Power Supply Soft Start Board (V3)

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This thread is for discussions about the Power Supply Soft Start Board (V3) in the store. This is an updated version of the Soft Start V2 boards, primarily to make them compatible with the 10x10 grid mounting pattern we've now standardized on so they can be easily mounted to Deluxe chassis baseplate, riser panels, front panels and/or heatsinks. Refer to the Soft Start V2 discussion thread for additional information.

Change History
  • 2.0 First Production Version
  • 2.0.1 Added board dimensions
  • 3.0 New Layout
    • Double sided board
    • Moved AC in and Txfrmr connections to ends of board
    • Added Keystone connectors as option
    • Conforms to 10mm mounting grid
  • For future changes

    • Add polarity markers for electrolytic capacitor

  • Product Page
  • BOM - Attached below (Last updated: Jan 14 2014)
  • Schematic - Coming soon
  • Dimensions - 110mm x 55mm


  • Soft Start board BOM v3.pdf
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  • Soft Start board BOM v3.xlsx.zip
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Assembled my V3 Soft Start Board tonight, with the parts I had previously purchased from the V2 BOM. After changing some designations, I went to work.

Pretty smooth assembly. It would help for a new schematic for this board be posted, the component designations are not the same as for the V2, while the circuit is the same.

The only 2 things that would have worked a bit better for me:

1) C3 could have a better polarity marking. There is the circle and square, but I had to go back to the schematic to be certain. A plus sign would have removed any worry.

2) I am using spade connectors for my power connections. You have pads with 8 through holes for direct connection of all sorts of wires, but only the 2 in the middle will hold a spade. It would be nice to have spots for 2 spades for each pad, perhaps the outer 4 corner holes spaced for the connectors, or whatever.

Very minor points to be sure, just suggestions for next run. I really appreciate the mounting hole spacing for the new cases, one of which I am using.

A question though. I am building the Aleph J, and have the parts for the original Pass design PSU. Should I be adding the 0.0033 filter cap, or is that taken care of in this board?
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Thanks for the feedback. We'll look at C3 marking for the next revision. We agonized for a while over connection options but decided in the end that the Keystone connectors were so awesome we just had to use them. We tried to make it so we could fit more spades on but things were 1mm out here and there, different sized leads, etc. My suggestion is use the Keystone connectors :)

I will try to find someone to answer your question about the filter cap.
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I did not look down at the connectors part of the new BOM, I used the V2 BOM back when I ordered my stuff. Those keystone terminals look pretty good, I will agree. I will withdraw my suggestion, and concur with your choice there. I don't think I'll de-solder the spades though this build though. Next time for sure though.
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A question though. I am building the Aleph J, and have the parts for the original Pass design PSU. Should I be adding the 0.0033 filter cap, or is that taken care of in this board?


The 0.0033 AC cap is for filtering AC mains noise and should still be used even with the use of the soft start boards.

You can conveniently solder this cap directly on your PEM, just a suggestion.



Thanks for working on and releasing v3
Hope you all are having a nice Christmas holiday

I'm tempted to build one of the power soft start kits. If you have built one did you notice any loss of dynamics or timing when playing music compared to the time before you installed it?
Yes, I have read the build guide, and it does say you can have some big toroids.

My toroid is a universal 2.4 kVA, with 5 60-0-60 outputs that can be wired to provide between 36 and 30 volts volts -- for a max of about 1.5 to 1.2 kVA.

This is going into a high bias F5T with 4 pairs of outputs per channel at about 45 volt rails. The bias current is limited by the heatsinking, which should manage around 3 amps per channel.

Yes, this toroid is stupidly oversized, but it is not great sounding as a balanced power source -- which was it's original purpose, and I want to reuse it... or sell it....

Well I think for amp builders there is no such thing as oversized. :D

Iirc, the largest load I had used the parts values in the BOM is for a two-toroid setup that has a combined rating of about 2kva only. I never actually worried too much about the relay since once the caps have their initial charge, shorting out the limiting resistors wasn't much of a problem.

Loading lots of capacitance and the extra load of the amp may need you to adjust the values of the limiting resistors so they don't get too hot during power ups.

Fwiw, my CNC's motor psu also uses the same soft starat. With 3 hungry Kelling stepper motors that each draws out about 4A during hold modes also uses the same relay in the BOM.