Re: Access-312 Build Thread
« Reply #600 on: July 28, 2020, 10:15:01 PM »
Hey all! I'm nearing the end of this journey, but seem to have hit a snag. Here's a shot of my project as it currently stands:

[IMAGE REMOVED by author to avoid "copycat" failure.]

Earlier today, I seemed to be getting sound out of one of my PCBs - the one furthest to the right.  However, something seems to have gone awry and, as a result, I'm no longer getting sound from anything. At this point, my suspicion is that the PSU is having issues; it's also possible that my grounding scheme isn't airtight. (I arrived at it after eyeballing a lot of other Access 312 builds on Google and Reverb, as well as in this thread.) That said, I wanted to lay out the project here and troubleshoot before arriving at any rash conclusions. This will be a little image-centric...


POTENTIAL PROBLEM #1: POWER/GROUND WIRING

SO, here is my current power/ground wiring diagram:

[IMAGE REMOVED by author to avoid "copycat" failure.]

As far as POWER goes, daisy chaining seems to work. I have tested continuity across each board's rail screw terminal (V-, V+, +48) and found them to be consistent. (The voltage numbers themselves are a bit weird... more on that in a second.) In practice, this looks like:

[IMAGE REMOVED by author to avoid "copycat" failure.]

I initially attempted to daisy chain the COMMON GROUND, but was warned away from that approach by a 3nity comment earlier in this thread. The grounding scheme shown above was adapted from both Whoops (though I did skip the 10R resistor and .1uF cap, as they didn't figure into other folks' diagrams) and another seemingly successful build I found somewhere between pages 20 & 25. In practice, it looks like:

[IMAGE REMOVED by author to avoid "copycat" failure.]


Also, as suggested by literally everybody, I connected the whole shebang to star ground using a blend of 3nity and Whoops' approaches:

[IMAGE REMOVED by author to avoid "copycat" failure.]

SO, that's one potential issue: I didn't wire things properly. If so, let me know! I've already miswired two major parts of the project at different points - the hot & cold on the 3-pin female XLRs and, likely more egregiously, the 5-pin XLR power jack. In the former case, I feel somewhat safe assuming that I didn't blow up anything (though I did test the +48 while it was wired backwards, so maybe that assumption's not so safe). In that latter case? Well...


POTENTIAL PROBLEM #2: MY PSU IS SHOT

I'm using this PSU,  the "CC-PSU" from Collective Cases:



Now, you'd think that an external PSU would limit my ability to completely foul up the power situation, but I'm an idiot and can foul up almost anything. The CC site lists the PSU's pinout as the following:

PIN1: SHELL:FG
PIN2: COM
PIN3: +16V
PIN4: -16V
PIN5: +48V

As you can see above, the PSU itself goes into further detail, providing a diagram of said pins. However, I somehow managed to never give the PSU a careful look, so that info was lost on me. Instead, I looked up "5-pin XLR pinout" online and merged that semi-meaningless information with the list on the CC site and.... wired the power connector backwards.

I know, I know... it's almost comically stupid. And, after a night of scratching my head at the weird clicking noises emanating from my pres, glaring at my multimeter, and rearranging my grounds/etc., I finally glanced at the PSU and, realizing my dumb mistake,  rewired the 5-pin XLR:

[IMAGE REMOVED by author to avoid "copycat" failure.]

 I tested the new wiring on one preamp and, for 15 glorious minutes, I finally got the voltages (~+/-16V & +48V) I expected/needed. I even used the 48v to power a condenser. And then... things took a turn for the worse.

After my modest success, I put the preamp back on my bench, and daisy chained the rest of the preamps to their appropriate rails. But when I came back, the preamps - even the one that had previously worked - were soundless. Even more perplexing, the rails that had been blasting +16, -16, and +48 with ease were now producing very strange (and choppy) voltages:

+48: 55.9V
+16: 0.9V to 1.9V
-16: -0.3V to -1.55V

SO, that's another potential issue: my PSU might have just bitten it. (Side note: Beyond the weird voltages, its "power on" LED seems dim - not a great sign.)


I'm not quite sure what my next move should be. Ordering a new PSU seems somewhat obvious, but I want to make sure that my wiring is tip-top/nonviolent before plugging another $75 power supply into this thing. That in mind, a few questions:

+ Am I on the right track in thinking that the PSU is the reason I'm getting no sound? If voltage is too low, do the preamps simply not work?

+ My XLR input hots/colds were wired backwards and I ran +48 through one of them. What might be the ramifications of this?

+ Does my current wiring look right? I assume my PSU went wonky because I initially wired the 5-pin XLR incorrectly, but if there's something else afoot, I'd like to know.

+ Given that I wired the rails incorrectly the first time around, should I be worried about my preamps? There are no exploded caps or smoking resistors, not enough heat went through the switches to really cause an issue, txers could probably withstand an atomic blast. My only concern is the DOAs, and then only because they're full of transistors - but, again, no smoking.  What parts of the boards should I eyeball?


Sorry for the long post! Thanks in advance - any help you could provide would be beyond appreciated.
« Last Edit: July 30, 2020, 01:29:47 PM by vizcities »


Whoops

Re: Access-312 Build Thread
« Reply #601 on: July 29, 2020, 04:22:52 AM »

POTENTIAL PROBLEM #1: POWER/GROUND WIRING

SO, here is my current power/ground wiring diagram:



Whoops

Re: Access-312 Build Thread
« Reply #602 on: July 29, 2020, 04:28:22 AM »
POTENTIAL PROBLEM #1: POWER/GROUND WIRING

SO, here is my current power/ground wiring diagram:



Your Grounding Scheme has a lot of mistakes and potential problems, you should change it.
Grounding has been talked a lot in this thread and I already posted here a great grounding scheme for this project.

For Future members building this project, please don't do this.

Whoops

Re: Access-312 Build Thread
« Reply #603 on: July 29, 2020, 04:28:53 AM »
This is how you should do it:

The Star Point in grounding is not the Bolt case but the 0V point where all the Access preamp PCB will connect on the PSU.
From the Star Point, only 1 connection is made to the Chassis Bolt through a 10R resistor and one 0.1uf capacitor in parallel.
"It is used to stop ground loops happening. Isolates the chassis ground from the audio ground by 10R with 0.1uF across it so no RF gets in as well."

Input XLR pin1 is connect directly to the chassis bolt

Output XLR pin1 is not connected, just leave it open, the shielding will be connected to ground at the input on the next box that is connected in the chain.

A recommended reading:
Grounding and Shielding Audio Devices
https://web.archive.org/web/20160306063456/http://www.rane.com/note151.html


« Last Edit: July 30, 2020, 07:40:25 AM by Whoops »

Re: Access-312 Build Thread
« Reply #604 on: July 29, 2020, 05:07:31 PM »
First, to reiterate Whoops' warning to other builders: YES, DON'T BORROW MY WIRING DIAGRAM. I posted it to get peoples' thoughts, not to provide an example. When I get my build working, I'll take it out of circulation and replace it with something more instructive.

Other than that:

Whoops - Thanks for checking in re: my ground scheme. I avoided your method because wiring it seemed like it would be an absolute PITA - the ground cup/pin on my 5-pin XLR power jack is pretty tiny - but now that I'm in the midst of things, I feel more comfortable figuring out a new approach. Based on your diagram, here's the method I have in mind:

[IMAGE REMOVED by author to avoid "copycat" failure.]

If you can see any reason why this wouldn't work, let me know!

Beyond that, my other Qs still stand. Does the power wiring look OK? I ordered a new PSU last night, so I'm officially marshaling resources before digging back into this thing. Again, thanks in advance for any thoughts you might have!
« Last Edit: July 30, 2020, 01:30:30 PM by vizcities »

Whoops

Re: Access-312 Build Thread
« Reply #605 on: July 30, 2020, 07:31:30 AM »
Whoops - Thanks for checking in re: my ground scheme. I avoided your method because wiring it seemed like it would be an absolute PITA - the ground cup/pin on my 5-pin XLR power jack is pretty tiny - but now that I'm in the midst of things, I feel more comfortable figuring out a new approach. Based on your diagram, here's the method I have in mind:

Hello Vizcities,
Pin 1 is connected to Case and not to the 0v reference.
Pin1 is a shielding connection, as it's the case
The Case has to be connected to the Earth safety pin on the IEC socket of the PSU, that's represented with the Red wire on the 5 Pin connector coming from the PSU.

0V reference and Safety Earth should only connect in one point via the  the 0.1uf Cap and the 10r resistor



______________________________________________________

This is not my method, it's the standard practise and what is advised by people that is much more knowledgeable than me, it's also what manufacturers use and it's a proved method.
A good read on Grounding from the Rane notes old website:

https://web.archive.org/web/20160306063456/http://www.rane.com/note151.html



« Last Edit: July 30, 2020, 07:43:48 AM by Whoops »

Re: Access-312 Build Thread
« Reply #606 on: July 30, 2020, 01:20:43 PM »
Whoops - Well, even if it's not technically your method, I appreciate your bearing with me (and even correcting my diagram!). It looks like the missing pieces of the puzzle for me were what to do with the Shell:Floating Ground connection and how it was different from the 0v. For some reason, I couldn't figure out how the FG related to the PSU & IEC wiring in your original diagram, so thanks for clarifying. Here's my "final" revision:



Does this look complete? Am I missing anything major?
« Last Edit: July 30, 2020, 05:57:38 PM by vizcities »

Whoops

Re: Access-312 Build Thread
« Reply #607 on: July 30, 2020, 09:39:08 PM »
Hi vizcities,
the drawing doesn't show the connection on the PSU side, but:

If PIN1 on the 5 Pin XLR connects to the IEC safety ground PIN
and if PIN2 the 0V reference only connects to the PSU 0V reference then all it's good.

But, you have to check how the 0V reference is connected to the IEC safety ground pin on the PSU itself, they would be connected inside the PSU already.
I don't know if are directly connected or through  resistor and a cap.
You should measure it with the multimeter.

If they are not connected it's fine.
If they are connected directly it will work but not as good as through the cap and resistor
If they are connected but through a cap and resistor you should remove the connection in the drawing between "COM" and the chassis/case bolt because that connection is already done inside the PSU, and you only want one connection and one only, that's really important.

Hope I could explain it, if it's confusing please let me know



Re: Access-312 Build Thread
« Reply #608 on: July 31, 2020, 01:03:04 AM »
Whoops - Thanks for helping me through this - I bought the external PSU specifically to avoid creating a headache for myself, but clearly things haven't worked out that way.  Just to make sure we all know what we're dealing with, here's a pic of the PSU:



When I checked continuity between the IEC into the PSU & the 5-pin socket on the chassis, it looked like this:



Here's an alternate drawing of same:



Basically, the ground safety pin, Pin 1 (Floating Ground), and Pin 2 (0v/Common Ground) are all connected to the same ground somewhere within the PSU. And... I'm not 100% sure what this information means. My inclination is to say it means this:



However, because I can't peer inside the PSU  and see if it uses the cap & resistor, it may make more sense to do this:

[IMAGE REMOVED by author to avoid "copycat" failure.]

Thoughts? Every time I think I have a handle on this, I hit a roadblock - but I'm intent on figuring it out.
« Last Edit: August 10, 2020, 12:38:51 AM by vizcities »

Whoops

Re: Access-312 Build Thread
« Reply #609 on: July 31, 2020, 01:47:46 AM »
Basically, the ground safety pin, Pin 1 (Floating Ground), and Pin 2 (0v/Common Ground) are all connected to the same ground somewhere within the PSU. And... I'm not 100% sure what this information means. My inclination is to say it means this:

With you DMM in resistance mode measure Resistance  between PIN2 and PIN1 and Safety PIN

If your multimeter as a Capacitance measure mode, measure capacitance between PIN2 and PIN1 and Safety PIN

In the case your multimeter doesn't have a capacitance mode, can you ask a friend for one?

I advice you to buy this cheap unit that turns out to be a great unit to have and a lifesaver sometimes, it measures all components including capacitance:

https://www.ebay.co.uk/itm/1PCS-MK-328-TRLCRESR-Transistor-LCR-ESR-tester-semiconductor-device-analyzer-M/191873654353?hash=item2cac8f9e51:g:afUAAOSwboVXOWKc


Whoops

Re: Access-312 Build Thread
« Reply #610 on: July 31, 2020, 02:12:19 AM »
Anyway,
as the connection between the 0V reference and Earth safety pin is already done inside the PSU, Don't do the connection inside your Mic Pre rack case, do it like this:



Always keep 0V reference and Safety Earth+Shielding separate. They are different things and serve different purposes.
Only connect them at one point, and one point only. Using a 100nf cap and 10R resistor for that connection is a good idea.
In your situation 0V reference is already connected to the IEC Earth Pin inside the PSU, so no other connection between the 2 should be made.
« Last Edit: July 31, 2020, 02:15:38 AM by Whoops »

Harpo

Re: Access-312 Build Thread
« Reply #611 on: July 31, 2020, 03:20:31 AM »
Your reverse connected 5-pin connector, once powered on, might have caused various faults per 312-board. With D1 and D2 fitted, a reverse polarity of the +/-16V rails was avoided, but the positive 16VDC rail was fed with a 32VDC supply voltage in respect to 0V reference voltage.  Was your C1 voltage rating sufficient for this 32VDC? Depending on DOAs fitted (some use a 0V reference voltage), these might contain blown parts from overvoltage now.
With 0V reference voltage and safety ground joined at the PSU (you checked this by ohming it out for close to zero ohms, NOT a multimeter continuity-test?), expect C5 to be blown from reverse polarity, if phantom power per 312-board once had been activated.
Disconnect all 312 boards and measure supply voltages again with a correctly operating multimeter (a nearly empty battery might give funny/false readouts). Maybe your PSU is still OK and only one or more 312 boards cause the PSU failure. If so, reconnect your 312 boards one by one with DOAs removed and obviously blown parts exchanged and check supply rails after each reconnection. When all boards operate with stable supply again, refit the DOAs one by one with supply check again.
Good luck
A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.  -Douglas Adams

Re: Access-312 Build Thread
« Reply #612 on: August 10, 2020, 12:29:19 AM »
Whoops & Harpo: Finally finished! They sound great... and I figured things out just in time for my band to demo before we lose our practice space, which is lovely. Thanks for the help!


SOME SPECIFIC NOTES

As it turned out, this diagram -



- made sense for my first PSU, which (as Harpo suspected) was still functional. (Shout out to Dan from Collective Cases, who also eyeballed and approved the diagram.)

Once I rewired the grounds properly, I used Harpo's troubleshooting method, taking out the DOAs and making sure all voltages were correct. Sans DOAs, three of the four had the right voltages; as it turned out, I'd forgotten to fully wire all the switches on one of my boards. Once I corrected that issue, all board voltages were consistent.

As I started adding DOAs back into the equation, I discovered that two had survived and two were terminally broken by my earlier backwards wiring snafu. (For whatever reason, the ones that died were both hand-soldered GAR2520s, while the Rogue Fives survived. One GAR went up in smoke, while the other just clucked rhythmically.)  Miraculously, the wiring mess didn't affect any caps on the boards - a relief, because desoldering PCBs is almost always an exhausting PITA.

After I swapped out the dead DOAs, I tested the pres (including pads and +48v) through my Apogee Ensemble. Beyond having to rewire the Gain switches - they were backwards - everything worked perfectly! I can't wait to road test these guys on my trap set.


An interesting side note: while the replacement PSU I received from Dan seemed to have a similar pinout (Pin 1:Chassis, Pin 2: Ground, Pin 3: +16v, Pin 4: -16v, Pin 5: +48) printed on its case, its Pin 1 and Pin 2 did not share ground when I checked continuity. For others who come across this PSU, I suggest using this grounding scheme (borrowed from Whoops):



And the PSU in question:



As everyone else has said, do the work first - if using an external PSU, make sure to check the continuity between the PSU's various ground pins and then choose the wiring diagram that makes the most sense.


I messed up about a million times making this thing, but I learned a lot - I hope all the above helps the next group of A312 builders!
« Last Edit: August 10, 2020, 12:41:02 AM by vizcities »

Whoops

Re: Access-312 Build Thread
« Reply #613 on: August 10, 2020, 10:24:10 AM »
Nice that you solved the issues and that it's working.

Rock n Roll time


 

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