Recapping PSU

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Recapping PSU

Postby paulrichards7 » Sat Feb 07, 2009 12:20 am

So Im gonna recap my PSU ... /PSU-1.jpg
Should I double the size of caps, but keep the same voltage?
Ive heard that PSU caps are severely underated

What about those green chicklet caps? ... s7/PSU.jpg

I also think Im probably gonna disconnect the phantom power supply to the channel boards
That should buy me some extra juice

Any other mods while Im in there?
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Re: Recapping PSU

Postby GJC Designs » Fri Feb 13, 2009 1:00 pm

There is no harm in installing higher value caps - understanding technical reasons why it is being done is important.

The physical issues of fitting larger caps may be a problem if space in the PSU is tight.

Looking at the rest of the PSU circuit, it has LM317T & 7915 regulators; these are capable of delivering 1.5A and 1A respectively, when fitted with an appropriate heatsink. The heatsink shown in your photo will not allow dissipation of the heat that these currents will generate, therefore suggesting that the console draws much less current than the regulators are capable of supplying. This points to the cap values as being adequate for the application. On rule of thumb design, the existing cap rating of 2200uF is OK (and Studiomaster found it so for production) so there seems little point in increasing the capacitance. Assuming the transformer is feeding the rectifier with 17.5VAC, the raw DC being applied to the smoothing caps will be a little under 25V, so there is no reason to change the voltage rating of the caps.

Testing the electrolytic caps for capacitance value and ESR will really determine how necessary it is to change them.

The green poly caps should be OK - just leave them alone.

Where I would worry about the design of the PSU is the use of an LM317T in the phantom circuit. A read of the data sheet will reveal the source of concern.

Disconnecting the phantom supply will gain nothing of any significance. What is the actual requirement for acquiring the extra juice?
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Re: Recapping PSU

Postby paulrichards7 » Fri Feb 13, 2009 8:28 pm

Hey Gareth
Thanks so much for that
So are you saying I SHOULD add a heatsink to those rectifiers or in a typical application YOU WOULD
As most of the channels in my desk are noisy and I cant seem to find the problem area
Im only currently using 4 boards(with TL072s)
Therefore i was thinking of upgrading ICs after recapping
Thanks again fro your advice
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