API 312 clone PCB sources?

[Matt C.]

so I'm thinking about building an API 312 style preamp and I'm wondering if anyone knows of current sources PCBs for this project. I know there's tons of information about this project on the web, but most of the discussions are a few years old and a lot of the PCBs seem to have come from group buys that are long gone.

should I use the seventh circle A12 kit even if I don't want to use their enclosure and all that stuff? or use the boards from classicapi.com even though I'm not putting it in a 500-series/51x rack? any other options you know of that are currently available?

[Nate Dort]

I have no affiliation or first-hand experience with these:

http://www.whistlerockaudio.com/cart/
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[bantam]

perfboard it! its like 10 components. i just did 2 channels in no time
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[wkrbee]

Classic audio products of Illinois-but you will end up buying alot more from them!
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[honkyjonk]

Yeah, Jeff Steigler at classic api That place is awesome. He can't be making much money at all from that stuff. It's cheap and it's the real deal. http://www.classicapi.com/

They have the Ed Anderson transformers. They sound amazing. You can buy 2520 kits or Melcor 1731 kits and build the opamps too. (Takes about an hour per opamp for me anyway. Last time I checked the opamp kits were like $17 a pop.) Bang for the buck ridiculousness.

Whistle Rock is cool too. I think he has DIY Jensen style opamps that can run at +/-24V. Actually, his power supply is really easy and great too. That's the power supply I used for the master buss amp from Jeff at Cassic API

That API master 2 buss amp is probably the single greatest DIY improvement I've ever done. I installed it in my Yamaha PM2000 mixer as the master buss, and it blew me the fuck away. I still can't believe it when I crank that thing.

However you go, you can't beat those GAR DIY opamps.
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[Matt C.]

cool. i'll probably get the channel PCBs from Whistle Rock since they are small and designed to fit in regular 1RU chassis. then get transformers and some other parts from classicapi.com

one detail of this project I haven't figured out is sizing the power transformer. I'm planning on doing 4 channels in one box, and I'd like to try running them at +-18V for higher headroom. so my questions about the input transformer are:

- if I want the PSU putting out +-18Vdc, can the power transformer secondary be at 18VAC or does it need to be a little higher?

- I'm not sure how much current each channel will draw, so I'm not sure what VA rating the power transformer needs in order to have to handle 4 channels. how do I figure this out?

thanks.

[Nate Dort]

I've got a 25VA Antek power transformer in my 4-channel 312 rack and it's plenty of juice. I've seen people get away with 20VA, no problem.

You'd need about 20VDC after rectification to get an LM317 to produce a stable 18VDC.

20/1.414 = 14VAC, plus a few volts for the full-wave rectification diodes, plus a little more to account for voltage sags at your outlet. So I'd think you'd be fine with an 18VAC secondary. If it were me, I'd go with a 20VAC secondary and do a couple CR stages after rectification to smooth out the ripple before it hits the regulator. Just heat-sink your regulator well and you'll be fine.
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