8 channel api preamp for a lot less

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bluesbaz

Well-known member
Joined
Jan 9, 2005
Messages
201
Location
San Francisco CA
Im a cheep bastard so I worked a few things out and build this 8 channel ratrod box. Its heavy but its been solid for more than a year now.
 

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And a shot of the guts. I used a whistlerock psu, which I use often, built into an ammo box. The boards are the aca summing. Transformers are cinemag and the reset are some relay boards i put together for phantom, phase, and pad. The whole thing was around 1200 for 8 channels.
 

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I've been asked if I have a writeup for this project. Well I used this schematic from 3nity ( buy his boards if you dont see how this can be done they work well for first time projects) http://twin-x.com/groupdiy/albums/userpics/312-schematic.pdf

I replaced the switches with off board relays. Everything before the input transformer is mounted on breadboard and I replaced the switches with relays. The support for the opamp and its volume go on the aca board which since jeff does not post the schematic to on his site I will not post my updates for it here. Needless to say It is EXACTLY the same as the 312 schematic the way I set up the board. 

I hesitated to post all of this for fear of upsetting anyone the aca boards are cheep compared to the preamp boards Jeff sells but the 500 format boards have a lot more going on and the way I set things up is far more simple No di, no calibrated gain, and no output attenuator.

I would say build this without the phase phantom or pad first and get signal flowing once that works add the rest. An api is amazingly simple power the opamp and send part of the feedback loop to ground to control the volume. spend time getting the first channel to work and just copy it.

-s
 
And there was me thinking I got there first!
Only just completed it......
 

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Nice one! What are those buttons? They look great! Looks like you have cleaner innards. Great job... Great big job. How do you feel about the sound?
 
Buttons are from Mouser http://uk.mouser.com/ProductDetail/NKK-Switches/HB16CKW01/?qs=sGAEpiMZZMvxtGF7dlGNptuNjavJu6Nr8Q4XSWCNEMI%3d
I changed the LED's that come with the lens' for high efficiency ones, otherwise at 20mA apiece the max draw would be 1/2 an amp!

I haven't personally listened to it yet, but it should sound identical to our API desk as I used exactly the same mic amp circuit , and just bodged modified the original API ACA boards.
What I really need is somewhere locally that can do front panel engraving to make it look professional.....  ;D
 
Bumping this thread to ask how you guys mounted the 2622 transformers upside down? I'm doing a similar project right now. I was thinking something like a hose clamp but can't really find one that can be properly mounted.
 
JW said:
Bumping this thread to ask how you guys mounted the 2622 transformers upside down? I'm doing a similar project right now. I was thinking something like a hose clamp but can't really find one that can be properly mounted.
Yep cap clamps https://www.ebay.com/i/233210474777?chn=ps&var=532710151663&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=532710151663_233210474777&targetid=1068323854270&device=c&mktype=pla&googleloc=9061088&campaignid=11755691265&mkgroupid=116570925080&rlsatarget=pla-1068323854270&abcId=9300462&merchantid=115021780&gclid=CjwKCAiAouD_BRBIEiwALhJH6IiwA2WVDv4-zLkEvln7-Co8Ml8xxVSwB_lc6jI3z8PVod0xYDFn-RoCHyIQAvD_BwE

But I have jb/welded a pre drilled plate to the bottom and that worked well too.
 
Walrus said:
Buttons are from Mouser http://uk.mouser.com/ProductDetail/NKK-Switches/HB16CKW01/?qs=sGAEpiMZZMvxtGF7dlGNptuNjavJu6Nr8Q4XSWCNEMI%3d
I changed the LED's that come with the lens' for high efficiency ones, otherwise at 20mA apiece the max draw would be 1/2 an amp!

I haven't personally listened to it yet, but it should sound identical to our API desk as I used exactly the same mic amp circuit , and just bodged modified the original API ACA boards.
What I really need is somewhere locally that can do front panel engraving to make it look professional.....  ;D
Those buttons are great. Good for Solo and Mute buttons on a mixer and there is a version that takes an LED too.

I know its seven years late but I found an affordable UK front panel source:

https://www.meface.co.uk/

Cheers

Ian
 
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