|
|
Post by jayson on Sept 20, 2015 9:38:00 GMT -6
So I'm running out of 500 real estate and I'm thinking I'll grab an 11 Space rack from CAPI and use a spare soundcraft cps275 I have laying around as a power supply. Is there any hole in that logic that sticks out to you guys? Would I be better off using one of Jeff's PS kits? The only thing that makes me a little intimidated at the prospect of doing this is the Soundcraft is spec'd at +/- 17 Volt and the API standard supposedly wants to see +/- 16. I can't see that as being that much of an issue but perhaps I'm mistaken? It would seem to me that I could just leave the 5 Volt circuit out of the equation entirely, and just jump the appropriate pins on the current console umbilical connector to an additional - as yet uninstalled - 5 pin XLR connector on the Soundcraft PS. I understand how, to some, this would seem like an unholy alliance by definition, but am I asking for trouble if I do this? Here's a snapshot of the Soundcraft rear panel; whaddya think? Attachments:
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Sept 20, 2015 11:19:10 GMT -6
Well 1 volt should not be the dealbreaker here. Why not if you have the psu spare...
|
|
|
|
Post by svart on Sept 20, 2015 12:22:48 GMT -6
Put two regular silicon diodes in series on each supply to drop a volt. Typical silicon diodes have voltage drops around half a volt..
|
|
|
|
Post by wiz on Sept 20, 2015 15:52:43 GMT -6
Put two regular silicon diodes in series on each supply to drop a volt. Typical silicon diodes have voltage drops around half a volt.. Geeze, its been over 30 years... but the voltage drop is ... .7V ?? isn't it? was it called, VBO? (voltage break over) or was that Zeners.. was fun trying to remember... 8) cheers Wiz |
|
|
|
Post by tonycamphd on Sept 21, 2015 7:03:26 GMT -6
It's a great idea J, I have a spare cps 650 that I will do the same with to power a 3rd 51x rack when it's time.
|
|
|
|
Post by tonycamphd on Sept 21, 2015 7:07:47 GMT -6
Put two regular silicon diodes in series on each supply to drop a volt. Typical silicon diodes have voltage drops around half a volt.. How much v swing can something calling for 16v take before problems? Is there a rule of thumb? |
|
|
|
Post by svart on Sept 21, 2015 7:23:29 GMT -6
Put two regular silicon diodes in series on each supply to drop a volt. Typical silicon diodes have voltage drops around half a volt.. How much v swing can something calling for 16v take before problems? Is there a rule of thumb? It depends on the device, and how the power system is structured! Some devices which reduce the voltage further on the board might be able to take significantly higher input voltages. Some which power devices directly from the input power rails might not. Generally speaking though, in analog circuits, adding another volt to each rail probably won't kill anything outright. I'd watch the heat from the parts closely during the first few minutes. Most devices will overheat before detonation if they are only slightly overvoltaged. I ran my CAPI preamps on +/-17V for years with no problems, and no overheating. Digital parts on the other hands usually have very little tolerance for overvoltage. Logic chips, processors will likely die a quick death. |
|
|
|
Post by svart on Sept 21, 2015 7:28:08 GMT -6
Put two regular silicon diodes in series on each supply to drop a volt. Typical silicon diodes have voltage drops around half a volt.. Geeze, its been over 30 years... but the voltage drop is ... .7V ?? isn't it? was it called, VBO? (voltage break over) or was that Zeners.. was fun trying to remember... 8) cheers Wiz Standard silicon is usually in the 0.3-1V drop range. It depends on the brand, the model, and finally the amount of current. Gotta read the datasheets if you want to know for sure. Try one, then try two. You can try power zeners and power schottkys too! Mix and match until you get what you want. |
|
|
|
Post by NoFilterChuck on Sept 21, 2015 9:16:37 GMT -6
don't forget that each module needs anywhere from 80mA to 200mA. that's why the PSU jeff sells uses a transformer that provides about 2 Amps. spread out over 11 slots, that's a bit more than 180mA per slot. so make sure that Soundcraft supply provides enough amperage, not just the proper voltage.
|
|
|
|
Post by jayson on Sept 21, 2015 9:44:00 GMT -6
Thanks for the feedback, everybody! Nothing better than re-purposing!
Th PS is rated at 5.25 amps at 17 Volts, I think it's probably going to be able supply enough juice. I'm more concerned with it being too much!
If I'm going to put in the diodes on the + and - connections, would I put the cathode facing up stream, toward the power supply on the negative lead and and the opposite on the positive? Is there a specific make/model diode that I should look for?
|
|
|
|
Post by gar381 on Sept 28, 2015 17:27:43 GMT -6
jayson Use the Soundcraft supply. It will be fine as is. I don't know of a DOA that can't handle +/- 17v just fine.  I actually burn-in my gars at +/- 18v. Plus as a bonus 5.25 amps will power lots of slots.  Gary |
|
|
|
Post by jayson on May 29, 2016 9:50:08 GMT -6
So here's an update on this. I finally modded the PSU and put together one of Jeff's racks and it works almost perfectly. I did wind up tweaking the output voltage for the +/- 17v down a taste - I'm not sure it was necessary, but the voltage still reads higher than 17v at it's lowest setting, so I'm not going to go too crazy there.
I tested it and everything is working as well as I could hope except for one very weird issue: phantom power seems to have some kind of glitch.
I've made sure the +48v has perfect continuity from the power supply all the way out to pin 15 on the edge connectors. If I hook a dynamic mic up to a pre in the rack it works just fine. BUT - If I hook up a condenser up to it, the +48v indicator LED on the module activates making it look as if everything's happy, but I get no signal at all. I've had the same results with multiple modules in every slot. My first thought was that I must have bridged a 48v solder point to the ground or something - but if I had I don't think the indicator light for the phantom on the modules would even activate. So I checked every solder point that's remotely close to any other ones and I can't seem to locate anything that's been shorted. Seems like I've tried every diagnostic trick in the book without any luck.
Any of you guys ever heard of an issue like this?
Truth be told; I took on this project to provide housing for compressors and EQs, so even if I never get to the bottom of it it's not much of a concern. For me this is just one of those things were it sure seems like I did everything right and it still ain't working and, frankly, that ITCHES!
|
|
|
|
Post by jsteiger on May 29, 2016 12:04:50 GMT -6
Phantom power needs a return path to a solid ground reference. The typical mic cable wiring utilizes the cable's shield as the return path. In a 500 rack, pin #1 of the input XLR typically makes a connection with card edge pin #1. The 500 series card edge pin #1 is designated as Chassis ground. In my rack (and most racks following the API protocol) pin #1 of the card edge connector is connected to nothing else but a dedicated pin of the power connector. Typically, this power connector pin will make a home run to the star ground point inside of the PSU. You should measure your phantom power inside the 500 rack by sticking your red probe to card edge #15 and black probe to card edge #1.
|
|
|
|
Post by jayson on May 29, 2016 13:13:52 GMT -6
Hi Jeff,
Thanks for getting back to me here.
Odd - but I think that helps. I'm wondering if Soundcraft might have been on a different page with their phantom ground scheme. I'm not showing any voltage at all between the 48 volt supply and the chassis ground: between the 500 edge connectors 1 & 15...or for that matter even if I test it inside the Soundcraft PS! I AM seeing 62 volts between the phantom supply and the 0 volt reference. For the record, pin 1 on the edge connector shows continuity with the chassis star-ground in the PS. Hmm...So maybe this is shedding a bit of light on things...
I guess I'm ok with knowing it won't work as long as I understand WHY. I think I'll probably just clip the jumper that I installed to the +48v in the Soundcraft PS- I don't really need it anyway.
|
|
|
|
Post by wiz on May 29, 2016 17:12:06 GMT -6
In Soundcraft 450 and 650 (they are the ones I own and have worked on) the plus and minus 17V supply has a ground, and so does the 48V, there is also a chassis ground.
They all get joined within the console, not the power supply.
cheers
Wiz
|
|
I actually burn-in my gars at +/- 18v.
