Access-312 Build Thread

[sr1200]

Some pics of my dilemma... iphone pics, best i can do right now

 

[toneboner]

@sr1200  --  totally jealous.  even with ur weird 48v voltages ur well on your way. i'm still saving up the scratch for my cinemags...!  what are using the 12v rail for?

@micdaddy  --  the bom i posted was from another thread (cant remember!) and will stuff 4 boards + extras.  Itd be nice to know what someone else thought of the parts -- errors, advice or substitutions...

 

[sr1200]

Got 4 of the 5fish LED VU meters to sit next to each channel.  Im not very optimistic about this one though.  Hopefully the rest of the issues arent anything crazy. I really should have documented the build step by step for this one, would have been easier to track down what i messed up. Lol

 

[3nity]

Ok..(looking at the picture)..the potentiometer...you jumper the wiper (middle pin) with the pin on the bottom WRONG.
you need to jumper the middle (wiper) to the top pin.

Now from the pot.. white wire goes to hole # 1 and black goes to #2.

For jumping JP2...you can use 2 of this below... jumpin 1-2 and 3-4 or just 1 and put on pins 2-3

Thanks.

 

[3nity]

If you dont make a connection at JP2 you wont have sound!
Thanks.

 

[sr1200]

Ok the 48v problem is solved. I rewired the pot as stated and still does nothing. Im using 10k rev log pots(as per bom) and according to the scematic, gain 1 goes to pin 1 and gain 2 goes to 2&3 (the way i had it before) i disconnected the pot and checked on an ohm meter, pot is functioning and values are correct.

Just out of curiosity, i put gain 2 to the wiper and gain1 on one of the outside pins and it works.... Oddddd.

 

[Le Roux]

I am also having troubles with the gain pot.  Nothing until the last 1/4 turn.  Shorting  the gain 1&2 pad, preamp works and sounds great!  Guess I'll try wiring the pot as above post.

 

[3nity]

the shematics says top view...but pins facing the top.
Just to make sure R4 is 100R and R5 is 10K??

If so review the pot pins to the top pin 1 is at the left, wiper: middle and 3rd is the right pin.
wiper and 3rd pin jumpered they go to hole #2 and pin 1 at the left goes to hole #1.

Good luck...

 

[Le Roux]

I also had the pot wiring backwards  :-[

One thing I am noticing though is the pot will not completely shut off audio signal?
Even with pot disconnected, there is still signal going through.

This is on two different boards.

Is this supposed to be like that?

Thanks

 

[sr1200]

Mine is like that as well, but keep in mind, theres really no reason for it to go to NOTHING, its a mic pre, not a mixer.

 

[manulaudic]

Hi, i'm wondering where did you order your PCB from?

manu

 

[okgb]

Some circuits & opamps are not stable at unity gain and not designed to be
see specs where it quotes min & max gain

 

[sr1200]

2 of my channels are working perfectly!
Just waiting on some new (read different) DOAs for my last 2 channels.  Figured id do a pair of 2520's and a pair of ML918's (just to see if I can hear the difference, and IF so, then I have a couple of flavors at my disposal.

 

[3nity]

what was wrong?
Thanks.

 

[sr1200]

Well, besides the 48v problem and the pot problem, there was an odd grounding thing, which i realized that the grounding pin was not attached to the ground pins on the XLR's which got rid of a TON of hum.  Once that was taken care of, i tidied up the case a bit and voila!

Its a pretty aggressive sound, but I like it, its very wide open.  Cant wait to hear what the ML's sound like, supposedly theyre a bit "smoother".

 

[manulaudic]

Have you guys ever compared those to the JLM audio Baby Animal kit?
You can get that Api tone with it too or go some complete different tone (Neve etc...)

Manu

 

[3nity]

Baby Animals are really good but honestly it doestn sound as an API-312 preamp.
Thanks.

 

[manulaudic]

Ok thanks 3nity

 

[frazzman]

Is this the pot at small bear that you're talking about?
Http://www.smallbearelec.com/Detail.bok?no=116
Thanks

Hey.
This build is pretty straightforward build if you follow the BOM.

To answer some questions i will update the BOM.

Thesystem i suggest you take a look at the Meta for some info before starting something that might help you a lot its looking at pics.
But here are some light to your questions:

1- 10K reverse pot 2.50$ at Smallbear good quality.
2- psu adjust voltages: read the meta and do some research.
3- There are too many power transformers so you better look something at RS-Farnell.
4- EA-2622: you need a 150K on RC, 10K at R7-R6 and 220pf at C8.
5- F2UEE are the pushbuttons to go on the access-312...
6- LED, any LED will do the job if it fits you front panel...you solder it to the lugz on the top of the switch.
7- Sockets are there so the op-amps sits on it ..it makes things easier.
8- Gain 1-2 are there so you solder the wires for the pot..you can use molex headers.
9- yes.

 

[3nity]

I cant see what your liks is.

But is a 10K reverse log pot at 2.50$