Axiom Home Page Forums General Discussion Technical Questions DIY Class D amps

Anyone tried this or have any real info on it? One hopes they're not ICE amps, but they probably are.

http://classdaudio.com/index.php/class-d-amplifier-kits/home-kits.html

My boss emailed me the link; I think he's thinking about trying it out. Probably means they got reviewed on 6moons or something.

That looks pretty cool.

Doesn't look like they're based on an ICE model. The only part reference I can find on their older ones is: CDA2092X2NR That doesn't show up anywhere but on their own site.

Their newer designs use TI's Digital Amplifier parts. That includes the "600W Class D Power Amplifier, Balanced Input, 2 Ohm". That amp looks really interesting. I might pick up the parts to build one. $235 for the kit, not bad.

Yeah, I looked at the instructions and decided it was probably beyond me (I'm not particularly good at soldering), but it looked pretty cool. Plus they don't really tell you what to do with the transformer... Bits and bobs would probably take it to $500, but that's still pretty good if it does what it says.

Those are some pretty nice kits.

I hope someone tries this, it looks to interesting to pass on.

How does someone get Audioholics to review a product? I'd love to see their test results for one of these before I fork over the cash.

While the design is pretty much a TI reference, there could be something wrong in the MOSFET setup which allows DC leakage or ultrasonic filtering (not uncommon with Class D amps).

I don't want to end up with an 600 Watt, 400 kHz radio station operating out of my living room, nor do I want to blow up my speakers with DC or high frequency noise.

Spent the last 90 minutes reading TI's docs, and comparing their reference design to the pictures on Class D Audio's website. Seems TI has done a very good job designing the chip which is the core of this amp. Leaves very little room for mistakes from the implimenter. The only thing TI stresses is the distance from the output pins to the decoupling caps. TI says this should only be limited by the size of the heat sink. Looking at Class D's picture, that's exactly what they've done, the caps are right next to the sink.

That makes me feel much more comfortable in picking one of these up without someone else testing it first.

The only place Class D's design differs from TI's, is TI uses two separate power supply inputs. One (50V) for the output drive, and the other (12V) to run the chip. Class D takes one, and performs "house keeping" on board to step the voltage down to power the chip. TI's design is intended to be used with TI's class G power supply (variable output for different amplifier demands). Class D Audio's power supply is of a more traditional fixed level output.

I also noticed that Class D's kit includes a transformer in that $235 price. So that's amp board, power supply, and transformer. And from the looks of things, it could actually be assembled with no soldering. It's really just running wires between the parts, and tightening screws to hold them in place. Of course if one wanted nicer RCA or XLR inputs jacks would have to be connected to a couple of those wires.

EDIT: I should have noted that the proximity of the caps to the output pins is what is keeping the electromagnetic interference to a minimum. And safety features in TI's design keeps the output MOSFETs from conducting DC during power up/down.

Think it would need further heatsinking or a fan? I see there's a fan pinout on the board.

The specs say, "Two Speed 12V Fan Output (most conditions will not require a fan)". One review says that the fan never turns on. If that's the case, and the fan doesn't normally run, I'll probably put one in the enclosure, just to be on the safe side.

I'm thinking about building it in a 2U rack mount case. I'll use the same phono/XLR connectors that Axiom does for input. Hooking the switch triggered by inserting the phono plug to the single ended/differential jumper. Although I plan on running my first one as mono bridged, I'll include both sets of binding posts, and just parallel them into the single set on the speaker (after setting the PBTL jumpers on the board, of course). But that'll allow me to just lift the lid, reset the jumpers to BTL, and connect up a right channel input and then have a stereo amp.

Where are you getting the case?

Probably just go with a generic Middle Atlantic case, and cut the holes as needed. Although, Bud Industries resales some with vented lids, and if I felt like paying more for actual machined holes and silk screening I'd definitely go with them. We use them both at work for project boxes.

Hmm. I lack a drill press, so I think that would be challenging for me. It seems like a fun project, and I'm tempted, but the case would be tricky.

If you bolted stand-offs onto the boards, then all you'd need to do is drill the holes in the right place in the case, and bolt everything down. The cases themselves don't have to be tapped. As for the input/output jack holes, again just drill a simple hole, and use a nibbing tool to cut the right shape out.

That how things are usually done at work, for one-offs. Although we do use a drill press for the holes, just because it's there. There's no reason that placing 4 dimples and then going at it with a hand drill wouldn't work.

Heck, it almost looks like with the TI kit, you could just take a busted amp and strip out the innards, then just put that one in. Just clip the input/output/psu wires, re-solder them (if that, even), screw in the transformer and the boards, and Bob's your uncle.

Bob sure must have gotten around.

Pretty much any of their "kits" have everything you need to replace the guts of a busted amp. Once the transformer is tied to the power supply, and the power supply to the amp board, all you need to do is hook up the inputs and outputs.

Their older models are an unknown design. But everything I've read about the TI Digital Amplifier chip, makes it sound like very well designed part.

Chris, were you still doing this? Just curious.

It's in my plans, just not immediate. I don't have any speakers which would really benefit from extra power at this point.

Actually just today I was just putting together my shopping list for the year. The amp kit's on it, but behind a pair of M80s. Also behind window blinds, a pair of air conditioners, and a few other things which I need to make my room more comfortable.