Isolated power supply

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laurie
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Isolated power supply

Post by laurie » Sun Feb 04, 2024 2:24 pm

I needed a fully isolated supply for my stereo board. The Strymon pedals need isolated power because of the digital hash they inject into the power supply when daisy-chained.
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Stereo-board.jpg
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Tried a few options and ended up with this. It is actually fully isolated, and cheap. About USD$40.

It does get warm. I do not know how long it will last, but for now it is working perfectly.
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laurie
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Re: Isolated power supply

Post by laurie » Fri May 10, 2024 12:13 pm

UPDATE - Caline CP205 power supply

After using a couple of these power supplies for a few months and dismantling one to see what is inside, I can report the following.
  • The 8 outputs are most assuredly isolated. There is no ground connection between them, or back to the power pack.
  • Each output is supplied from an independent winding on a small transformer through 7809 linear regulators.
  • The filter capacitors on the linear regulator are 220uF.
  • No-load input to the 7809 is 15VDC, and fully loaded the input is 14VDC.
  • There are no heatsinks on the 7809 regulators - they are free-standing, inside the case with no air-flow.
Bottom line - at 300mA the 7809 regulator is dissipating 1.5W which is enough to cause a temperature rise that pushes the 7809 into thermal shut-down. With high draw pedals (e.g. my Strymons) I am experiencing random drop-outs due to over-temperature cut-out of the regulators.

Running pedals with much lower current draw (e.g. 20mA for a distortion pedal) these power supplies work perfectly.

They are good power supplies, but just can't run my Strymon pedals. They have been moved to my lower current boards, and I've made the expensive decision to buy a Strymon Ojai supply for my main board full of high current pedals.

The Ojai is fully switched-mode (does not use 7809 linear regulators) so does not have the same heat issues as the Caline CP205.
Last edited by laurie on Fri May 10, 2024 12:27 pm, edited 2 times in total.

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laurie
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Re: Isolated power supply

Post by laurie » Fri May 10, 2024 12:20 pm

CP205-2.jpg
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CP205-1.jpg
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laurie
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Re: Isolated power supply

Post by laurie » Wed May 15, 2024 12:27 pm

laurie wrote:
Fri May 10, 2024 12:13 pm
Bottom line - at 300mA the 7809 regulator is dissipating 1.5W which is enough to cause a temperature rise that pushes the 7809 into thermal shut-down. With high draw pedals (e.g. my Strymons) I am experiencing random drop-outs due to over-temperature cut-out of the regulators.

Running pedals with much lower current draw (e.g. 20mA for a distortion pedal) these power supplies work perfectly.
I sent a note to Caline support about this. I'll let you know if I hear back...

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Zerksies
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Re: Isolated power supply

Post by Zerksies » Wed May 15, 2024 2:47 pm

I hate doing this myself because of the bulk, Have you tried just using their supplied power supplies.
I.B.B & F.Y.s

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laurie
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Re: Isolated power supply

Post by laurie » Fri May 24, 2024 3:44 am

I've solved the overheating problem permanently.

I de-soldered the 7809 regulators, ran 2 inch wires from the PCB to the regulator, and bolted the regulators to the power supply lid. The lid is 1.2mm Aluminium so is an adequate heatsink.

So far, so good.

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laurie
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Re: Isolated power supply

Post by laurie » Fri May 24, 2024 12:13 pm

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bigtone23
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Re: Isolated power supply

Post by bigtone23 » Sun May 26, 2024 6:51 am

Nice. A hot rodded power supply! Very smart to use the lid as a heat sink.

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laurie
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Re: Isolated power supply

Post by laurie » Wed May 29, 2024 1:53 pm

I've now done the mod to my spare Caline CP205. For this one I've used a 1N4148 diode to "jack up" the output voltage to 9.6V on 5 of the 8 outputs.

See here for how the 9.6V output is done:
viewtopic.php?f=13&t=10&p=8508&hilit=7809#p8508

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Last edited by laurie on Wed May 29, 2024 1:59 pm, edited 8 times in total.

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laurie
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Re: Isolated power supply

Post by laurie » Wed May 29, 2024 1:53 pm

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