API 312 layout/PCBs

**fallout** · 10-03-2003 10:48 AM

Well, i guess it's API fever time now that the output trannies rolled in.. So has anybody come up with any PCB layouts yet? [img]smile.gif[/img] My plan is to make 4 with the Avedis 1122's and 4 with 990's, incorporating a phase reversal switch and phantom power to the circuit. I'd assume the only differnces in the layout would be for the input transformers? Perhaps the Lundahl 1538 XL for the 1122's and a Jensen model for the 990's? Is anyone up for a group order of PCBs, perhaps some nice plated through hole types? I'd be willing to do the ordering.. Let me know what you guys think..

-Jay

**kato666** · 10-03-2003 11:47 AM

I've asked about this before with no responses. As far as I can tell, nobody has a PCB file yet - at least not one they care to share.

So, since this is DIY, I decided to DIM. (do it myself.) However, this will be my *first* PCB EVER - so you can't really count on me to do it right - but I promise to do my best. And I'll be happy to share when it's done.

I just downloaded some software to make schematics / PCB traces and I'm learning how to use it now.

I will post my artwork when it's finished (hopefully next week.) I'd love some feedback if the experts want to check it for errors. Stay tuned!

More thoughts on the subject:
I think the main reason we don't have an API 312 Group standard PCB trace is that it will be impossible for everone to agree on a configuration. Some are using Jensen inputs, others Lundahl - some will be mounting them on the PC board, others will use the standard ones with wires hanging out, etc.

If anyone out there has an unpopulated 312 card, please drop it on your scanner bed and make a scan. It would be an excellent starting point that most people could agree upon. Then we can all modify to our hearts content...

Kato

**rascalseven** · 10-03-2003 01:01 PM

I have a couple of Brent Averill-racked 312's at the studio. I'd be glad to take a couple of pictures and send them to anyone interested in laying out the circuit.

I won't be able to do it till Monday, however (not going back to the studio over the weekend).

If anyone is interested, PM me.

Peace,

Joel

**Mark Burnley** · 10-03-2003 01:06 PM

But for now, this'll have to do!
(I can't remember where I got this from- I just snagged it and put it in my "useful TechTalk Folder"- thanks to whoever posted it originally [img]graemlins/wave.gif[/img] )

...I reckon I'll have to get in on the next batch of transformers...

Good luck to all you API'ers, looking forward to seeing some top projects!

[img]graemlins/thumbup.gif[/img]

Mark

**fallout** · 10-03-2003 02:02 PM

Do you guys think a phase reverse switch would be too much trouble to implement in this circuit? The only thing i really 'need' is phantom power, which shouldnt be a problem.. Anyone have a nice power supply that work well with the 312 w/ Phantom power?

-Jay

**Tadgos** · 10-03-2003 02:32 PM

Hey guys,

I have a pcb layout I've made with express pcb. It's the first prototype but it is functional. It's layed out for the Sphere input transformers that Dan Kennedy has for sale and the TX's we got from James. I've already made one card (but used the 2623 output TX) and everything works fine. I used Peter C's green pre psu (+15/-15v) to test. I'm very pleased with the result. If anyone would like to get a copy of the pcb file they're more than welcome to it. You can alter anyway you see fit for your purposes.

Later,

**ciminosound** · 10-03-2003 02:50 PM

Hi John,

I'd love a copy, sent it to ciminosound at yahoo.com

Gerry

**Flatpicker** · 10-03-2003 03:25 PM

I'd like one too, John. Thanks!

**Tadgos** · 10-03-2003 03:43 PM

Hey Gerry,

Check your email. Flatpicker, Could you pm me your email?

Oh yeah, I don't have onboard phantom or phase yet. I will put phantom on there. Probably no phase though. My console and my daw both have this function so it's not neccesary at this time.
later

**moby@ptt.yu** · 10-03-2003 06:32 PM

Hi everybody. Are you talking about 312+ 2520 onboard, or some other op? If sobebody finally made 2520 traces it will be nice to hear and have a copy of that! [img]graemlins/wave.gif[/img]
Sergio
P.S. Something interesting, please email at moby@ptt.yu

**Tadgos** · 10-03-2003 06:49 PM

Hi guys,

My layout is for the 2520 op-amp.

later,

**moby@ptt.yu** · 10-03-2003 07:58 PM

Thanks John! Unfortunately i cant open the file because im on Mac, but in the next few
days im gonna do it on the windoze machine....
[img]graemlins/peace.gif[/img]

**kato666** · 10-06-2003 08:22 AM

John, it will be great to see your ExpressPCB file. I'm working in ExpressPCB also. I'm not familiar with the Sphere input tx but I will modify yours to work with the Jensen 115k and Lundahl 1538XL which seem to be the popular choices for input. Thanks for sharing your work!

Moby, making traces for the 2520 is fairly easy; API made the datasheet available with pin spacing and dimensional details. That's the only part of my in-progress board I'm sure of - that and the input transformers. It's the capacitors I'm having trouble with because I don't know their exact dimensions.

BTW - the 2520 pins should be compatible with other op-amps in this class - the 990 and 1731. Somebody correct me if I'm wrong.

Jay, I was planning to wire mine without phase reverse or phantom but it should be pretty easy to include both of these. I'll give it a go. Later,

Kato

**cjenrick** · 10-06-2003 10:15 AM

Easy layout. Not much there. It's all in the opamp. Don't think card connector is the way to go. Hard wire to input jacks better.
I have an idea for phase reversal. Since the output tranny has 3 output windings, you have a built in splitter/phase reverse capabilities already! Just layout 6 output terminals for the secondary to wire as you please. You could have seperate output jacks, or a switch.
I loaded down the secondary with some pretty heavy termination resistors when I did the transformer testing, with very little signal degradation. You could drive a locomotive with this thing!

So, 75 ohms out from 3 different places, lots of possibilites, 600 with 75 reversed, etc.
CJ

Just a note, since the output tranny is not gapped, you want to make sure you trim out all the offset in the opamp so no dc gets on the primary. So you might want some jic (just in case) holes on the board for a multiturn trimpot for fine tuning the trim resistor.

**kato666** · 10-07-2003 10:59 AM

Cjenrick - Yeah I'm not planning to mimick the API card slot connector. I just wanted to see the original API traces for inspiration.

The ExpressPCB "mini-board" is the most affordable for those who don't want to make PCBs - but it's limited to 2.5 inches wide. Incidentally, that's just the right size for the slot connector for someone who wants to attempt it - but I don't have an API power rack so that would be pointless for me.

Taking a look at Tadgos pcb is really helpful in figuring out the correct pad and hole sizes. He uses several different hole sizes so I guess they're not just random.

But why is the whole board covered in ground? Is this a noise rejection technique? Or just for convenience? I'd like to know before I finish my first board. (still messing with the schematic.)

Kato

PS - for anyone who cares about the hole sizes, Tadgos PCB uses .110" pads with .061" holes for the meter, the opamp, the output tx ground, and the corner standoffs. It calls for .100" pads with .035" holes for signal input and output, output tx, input tx, power, and gain controls. It calls for .056" pads and .029" holes for resistors R2, R3, and R4 and caps C3 - C7. It calls for .075" pads and .040 holes for the diodes. And it calls for .080" pads with .035" holes for the big caps (C1 and C2). Also, the output tx cutout is approx. 3/4" x 1.1"

**bauman** · 10-07-2003 11:57 AM

Yea, it's a very simple board. Just keep connections to opamp as shorts as possible, don't run input and output sinals close or in parallel and use some GND cooper plane. If you do tracks with, lets say 40/50 mils with spacing between them about the same, you'll leave room to the plane cover all the board. Board holes you describe looks ok (at first glance).
[img]graemlins/beerchug.gif[/img]

**Kev** · 10-08-2003 12:00 AM

Originally posted by KCJenkina:
So, since this is DIY, I decided to DIM. (do it myself.) However, this will be my *first* PCB EVER - so you can't really count on me to do it right - but I promise to do my best. And I'll be happy to share when it's done.

Thanks Kato.
.. this is on my list of things to do but as I don't have an oputput trafo ... or an op-amp .. or an input trafo, I'm afraid it is outside the top ten for me. I will get to it eventually but for now ... it just aint gonna happen.

**cjenrick** · 10-08-2003 08:51 AM

Here is a board for an API type amp. It's not the same as the mic pre but it will give you an idea as to trace size and spacing, groundplanes, etc. The opamp pins are located at the top center of the board, the five in a row, and the two input pins underneath them:

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