need -30v power supply

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arkestra
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need -30v power supply

Post by arkestra » Sat Oct 30, 2010 10:06 pm

yup for some ba71 preamps.

can I turn a +28v supply into a -28 supply?
how is building a negative supply different than a positive one?

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Scodiddly
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Post by Scodiddly » Sun Oct 31, 2010 5:15 am

It's really not that different. If you've got a separate +30 power supply you can almost always use it as a -30 power supply just by connecting the + output to ground and the - output to -.

Otherwise, if you're building your own, you just do everything negative and use a negative regulator chip instead of positive.

arkestra
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Post by arkestra » Sun Oct 31, 2010 9:16 pm

that is what I thought but I found this post:

http://forum.allaboutcircuits.com/showthread.php?t=876

and got to thinking about the direction of current flow.
Why does this post seem to be contradictory?
I guess I could always try it out but the guy in the post wants to do the same thing and is being told not to. ??

thanks for the response

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Post by ckeene » Mon Nov 01, 2010 8:31 am

Yeah Scodid is right. I used a fivefish P/S for a couple BA72s and it worked great and was cheap.

You gonna do fixed gain for those 71s or use a stepped pad thing?

arkestra
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Post by arkestra » Mon Nov 01, 2010 10:48 am

Cool. Mind as well try it out. Does five fish do a 30v? I'm going to do a fixed gain with switchable input pad. Still confused by that other post I linked to though. Thanks

ckeene
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Post by ckeene » Tue Nov 02, 2010 9:55 am

arkestra wrote:Cool. Mind as well try it out. Does five fish do a 30v? I'm going to do a fixed gain with switchable input pad. Still confused by that other post I linked to though. Thanks
The fivefish supply goes to something very close, like -28 or something.

User "EMRR" our resident authority on RCA stuff. He helped me out a lot when I racked up my pres. Maybe he'll chime in here...

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HeavyHand
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Post by HeavyHand » Sun Nov 21, 2010 3:54 pm

im in the same boat. i just picked up a variable PSU. 0 - 30V and 0 - 4A. im crossing my fingers that i can run 7 pre's from just that one PSU. im so lame at this stuff so it's taking me forever.

i need to do a stepped attenuator type of thing for 2 of them though... i was looking to do that kind found on the Hamptone site but i have little knowledge about it all. any ideas???

p.s. sorry to be piggy backing on the OP but it seemed like a good fit.
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calaverasgrandes
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Post by calaverasgrandes » Wed Nov 24, 2010 7:14 pm

fivefish make one ha is 24 and one ha is 44 volts They also have 48 volt outs for phantom.
I built the 44 volt model for some PM1000 pres I racked amd it actually has a trimpot that varies the output voltage. Not sure how low that goes though, and of course "under load" is a different story.
$70 with a transformer and everything else but the project box.
I have also bought stuff from Marlin Jones and assoc before. They are less audio focused and more hobbyist, but they have every PSU known to man.
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