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Old 6th January 2015, 06:15 AM   #1
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Default ACA Concept

Greetings DIYAers; I thought some here might be interested in my next build, a pair of Amp Camp Amp monoblocks. While I've gathered a few of the more basic parts, at this point the project is mostly conceptual. That doesn't mean it's vague or undefined. To the contrary it's pretty much fully planned out, and I think the end product will match the design almost exactly.

Electronically, it will be a pretty straightforward ACA build (albeit P2P on perfboard), with the Add-A-Watt mod naturally. I'll also be adding a latching pushbutton power switch circuit.

The fun stuff will be in the chassis design, and its fabrication. I've come up with a short list of design objectives (most of which germinated during, rather than prior to, the design process):
  • Outside-the-box thinking. Literally; no rectangular box
  • A mix of materials that I like: Metal, Wood, Glass
  • No exposed screws or fasteners anywere on the outside of the chassis
  • Low-profile audio connectors
  • Stealth ventilation
  • No visible power switch
  • Glowy!
  • Multiple uses: can serve as bookends, door stops, or boot scrapers
  • High DHF (Domestic Harmony Factor)

The attached pictures show the finished design.

Fabrication will be a challenge (especially doing two mirror-image monoblocks), but should be well within my capabilities.

This will be a drawn-out build, since I have other demands on my time (bed, bath, & kitchen remodel that's long overdue for completion; cabin bathroom remodel; kids; pets; and a job to pay for it all). But, I'm committed to completing it and I'll post sporadic updates as I make progress.
Attached Images
File Type: jpg ACA 1.jpg (165.8 KB, 620 views)
File Type: jpg ACA 2.jpg (86.1 KB, 597 views)
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Old 6th January 2015, 06:18 AM   #2
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Another pic to show scale. Power will be turned on/off by gently pushing the glass panel on the front. An LED behind the glass will provide a soft glow when powered on.
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File Type: jpg ACA 4.jpg (163.5 KB, 589 views)
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Old 6th January 2015, 06:27 AM   #3
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Ventilation detail. Ventilation will be provided by cut-outs at the top and bottom of the heatsink. This is one area where I may have to compromise on my design objectives. If it gets too hot in there, I may have to cut additional ventilation holes in chassis. Or, to avoid that, I may be able to provide active ventilation (laptop fan running at low RPM?).
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File Type: jpg ACA 5.jpg (180.6 KB, 577 views)
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Old 6th January 2015, 06:30 AM   #4
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A peek inside...
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File Type: jpg ACA 6.jpg (173.1 KB, 567 views)
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Old 6th January 2015, 06:32 AM   #5
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Preamp, anyone? Maybe JBOZ?

That's it for tonight. Again, I'll post updates as I make progress...
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File Type: jpg ACA 3.jpg (123.6 KB, 124 views)
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Old 6th January 2015, 03:59 PM   #6
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Here's the latching switch circuit wired up. It's based on the circuit found HERE. It uses a little surface-mount dual MOSFET. The one specced on the linked page (IRF7319) didn't quite have the capacity to run the ACA circuit without a relay, so I used IRF7105 which is rated for 25v Vdss/2.3A Id (on the P side). I think that should be able to handle ACA (~20V, 1A); correct me if I'm wrong.

I'm new at this so the layout probably could have been better (a few crossing wires), but I was constrained by the pinout of the dual MOSFET. Anyway, the switch works and it was good practice for when I wire up the main circuit...
Attached Images
File Type: jpg photo 1.JPG (170.4 KB, 108 views)
File Type: jpg photo 2.JPG (120.1 KB, 107 views)
File Type: jpg photo 3.JPG (121.9 KB, 112 views)
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Old 6th January 2015, 04:28 PM   #7
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interesting thread

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Old 10th February 2015, 06:39 AM   #8
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Well, I wired up one channel. Due to space constraints, I arranged the resistors "soldier style." This was both time-consuming, and perhaps beyond my abilities at this point. When I tested the circuit, the LED was throbbing, and the voltage at the drain pin of Q1 was oscillating between ~4V and ~5V, give or take. Obviously I had gotten something wrong in soldering up the circuit.

Rather than spend yet more time trying to diagnose the problem with my limited knowledge, I decided to go the easy route and ordered the boards from the diyAudio store. They're almost ready to go; just watching the mail for the output caps to arrive.

In the meantime, I've gathered up all the rest of the parts and materials I'll need...

...And today I mounted a new blade in my miter saw, and set about to cutting the heatsinks, with much trepidation. To my surprise and relief, they cut pretty cleanly, with just one cut slightly out-of-square, which I should be able to rectify when I lap the cut faces with sandpaper.

See attached photos if interested. More updates to follow as I make progress...
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File Type: jpg photo 1.jpg (599.5 KB, 173 views)
File Type: jpg photo 2.jpg (881.7 KB, 193 views)
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Old 16th February 2015, 12:21 PM   #9
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Nice! I'll be watching.
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Old 25th February 2015, 01:06 AM   #10
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Progress is being made, slowly but surely.

The boards are done and working nicely. The attached pic shows one mounted to a piece of scrap heatsink, and playing the left channel of Over the Hills and Far Away.

It turns out the pulsing of my original perfboard attempt was due to a simple and stupid error; I had accidentally used an IRFP9240 for one of the output devices.

Since I went to PCBs for the amp, I decided to get pushbutton power switch circuits from http://www.pololu.com. The switch is rated for up to 20V, but the description states that it may not turn off reliably at the upper end of its rating. Sure enough, it didn't, so I added a relay and a voltage regulator to bring the voltage to the switch circuit down to 8V, and it now works perfectly.

I'll be starting on the chassis next. Going to be using some new techniques so it should be educational... Updates to come sporadically as usual.
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File Type: jpg Photo Feb 24, 4 46 50 PM.jpg (819.4 KB, 143 views)
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