DIY +/- 18V Power Supply

[killie99]

I'm going to build a +-18V power supply for my Project Phono RS. It currently uses a Wallwart which supplies +18V, -18V and Gnd using a 3 pin mini din socket.

I've only ever built 5V supplies before (for my Logitech Touch and Rpi) so thought I'd ask here before rushing in like a bull in a china shop.

Ebay has plenty of ready made ac/dc converter boards, a couple of examples are here and here.

Are these any good or can someone point me to a UK or Euro supplier?

Is a 2x18V-45VA toroid the way to go? What about C Core or EI core?

Any input greatly appreciated.

[danilo]

Don't be overlooking Batteries.
Even a pair of 9 volt dry cells will surprise.
Likely the draw on the phono stage is in the 60 mwatts range. Even alkaline Batteries would live long.
Nicad batteries are V Good Power Supplies (arguably best possible).. testing better than Lab Grade Measuring devices can reliably read.
Not overly easy to find these days tho... but they are out there.
Output voltage of a transformer will be multiplied by 1.4 ~ by the diode /rectification stage...so 18 v is too much.. producing a 24v PS
Toroids are a Fine choice in PS transformers.

[killie99]

Re 18v toroid. Does it really matter as it gets stepped down by the lm317 to 18V? Granted it'll create a small amount of heat on the regulator, is that a problem? Is there another reason why I should really use a lower toroid voltage of say 15V?

[struth]

15v or 18 tx and as you say a lm317, 337 would give you enough current I'd think adjusted to 18v. the reg will take care of any over volts. its rated to 37v I think

[tubehunter]

These are very good

http://www.amb.org/audio/sigma22/

Much better than the lm317 etc...


Happy days

[RothwellAudio]

Ebay has plenty of ready made ac/dc converter boards, a couple of examples are here and here.

Are these any good or can someone point me to a UK or Euro supplier?

Is a 2x18V-45VA toroid the way to go? What about C Core or EI core?

The first link is to quite a sophisticated board (apparantly) which uses various semiconductors and MOSFETs as pass transistors. The second one is a much simpler LM317 type circuit.
The mains transformer doesn't have to be huge and I'm not a big believer in any benefits to an oversized transformer. In fact, they can cause more problems by radiating more of a magnetic field. 15VA should be as much as you need. I would choose a torroid for the low magnetic field. 2x18V would cause the regulators to get a bit warmer than 2x15V but would give the regulators a bit more headroom. Bear in mind that the voltage rating of a transformer is the voltage it should give when running flat out. When it's cruising it will have a higher voltage. 2x18V at 45VA will probably give you at least 10% higher voltage when running the Project. That's more heat dissipated in the regulators.

[killie99]

The Sigma22 board looks really good but $37 to ship the bare etch that costs $14 to the UK, blimey not cheap!

[tubehunter]

Look at this on eBay:

https://www.ebay.co.uk/itm/121720228275

HP-X amp Power supply kit base on A22 σ22 for B22 β22 (beta 22) 5-36V L158-2

[Arkless Electronics]

A quick glance at a couple of photos of the board shows it to require AC power.... and, although I can't make out sufficient detail in the photos to be certain, it has what looks like separate regulated supplies for each channel already..... All assuming of course that we are talking about the exact same model:This is what I'm looking at... https://www.google.co.uk/search?q=Pr...VCXw9zY7cxM%3A

[killie99]

It's +-18V DC, description on the wallwart, in the manual and the Power Box RS Phono manual