Access-312 Build Thread

[emtee]

Well in answer to my own question, I'm going to give these a go -

http://www.ebay.co.uk/itm/80-x-Socket-Pins-for-Nixie-Tubes-IN-12-IN-18-IN-2-IN-8-IV-22-VFD-Valve-PCB-Gold-/161111364744?pt=UK_Sound_Vision_Other&hash=item2582fc5488

May need a little trimming but all the specs seem to add up.

Well to answer my own question again, & for future reference, these work just fine. 1st channel fired up tonight without issue.  8)

 

[toneboner]

Warning!!!  ***Perhaps dumb question Disclaimer***

Why is there no value for C6 on the current BOM?  Is it dependent on some other component choice?  The previous version has 1500uf/6v.  Advice/enlightment would be appreciated.  Also would ceramic for C7 be ok?  Is there a different cap type recommended? 

And most importantly, I'm trying to reconcile info in this thread for optimal zobel values for OEP a262a3e with values for RC, R6-7, and C8:  http://groupdiy.com/index.php?topic=6045.20

If I follow advice from that thread -- zobel 22k / 800pf , 68k loading resistor -- would it be: R7(RC) = 22k  C8=800pf  R6(R7-R6) = 68k  ???  ***designation in parenthesis are what's on the silkscreen***

Am I on the right path? I've seen from one of 3nity's pics with an OEP there is something stuffed for C8 but not RC or R7-6...
thanks, sasha

 

[3nity]

Thanks for pointing that out.
OEP what worked better for me was a 25K @ R6-7 and  1000pf @ C8.

Dont get all nervous you are on the right way!

 

[3nity]

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

 

[toneboner]

Thanks for the quick reply 3nity. It's been 2 years since I bought your boards! Finally have been able to put some $ to getting them done, so yeah, probably over excited.  I'm gonna try it your way 1st...
Just to confirm - RC stays unstuffed as it is parallel with r6-7 ?  If someone doesn't mind a quick lesson, what is the function of R6? 

 

[toneboner]

how are people attaching the screening can to their trafos? ive got oep with the bottom plate. glue?

https://www.dropbox.com/s/3qx3ydaepcw9psm/screen%20can.jpg

 

[3nity]

install the plate.
Let your iron get really hot and do some spot welds. on the middle of each side both parts touching !

Good luck!

 

[dacapitan]

Are there any boards left? I would like to please buy 4 if possible?

 

[bieckmusic]

Hello everyone and Merry Christmas, happy holidays 

I'm having a problem with my access 312 build...  All four channels pass audio and sound very api'ish and great with a dynamic mic!  However, I'm an not able to get the phantom power to work on any of the 4 channels.

Testing with a DMM and a mic, the 48 volts will not pass from the switch to the mic-in terminals on the back of the board??  I'm thinking it's a short somewhere, but it does seem suspicious that I have the same behavior on all 4 boards.  I've double checked r1-3 and c5... Been buzzing it out with a continuity checker and the schematic, it eludes me...  Probably some dumb mistake somewhere.

My DIY parts supply PSU is working great.  Though I did have to replace a LM317 I somehow fried the first one.  Probably related to the issue...  Any thoughts would be amazing.

best!!
Greg

 

[3nity]

Frist of all make sure your 48V is solid.
Then is your XLR input pin 1 grounded well?
If not its not going to be working.

In the meantime if 48V is good the LED should light!

 

[Harpo]

Testing with a DMM and a mic, the 48 volts will not pass from the switch to the mic-in terminals on the back of the board??

With mic connected, hopefully not. The voltage will drop a lot as the 6K81 resistors in your preamp and the corresponding resistors inside the connected mic form a voltage divider. Measure and trim for +48VDC at the junction of the 6K81 resistors (junction of R1,R2,R3,C5) in respect to phantom power current return at XLR-pin1.

 

[bieckmusic]

Thanks Harpo and 3nity!!

Well the +48 led lights perfectly when the switch is activated.  At the resistors R1 and R2 (both sides) I'm getting 0mV.  At R3 I'm getting -48V.  Also, measuring the top of the Cinemag input transformer can and I'm getting 48V!!  That doesn't sound right to me??  I triple checked the ground to the XLR and it's good.  Also I notice plugging in a Condenser mic, even with phantom off makes a loud popping noise?

best!
Greg

 

[Harpo]

Well the +48 led lights perfectly when the switch is activated.

so at least there is a supply voltage present (at whatever voltage).

At the resistors R1 and R2 (both sides) I'm getting 0mV.

>>at the junction of the 6K81 resistors (junction of R1,R2,R3,C5) in respect to phantom power current return at XLR-pin1<<,
this is assuming XLR-pin1 connecting to phantom reference voltage (0V). The XLR-IN-1 from schematic is NOT XLR-pin1. XLR-IN-1 connects to XLR-pin3.

At R3 I'm getting -48V.

you mixed up the multimeters black and red probe wires.

Also, measuring the top of the Cinemag input transformer can and I'm getting 48V!!

see previous possible mixup at XLR-IN-1/pin1. You need a little luck that your DOA survived if you got this wrong.

I triple checked the ground to the XLR and it's good.

to XLR-pin1 ?

Also I notice plugging in a Condenser mic, even with phantom off makes a loud popping noise?

Without a mic connected, you should confirm a readout of +48VDC at both XLR-pin2 and XLR-pin3 in respect to XLR-pin1. Don't plug in anything other than your multimeters probes unless this gives a correct readout. For the popping noise (always turn down/mute your monitors when activating phantom voltage) you want R1 and R2 close matched, IE better than 0.1% and same value is more important than absolute value.

 

[3nity]

Remove the DOA if possible while your 48v issue is fixed.
Maybe I'm a stupid but you haven't confirmed your xrls are properly grounded from pin 1 to a star ground.
Is your c5 oriented in the right direction??

Lets us know any developement.
This could mean a merry, merry Christmas.

 

[bieckmusic]

Thank you again I have had xlr pin 1 star grounded.  And I noticed the word xlr1on the schematic and fortunately did not mess up the xlr ins.  Pin 2 of the xlr goes to silkscreen pin 2 pin 3 goes to silkscreen pin 3...

Is the input transformer case supposed to be showing 48 volts?  I wonder if I shorted a mic input transformer pin to the pcb?

Best! Greg

 

[3nity]

Thank you again I have had xlr pin 1 star grounded.  And I noticed the word xlr1on the schematic and fortunately did not mess up the xlr ins.  Pin 2 of the xlr goes to silkscreen pin 2 pin 3 goes to silkscreen pin 3...

Is the input transformer case supposed to be showing 48 volts?  I wonder if I shorted a mic input transformer pin to the pcb?

Best! Greg

Is it the same problem on all 4 channels?
If not can you take a look at this document and confirm the 48V and 0V connections at the screw terminals?
http://twin-x.com/groupdiy/albums/userpics/312-Layout_.pdf

 

[3nity]

could you post a few pix of one channel top and bottom?
Thanks.

 

[bieckmusic]

Here are a few pictures...

 

[bieckmusic]

Backside

 

[3nity]

One more thing.
From the PSU +/- the 0V did you sent it to Star ground?
It you havent it should help you avoid any ground loop.