Old School Audio OSA Track Pack differences from API VPR 500 series standard

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emrr

Well-known member
Joined
Apr 12, 2006
Messages
8,525
Location
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The Old School Audio Track Pack is an 8 space 500 series lunchbox type rack with hardwired power umbilical and external PSU.  It differs from both the VPR spec and the newer 51X spec.  OSA ceased production, and info is scant on the ground.  Here's what I found.

pin
1 not connected - to anything, anywhere
2 + out, hardwired to XLR pin 2
3 -2 out, jumper to XLR pin 3
4 +4 out, jumper to XLR pin 3

5 M and F XLR pin 1's / not connected to card edge pin 13
6 one jumper for link to adjacent, and second jumper for bus connection to all 8 channels; bus has no external connection
7 not connected
8 hardwire XLR pin 3
9 not connected
10 hardwire XLR pin 2
11 link jumper to adjacent
12 +16VDC, power pin 3
13 PSU common, power pin 2 / not connected to card edge pin 5
14 -16VDC, power pin 1
15 +48VDC, power pin 4
output XLR's shell connected to chassis
circuit board has points for additional parallel input and output XLR's


VPR standard for comparison
pin
1 chassis
2 +out +4
3 +out -2
4 -out
5 common
6 525 link
7 -in -2
8 -in +4
9 +in -2
10 +in +4
11 gain trim
12 +16VDC
13 PSU common
14 -16VDC
15 +48VDC

 
I have one and have run across a few modules that do not function in the rack.

For future reference:

Modules that DO NOT work:
Purple Audio Action Compressor
Golden Age Pre-73 500 Series

Modules tested and working:
A-Designs P1, Silver, EQP500
Classic API VP-26
Eisen Audio DIY 500 series pre
Shadow Hills GAMA
PeterC's 553
Audiox Studer 169


Also to note: I had +48V drop to +25V due to faulty 10k trimmer in phantom supply. (Cheap Chinese parts were used throughout PS).
 
If possible please define why those two modules don't like these racks, specifically. 

There seem to have been a number of different PSU used by OSA. Probably a different topic.  The one I have uses an off the shelf International Power linear module with an add-on homebrew phantom supply. It is rock solid, no technical faults. 
 
I'm unsure at the moment why they don't work correctly. I dropped the GAP in for a session and it powered fine, but I didn't get a signal till about 2 o'clock on the stepped gain, then all I got was a weird oscillation. The person I bought it from told me his Purple Actions didn't work in them but that was all the info I got (OSA sent hime a new rack and PSU when he told them about it).

My PSU looks like a custom design. +48 is on the board, transformer has 2 taps @ 50V and multiple taps at 16V (either 4 or 6, can't remember right now). A single trimmer for +48V and a single trimmer for +/-16V. Not a lot of filtering caps in this supply.

I think it's some sort of grounding issue somewhere causing the modules not to behave correctly. I definitely have more testing to do but that's my first thought at least.
 
Yeah I have one too , thanks for the table Emrr ,
I gather both sides of the connector are not tied together ? but I've found some slots not to work
[ no phantom ? ] didn't investigate just assumed it had problems but not consistent to all slots ?
 
Edge connector pin 1 should be chassis. Is there a chassis connection back to the PSU? Input XLR's should have their pin 1's connected to chassis and back to the PSU somehow or phantom won't work.
 
Pin 1 goes nowhere, not even to the adjacent channel pin 1.

Add CAPI FC526 to list of modules that don't work correctly in the OSA Track Pack.  In this case, you can't align the meter, all else works. 
 
Did a rewire to get back to 'standard' as much as possible. 

Cut trace connecting CE5 to channel XLR1's.
Wire XLR1’s to CE1’s per channel.
Bus CE1's together, joined to CE13 at power connector.
Bus CE5’s and joined to CE13 closest to power connector.

This power umbilical is attached to the rack, soldered to busses, only has a connector at the PSU end, so at some point I can change the PSU connector to a 5 pin type and  get chassis on it's own run back to the PSU case ground point along with the addition of a power connector at the rack. 

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Hi. I'm now in the same boat. My OSA power supply is crap and has issues. Buying the CAPI floor power supply.  Did this mod work for you? Thanks!
 
It has been fine since I rewired it.  I did eventually add 5 pin connections that disconnect on both ends.  I keep it as a small portable rig. 
 
Oh, no, I have an International Power linear supply in a box, home made piece.  It's actually running two CAPI racks and this OSA box.  Meanwell 48V switcher for phantom....even though I have no 500 preamp modules.
 
Oh! I have the OSA 8 Track pack and also an 11 space rack he also made. I have two separate power supplies that are completely different. I'm thinking of building this CAPI supply because Jeff advertises it can power 22 modules! Thus, powering both units. I'm going to make your mods to the backplanes and bring them up to standards with the 5 pin connection.  Should work.
 
It should work well, but also consider cost of retrofitting an International Power linear and Meanwell switcher in an OSA box if it'll fit, might be a lot cheaper. 
 
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