Access-312 Build Thread

[3nity]

wow didnt notice those jumpers untill now!
cut 1 of them at least.

 

[soundsactive]

how much more should i increase the phantom caps for 4 units? a few uFs or more? would 230uF be enough? i'm not sure the equation to calculate, if you have that handy that would be awesome too. thanks!

 

[bieckmusic]

any chance more boards will be offered??  it's a great project

 

[rodcaster]

Hi there,
somebody knows what is this noise at turning off the preamp?
https://www.dropbox.com/s/wz64cowf3r7dgg7/Turn%20off%20noise.mp3

i think is the opamp, because i tested it with an JH990C resulting a quiet turning out. The preamp with the ML 2520 is working fine. Another thing i've figured out is when the gain pot is all way down still pass a low level audio, i tested it with and Sm57. is this normal?

Cinemag CM7-5101APC, jumpered at 1&2 and 3&4
Whistlerock audio ML2520 opamp
Cinemag CMOQ-2S

Psuniversal power supply

Best regards

here is the link with the noise

 

[mikefatom]

Hi rodcaster,

As mentioned in my last email, this is completely normal and is typical of 2520 clones.

Cheers!

Mike

 

[dacapitan]

Hi guys, I have finnished building my unit - 4 channels in total -2 with cinemag transformers and 2 with CAPI EA transformers, DOA are from Scott Liebers SL2520 (cinemag with blue dots and EA with red dots) I have the unit passing audio at a constant level regardless of where the gain pot (10k alpha rev log pot) is turned (ie. gain pot has no effect on level) I have read a few people had the same problem but I was not able to draw any conclusions.

Some additional info: (I have 100R at R4 and 10k at R5) measure 0 and 10k when pot is turned CW and CCW, looking at the pot from the back - far right pin on the pot is at 2 on the board and far left pin on the pot is at point 1 on the board

I am a n00b and I am not sure how to check if I am getting the correct voltages on my op amp pins, where do I place the common multi meter pin when measuring? I am using diypartssupply PSU with 16v+/-

Please let me know if I can provide any more info to help solve this? Would really really appreciate some help

 

[3nity]

Unhook the potentiometer do you have any sound?
Hows your potentiometer wired?
let us know.

 

[Harpo]

...looking at the pot from the back - far right pin on the pot is at 2 on the board and far left pin on the pot is at point 1 on the board

looking at the pot from the back, pins pointing down, the jumper between center pin and rightmost pin at the pot is missing. Only connecting to the pots outer pins will make the pot behave as a fixed value resistor.

 

[dacapitan]

Thank you very much for your replies Harpo and 3nity - much appreciated. Harpo you are spot on once again, I jumped centre and right pin and now have gain! You are always so helpful and I really appreciate it!

The unit is passing audio with gain but I have another problem now; I seem to have a constant scratchy/static/noise/popping sound which gets louder with more gain and the longer the unit stays on the worse it gets - This is happening on all the channels. I have thoroughly checked the the grounding and continuity on grounding. Working with one Board, tried re flowing a few solder joints, generally my soldering isn't too bad. This noise is really a pain

Also the PAD and POL switches are very noisy/scratchy when engaging them - is this normal?

Any idea?

 

[3nity]

not normal to be noisy.
post some pix of ur build to analyze it please.

 

[Harpo]

Also the PAD and POL switches are very noisy/scratchy when engaging them

Most likely cause are dirty/oxydized switch contacts. Some contact cleaner and exercizing the switches might help.
Appropriate (sealed, hard-gold plated, micropower) switches that don't suffer from these artifacts cost an arm and a leg -or two.
Remember to always disable phantom power before switching POL in this circuit.

 

[dacapitan]

@3nity: Would appreciate it if you could take a look, thank you so much. I have uploaded a high res image here as the forum only allows for 1x 1mb file per post: https://www.sendspace.com/file/7uthvs

Audio sample of noise - it was a lot worse the other day, it seems to randomly get better and worse; https://www.sendspace.com/file/9f5g5q

Some side notes; Dan's case would only allow for external PSU (Using diyparts PSU and VPT36-690 in external box ) so pwr switch is just for show. You will see the IEC gnd and PSU gnd coming through the back with the V+/- 48V.

I have also tested a single board with out the looped cable/gnd connections between each board and get the same problem.


@Harpo: Thanks for the tip, I will give that a try, also did not know Phantom should not be engaged when switching POL - will keep that in mind. As for the other switches I think I'll keep my arms and legs for now 

Thank you so much for the help!

 

[3nity]

Is this your ground scheme?
It goes from every pre, dont sidechained them!

 

[dacapitan]

Thanks for the feedback 3nity. Essentially it is like that, as mentioned I disconnected the side/daisy chain to only have it on the first pre which has separate wires going to star - which gave the same issue

Solved: bad insulation on ground wire coming in from power supply... Seems to be okay now

 

[buildafriend]

Are any access 312 cards available at the moment? I only need one.

Best,

 

[buildafriend]

Is anyone else having trouble viewing the BOM? I'm trying to repopulate a used card..

Edit* found it via google search. the one on the first page of this thread won't work for me for some reason.

http://www.twin-x.com/groupdiy/albums/userpics/Access-312bom-2013~0.pdf

 

[3nity]

no cards unless another user has 1 for sale.
1st page of this thread 2 post...bom is viewable

 

[Guitaratomxbest]

Hi!

I just finished building 2 channels of the access 312. It's my first DIY project so I'm still really a noob.
I seem to have a clean and stable +15 dB of gain with the pot but once I pass a certain point on the pot (3/4 approx), the signal drops a lot and I have pretty much just noise. I tried bypassing the gain pot to have the full gain of the pre, but it did the same thing. And I have this problem on both channel.

Does anyone had this problem before? I looked on the topic and couldn't find an answer.

Thanks!

*P.S. sorry for my bad english!*

 

[3nity]

SAlut.
Did you make sure the op-amp is good 100%??
Transformers not touching any pads? good ground scheme?
All xlr connections good?

Try to post some pix please!

 

[Guitaratomxbest]

I'm not really sure how I can troubleshoot the opamp...

I'll try to post pics soon!