Tube Preamp SMPS

[DummyLoad]

Nifty little DC-DC converter - 9V > 250V + 6.3V - Rated at 250V 15mA / 6.3V @ 1.5A. Works really well. Have a 12mA R load on the HT (22KΩ 6.5W R), and about 1A on the 6.3V output. Pics in link. Performs well, about 100-150mV ripple on the HT output. link to part on Amazon. Beware, that the power source (5.5mm x 2.5mm jack) the tip is (+), and not tip (-) like for pedals. May build a guitar pre with it. Use a polarity inverting cable to use pedal wall-wart. 

Link to pics.

Link to SMPS on Amazon.


--Pete

[Jonas]

THANKS PETE!!! I HAVE A COUPLE ON ORDER

[DummyLoad]

THANKS PETE!!! I HAVE A COUPLE ON ORDER

 

[Jonas]

Pete, what was your approach to eliminate the switching noise? Do you have any recommendations of things to try?

thanks!!!

[DummyLoad]

Tamed it with a with a pair of Pi filters - The first iteration I used a single 20H 10uF Pi filter, was ok, but still had some pop/buzz - Added a second Pi filter with 100uH 4.7uF, fixed most of the noise. Not perfect but tolerable and usable. Has about 23-30mV of ripple now, down from about 150mV average. I wound the toroid myself - Had some ferrite cores from a lab that was shutdown, so wound a  Micrometals T68-3 with 25 turns of 24AWG, salvaged and stripped wire from an old ethernet cable. No, you don't need 1W Rs in HV string, that's what I had in the bins. 

Schema attached.

Pic of ripple measurement of B+ line - Link below.

https://www.dropbox.com/scl/fi/z9kjf10i7owtmwhq1g5ot/IMG_20260608_021259634_HDR.jpg?rlkey=xgynz75541ry58kwv7kcrz7vc&st=fjdakbg0&dl=0

--Pete

EDIT: The 1W resistors in my application are overkill, my circuit draws about 3mA total. YMMV - Depends on the PS current load.

[Jonas]

test

[Jonas]

thanks Pete and nice job! - I will give that a try

Are you getting any noise form the 6.3v heaters?

I an not using the on-board dc jack, wiring direct (tried to upload a pic no success - attachment options is not working for me???)