Power Supplies in a nutshell.....

[John Egerton]

Hey guys...

I've read numerous build reports regarding DIY power supplies however I would like you to clarify some things for me... Sort of, from the horses mouth so to speak.


When most people ask how many pedals can be run from a particular DIY build and the replay is "It depends upon your transformer". Does that mean that there are many different transformers that can deliever various amounts of ma?

I qould like to buld a power supply that can deliever 9v to about 10 pedals daisy chain style... Would most transformers handle this taking into account I am using mostly boss pedals and diy builds such as phase 90s etc...?

I have a few PC power supplies that convert 240V to 12v and was wondering, could i wire, as well as the DIY power supply build, a straight jack coming from the output of the transformer to deliver a single 12v supply as well?

Also... Which DIY power supply build woul you reccomend for my application?

Also... would you reccomend an un earthed plastic box (obviously) or a metal enclosure with a ground wire connected to a fuse for safety?

Thanks in advance guys...

John

[MartyMart]

John, hi,  I have not built one, but to partly answer your question yes it does depend on what current your pedals require, if they are all between 10-30 ma then you can run several quite easily with a 200ma rated PSU, like a Boss PSA 240  for instance.
Pedals such as delays or the Boss "Metal Zone" will draw 70ma !  so you just have to keep that in mind.
I bought a "One spot" PSU  rated at 1000ma ! this will power a LOT of pedals ( with a daisy chain connector)  and cost me £25  !!
There you go,
Cheers, Marty.

[cd]

Hey guys...
When most people ask how many pedals can be run from a particular DIY build and the replay is "It depends upon your transformer". Does that mean that there are many different transformers that can deliever various amounts of ma?

Bingo.  Larger transformer can handle more current.  For example, your home stereo probably has a big transformer in it that can provide lots of current, say 2000mA or more.  That would be overkill for a pedalboard power supply, so a smaller one is sufficient.

I qould like to buld a power supply that can deliever 9v to about 10 pedals daisy chain style... Would most transformers handle this taking into account I am using mostly boss pedals and diy builds such as phase 90s etc...?

Depends on the transformer.  Say your 10 pedals require an average of 20mA each.  10x20mA = 200mA, so a 250mA transformer would be fine.

I have a few PC power supplies that convert 240V to 12v and was wondering, could i wire, as well as the DIY power supply build, a straight jack coming from the output of the transformer to deliver a single 12v supply as well?

Technically, it would work but it won't sound good.  PC power supplies are typically switching power supplies, which equals tons of switching noise.  It's not really putting out 12V, but rapidly switches between 240V and 0V (or some other fraction), which averages out to 12V.  i.e. if you turn "on" the power at 240V for half a second, and turn it off at 0V for another half seocnd, the average over one full second = 120V.  Decrease the time and you decrease the average.  This works fine in computers but the noise of switching back/forth is not good for audio.

Also... Which DIY power supply build woul you reccomend for my application?

See the Spyder at www.geofex.com

Also... would you reccomend an un earthed plastic box (obviously) or a metal enclosure with a ground wire connected to a fuse for safety?

Metal for shielding, since transformers can radiate noise on their own.

[RDV]

I used a 300ma transformer for mine and I've plugged a whole bunch pedals in it and had no problems.

RDV

[John Egerton]

Thanks for replying so fast guys...

I had a guitar pedalboard power supply that could handle 400mA.. but the problem was that it had an overload protection and would cut the power to the pedals if the mA got anywhere near that marking... I actually doubt it was 400mA to be honest.

I was wondering.. say I did overload a DIY build... What would happen?

I hope your first words are not kaboom!

Thanks again guys...

John

[RDV]

Well, the LEDs would dim a bit.

RDV

[Mark Hammer]

A wallwart/transformer with a 300ma capacity is adequate for a big chunk of the floor-pedal pie.  Most wahs will not need more than 15ma, most fuzzes will not want more than that either.  Same goes for chorus and phaser pedals.  Right there you pretty much have the standard pedalboard, with at least 200ma current to spare.

At the same time, there are plenty of pedals that require much more than that.  One of the new Line 6 pedals I have has an approximate 60ma current requirement (new Duracell 9v lasts about 6 hrs).  Put a couple of digitally-based pedals in your floor, and 300ma can be eaten up pretty quick.  According to the Line 6 programmer I spoke with, the more you ask a DSP chip to do, instruction-wise, the more current it generally needs.

Aside from the convenience aspect (such as the elegance of a single supply vs multiple ones) I wonder if there might be advantages to using multiple wallwarts with respect to keeping line noise down or other types of audio gremlins.  Certainly, when one looks in the audiophile literature, it is common to find separate power supplies for each channel on high-end power amps.  Now, I realize that this same literature is also responsible for preposterous claims about the audio impact of knob choices, so I'm not about to run with everything that comes out of that literature.  At the same time, there may well be something to the idea that sudden current demands by one part of the chain may have some impact on other parts of the chain if the power supply is "just enough".  So, if I had a 2amp supply, I probably wouldn't be concerned with the impact of a sudden 50ma draw from one pedal.  One the other hand, if I have a 200ma supply and stepping on a stompswitch results in a sudden need for a significant portion of that current, maybe I ought to use a separate supply.

Keep in mind, I'm not saying this is necessarily the case.  I'm just wondering out loud if there ARE circumstances under which having a few separate wall-warts might be a good idea, just to keep the low-current and high-current pedals playing nice with each other.

[niftydog]

PC power supplies that convert 240V to 12v

most (read; cheap) computer power supplies aren't suitable for audio applications. A really high quality one would probably be ok, but they're not cheap by any means!

would you reccomend an un earthed plastic box (obviously) or a metal enclosure with a ground wire connected to a fuse for safety?

for shielding and safety, a properly grounded metal case with a fuse. Also, insulate the internal mains power connections with heatshrink tubing.

say I did overload a DIY build... What would happen?

totally dependent on the design. If it involves a simple 78XX series regulator circuit, then the regulator simply shuts itself down if it gets too hot, thus your supply would just stop working until the regulator cooled down. Such a regulator is capable of up to 1A if properly heatsinked. In most cases this is more than adequate.

The Spyder comes highly recommended.

[STOMPmole]

So is it really worth it to build a DIY power supply?  It just seems that when you can buy one like the Godlyke Power-All that supplies 1500mA and comes with a daisy-chain and adapters for $39, it's hardly worth the time and trouble.

Are DIY supplies THAT much better?

[niftydog]

DIY isolated supplies like the Spyder are the bees knees when it comes to avoiding ground loops. Otherwise, sure, go with whatever you've got! However, wall warts are often cheaply made and have poor filtering.

[Hal]

So is it really worth it to build a DIY power supply?  It just seems that when you can buy one like the Godlyke Power-All that supplies 1500mA and comes with a daisy-chain and adapters for $39, it's hardly worth the time and trouble.

Are DIY supplies THAT much better?

not sure how much ure times worth, mine's pretty cheep.  All in all, my DIY unit cost about $10, or less.

[John Egerton]

ok.. I've looked into the spydar on the Geofex site and consider this a fun way to go...

I'm looking at the version in the middle of the page that says you can use as many outputs as you like...

Am I assuming that it means that I can keep adding as many transformers and regulators as I like?

Would you suggest using a transformer and regulator for each pedal, or would you think I could get away with daisy chaining a few? It doesn't really matter for me to get a load of transistors from smallbear as they are very reasonably priced.

Also... can anyone tell me a way to modify one of the spydar outputs to regulate the power supply and provide 12v??? I have a wireless guitar reciever that would benefit from this...

Also... for the spydar... are these the transfomers to go with from the smallbear site? :

12 VCT @ 200 ma. Flat Pack! Small, powerful and inexpensive, made for Small Bear! Compare to Magnetek FP12-200!


Thanks guys...

John

[niftydog]

Am I assuming that it means that I can keep adding as many transformers and regulators as I like?

Within reason, yes.

Would you suggest using a transformer and regulator for each pedal, or would you think I could get away with daisy chaining a few?

if you're goint to the effort to build a Spyder, then you definately want to keep each pedal on it's own transformer. If you start daisy chaining, then you may as well not have bothered building a Spyder in the first place!

can anyone tell me a way to modify one of the spydar outputs to regulate the power supply and provide 12v???

it's possible. Provided the transformer provides sufficient voltage, you simple change the regulator for a 12VDC one instead of a 9VDC one. This may mean that you have to get a tranformer with a larger secondary voltage than the others.

Those transformer sound ok to me.