Purpose-built Boominator PCB project
The "cAMP" purpose-built Boominator amplifier will be available soon from Canopy Sound!
--- rest of thread is a historical design blab and can safely be ignored... ---
Saturnus's Boominator project is awfully nice, and I'm currently working on a smaller version of it to use as a solar powered camping stereo.
I've decided to make my own custom PCB for running it, with features that would be hard, impossible or impractical to do by combining pre-bought pieces. It will provide the following:
- Class D amplification for playing music from MP3 players, cellphones, CD players, etc.
- MPPT-tracking, solar battery charger. Set up for 12V SLA batteries in my application, but capable of doing lithium ion with resistor changes.
- Able to charge from an external AC adapter also.
- Battery protection. Everything shuts off if the battery gets too low.
- A 5V USB port or two for charging phones, MP3 players, etc.
The audio section will consist of:
- A stereo audio receiver that's tolerant of ground loops, so you can charge the device you're playing audio from without hearing charging noise.
- An Analog Devices SigmaDSP chip. This will perform volume control with a pot acting as a volume knob, equalization, noise gating, bass/stereo enhancement, crossovers for bi-amping, any number of other things to make the stereo sound better.
- Four total class D amplifier channels, each set up for driving 4 ohms, but capable of 8 ohms with inductor/capacitor changes. I'm planning to bi-amp the woofers/tweeters in my stereo, but you could use external crossovers instead and double the output power.
Right now I'm nailing down the parts list, mechanical form factor, etc. I'm designing this project in Eagle, and I'll share the design files under a CC license when it's done.
I won't say "group buy" just yet, but if enough people are interested in such a thing when the design is done, it could be arranged. Right now, this thread is intended to be a design log more than anything.
Sounds great! Big project. Can't wait to see what you come up with.
With the DSP, it wouldn't be to hard to add a digital input, right?
Sounds great. I designed a Class D power stage with TI components. But I found so difficult to build a high end feature-rich volume control circuit. And I'm interested in your volume control design. Share it with us once you are finished
Best wishes brother.
Digital input wouldn't be too hard to add. Requires a SPDIF receiver and an ASRC chip, which can be done with something like a TI SRC4382 chip, or by using a different SigmaDSP chip which implements SPDIF/ASRC bits.
Though, for what I'm using it for, I don't have any plans of adding such a feature. Nothing I plan on carrying into the woods has a digital output...
For form factor I'd recommend something that fits into a Hammond 1590N case as that is what is recommend for the Boominator. That's because the width is given by the battery's width, 66mm, and the length is limited by the space available between cooling cut outs. Typically around 122mm.
So a board size of max 60x115mm and total internal height of max 33mm including stand-offs.
I was originally planning on putting all the "user interface" stuff (enable switches, USB connector, audio input, DC charger input, volume knob) on one end of a circuit board, and a screw type terminal block on the other side for solar, battery, and audio connections.
The board would be bolted upside down to the underside of the top of the enclosure, between the two speaker enclosures and above the battery. For a more protected install, it could be bolted to a bent metal plate which provides a user interface "panel". The size of the card would match a 12V/7AH SLA battery.
I'll toss the idea together in Sketchup sometime.
Mounting a card like this in a 1590N style case is possible, but it's a bit hard to knock holes in a plastic hobby case while making it look good.
Are you planning a MOSFET / relay based system for the low voltage cutoff?
more details! :D
Here's the tentative parts list:
- Linear LT3652 MPPT solar charger IC.
- 2 x Analog Devices ADAU1592 class D amplifier IC
- ADAU1701 SigmaDSP chip + self-boot EEPROM + 24M oscillator.
- 12V-5V switching regulator for USB output.
- 12V-3.3V switching regulator for SigmaDSP, op-amps, etc.
- Low-Iq linear regulator/reference and low power comparator handling low battery shutdown.
- A couple of toggle switches to enable USB power and audio.
- A couple of LEDs to indicate charge state, a low battery shutdown condition, etc.
To configure the DSP, you'll need to construct a Ponyprog or similar device that can program an I2C EEPROM, and download a copy of SigmaStudio from Analog Devices to set up the processing configuration and generate a programming image.
The 1590N is a watertight aluminium enclosure. The casing itself will provide all the cooling you need.
Tell you what for use in the Boominator following limitation must be met:
- the casing must be aluminium, or otherwise adequate cooling must be reach by other means while observing the below requirement.
- the casing must be watertight, this includes all contacts and switches that might be on the case
- the casing must be absolute maximum 66x61x122mm in size.
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