bluesbaz

8 channel api preamp for a lot less
« on: August 03, 2013, 03:52:24 PM »
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.


bluesbaz

Re: 8 channel api preamp for a lot less
« Reply #1 on: August 03, 2013, 03:56:02 PM »
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.

bluesbaz

Re: 8 channel api preamp for a lot less
« Reply #2 on: August 04, 2013, 06:30:59 AM »
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

grubbyliver

Re: 8 channel api preamp for a lot less
« Reply #3 on: August 04, 2013, 08:02:46 AM »
Ooooh nice! Great idea to re purpose the aca boards like that.

Ben

EmRR

Re: 8 channel api preamp for a lot less
« Reply #4 on: August 04, 2013, 08:29:12 AM »
Proper DIY here, rather than kit building. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

Re: 8 channel api preamp for a lot less
« Reply #5 on: August 04, 2013, 09:34:40 AM »
I like the hand writing...

Indecline

Re: 8 channel api preamp for a lot less
« Reply #6 on: August 04, 2013, 06:50:16 PM »
Nive diy on the front end too :D

bluesbaz

Re: 8 channel api preamp for a lot less
« Reply #7 on: August 09, 2013, 07:19:49 PM »
Thanks guys!

Walrus

Re: 8 channel api preamp for a lot less
« Reply #8 on: August 13, 2013, 09:42:17 AM »
And there was me thinking I got there first!
Only just completed it......
Kevin.

bluesbaz

Re: 8 channel api preamp for a lot less
« Reply #9 on: August 13, 2013, 01:15:24 PM »
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?


Walrus

Re: 8 channel api preamp for a lot less
« Reply #10 on: August 14, 2013, 09:09:57 AM »
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
Kevin.


 

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