I have here a few ideas I have been throwing around inside my head, and I'd like your opinion on them.
Add a power amp
I think we'll all agree already that this is a must. I'll take it as read that you all agree with this one.
Change chips
I am thinking of replacing the dsPIC33FJ128GP802 with the dsPIC33FJ128GP804. Inside it's exactly the same chip, it just has more pins. The 44-pin package would give us much more access to functionality, and make the system able to do so much more. However, to save space at the same time it would be in a 44-pin QFN (Quad Flatpack No-leads) package. You know the things - a black square about 8mm by 8mm, with no visible connections to the outside world. Not quite a Ball Grid Array (BGA), but still saves quite a bit of space without all those pesky leads sticking out. It does make it harder to build though, but I guess that's my problem, not yours ;) It would add about 30p ($0.48) to the cost of producing each board though.
One further advantage, with all those IO ports, would be that more LEDs could be added, to give even better VU meter / spectrum analyser output ;)
Add better volume control
With the added IO that a bigger dsPIC would give us it would be possible to interface to all sorts of things. One I have in mind is a digital potentiometer chip (I am looking at the AD5243 or MAX5387 - two channel 256 step 10KΩ) to act as a proper volume control (attenuator). At the moment volume control is done completely in software. This is fine, but it just turns down the sound of the samples, and not the sound of the background hiss imposed by the DAC. Using an analogue volume control like this makes controlling the volume much nicer. However, it will add more to the build cost of each board - about £1 ($1.60) a time.
I'm running the risk of the cost rising too high to make it profitable - don't you just love feature creep?
So, what do you think is important out of this lot? I was aiming for a RRP of no more than £25 ($40). I know that's considerably more than the AdaPoop shield, but you get so much more.
Last edit: Majenko Technologies 2012-11-04
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I'm current with v.32 have had a chance to play with the loop/queue notification feature and with the vu meter on the leds. Everything's working great so far this side.
You seem convinced of the need for a power amp, but I feel the WavePro is plenty loud - or at least loud enough for my application, which is feeding line level signals into a mixer. As is, the WavePro is too loud to comfortably listen to over headphones. My feeling is if listen to the WavePro over an 8 Ohm speaker, you're going to lose out on its best feature - the quality of the audio it produces.
Some more questions - how much current draw will a power amp add, especially for people who like me who want to stack WavePros? If there's a chance that adding an amp can impact the sound quality (ie. introduce noise), would it be possible to add a header to tap the audio signal before it reaches the power amp?
Haha, yeah feature creep! Seriously, I'm not sure you need to add any additional hardware features. The thing to remember is that the WavePro already knocks the socks off the competition in the most important regard - sound quality. Maybe save further features for the WavePro v.2 ;^)
Last edit: MoShang 2012-11-07
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Well, I am not so sure about the power amp now either. I have just built an add-on board with a TPA6111 on it, and I can't hear any difference between that and the normal output. I have an LM4880 to try on it too, see if that sounds any better, but so far it seems pretty pointless.
I am thinking a hardware volume control of some form might be a good idea, so you can reduce the volume without decreasing the SNR.
The original idea was to add daughter boards to the WavePro to add all these kind of things - the header pins down the sides are the audio in, out and power - exactly the same as the jack sockets - that you can use to build power amps, preamps, etc in to the system to suit you. I guess the power amp and volume control can be an add-on board easily enough.
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Actually, I just heard a difference. A particularly loud bit of Røyksopp just distorted through my little 8Ω speakers on the normal output, and when I plugged them into the power amp instead they didn't distort. So, if you want to use little speakers in an embedded system (which you might) then you really need a power amp too. And I am thinking of expanding the 3-pin headers to be 5-pin, so you can interrupt the audio path to insert your own circuitry between the op-amp and the power amp (or output if there is no power amp).
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I know it's a balance between cost/features, but some kind of power amp solution would be really nice. I'll be running this from embedded speakers. Having those extra pins to throw in your own circuitry is a great idea.
I've ordered up a bunch of parts and will start breadboarding one of these as soon as they arrive. By the way, what op amp do you currently use on the outputs?
Awesome project!!
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For the output buffering pretty much any op-amp that is single rail, Rail-to-rail I/O, with a minimum supply voltage at 3.3v or below, and with enough bandwidth will do. I use the TSV912IDT from ST.
The re-design I am working on has the TPA6111 integrated as a power amp (with pre-power-amp breakouts for those that want to bypass it).
Last edit: Majenko Technologies 2012-12-25
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I have here a few ideas I have been throwing around inside my head, and I'd like your opinion on them.
Add a power amp
I think we'll all agree already that this is a must. I'll take it as read that you all agree with this one.
Change chips
I am thinking of replacing the dsPIC33FJ128GP802 with the dsPIC33FJ128GP804. Inside it's exactly the same chip, it just has more pins. The 44-pin package would give us much more access to functionality, and make the system able to do so much more. However, to save space at the same time it would be in a 44-pin QFN (Quad Flatpack No-leads) package. You know the things - a black square about 8mm by 8mm, with no visible connections to the outside world. Not quite a Ball Grid Array (BGA), but still saves quite a bit of space without all those pesky leads sticking out. It does make it harder to build though, but I guess that's my problem, not yours ;) It would add about 30p ($0.48) to the cost of producing each board though.
One further advantage, with all those IO ports, would be that more LEDs could be added, to give even better VU meter / spectrum analyser output ;)
Add better volume control
With the added IO that a bigger dsPIC would give us it would be possible to interface to all sorts of things. One I have in mind is a digital potentiometer chip (I am looking at the AD5243 or MAX5387 - two channel 256 step 10KΩ) to act as a proper volume control (attenuator). At the moment volume control is done completely in software. This is fine, but it just turns down the sound of the samples, and not the sound of the background hiss imposed by the DAC. Using an analogue volume control like this makes controlling the volume much nicer. However, it will add more to the build cost of each board - about £1 ($1.60) a time.
I'm running the risk of the cost rising too high to make it profitable - don't you just love feature creep?
So, what do you think is important out of this lot? I was aiming for a RRP of no more than £25 ($40). I know that's considerably more than the AdaPoop shield, but you get so much more.
Last edit: Majenko Technologies 2012-11-04
I'm current with v.32 have had a chance to play with the loop/queue notification feature and with the vu meter on the leds. Everything's working great so far this side.
You seem convinced of the need for a power amp, but I feel the WavePro is plenty loud - or at least loud enough for my application, which is feeding line level signals into a mixer. As is, the WavePro is too loud to comfortably listen to over headphones. My feeling is if listen to the WavePro over an 8 Ohm speaker, you're going to lose out on its best feature - the quality of the audio it produces.
Some more questions - how much current draw will a power amp add, especially for people who like me who want to stack WavePros? If there's a chance that adding an amp can impact the sound quality (ie. introduce noise), would it be possible to add a header to tap the audio signal before it reaches the power amp?
Haha, yeah feature creep! Seriously, I'm not sure you need to add any additional hardware features. The thing to remember is that the WavePro already knocks the socks off the competition in the most important regard - sound quality. Maybe save further features for the WavePro v.2 ;^)
Last edit: MoShang 2012-11-07
Well, I am not so sure about the power amp now either. I have just built an add-on board with a TPA6111 on it, and I can't hear any difference between that and the normal output. I have an LM4880 to try on it too, see if that sounds any better, but so far it seems pretty pointless.
I am thinking a hardware volume control of some form might be a good idea, so you can reduce the volume without decreasing the SNR.
The original idea was to add daughter boards to the WavePro to add all these kind of things - the header pins down the sides are the audio in, out and power - exactly the same as the jack sockets - that you can use to build power amps, preamps, etc in to the system to suit you. I guess the power amp and volume control can be an add-on board easily enough.
Actually, I just heard a difference. A particularly loud bit of Røyksopp just distorted through my little 8Ω speakers on the normal output, and when I plugged them into the power amp instead they didn't distort. So, if you want to use little speakers in an embedded system (which you might) then you really need a power amp too. And I am thinking of expanding the 3-pin headers to be 5-pin, so you can interrupt the audio path to insert your own circuitry between the op-amp and the power amp (or output if there is no power amp).
Oh, and the power amp seems to add no more than (depending on what's playing) 7mA to the load.
With a power amp I can directly drive my nice big Monitor Audio speakers, and they sound gorgeous. Without, they sound really shite and crackly.
I know it's a balance between cost/features, but some kind of power amp solution would be really nice. I'll be running this from embedded speakers. Having those extra pins to throw in your own circuitry is a great idea.
I've ordered up a bunch of parts and will start breadboarding one of these as soon as they arrive. By the way, what op amp do you currently use on the outputs?
Awesome project!!
For the output buffering pretty much any op-amp that is single rail, Rail-to-rail I/O, with a minimum supply voltage at 3.3v or below, and with enough bandwidth will do. I use the TSV912IDT from ST.
The re-design I am working on has the TPA6111 integrated as a power amp (with pre-power-amp breakouts for those that want to bypass it).
Last edit: Majenko Technologies 2012-12-25