Access-312 Build Thread

[talkieparade]

OK

I did the measurements and the F2UEE push button switch is exactly 17.5mm apart from center of one switch to the next.

I bought the hardware chassis mounts for 17.5mm and it fits perfectly.

 

[talkieparade]

I am also wondering about the details regarding the input pad, because I would like to mod my input pad to be -10dB in attenuation.

In the Access 312 circuit, is the pad an H-Pad, a T-Pad, or a U-Pad?

I'd like to change the resistors to produce a -10dB pad.  I think right now the pad is about -19dB with resistors R8 = 120r, R9 = 470r, and R10 = 470r

The input Z of my input transformer is typically 1500 ohms.  And I think its typical for a mic output impedance to be 150 ohms, right?
So I am not sure a -10dB pad is possible with my given impedances?

I used a T-Pad / H-Pad calculator at http://www.nu9n.com/tpad-calculator.html
The calculator could not compute a -10dB pad with these impedances...
and the only way I got close to the current -20dB pad was by making both input and output impedances both 600 ohms...
The results from the T-Pad were R1 = 491, R3 = 491, and R2 = 121 (bridge power load resistance)

Just trying to figure this out. If any one knows please offer your understanding. Thank you

 

[Whoops]

I am also wondering about the details regarding the input pad, because I would like to mod my input pad to be -10dB in attenuation.

In the Access 312 circuit, is the pad an H-Pad, a T-Pad, or a U-Pad?

Read this page, the answer is there:

http://www.uneeda-audio.com/pads/

 

[alisowski]

I’m having some trouble with my phantom power. Everything is grounded according to the diagram drawn out in the earlier replies and I’m using the collective cases external PSU. I’m getting ~ 50V in from my power supply to the phantom in screw terminal. LED on the switch is working. R1, R2 both  show ~ 40.5V and R3 shows 46V when referencing pin 1 on my XLR input. XLR pin 2 shows 0V and pin 3 shows .5V. Any thoughts on what might be causing this? Bad cap?

I’ve triple checked for any accidental solder bridges and reflowed everything a couple times now just to be safe. Pre seems to work fine with mics that don’t require phantom.

 

[Whoops]

I’m having some trouble with my phantom power. Everything is grounded according to the diagram drawn out in the earlier replies

Hi,
what diagram are you following for the grounding?

I posted some grounding layouts that are more efficient than what's been said in the early posts of this thread

 

[3nity]

Whoops thanks for your kind support on this project.
Im bussy working and you always give good advice!
I appreciate it!

 

[Whoops]

Whoops thanks for your kind support on this project.
Im bussy working and you always give good advice!
I appreciate it!

I try to help and give the advice I can, but I feel that in the last years in this forum new users don't even read the project pages.
I think some forum Etiquette is being lost, it was definitely not like this in the past.

Most of the questions being constantly asked by a new user in this thread were already answered a few times before.

With the nice layout you have made and your pcb, your documents, plus reading this thread for some other ideas and info it becomes really easy to do an API type mic pre project, but people seem to  don't want to put any effort.

 

[3nity]

True.
The thing people look nowadays is the result not the learning... Thats what was cool when i came here learning and share..

 

[Whoops]

True.
The thing people look nowadays is the result not the learning... Thats what was cool when i came here learning and share..

Yes, totally agree, that has been lost since this forum became like a superkarket

There should be some rules and guidelines for new members, since the registration of new members boomed, so that the nice Etiquette this forum had would not be lost.

 

[talkieparade]

Well I think this thread is awesome and definitely appreciate everyone's help and advice here, props to Whoops and 3nity. I've read this thread many times now,
Looking for answers but sometimes the answer isnt totally obvious and one just has to ask   

 

[3nity]

Talkieparade
Its normal dont worry.
The non obvious stuff its part of the fun it makes you learn and discover.. It can be very long i know but you have to be willing to read and search.

If not just ask.. We dont mind sharing.

 

[Whoops]

I’ve just finished reading through the whole thing.

BOM, schematic, layout?

Did you really read the whole thread?

Because you have Parts list/BOM on page 19, Schematic on page 19 also, Layout on page 24, and Grounding scheme on page 28.
All the docs you ask are on this thread

The question I have, is the BOM from dan’s collective cases the rev3?  All the links on here are dead.

I guess you have to ask Dan from collective cases, but saying this, this project is really simple it used only 11 resistors, 8 caps and 2 diodes,  with such a lower component count you can even just follow the schematic

 

[dr_daw]

Constructive criticism to the discouraging comments above regarding people not wanting to put the work in. Some of us do put the work in.  If you’re a moderator....

Why not have a locked post at the beginning that has the docs, and answers to FAQ’s?

The BOM from Dan at  collective cases,  the schematic, layout and star grounding are below.

 

[dr_daw]

BOM BOM BOM BOM BOM BOM BOM BOM BOM BOM BOM BOM

 

[dr_daw]

SCHEMATIC

 

[dr_daw]

Layout

 

[dr_daw]

Grounding

 

[Spencerleehorton]

got a bit of a weird one here!!!

Have built 8 x API-312 channels in 3 different cases, a 4 channel, a 2 channel and another 2 channel.
the 4 channel version works fine and has red pcbs i cant remember where from, im using the same basic psu for all x 3 so i dont think its a psu issue as im getting +/- 18v on each unit also getting 44-48v on each unit for phantom.
My issue lies in the two stereo units, when nothing is connected I get 44-48v phantom no problem, as soon as i put in a mic, then phantom drops to 23-30v on pins 2 and 3?
my input txf are sowter 4220 which are 4.71:1 which i use in reverse, im using a 25k rev log gain pot and im using 2520 in one unit and 990 in the other for DOA.
resistors and caps on phantom section are 6.8k to pins 2 and 3 with the 220uf/63v and 470R, the led and 6.8k.
the pad is the 120R and the two 470R.
The R7 150k and 220pf i've left out and R6 is 10k
R5 is 10k, C7 is 100pf , R4 is 100R, C6 is 220uf.
one of the stereo nit has OEP 1:1 as output txf and the other has the proper output txfs.

can anyone help with why both units are dropping in voltage when mic connected please?

 

[Whoops]

got a bit of a weird one here!!!

Have built 8 x API-312 channels in 3 different cases, a 4 channel, a 2 channel and another 2 channel.
the 4 channel version works fine and has red pcbs i cant remember where from, im using the same basic psu for all x 3 so i dont think its a psu issue as im getting +/- 18v on each unit also getting 44-48v on each unit for phantom.
My issue lies in the two stereo units, when nothing is connected I get 44-48v phantom no problem, as soon as i put in a mic, then phantom drops to 23-30v on pins 2 and 3?
my input txf are sowter 4220 which are 4.71:1 which i use in reverse, im using a 25k rev log gain pot and im using 2520 in one unit and 990 in the other for DOA.
resistors and caps on phantom section are 6.8k to pins 2 and 3 with the 220uf/63v and 470R, the led and 6.8k.
the pad is the 120R and the two 470R.
The R7 150k and 220pf i've left out and R6 is 10k
R5 is 10k, C7 is 100pf , R4 is 100R, C6 is 220uf.
one of the stereo nit has OEP 1:1 as output txf and the other has the proper output txfs.

can anyone help with why both units are dropping in voltage when mic connected please?

Hi Spencer, I don't know which project did you build,
this thread is for the Access 312 and as far as I know the PCBs are all green.

The Red pcb's are from other 312 type project, not the Access 312, I remember seeing them but I don't remember the name of the project at this moment

 

[Spencerleehorton]

Yes, in the units I was talking about they are green, found the problem now anyways, felt like I  wasted a day rewiring but both units have correct GND config now and no noise or hum, only noise i can hear is the sound of the room when i turn up the gain really high!!!

problem turned out to be 2 x XLR cables i was using!! and a few other little mistakes within the unit which I corrected.

I'm testing all my leads now!!!