Title says it all really. I need to invest in a bench power supply for DIY audio gear builds. Budget up to £100 but cheaper would be preferred. Any good new or second hand recommendations (or the opposite) appreciated.

I'd thought about hacking a spare computer PSU, but not sure I want to do that...

Thanks in advance!

We've got a couple of the ones at

http://cpc.farnell.com/unbranded/in05526/power-supply-bench-led-30v-5a/dp/ IN05526

for general electronic development work which seem to work fine. I notice CPC also have something slightly cheaper at

http://cpc.farnell.com/tenma/72-8690/power-supply-bench-2x-32v-3a/dp/IN060 94

The thing is, you need dual outputs for most audio work which pushes the price up.

DIY would be cheaper - you don't really need a variable voltage so it wouldn't be that complicated but you need to know what you are doing on the mains input.

The other alternative is to buy some cheap gear that incorporates a suitable supply and then just remove the bits you don't want and keep the power supply.

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

If it is aimed at D.I.Y. projects I recommend the following:

Get a really cheap unregulated PSU that can deliver a respectable output current - ideally at 24V, make sure one side of the output is properly earthed. This is the only point that needs an earth, and takes care of the safety aspects.

Get a bunch of isolated DC-DC converters with an input voltage range that suits the PSU. The 18-32V range is ideal if you have the 24V supply. You'll probably want +-15V (very common and can be in a single DC-DC converter) 5V, 12V (maybe a couple of these last two so you can get other voltage combinations)

Put all the DC converters on individual breadboards along with PCB screw terminals for easy and repeatable connection (usually it's a good idea to add a few 100n filter caps on both input and output).

This looks messy, but I find it is extremely flexible. As all of the converters are isolated there is no continuous earth, so no hum loop problems and pos and neg of the converters can be juggled for almost any combinations. Also, almost all modern units are S/C protected so will handle the occasional accidents.

Just start out with the basics at first. If you get rich, and/or need more combinations just get more converters

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It wasn't me!
(Well, actually, it probably was)

thanks gents. The CPC ones are too pricey, I'm afraid. Not bad for what they are, I'm sure, but they're too much for me right now (I recall them being bad for postage costs on single items too).

I need to keep things fairly tidy too, as the missus needs to walk through the room I'll be using

Would something like this eBay jobby suffice as a starting point for experimentation? I figured the 48V starting point would open more voltages to me than 24, not to mention allow me to create things that can run on phantom power... and it appears to have two separate IO. Am I being over simplistic here!?

Do not have 48volts about the test bench!
Not because of your personal safety, tho' it is technically possible to be electrocuted with 48 or less volts, no, it is the chips etc. Most active electronic devices, TL's NE's di da, can handle 18, maybe 24volts on any pin, maybe, a bit, but 48 volts will bork them instantly! This is the only real danger of phantom power, if by error it gets to the input of almost any device, toast.
For a bench supply I would buy a pair of 12 or 15 volt switch mode rats then bring the plugs up to the bench (I used a sheet of 9mm MDF and 25x25mm ally angle to mount connectors, switches etc on.)If you want to play with phantom power do as Folderol suggests and get a dc-dc conveter (and sorry Will but your idea DOES seem a rats nest!).

My 12-0-12 supply was a pair of car batteries under the bench that had long since failed to crank the Ford. I would still suggest them but for the fact that someone will surely point out that a 100amp capable supply can be dangerous!

Dave.

Thanks Dave & James. As you see, I'm rather a novice at this stuff. I'm very used to playing with the finished thing, but less with the technical tinkering, even if I can wield a soldering iron with reasonable competence... I do want to learn more, though.

Can you see any problem with adapting a PC PSU along the lines described on this page? There are a few such hack tutorials on line and they don't all seem to agree with each other. I have a couple of spare computer PSUs lying around so this would be a cheap and relatively tidy solution if it's reliable...

+1 on keeping +48V out of the way.

Many mics (although not all, by any means!) can make do with lower phantom power voltage anyway. So you can experiment with more sensible voltages, and then add +48V in your final boxed-up-and-ready-to-go circuit.

I really don't have any experience with PC supplies. I have had the tops off and blown them out, robbed the odd heatsink out of a dead one!

Looks a lot of work but if you are into DIY and enjoy it .....?

I have two main reservations.
1) AFAIK the supplies are not short circuit proof, now cheap SMPUs also might not be but this moot to point 2...

These supplies can shove out huge currents! Far in excess of anything you need for mic amps or mixer circuit experiments so, the time you spend building the thing could be gone in a flash!

Actually I am remiss. I should have said fit 2 (open type) 20mm fuse carriers to each of whatever PSU you go for and MOST immportant a LOCAL DP switch! Fuse values to suit the task in hand.
Oh! And don't wear rings!
Dave.

PC PSUs are great for 5V logic, but less useful for audio. You typically want well-regulated +/-12V (or higher) for audio circuits. PC PSUs are not very well regulated on these supplies though, and that will have a knock-on effect on your circuit. This is one reason why built-in audio on PCs can be a bit iffy - unless the audio circuit has its own supply regulation, it's going to be getting crud off the supply.

I wouldn't bother with PC supplies for audio projects although they're probably fine for digital projects. That 48V supply is also useless for general audio work as no standard audio parts work from that kind of voltage (apart from condenser mics).

Do you have any Alesis AC output wall warts hanging around? Two diodes and a couple of capacitors on a piece of veroboard on the output of one of those would get you started. Add a couple of voltage regulators and a couple more capacitors if you want a regulated output.

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Ah! James!
Good one: http://www.maplin.co.uk/ac-ac-fixed-voltage-high-current-power-supplies-24 0?ordercode=L55BR Two of these will give you a safe start and a bridge rectifier each will give~ 36V dc off load (but will drop quickly with even a small load. You can also fork about with voltage doublers to get 48V at a few mA).

As you say, build a pair of regulators, 78/79 types or the 317 if you want variable. Note, IC regulators are supposed to be s/c proof, not always! I have an old WWorld circuit for a guaranteed blow up proof regulator, not very efficient but really is bombpoof!

Dave.

Thanks again. Warnings on PC PSUs noted. Ditto on fuses etc.

I don't have any Alesis PSUs knocking around, but I'm sure I can source suitable AC wall/in-line warts if that's genuinely the best way to go. In fact I may already have some of another brand tucked away in a draw...

Not sure what your power requirements are, but if under an amp, and you're competent with a soldering iron,you could try this 12-0-12 DIY supply:

http://www.musicfromouterspace.com/mfosweb/navigate.action?MAINTAB=SYNTHDI Y&PROJARG=WALLWARTSUPPLY/WALLWARTSUPPLY.php&CATPARTNO=DELAYMOD2011

You can get AC/AC wall warts with 12V output from Farnell:

http://uk.farnell.com/stontronics/ac-12100bs2-1/adaptor-12vac-1a-uk-2-1/dp /1279502

Other components need from them too, or cheaper at Rapid usually.

I suspect that Music From Outer Space kit would be a good buy, as it’s well smoothed and doesn’t involve switching PSU circuitry that can sometimes introduce interference to your circuitry. +/-12 volts is a useful value as well, although if you making mic preamps then +/-15 or +/-18 volts will give you more design headroom.

However, I must say that when I still used a bench power supply for breadboarding circuit experiments I found comfort in being able to switch on the PSU and slowly raise the voltage while monitoring with my digital voltmeter at an appropriate point on the circuit.

That way if any component has accidentally been put in the wrong way round or something shorted out you get some warning rather than a bang and a puff of smoke


Martin

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YewTreeMagic

Getting back on my hobby-horse, this is the sort of thing I was suggesting for your += 15V. Look at the price! Then consider it's features.
1.5kV isolation, not lightning proof, but just about everything else!
200mA O/P, more than enough for most purposes.
9-36V input range, so you can run it off the shittiest wall-wart that's out there.
S/C protection, for when you slip with that meter probe.

It is really, really easy to stick this on a bit of board as I said, and if you really insist on making it pretty and posh, plonk it in a metal box (earthed - but keep the O/P isolation) along with any other bits and bobs, then stick 4mm terminal posts on the front.

Of course you can add as many other converters as you like including a lower power 48V one if you need it. A couple of nicely isolated 9V ones wouldn't go amiss either for those pedals you're working on that have horrible earth configurations.

P.S.
Don't forget that seeing as they are fully isolated you can wire them in series to get all sorts of voltage combinations.

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It wasn't me!
(Well, actually, it probably was)

Edited by Folderol (21/10/11 06:54 PM)

Any of these any good?

http://www.quasarelectronics.com/power-suppy-kits.htm#Positive-Negative-Po wer-Supply-Modules

I've not used them myself but I was looking for a supply and came across the site while searching.

Quote fay spook:

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Any of these any good?

http://www.quasarelectronics.com/power-suppy-kits.htm#Positive-Negative-Po wer-Supply-Modules

I've not used them myself but I was looking for a supply and came across the site while searching.

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Yes Fay they look quite useful but "The Management" here might be very wary of suggesting equipment that needs connection to "raw" incoming mains. Yes many here are qualified to do that but many are not, tricky call.

Then some caveats: Do not think those supplies are bombproof. They seem to use conventional 78/79 and maybe 317 type regulators and despite mftrs' claims these WILL punch through!
Some of the supplies seem to indicate that they are dual, variable output? My closer reading suggests to me that this is not the case.

Dave.

Quote ef37a:

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Some of the supplies seem to indicate that they are dual, variable output? My closer reading suggests to me that this is not the case.

Dave.

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Hi Dave!

Yep, that fooled me for a moment as well - on the cheaper models the output voltage actually depends on which pair of 78xx and 79xx regulators you buy in addition to the kit, while on the Audiophile version you change a pair of zener diodes

Still some good prices though - might be tempted myself to buy one of these to save time when I get started on my modular rack effects design


Martin

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YewTreeMagic

Hi Martin,
For the quietest possible supplies I have been told that the 317 series regulators are better than the bog standard fixed 78/79's. Maybe Will or Dan can advise?

Then the 317s give you the option of trimming a symetrical supply for exact balance.

Dave.

Quote ef37a:

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Yes Fay they look quite useful but "The Management" here might be very wary of suggesting equipment that needs connection to "raw" incoming mains. Yes many here are qualified to do that but many are not, tricky call.

Dave.

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Correct and point taken, this bit of the power supply is the bit that can kill.

For audio equipment a +5, 9 and +/-12 or 15 volt supply will cover most things outside power amps. I looked at a couple of Maplin badged supplies and they might look like dual supplies (+ 0 - outputs) but they were only single ended and the description was a bit vague. Current limiters are usually part of the spec and these will stop you frying your boards. As an aside I connected my MFOS Ultimate the wrong way round to a dual bench supply with current limiters, the meters told me something was wrong and so I switched off the supply. The result? The board still worked OK. Well done MFOS and more fool me.

Thanks all for your help and advice.

Problem solved: not quite what I asked for, but I can simply take power and audio I/O feeds from a spare slot in my Lunchbox rack. Inexpensive, and perfect for most of projects I have in mind.

Don't know why I didn't think of that sooner!

Quote Mixedup:

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Thanks all for your help and advice.

Problem solved: not quite what I asked for, but I can simply take power and audio I/O feeds from a spare slot in my Lunchbox rack. Inexpensive, and perfect for most of projects I have in mind.

Don't know why I didn't think of that sooner!

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Good idea! BUT. Build a box with a DPDT switch, 2 LEDs and a fuse in each line well below the Lunchbox current capabilty.

Dave.

Pleased to hear you're sorted Matt, although one advantage of many bench power supplies is that they incorporate a variable current limit, so if you power up and your circuit board is a dead short the voltage never gets high enough to result in burnt out components and puffs of smoke.

Do be careful with your Lunchbox rack PSU - they aint cheap!


Martin

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YewTreeMagic

Good point... can't afford to put the Lunchbox out of action... though ultimately I will need to test things in there at some point...

Don't be afraid to use a string of PP3 batteries for test purposes - I suspect very few 'professional' audio circuits such as mic preamps, compressors would fail to work with +18 or +/-18 volts for dual supplies, as long as you never exceed the expected official voltage to avoid blowing electrolytic capacitors in particular.

Many (including all the guitar-based effects) would give a useful output with +9 or +/-9 volts for quick test purposes, to make sure your circuit is essentially working before you plug it into your Lunchbox


Martin

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YewTreeMagic

Quote Mixedup:

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Good point... can't afford to put the Lunchbox out of action... though ultimately I will need to test things in there at some point...

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If you PM me I can help you with a very old (ex wworld "circuit ideas")regulator circuit that I GUARANTEE will current limit and be blowup proof (unlke 78xx's!). Constitutes 2 transistors, zener and one or 2 1N somethings, some resistors.

Dave.

Hi Mixedup!

Rapid Electronics just sent me an email detailing their latest special offers, which include a 100w Switch Mode Bench Psu 60v 1.6a with price reduced from £83.74 to £54.88:



Spec looks fairly good to me (including current limiting), and for this price it's a bargain:

www.rapidonline.com/Electrical-Power/100w-Switch-Mode-Bench-Psu-60v-1-6a-8 5-1903


Martin

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YewTreeMagic

I have passed that link on to the technical director at my last place of employment.
He will probably buy at least two so get in quick!

Dave.

Yep, good offer!


Martin

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YewTreeMagic