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Forum Index : Microcontroller and PC projects : MMBasic audio
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Mixtel90 Guru  Joined: 05/10/2019 Location: United KingdomPosts: 8298 |
Can someone confirm (or otherwise) this? OPTION AUDIO x,y defines two PWM pins to be used for audio. They can specified in any order, but the PWM A pin will always be the Right channel and the PWM B pin will always be the Left channel. So OPTION AUDIO GP6,GP7 is identical to OPTION AUDIO GP7,GP6 and GP6 will always be the Right channel (they are both on PWM3). Sorry if this is so simple, but so am I sometimes... :( Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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hitsware2 Guru Joined: 03/08/2019 Location: United StatesPosts: 735 |
If we define 'right' or 'left' by the 'r' or 'l' in the PLAY SOUND statement, mine is reversed to that ..... I.E.. No matter the sequence of the 'GP' numbers in the OPTIONS statement, GP6 responds to 'l' and GP7 responds to 'r' .....(Pimoroni Tiny 2040) .... my site |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8298 |
I think I have this sorted out now. I've had another play since this morning. The PicoMite manual gives an example: OPTION AUDIO GP0,GP1 (that's PWM0A, PWM0B) then shows a schematic connecting PWM A to Right output, PWM B to Left output. (GP6 is PWM3A, GP7 is PWM3B) PLAY TONE will not accept a single argument, no matter what the manual says. :) The order of the arguments in OPTION AUDIO *definitely* makes no difference. GP6 (PWM3A) is producing the Left channel, not the Right as expected. Verified using PLAY TONE 1000,0 for Left and PLAY TONE 0,1000 for Right. I was confused this morning because the jack socket is marked up with the channels reversed. Consequently I had my headphones on the "wrong" way round. So, there are two manual errors: the example is wrong and PLAY TONE should show that the second argument is mandatory. It doesn't really matter to me which way round the PWM A and PWM B pins are so long as I know. :) It's just that it can't be corrected in software using OPTION AUDIO if it's wrong. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| hitsware2 Guru Joined: 03/08/2019 Location: United StatesPosts: 735 |
Better that than Your head ...  my site |
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Rickard5 Guru Joined: 31/03/2022 Location: United StatesPosts: 463 |
Since I Built my PM VGA I've been thinking of building another CMOY headphone amp to use as a Preamp for a set of Cheep 8ohm powered Dell speaker bar Total BOM Cost like $4  I may be Vulgar, but , while I'm poor, I'm Industrious, Honest, and trustworthy! I Know my Place |
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| KD5ZXG Regular Member  Joined: 21/01/2022 Location: United StatesPosts: 53 |
Thats an 8MHz amp, don't it need some 20KHz lowpass? |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8298 |
*This* is a headphone amp. :) Paralleled ECC82/12AU7 direct coupled to a MOSFET source follower to drive headphones. The valve heaters are the MOSFET source resistor. It sounds beautiful - but isn't as portable as the Cmoy - especially with the SMPS that powers it. lol It's the "Starving Student" circuit, slightly modified to use a valve that's are actually available. The two shown in the photo are probably not far off my age. My late dad and myself took a lot of old valve TVs to pieces between us when I was a youngster (to re-use the components) and I kept a lot of the valves.  I'm intending to try Volhout's emitter follower and a couple of variations today. I could do with a different arrangement for the next revision of PicoGAME really. I suspect it would be used with headphones more than with speakers. I'm beginning to suspect that it won't be possible to run the PicoMite SMPS and that a linear regulator will be necessary. That's purely because of noise levels. It doesn't really matter - the regulator is cheap and quite easy to get and there is no big current demand as there is no external I/O to worry about. To get a decent output volume to headphones I need a big output from the PicoMite as an emitter follower reduces the impedance (increases the drive current) but has no voltage gain. Consequently any noise from the PicoMite (or on the 5V supply) is going to go to the headphones. At the moment I'm thinking of filtering the 5V a bit to help with that. Edited 2022-04-17 17:26 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| hitsware2 Guru Joined: 03/08/2019 Location: United StatesPosts: 735 |
I love stuff like that  Using outboard 3.3V regulators rather that the onboard Pico regulators has been suggested for the noise problems . my site |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8298 |
A linear reg helps a lot as the onboard 3V3 SMPS is so noisy. With 470R resistors for the phones and a linear reg there's virtually no noise. I can live with that now. It's not hi-fi but it's not intended to be. Headphones are some Skullcandy ones that I've had for some years. Not my best, but the ones I usually use with the computer. I've used two WAV test tracks: Africa - Toto Around The World - ATC (from https://www.ee.columbia.edu/~dpwe/sounds/music/ ) They seem to be recorded at slightly different levels, with Africa being a bit quieter. Sound quality is pretty good, and the bell-like sounds at the beginning of Around The World have a nice ethreal quality. Bass is pretty good, especially when you consider the limited current drive available. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Rickard5 Guru Joined: 31/03/2022 Location: United StatesPosts: 463 |
Mick I'm so in love with that Tube amp, Right now I have a Pr. of awesome Block amps sitting storage waiting for Tubes I'll Never be able to afford :( I may be Vulgar, but , while I'm poor, I'm Industrious, Honest, and trustworthy! I Know my Place |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8298 |
What valves? It's surprising what you can swap around with minor changes - and you're unlikely to hear a difference. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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