cpu power supply for use with breadboarding etc bad idea????

[njkmonty]

I have a few half decent cpu power supplies lying around, and have seen someone else convert them into test bench power supply.
would this be ok for pedal breadboard etc ? or would the non transformer style psu create noise/ and other problems ?
any thoughts?

http://www.instructables.com/files/orig/F88/8JHO/FSSIQIA5/F888JHOFSSIQIA5.pdf

[njkmonty]

anyone

[R.G.]

Computer power supplies may (!) have large amounts of noise, both radiated and conducted. For breadboarding, you may be able to ignore this, or not. Or you might get a good one and be fine. There isn't any good way to tell ahead of time. They're meant for supplying large amounts of power as cheaply as possible.

You're betting your time and effort in doing any conversion work (and the safety issues it raises) that it'll turn out OK. There are known problems. Do you feel lucky?

[iccaros]

R.G. has good points, I will only give my experience, which is this.

On the 5 and 12v lines I have not found a nosy supply when using it for the bench, Serial and SAS drives are very sensitive to bad power, and while not audio, they do not appreciate spikes or sudden drops
3.3v lines can be poor as they are less commonly used, and so some do not pay attention as much and the parts using them are not as sensitive.

use a good supply, you should expect better results.

Note: if you use a SMPS with a computer supply there may be issues with heterodyning

in the end I have had my best luck with 12/5v supplies from Enterprise Quality Raid arrays. Like a old Sun 4 disk SCSI array I got off ebay for $5. It was designed for high demand datacenters so it was built like a tank with high quality parts, plus its smaller then a mini-ITX supply.

[earthtonesaudio]

Only using a super clean power supply in the design phase can come back to bite you later when you (or someone else) discovers your circuit doesn't play nice with a less-than-super-clean power supply.

I think of a noisy power supply as a tool for testing real-world robustness.

[NazzTazz]

Why would you force yourself to deal with a computer PSU when you can build this for 20 bucks ?


(click for full size)

You can even use a standard wallwart transformer and connect it after bridge. This can easily fit a 1590BB box...

[Fender3D]

Instead of NazzTazz's 7809 you may consider using this

Then, on EBay stuff like this

comes really cheap and you'll have a variable DC supply

[iccaros]

Why would you force yourself to deal with a computer PSU when you can build this for 20 bucks ?


(click for full size)

You can even use a standard wallwart transformer and connect it after bridge. This can easily fit a 1590BB box...

some of us have a lot of computer supplies sitting around..

[njkmonty]

yes i do have plenty of good quality  pc power supplies lying around, and would prefer not to just land fill them, they also have -12v  although not huge amount of amps .
also have several old cheap lcd multimeter's lying around too!
would extra filtering with caps be needed for each power line, to help with noise?
again for some people , having to go out and buy stuff for this may not be economically, worth , it,
but i have plenty of components lying around, including regulators caps and previously mentioned Dmm to be modified

[iccaros]

if you have a scope, read the power output, they are already highly filtered.
Since they are switch mode power supplies they switch at a frequency, if that frequency is in audio range it will create noise. Its hard to filter audio range as that is a range you are working with in the pedal. build a test circuit and test before you modify, this will tell you how well the supply will work for you.

[PRR]

> 3.3v lines can be poor as they are less commonly used

Actually they are _always_ used.... to feed a 2.8V, 2.2V, or 1.8V regulator for modern hi-speed lo-volt CPUs.

> ok for pedal breadboard etc ?

It's like 100 times the power most stompboxes could ever need. It can make major smoke and heat very quickly. Yes, most PC supplies shut-down reliably on a dead-short, but not a partial short. 480+Watts of DC power in the thin wires we use can be very dramatic (I've had it happen, while driving, at night).

A guy near me has a 300 Horsepower lawnmower. That does not mean a 300 Horse mower is a good idea. If it snagged a hose it might pull pipes out of the house.

Call me old fashioned. I like filament transformers. 6V 0.5A into FWB and 2,000uFd cap will power a lot of electronics, clean enough to judge good/bad, and is unlikely to do great harm.

[Processaurus]

Yes, the capability of providing obscene amounts of current is actually a drawback for making little audio circuits.

One of the most important aspects of a good bench power supply is it momentarily shutting off and showing some indication, either with a sound or a light, when something is shorted out/ drawing too much current, rather than sitting there and pouring industrial amounts of current down your pitch pirate or what have you.

[njkmonty]

ok, ok , i have since removed the pcu guts and putting in various trnasformers within the pc p ower supply, i think 3- 4 will fit.

ive asked a similar question before here but never realy got a response.

one of the things ive been reading, and thinking about is being able to run my pnp transistor devices too.
i know i can derived  bipolar transformer + - voltages  and or even use a surge pump, similar to amz power supply setup,(see below)
but how does that work for a pnp fuzz pedal for example?
ie standard pnp fuzz circuit  has   positive 9v to ground

if i use -9v to run a pnp circuit, where do i connect it to?

http://www.muzique.com/power.htm

This is the complete schematic for the circuit that is contained on the AMZ Power Supply PC Board. It features 5 linear voltage regulators and a voltage converter chip that outputs -9v to power PNP pedals that require negative voltage. The basic idea is to create a single pc board that can be used to produce clean, noise-free power for your pedals.

[Seljer]

I've rehoused an ATX PC power supply into a larger box, added an onoff switch and banana jacks for all the voltage levels (+-12V and 5V). I also added a 9V output with an 7809 regulator on the +12V line. Its usually a bit noisy for pedals, you have to add some filter caps to whatever you're doing. The 9v linear regulator helps this quite a bit though.

The built in shortcircuit protection works well enough to prevent you from burning your breadboard (though be aware you can draw quite a lot of current from it so components are not necessarily safe). So far, with my use of it, the extra current is only useful for stepper motors/electrolysis etching experiments, if you want to do higher power audio stuff you need a supply that puts out more than 20 volts.

I have a friend who bothered to reverse engineer a power supply and added a potentiometer into the feedback section of it's voltage control to have a true variable supply (I believe he also took out all the limiters).


I also use it to power a 120mm PC fan on my bench to suck away solder fumes.


edit: another problem I had was with an older supply, that it wanted a minimum load connected before it would turn itself on. I used a different one that didn't seem to have this issue.

[njkmonty]

ive asked a similar question before here but never realy got a response.

one of the things ive been reading, and thinking about is being able to run my pnp transistor devices too.
i know i can derived  bipolar transformer + - voltages  and or even use a surge pump, similar to amz power supply setup,(see below)
but how does that work for a pnp fuzz pedal for example?
ie standard pnp fuzz circuit  has   positive 9v to ground

if i use -9v to run a pnp circuit, where do i connect it to?

http://www.muzique.com/power.htm

This is the complete schematic for the circuit that is contained on the AMZ Power Supply PC Board. It features 5 linear voltage regulators and a voltage converter chip that outputs -9v to power PNP pedals that require negative voltage. The basic idea is to create a single pc board that can be used to produce clean, noise-free power for your pedals.

[Seljer]

In a computer power supply, there is a blue wire that should have -12V. You can hook that up to a 7909 voltage regulator (the negative companion to the 7809, be careful when building it because the pinout is different) and have a relatively clean -9V voltage.

edit: in that AMZ power supply if you're powering a positive ground pedal you would use ground and the -9V output

[njkmonty]

thats what i was wanting to know!
so in the picture below..
ground would be like a normal pedal ground,
and the 33k / 470 ohm resistors would be connected to -9v?

[Seljer]

Precisely that

[Perrow]

As you seem to have noticed, the PC power supply casings make nice PS enclosures, AC jack built in, grounded enclosure and quite nice size for the purpose.



I'm looking to replace the VU meters with real (digital) meters for added precision. I built mine using LM723, there are better, more modern, chips, but I had a nice description of a variable supply using that. I can recommend going for one with variable current limiting. Feels nice to be able to turn a new circuit on and slowly increase the current limit watching the volts and amps on the meters and cutting power if need be.