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Old 10th January 2013, 04:50 PM   #1
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Join Date: Dec 2003
Location: Massachusetts
Default Is this a bad idea?

Hi Folks,

I'm currently making a Pass DIY B1 preamp/buffer and was going to use a recycled power supply I got which is basically brand new. Its a 24v 3.2amp switcher made by Cosel:

http://www.cosel.co.jp/en/products/pdf/SFE_LCA.pdf

(pic attached)

Its the LCA75S-24. It has a switching frequency of 190kHz. I'm having second thoughts about using this PSU now, the frequency is well outside the audible range and the B1 board incorporates at least 15,000uF of PSU filtering capacitance. Plus I'm loading the PSU at such a low level it should minimize ripple.
Should I not be worried about this? Should I add a big series inductor and some chokes on the DC side to try and knock down any high frequency ripple?
I do have access to a nice PC based oscilloscope which I could use to measure the rails and probably the B1 output to look for any ripple etc.

Any advice is appreciated.

Chris
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Old 11th January 2013, 08:38 PM   #2
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Default update

I decided to add a linear regulator stage after my switcher, I figured it would help smooth the output of the PSU down. I put a clip on choke on the DC supply from the regulator to the B1 board.

I got the pre-amp finished and tried it out and there is no noise on the output that is audible, I'll check with an oscilloscope to confirm its all good now:
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Old 11th January 2013, 09:50 PM   #3
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Join Date: Sep 2010
Location: Melbourne
Cute , is that a baking tin? I never thought of using one as an enclosure
Good to see the signal wires twisted. While linear regulator might be helpful, Using an SMPS with a proper enclosure would probably have given more benefit. You could still put a full height metal strip attached to the case at both ends to separate the power and signal if desired. The ferrite on the supply lead to the amplifier is a step in the right direction though these provide little attenuation until well above 1MHz, a common mode choke of say 1mH would have been my choice, these attenuate well into the the audio spectrum and are normally used close to the SMPS input or output, your mains filter will probably contain one. The things I mentioned are not critical and if the output is clean just enjoy it
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