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emtee said:
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)
 
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

 
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!
 
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? 
 
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
 
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!
 
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

 
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!
 
bieckmusic said:
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.
 
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

 
bieckmusic said:
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.
 
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. ;)
 
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
 
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
 
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.
 

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