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Old 12th January 2007, 01:21 PM   #1
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Default smps on ebay

this looks like a pretty decent deal for a switching power supply, and seems like it would be perfect for running an lm3886 chip amp.

http://cgi.ebay.com/ws/eBayISAPI.dll...4126&rd=1&rd=1

thoughts???
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Old 12th January 2007, 01:41 PM   #2
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with +/- 42V you are just at the edge of needing a flameproof LM3886 -- and 2 amps is below the margin of load delivery.

you will definitely want to shield the switching supply from the chipamp -- radiated RFI causes differential input voltages and mysterious offset voltages (not so mysterious when you understand that a BJT opamp is actually a crystal radio set)
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Old 12th January 2007, 03:04 PM   #3
traw is offline traw  United States
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i've used them with good results. can get them down to 39volts usually. i had also used them applying a secondary basic emitter-follower regulator (like shown toward end of the mod notes) to get them down to 35 volts or so, but burning some power off.
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Old 12th January 2007, 03:25 PM   #4
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Quote:
Originally posted by traw
i've used them with good results. can get them down to 39volts usually. i had also used them applying a secondary basic emitter-follower regulator (like shown toward end of the mod notes) to get them down to 35 volts or so, but burning some power off.
you can get rid of some of the switching noise with a post-regulation via linear regulator (and burn off some watts at the same time) -- one of the techniques described by Wenzel Associates (cited too many times on DIYAUDIO) is "Finesse Voltage Regulator Noise" -- http://www.wenzel.com/documents/finesse.html -- although you will have to beef up the components.
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Old 12th January 2007, 03:40 PM   #5
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Ive used a few of these, with no post regulation and some minor mods the supply will produce over 300W, reduceing the current resistor alone can net you another 50W, the cores are decent to around 300W continuous output without saturation, but you need to change the mosfet and use a small fan to keep it cool. And I have had very little noise problems.
The supply does need better output diods on the HV side to take advantage of the better mosfet and current sense reduction.
I have been running 2/with mods/ to power a new BPA200, one per channel without a problems even on long term high power tests.
They are deffinently worth the money

PS under normal useage the supply sags to around 37 to 39V with out any mods to the regulation side, for a single 3875 or 3886 just watch your load and heat sinking.
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Old 12th January 2007, 04:01 PM   #6
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Old 12th January 2007, 09:46 PM   #7
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thanks halo. i'm very glad to hear it (i actually had gone ahead and bought one before i even posted. . . so i'm very, very glad to hear it).
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