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Old 13th June 2011, 12:40 PM   #11
gmarsh is online now gmarsh  Canada
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Whoops. Took one look at the box, saw the ribs on the inside of the enclosure and thought "plastic".

I'm not as concerned about watertightness since every speaker efficient enough to be used in a Boominator (HP-10W, GW-1058's, the Eminence ones I'm considering) are all paper cone - you don't want to leave it outside in a rainstorm. The MDF box itself also won't be water resistant unless it's given a very generous coat of marine paint or similar.

By poking this card under the lid of the box you're providing direct shielding from the elements, and to handle mist/condensation I'm planning on using gold plated connectors for corrosion resistance, watertight pot/switches and coating the assembled PCB in clear conformal coating.

If I got rid of the "user interface" on the PCB and went to terminal blocks instead, which I'd have to do for an aluminum box, here's what would have to be on it:

- DC input (2 wires)
- audio input (3 wires - L/R/audio ground)
- USB power output (2 wires, 5V/ground)
- USB enable switch (2 wires, one side grounded)
- volume knob (3 wires - 3.3V/volume/ground)
- audio enable switch (2 wires, one side grounded)
- "charging" / "low battery" LEDs (4 wires)

Which is currently 16 wires. By combining grounds, making the LED a single bicolor LED, etc. I could get it down to 12 to match the rear terminal block.
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Old 14th June 2011, 08:50 AM   #12
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Quote:
Originally Posted by gmarsh View Post
I'm not as concerned about watertightness since every speaker efficient enough to be used in a Boominator (HP-10W, GW-1058's, the Eminence ones I'm considering) are all paper cone - you don't want to leave it outside in a rainstorm. The MDF box itself also won't be water resistant unless it's given a very generous coat of marine paint or similar.
No one in their right mind would go against all warning to the contrary and build a Boominator, or any speaker meant to be used outside out of MDF. Plywood is the only thing that should be considered for any professional loudspeaker box.

And they might be paper cones but they are all weather resistant coated. They wont last being soaked in water for very long while playing but the occasional rain storm doesn't have any effect. I tested this the hard at Roskilde Festival 2007 which was the rainiest festival ever in Denmark.

The reason I insist it must be water tight is because of the use conditions dictate use under very high under cooled humidity situation, ie morning dew. The first year I just had the PCB board naked with no casing which resulted in visible drops of dew dripping of the PCB while playing. Luckily nothing happened but it a risk. Next year I stuffed in a case but didn't take into account that it had to be water tight which resulted in some funny noises from the amp after 4 days of playing more or less constantly. When I opened the case to check I found that there had assembled a small pool of water inside the case that shorted the input ground to the case. Shaking it dry and leaving it in the Sun for 30 minutes was enough to revive it.

Last edited by Saturnus; 14th June 2011 at 08:57 AM.
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Old 16th September 2011, 12:57 AM   #13
gmarsh is online now gmarsh  Canada
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Switched jobs so I haven't had much time to work on this project since initiating it, but lately I've found the time to work on it again. Design update:

- Switched to a TI BQ24650 MPPT charger IC.
- Added a MSP430 to the design. Handles LED blinking, low battery shutdown, SigmaDSP booting, buck converter synchronization, other odd duties.
- Audio stuff is 100% figured out. Spent some time playing with SigmaStudio on an evaluation board and the ADAU1701 SigmaDSP is an awesome chip.

Remaining bits to figure out:
- Mechanical form factor, user interface, etc. The new job has me designing stuff which has to exceed IP68, and stuff I've learned has made me paranoid to even use the Hammond box
- How to get a board full of QFNs built without going completely over budget.
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Old 19th September 2011, 02:05 PM   #14
dangus is offline dangus  Canada
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If there's a DSP... an option to biamp using one or two subs might be of interest. If the woofer doesn't have to cover midrange, it could go in a bandpass enclosure or maybe tapped horn for extra punch.

As for connections to the board, it can be very nice to just unplug one connector. Having to unscrew or worse, desolder a bunch of wires can get old very quickly. There are terminal blocks that consist of a screw terminal block that plugs into a socket on the board. Phoenix, Weidmuller, etc. I'm tempted to suggest 0.1" headers, but crimp tools are expensive. The Molex 0.156" connectors can be crimped with a relatively cheap tool, or bodged with pliers in a pinch. They aren't that great electrically, but I think I saw gold-plated versions somewhere (Digikey?). Maybe if board area allows, provide a couple of options.

Last edited by dangus; 19th September 2011 at 02:19 PM.
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Old 20th September 2011, 07:01 PM   #15
gmarsh is online now gmarsh  Canada
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I was thinking of having the DSP configured two ways:

(1) Biamping, 2 channels going to stereo tweeters, 2 channels going to stereo woofers, and front/back speakers wired in parallel. This is how I plan to wire my cabinet when I build it.

(2) Full range, but driving "front" and "back" speakers with separate amplifiers. This gives double the output power for a louder system, but requires 4 ohm speakers and a passive crossover.

I have access to a calibrated mic and Audio Precision gear. I think I'm going to build a "classic" Boominator cabinet with GW-1058 and NTX3711 components, wire the cabinet in both configurations, and EQ the cabinet flat.

Still scratching my head on what connectors to use. Contemplating a 12x2 double row terminal block, or even a DB25.
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Old 9th December 2011, 12:37 PM   #16
gmarsh is online now gmarsh  Canada
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Schematic's finalized. Working on layout now, about halfway there. I started out hoping to make everything work on a 2 layer board, but I'm moving to 4 as it makes for a much neater, compact, electrically better design. And the PCB isn't that much more expensive.

I'm doing the "bare PCB bolted to the bottom of the lid" mounting method (Sorry Saturnus ) to give a single user interface. The card will be assembled with everything but the connectors, given a dip in conformal coating to protect against condensation/moisture, and the connectors soldered on afterwards. This way the only water damage you can get is to the connectors themselves, and that's straightforward to fix. But there's no reason you can't run wires to a remotely located user interface and put the card in something completely sealed.

The board will be 3.5" wide to match a single 12V/12aH battery. These batteries are the same shape as a typical 12V/7AH battery but a bit wider, and they're commonly used in UPSes. Going with one of these batteries instead of two 7aH makes a fair bit of room available, giving a nice sheltered compartment you can tuck your MP3 player into.

User interface is: 3.5mm audio input, rotary encoder, bicolor LED, double USB port for charging, 5.5/2.5mm DC input for charging. Rotary encoder turns to give volume control, you push it to turn the system on/off. LED blinks with on/off status and battery status. On the opposite end of the card is a 12-pin terminal block with 8 speaker leads, battery connection and solar panel connection. The front DC connection can be used for solar charging also, if you want to use a separate solar panel instead of building one into the top of the box.

When I'm done, I'll post the files here under a creative commons license for people to use, modify, whatever. I'm using the hobby/non-profit/student edition of Eagle for layout (required for doing 4 layer boards, unfortunately).
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Old 4th January 2012, 08:48 AM   #17
hoffsta is offline hoffsta  United States
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This is exciting! I'd be interested in getting one when it's all hammered out.
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Old 4th January 2012, 11:59 AM   #18
gmarsh is online now gmarsh  Canada
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I laid out the board as 4 layers, then decided to go for 2 layers and 8x10cm to fit the free Eagle tools - and I've got most of it done. Excepting the 5V/solar switchers and class D filters, which I still have to lay out, I've got a fairly tight but electrically decent layout done.

I've run into a couple of snags:

(1) 5V USB regulator: I still haven't found one I'm happy with, for various reasons (thermal, parts count, standby current, price, etc..)

(2) Output inductors: I chose Coilcraft JA4575 duals but you can only order them direct from Coilcraft. I've considered some other options (T60-2 toroids, etc) but since there's 8 of them, they take up a lot of space on the board. At this point I think I'll just bite the bullet and go with the Coilcrafts.

(3) Enclosure... I'm designing my card to fit my own modified Boominator enclosure, where it'll be conformal coated and mounted bare under the lid. But at the same time I'm trying to design a card everyone else can use in the stock Boominator, and that means using an enclosure.

The Hammond case Saturnus suggested doesn't have "proper" PCB supports. Not really an issue for an Amp6 since you can just screw the Tripath chip to the box, but in my case everything's mounted to the PCB, and the PCB has to either slide into the case or be screwed to the case. I s'pose I could use snap-in PCB mounts that glue to the case. Secondly, if the thing's mounted in an enclosure, you have to get wires in/out of the enclosure. Which means either IP rated connectors ($$$) or an IP rated cable crimp which will protrude into the box and potentially create mechanical issues.
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Old 4th January 2012, 05:10 PM   #19
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The mounting problem can be easily solved by using non-electrically conductive double adhesive thermal conducting tape since I suppose the PCB will need some sort of cooling contact with the enclosure anyways.

As for contacts I just use RCA phono plugs. Neutrik types costing less than a buck each are rated at 16A per contact at 50V, plenty for a low powered amp. But your design might need more contacts than the 6 phono plugs needed on the amp6 (actually only 5 needed, 4 for left/right input/output, 1 for power, and the final one is used for MUTE as I use a mini-jack with a built in DPST switch on the connection panel that turns off mute when a minijack is inserted correctly into it).

Last edited by Saturnus; 4th January 2012 at 05:14 PM.
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Old 4th January 2012, 07:21 PM   #20
gmarsh is online now gmarsh  Canada
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I actually thought of that idea right after I made that post - using a Berquist "Gap pad" to glue the board to the case. It'd definitely work, I just wish the stuff wasn't so expensive. There's probably cheaper stuff available, plus the ground plane of the card provides a lot of heat spreading so there isn't really a need for a high performance material.

Using the 3.5mm jack to switch the audio on and off... I think I'll implement that, that's a damn good idea, gets rid of the audio enable switch. Only thing left to get rid of is the USB enable switch.

I really wish they'd make a USB connector with a connector presence switch so I could make the USB charger turn on/off automatically. Such a connector strikes me as something that should have been invented already, allowing USB wall chargers to go into a lower power standby.

Or, I wish they made the stupidly-low-Iq, Linear LT3690 in a nicer package. I'd just leave the USB port on all the time.
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