Cheap DC-DC converters tapped off +/-15VDC rails? (PSU for Soviet synth)

[Blue Jinn]

Hello,

I have a USSR build string machine (sort of a Crumar Orchestrator/Multiman-S knockoff) with a bad power supply. The PSU is complicated and zener regulated. I've actually purchased NOS Soviet parts to rebuild it. But:

I'd like to replace with a universal PSU and an IEC mains connector.

The PSU supplies

+15VDC
-15VDC
+3VDC
+3VDC
-3VDC (give or take)

I had thought about getting a cheap eBay LM317/LM337 board for the 15 volt rails and then tap the from positive supply a couple of "bucking" converters for the 3 volt rails and use a Triad VPP36-1560 (which I have on hand) which has dual primaries and two 16 volt secondaries which can be wired as 16-0-16 for the +/-15v supplies. I've found several DC-DC converters that will give me the positive and negative 3 volts. The LM317/LM337 boards are fairly conventional. Am I OK in using the buck converters like these https://www.ebay.com/itm/295509745182?hash=item44cdc0de1e:g:73cAAOSwkFpj3hZs&amdata=enc:AQAIAAAAwHuKobOcFq3lsU4Hc/NenVCH5lzim+MBJtrVFzugIAof0LC1Y1ojk99Lg41rnQIS/Nk+qI5CKsqIw3cwdcPPYBrOwhbQKVBm/X4mDZoBeu2lzxejZDzChdNHS3JGBOeIN0p/iM9naovEChD48RUZZA+El0LOkxcWCc/JMsh3eyUlPj404quNu2JC99gnimeZMTAGNzAOUKMU6YzvyAMhzcreVB8L9Ut2sLlChd4YfpBzbABX9JCpa8mefCAV6B84zQ==|tkp:Bk9SR_CYlZu4Yg tapped off the +15v rail? Or even two buck converters off the +15v rail and a LM337 I found online off the -15v rail?

I've heard that the switch mode supplies can be noisy. As an aside I did use a laptop supply to power a 6418 tube distortion box, and had to add extra filtering as it was really noisy.

 

[ecc83]

Morning Blue, first off, if you can get a look at the section on power supplies in Douglas Self's book 'Small Signal Audio Design' lot of good tips there.

I have messed with small encapsulated DC-DC converters and not had any RF breakthrough. I am well acquainted with a Blackstar HT pedal that uses a 'boost' circuit to derive 300V from about 22V. That has a lot of stuff crammed inside but 'hash' was never a problem.

I would suggest a logical shielding and grounding policy. The whole circuit should be encased in metal and that mains grounded. Do not use THAT ground to supply the circuits, run +ve and _-ve to each section right back to the supply.
You can wind your own inductors on ferrite rings to make some LC filters but you may not need them.

Dave.

 

[Blue Jinn]

Morning Blue, first off, if you can get a look at the section on power supplies in Douglas Self's book 'Small Signal Audio Design' lot of good tips there.

I

Thanks!

I also just realized the negative 3v is for driving LEDs I think the cheaper one should be ok