API 325 to 312...help please.

Hello everyone. This is my first post ever on anything. I have no idea what I'm doing so I apologize in advance for any nubeness. I've tried searching through the archives and found much useful information but the main threads about API 325 to 312 conversion seem to be dead links. I have a couple 325 cards and a couple AP-2622 transformers along with some other parts. As far as I can see all I need are a few capacitors and resistors, a couple male and female xlr's, some wire, the mating connectors, a chassis, a whole lot of guidance from more experienced people (you) and i can be on my way to being a much happier sound engineer. Can anyone point me in the right direction. I guess a parts list and guidance is really what I need. I already have the schematics for the 325 and the 312 cards. Any info is greatly appreciated. Thanks.

Welcome! It's a bit easier than you think. Check out JLM Audio's page for Power Supplies and Utility switching.

I don't have any specific info for you. But I know Soundguy Dave has done this conversion. I don't know if his page is still up but you can find it cached on google.

www.jlmaudio.com

I've done a few of these conversions. Ask away.

Good, ain't he? :green:

How I did it:

1) Get schematics for 325 and 312
2) Buy stuff that you're missing
3) Remove stuff you don't need
4) Jumpers and Solders and Caps, OH MY!
4.5) Oh yea, you need to mount that transformer somehow...
5) Put it in a box with an edge connector
6) Audio connectors: Gotta love 'em
7) Power supply - - +/-17 and +48v 'phantom power'
8) Enjoy

I took about a year to work up the courage to mess up my first API 325. Took perhaps a little too much time to get to it, but it turned out well.

Why 17 volts? I thought API gear runs on 16 volts?

I think anywhere between 15 - 18 seems to work fine...

If you are looking for schematics, Dan Alexander has 'em:

http://www.danalexanderaudio.com/ApiInfo/api312schem.jpg
http://www.danalexanderaudio.com/ApiInfo/api325schem.jpg

They're supposed to be happy with +-15V to +-20V.

I liek the way mine sound at 18 volts, been running them like that with no incident for a while now.

dave

Wow! You guys are awesome! Your api pre's look great.

I have a wannabe lunchbox thing happening with two 560 eq's and two 554 eq's that I powered up with an Aphex +/- 15V power supply that I tweaked to put out +/- 18V. My intentions are to incorporate the 325/312 pre's into this same chassis. So the power supply part of the project is already taken care of. Although I do want to add phantom power to this eventually.

I did not know that I had to modify the 325 cards themselves. I thought it was all adding stuff outside. I did print out the schematics and saw the differences between both circuits. Again, sorry for my lack of understanding of the subject and if this has already been discussed in the past and I missed it during my searches I will refer to that instead.

So, what modifications have to be done on the 325 cards?
Oh yeah and...where can I buy the edge connectors?

Thanks again.

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[quote author="furmound"]So, what modifications have to be done on the 325 cards?[/quote]

These are the mods I make to 325 cards... R3 will depend on what you are using for a pot.



Edac connector available at Digikey EDC306150-ND.

peter

[quote author="drpat"]Oxygen free ground wire too? [/quote]

Ordinaire, but thick..!!

...

Thank you so much gentlemen.

The mods do look pretty easy. I will order the parts today.

-Just out of curiosity, why change C1 & C2 to 220 uf 50V if they're actually the same on both schematics?

-I know that there's a big thread regarding what pot to use for 312's, but it was too much information for me to handle. I have old api gates that I don't intend to ever rack so I would like to use them for parts. They have three pots on them. They are labeled:
(2)"PEC CANADA SA5022R18 5K K4"
(1)"PEC CANADA RV6NAYSD104A 100K K3"
I also have some spare Yamaha pm-1000 modules that have aux sends that I'll never use. Those pots are labeled:
-M10K ohms A 1630
If I cannot use these can you recommend any? I cannot afford stepped attenuators right now unfortunately.

-Regarding C5 "replace with correct termination for xfrmr." I will be using original api 2622 input transformers. What would I replace C5 with? Or do you mean that I have to remove that cap completely and replace it with the appropriate transformer terminals? Just want to make sure I'm interpreting the information correctly.

-And finally...uhm...I forgot. Guess I'll post when I remember.

I'm glad I won't be doing any trace cutting. That sounded kinda scary.

C1 & C2 changed for more effective power supply bypassing.
The pot wants to be a 'REVERSE LOG TAPER'. 10K to 50K, depending on what you see at R3.
Transformer termination C5 for a 2622 needs to be 220pF & 5K1. Take transformer secondaries (via leads) to HI pin 5, LO pin 4.

peter

http://www.vibroworld.com/parts/tech14.html#pots

Get a 50K REVERSE audio taper from these guys. They sell them super cheap and it will work until you want to make a gain switch.