[velmeran42]

Okay, I'm putting some basic info here at the start of the thread in case people aren't willing to read the whole thread:

1) I'm not using a PCB, I'll be doing point to point
2) Yes, those are SMD tantalum capacitors in the photo, they're for my power rails (only two of them, the other one was just to get my digikey order over $25)
3) I haven't began machining anything yet, but I will probably get started this coming week (around Halloween)
4) I'm no longer planning on using any plexiglass, the logo in the front will be epoxy with silver particles suspended in it (a professor suggested the silver particles and is supplying them)
5).... ummm, I don't know, the "black thingy" is a 400mAh 11.1V Li-po cell with protection PCB

img added 11/9/06


img added 11/14/06


img added 11/15/06


img added 11/22/06


img added 11/22/06


img added 12/1/06


img added 12/1/06


img added 12/8/06


img added 12/8/06 (This one is an AlienDAC case)


img added 12/28/06
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(original post starts here)
OK, I've only got a few minutes before I have to hit the bus...

I'm machining an aluminum and plexi CMOY pocket case for a CNC machining class (details to come later today).

I'm trying to build a "top shelf" CMOY w/o going to crazy (bit late for that really), and I want to keep size down as much as possible w/o taking a quality hit.

I'm using a 400mAh Lipo (11.1V) w/ protection PCB, (57x24x18 mm) for the sake of power density and coolness factor. This is the only component I already have on hand. For everything else, please feel free to make comments / suggestions.

OPA: AD8620 - low voltage cut off, good current supply, good sound. It'll play fine all the way up to when the Lipo's protection circiut cuts off.

Resistors: Vishay Dale 1/8 1%, as per parts list except for a gain of 6, no R5, and RLED of 1K ohm (in front off 4 low current red LEDs in series giving them the 2mA forward voltage they need right up till the power dies)

Virtual ground: TLE2426 w/ 220uF 16V Panasonic sitting on battery side (would it be a good idea to cap the output rails, if so, how much?), not sure on the CNR, probably a Panasonic as well, but the lowest V is 50, so the cap is a bit bigger than I'd like. Any suggestions on something smaller for that location?

Pot & Power: ALPS RK097 from Tangent. Seems to be the best compromise of quality and size, like the integrated power switch.

Input Caps: I really don't know what I want to use here yet, I really don't want to sacrifice on quality since this is such an expensive project. Any recommendations available from Mouser or Digi-Key (supperior to the Panasonics on the parts list).

Thanks for any input guys, gotta jet.

Edit: changed thread title to say I put in some pics 11 Oct 06, 11:28pm

 

[Pars]

As far as input caps, look at the BC 416 series from Digikey. Haven't looked at what Mouser has from Vishay...

Also, since you are making such a cool case for it, I would seriously consider board-mounting the input and output jacks (without a mounting nut) and doing something cool on the front panel such as headamp does on the Gilmore lites and I presume the AE-1. You might want to consider etching your own PCB for this.

 

[velmeran42]

Thanks for the first reply Pars. I was actually already planning on doing nutless mounting of most components (all but the volume knob). Part of the joy of CNC machining the project is I will actually be making pockets for all the jacks w/ chamfered walls to allow them to drop into the pockets. Once I have everything soldered up (nice 3-d point to point), and tested I will be potting the whole mess in thermally (and non-electrically) conducting epoxy, thereby locking everything in place solidly w/o the need for the mounting nuts.

I also intend to make use of the micro-CNC-mill in the rapid prototyping lab to etch some labels into the Al, and make a nice logo on the whole thing. I'm also thinking of enameling the etchings for better contrast.

Like I said above, I don't plan on a PCB, just point-point with a final encapsulation of epoxy. I'm going to ask an electronics packaging TA about acquiring some from the packaging lab, I'm sure he won't mind.

I'm still on campus for the day, when I get home I'll see about uploading some rough models of the case as I have things laid out currently so everyone can get a better grasp on what I have in mind. (lots of views so far, but only one response. I know many of you guys have some input, positive or negative, let me have it.. please?)

 

[awptickes]

Won't the epoxy change the impedance slightly, thus changing the sound?

 

[velmeran42]

Quote:

Originally Posted by awptickes Won't the epoxy change the impedance slightly, thus changing the sound?

You know what, I really hadn't thought of that. I'll have to ask when I go in search of materials, the guys doing his masters on encapsulants and substrates, so he'll probably know.

 

[ATAT]

Marine epoxy is nonconductive, so is most mixes of epoxy. That's hte least of your worries (for a cmoy), that's like saying FR4 changes the impedance of the circuit.

how are you doing this btw? a bridgeport? I'd like to see how your lay it out.. square extrusion cut at the ends? machine all of the sides?

Also how do you intend to recharge the batteries?

Electrically,

#1 Why have input caps at all? Id just not use em..

#2 Put caps after the TLE, the TLE is not a high power device.

 

[ex0du5]

Hey,

I've decided to make myself an amp based on the CMOY design. I'm currently in computer engineering and have just started a circuit theory class this semester, with more electronics and circuit courses to come. I wanted to make myself a CMOY amp this year so that in the future, I can see what I can bring to it with my newly acquired knowledge ;D

Anyways, I'm about to order sample parts from Texas Instruments and I was wondering what parts should I order? I'm gonna get the OPA2132P Op-Amp for sure, but I'm wondering if theres any point ordering any thing else while I'm at it since I will be paying the shipping charges anyways.

Are there any better Op-Amps I can order at the same time, or any other usefull equipment for that matter for any audio DIY project I might have in the future.

As well, would I be better ordering a pay-sample, a more expensive Op-Amp?

 

[ATAT]

OPA2107, you'll thank me when you're done. Its an unconventional opamp to use,but a damn good one. Filburt's OPA2107 CMoy apparently sounds unnaturally good, and my OPA2107 PPAS sounds amazing.

The OPA2132 is certainly darker though, so if you like that kind of sound, go ahead.

Also buy your resistors and capacitors from digikey, minimum order fee right?

 

[velmeran42]

Quote:

Originally Posted by ATAT how are you doing this btw? a bridgeport? I'd like to see how your lay it out.. square extrusion cut at the ends? machine all of the sides?

I'll be using a few things, the Al work will be mostly on a Bridgeport V2XT (3 axis CNC). I'll also use one of the two axis EDIT: TRAK K3E (said it was a Bridgeport too) machines (2 axis CNC) since they're much faster to program for pockets and holes. I'll also be using a CNC waterjet cutter to cut out the middle plexi ring.

Quote:

Originally Posted by ATAT Also how do you intend to recharge the batteries?

To recharge the batteries I'll be using a 2.5mm mono connector w/ a sleeve shunt. Plug out battery powers circuit, plug in, the battery is disconnected from the circuit, but connected to the charger (yes, smart Lipo charger w/ proper charge rate). The jack and connector are rated for 1A @ 12V, I'll be putting no more than 400mA through it.

Quote:

Originally Posted by ATAT #1 Why have input caps at all? Id just not use em.. #2 Put caps after the TLE, the TLE is not a high power device.

#1. Input caps... well, if I trusted every source to not have significant DC offset, I'd be right there with you. For safety's sake though, I'd like to have input caps to reduce the risk of damaging any headphones given my habit of using random sources while I'm out and about.

#2. Yeah, after looking at the spec sheet closer today, I realized that I'd need the caps after the rail splitter since it's not good at pushing current.



And now for some pretty pictures:

The case is 2.5" x 2.0" x 0.98" at the momment. All walls are 0.125" thick currently, I might knock that down on some of the faces still. This isn't a final version by any means, just a layout test. I think I can cram all the necassary electronics in the remaining space between all the large components (I'll make little models of the larger components and see how it looks tomorrow).

That should give everyone a good idea of the direction I'm headed at least.

 

[ATAT]

Very nice... going with pressfits using loctite or something for those jacks?

I'm fairly sure you can trim that 1/8th wall to 1/16th. especially if you're taking a solid peice and milling out the whole case (wow, thats's alot of metal removed there)

How are you connecting top and bottom parts of the case? you'd ideally want both metal parts to be connected via a conductor (for shielding) not that it matters too much, but its just a good idea when near CRTs or whatever.

Nice that you're using a bridgeport (a cnc too!) we've got a 2 axis DRO'd bridgeport so I know what fun it is to work with those..

Also, what cad program are you using:?

 

[velmeran42]

The top and bottom will be connected using 4 countersunk allen head screws (6-32 probably), at least that's the direction I was thinking in (they'd be conductive to boot).

The jacks will be "press fit" to a certain degree, probably throw some CA glue on them too, but I'll be backfilling the entire bottom section of the amp w/ epoxy, so they won't be going anywhere once that's done.

Yeah, the University of Washington's Mechanical Engineering department has a pretty amazing student shop given we're engineers, not machinests. We have 3 two axis CNC mills (soon to be 4), 2 DRO mills, 1 three axis mill, 4 DRO lathes, 1 CNC lathe, a CNC plasma cutter, and a CNC abrassive water jet cutter, not to mention all the lesser machines (saws, sanders, drill presses, etc.)

Oh yeah, I will be starting with two sheets of Al plate stock (we have tons laying around in various thicknesses). One thing on the thinner walls is the plexi band can only be cut so thin on the water jet, and I need some meat for the screws to go into (I'll still have to add some back in w/ the 1/8" walls). Plus having a crush proof case is always nice.

Edit: the stuff seen above is done up in Autodesk Inventor, my personal choice. We use Solidworks and Catia on campus (Rhino too if you're so inclined).

 

[awptickes]

Heh, that case will be really sweet after you get done.

Yeah, crushproof is a good thing, having lost two CMoys to boots and car doors.

Neoprene with an anti-static bag isn't a good case.

 

[velmeran42]

Small update: ~$63 later and all the components are on their way to my door. I've updated the model a little bit to reflect the components selected and address how I'm actually going to screw the two halfs together. I probably won't be using alen cap head screws, but that was what was sitting on my desk when I went to model it. (I will be using #6-32 screws though, that's as small as I'm willing to go).

That's where it stands now. No the components aren't really arranged as they will end up, I just wanted to see how much space I had to play with. I also need to make an accurate model of the Lipo cell (not just a volume holder), so I can get a better idea of just how much I can wedge it into the corners.

Small thought, I still don't have a pocket clip. I'm looking at different knife makers trying to find a suitable one, but am having a hard time. I'm thinking of scavenging at the local thrift stores for something suitable, but was wondering if anybody had any good suggestions of where to come up with one?

 

[Sybaek]

What about those clips from retractable tape measures? The larger ones have some nice solid metal clips. Might be able to cannablize one. Interesting project, I look forward to seeing how it will turn out. Best of luck.

 

[velmeran42]

I actually found some clips for sale at a knife kit site. knife kit site. I bought 5 of the small ones, figured I might as well since I had to pay shipping and I'm planning on taking a rotary tool to it. There are a few knives in their gallery that have modified versions of the clip.

Oh yeah, never one to be satisfied with one project at a time, I just ordered a few Alien DAC boards. Assuming this build goes well, I intend on making one for the DAC too.

One last thing to tack on to this one. I've been toying with a few designs to etch onto the case. I modeled my current favorite today, the op amp diagram needs to be scaled up, but I'm cooking curry, so that'll have to wait a while.

Oh yeah, I assume the generic three semicircle headphone logo on my amp won't upset anyone? If so, just speak up. I thought a headphone w/ an op amp in the middle was a good looking way to get the point acrossed.