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Forum Index : Microcontroller and PC projects : audio out .........
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| hitsware Guru  Joined: 23/11/2012 Location: United StatesPosts: 535 |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
R14 and R16 should become OPEN .... R13 and R15 should be SHORTED ..... |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Why do you say that? If you were to do as you say you would change the output to be 0-3.3v (depending on the load you plug into) which as far as I am aware is too high for driving an audio amp.. The circuit as shown should provide a signal that swings between 0 to 0.5V and is a squarewave that is `rounded' by the 2 Capacitors... Now looking at the design `maybe' (I am no expert here) the swing should be closer to 0 - 1.0v for proper output levels of typically 0.775V RMS.. Also `maybe' the outputs should be capacitively coupled to filter out any chance of DC offsets.. I am no expert on audio stuff and I do agree that the sound level appears a bit low out of the Sound Jack but a decent amplifier works well enough with it. Maybe Geoff will have further comments here. Regards, Mick EDIT ***** Unless your proposal is for the PWM use of the ports.... which might need a different specification (I have never used PWM and dont know the specifics.. but I am aware of the principals of PWM) Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
I prefer as 'hot' as possible within wanted frequency response The first LP ......4.7k with ? to ground is enough. Any load actually weakens the rolloff slope. Another stage of LP would make sense ..... But not pure attenuation. BUT ...... I see your point about matching exisiting amps . FWIW: http://www.t-linespeakers.org/tech/filters/passiveHLxo.html |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3194 |
I am no expert on audio either so I just designed it to be quite loud with the powered speakers that I use. But it is easy to modify, just change R14 and R16. There is a DC offset on the output but all the amps that I have checked have capacitors on their inputs and, as I was trying to keep the component count down, I figured that an extra capacitor was superfluous. No, that is not quite correct. The output is PWM at about 100KHz so the two capacitors are used to average the PWM signal (ie, remove the 100KHz carrier leaving the audio). Geoff Geoff Graham - http://geoffg.net |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
Easy for you .... :) I'll have to look at your SMD article....... |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Ok Thanks Geoff, I just looked at the circuit in question and tried to work out what the affect of the two caps would do to the square wave outputs from D1 and D3... I wasnt really thinkng of the output as PWM... so it is a Low Pass filter then? Hence HITSWARE's reference to LP which I admit didnt click with me what he was saying there. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| hitsware Guru Joined: 23/11/2012 Location: United StatesPosts: 535 |
For sure. I have a DuinoMite that has the audio out jack(s) wired (I think) direct from the mainchip .... No filter BUT ! ...:( No stereo ! or dual PWM channels ..... Mr Duino needs to hop on the Music Wagon  |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2350 |
try replacing R7 and R8 with 100uH inductors, and up C15 and C16 to 220nF. assuming a source impedance of about 40 ohms at the pin, this will produce a far more pleasing filter effect, flat up to about 10kHz and 20dB down at 100kHz. |
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