono in headphones, but I never wind up using that so I didn't mind. The pot controls the volume on both headphone jack and speaker.

You can still get stereo out when plugged into HDMI, though.
Sorry for the long wait. I just came back from vacations. Thanks for your help. I will try it out. I know you only get mono but can i get both sides to get to come out from the speaker/headphones? Can i merge de audio signals by connecting them? I do not want to miss left or right side. :roll:

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