Hm, I can't remember if I did ground the inputs for those tests. I think I did, but it doesn't matter now that my DC is pretty much zero.
Anyways, on to the main event. I finished building my PIMETAv2 last night in preparation for the Calgary meet this Saturday. I installed Class A just yesterday night, and biased my RBLIM of 287R to have ~0.56V across it, about 2mA of bias. I tweaked my BB to only have the pot and caps in parallel (no R4, so it's in unity boost), so it's plenty deep right now through my normally airy SR60s. I must say, I may be a bass junkie.
My pot is 50K, and I have 0.22uF K42Ys from my Millett Max build paralleled with an additional 0.1uF of Wimas I grabbed from Mouser. Wow, I can get used to this much bass. All these values weren't really calculated. Class A could be biased deeper, but I don't know if I really need to; I could stand to with the additional PS headroom. The bass sounds great to me, so I have little impetus to get it "just right."
Here is my configuration:
- SMD build. All resistors are SMD, and so are C3, C4 and C5. It was good experience, but I much prefer having through hole. It's easier to see what you installed because it's all on top of the board.
- AD8620 and AD8610. I used to have OPA627s with my PIMETAv1.1, but i think I might have blown them up
- R7s are 101R
- R4 is absent. I have the amp set up in unity boost.
- C4 is 1.5uF
- Class A 2mA. Trimpot 5K and RBLIM 287R. Both my LEDs have Vf 3.5V.
- I went with the 1.1mA CRD for RLED
- Volume pot is Alps Blue
- BB pot is 50K Alps RK097
- Jacks are nothing special
- No switches for PWR and BB. If I'm not using the amp, I don't really care to shut it off. If I don't want BB, I just turn down the pot. It turns on when I plug it in.
- Case is 1455K1201.
- PSU is a 24V AC/DC wallwart into an LM7818
. Here's the different part for me. No particular reason I did it besides proof of concept. You install it the same way you'd solder in the LM317
, but you don't connect any diodes. Instead, you bridge their anodes (non=striped ends), and connect pin 2 with V-. You can use the other end of RCCS to do this if you don't want to solder directly to the LM78xx. If you just compare the two pinouts with the schematic, you'll see what I'm talking about. I've linked them for your convenience. Plus, you have to make sure you include the proper stability capacitors. I don't know if tangent plans on incorporating this into the next design, but it can be done with this revision of board if you so desire. I also got a huge heatsink for the VREG, which I don't think helped with the casework. Nevertheless, huge heatsinks are always cool.
If any of you are familiar with my workmanship, it's not as it should be. I usually only use one type of hookup wire and I don't have any heatshrink. Just lazy to invest in the proper tools, but I'm getting there. I'm a little hesitant to show the internals, but since I'm a prototyper and not just doing my own thing, I'll share. You'll understand when you see it.
Anyway, just wanted to report a successful build with no major complications. If anyone wants my BOM, I can share that too. Thanks, tangent, for including me in the proto group. I really liked the card. Classy.