Power supply filters

[kepeb]

hey people.
I have been experimenting with my Guitar pedal boards power supplies.
it seems almost at random, noise can be introduced through grounding and power supplies. i am currently running 4 analogue and 5 digital pedals through 4 adapters (one ac for whammy) and some of them really make a fuss when powered on the same chain.

i have found two example of a 9v filter i can put between the ac supply and my pedals.

http://i109.photobucket.com/albums/n.../9V_filter.gif
and
http://i109.photobucket.com/albums/n...ringInside.gif

they are very slightly different, is the placement of the components or more importantly... the values of these parts critical?

and in both examples there are green 'mylar' caps(?) is this essential? are electrolytic's not suitable here?
why?

i have some parts, and some time today so i am about to experiment some...
any thoughts or advice for me ?

[Manic]

hey people.

i have some parts, and some time today so i am about to experiment some...
any thoughts or advice for me ?

...if You cant get it fixed....

Voodoo Lab - Pedal Power 2 Plus

Good luck

[kepeb]

ha,
cheers man, i have looked at some of those. i think you pointed out the best one. i may well end up on that route

wanna have a go at smoothing the cheap way (? really?) first to improve my knowledge.

as i understand. one of the caps in the filters i linked to, smooths the already rectified dc current by discharging after the rectified peaks to create a 'smooth-er' constant current. which one is this and whats the other one for?

is the diode removing noise or for reverse voltage protection?

cheers

[Mark Hammer]

The diode is for reverse voltage protection.

The two circuits are essentially the same with three differences. One assumes an LED to tell you the power is on where the other doesn't. The one with the LED has slightly less regulation that the veroboard drawing. The one without the LED limits the current more.

Personally, I prefer the more complex one, although I would increase the 100uf cap to 220uf or even 470uf for more smoothing. The lower-value parallel capacitor is standard practice to bleed higher-frequency line noise more effectively.

One of the things I like to do is to make a "power distribution box", like the one shown below. This one is simpler than the schem you link to, but there is no reason why it can't be "upgraded" to include status indication and reverse voltage protection. The idea is basically that you have a box you can plug a wallwart into in order to smooth out the power a bit and permit use of multiple power patch cables that can be tailored to be just the right length or be "mini-daisy" types with 2 or 3 connections, or even power cables with different sorts of plugs on the end (phone type, reverse polarity, etc). The other nice thing about this arrangement is that you can stick the distribution box on the pedal board, and simply unplug the wallwart from it at the end of the gig for packup.

[kepeb]

thats a great enclosure and a good idea about the multiple outs. i may just solder the wires in to save costs and time. i think i will be using the more complicated one.

during my searches i found a really informative page on another forum if anyone stumbles across this in the future.
i hope thats ok to post here, if not i'll remove the link.
i found it useful tho.

using 12v on a 9v circuit?

[kepeb]

right. following what i interpreted from the links above, i created a little filter on some strip board.

the 9v in goes through a 100 ohm resistor to the + side of 5 caps (1000uf, 100uf, 10uf, 1uf electrolytics and a 0.1uf mylar) to give what i understand works as a wide band noise filter with common ground.

this seems to work just great! there are a couple of things i'm unsure about tho.the adapter now doesnt power as many pedals as it did unless i flip the voltage (on the original wall wart) to 12v.



what is going on here, i guess i have restricted the current flow?? maybe the choice of caps is wrong? maybe the higher voltage may damage something? (although it seems fine)

is there a simple method of bringing the voltage back down and current back after the filter?
or am i just going about this the wrong way?

[rockin roy]

I'd question the series resistor.

I'd also rethink the wall wort. They come in two types; battery eliminator and battery charger. Sometimes I find only one diode inside these. These usually say something like 9V 50 ma. If yours doesn't offer at least an amp consider buying a DC suply on ebay (Power One, lambda, keepco).

The "filter Cap" used to eliminate ripple is being used like a battery. Biggest is best. The small ones .01mfd "filter" the spike when you unplug the transformer. This can produce a surge that can be in the range of hundreds of volts.

[rockin roy]

Just over thinking this now. Resistors are generaly added across the caps to disipate charge when you are finished using the device. Try a very high value (in the megs is ok).
All the caps after the 1000 Mfd are just for looks and add more things that can go bad latter.

[rockin roy]

Is it time to go home yet?

The series resistor is from your first photo bucket. That is a Zenier regulator.
I don't think you are doing that.

Cheap transformers; like the ones in wall worts, can drop as much as 20% across them when under load. if you overdrive them then you are creating a Suzzy Home Maker Oven with out knowing it.

A quality transformer will drop 5%. That is why filiment suply transformers are 12.6 or 6.3v. The transformers made in the orient just don't have the copper they should.

You can use a lamp (12V) as a series resistor. it has a very low resistance when it is not burning but goes high when it lights up (and then limmets current). Once again this is a battery charger trick and is not a quality power suply option.
The only correct answer so far was the votage regulator.

[kepeb]

cheers for the thoughts.
i should of been clearer on exactly what i have and what my goals are.

i dont intend to spend money on the project really (probably get voodoo PS eventually)

atm i have my board setup with a mains extension which has the transformers plugged in and i arranged the 3 daisy chains to give the least amount of noise, i'm happy with the setup but i thought i could definitely improve on the noise levels with a few spare components while i have some down time.

the 50/60hz hum was dramatically reduced when i put this filter inbetween the adapter and my pedals, so thats a result!

it seems to have changed the current tho. the adapters are 3-12v (selectable) 300ma each.
with the filter in place i need to switch the voltage up from 9 to 12v before i get enough power to the pedals.

I don't think you are doing that.

what?

The only correct answer so far was the votage regulator.

which is what i have? or you mean another component ( 9v regulator) ?

Resistors are generaly added across the caps to disipate charge

is this the 100 ohm i have in there? or you mean a resistor from the + to the - legs of the cap?

it seems like they're ok like this but the main questions are will i do damage via over voltage to my pedals.... or damage the transformer trying to pull more power etc?
cheers

[kepeb]

i am happy with the results noise wise... much better.

just kinda checking its safe/reliable like that long term.
i would hate to bolt all the board back together with my new filters and have it go dead at a gig :O

[rockin roy]

"the 9v goes through a 100 resistor" this leaves you with around 100 ma max. Increasing the voltage only gives you slightly more current to use.

The higher voltage from these transformers when they are not being fully loaded has always been a concern to me.

A zener regulator shorts out at a certain voltage there by clipping the higher peaks. of course it would blow up without a series resistor to limit the current through the zener. That is what I see in the first picture.

A regulator requires a trip to radio shack (and a heat sink) but is well worth it, It is going to cost less then the gas and does a great job.

The caps add in parallel so you have 1111 mfd. You are just as good with the big one only. It has a rating of +100-20 which means it could be 900-2000 and be in spec.
I have seen these crimped into a star shape to increase their value. You don't normally see them paralleled because it is easy to just by a larger one. In circuits where huge is required and they need many caps to get there the resistor across them not only drains the voltage when they ore turned off it makes sure the voltage across each cap is the same.

Just for fun measure the voltage across you power supply without a load and then do it again with your cap added (again no load).

[kepeb]

ok. read through what you said cheers

so with that resistor i am effectively wasting the capability of my transformers.
is it simply a case of increasing the resistors size to allow the full 300ma through? by how much? can i just replace it with 300 ohm?

i wasnt sure if the diode was zener or not...i used a n4001, are all non 'signal diodes' zener? i thought that was just for reverse polarity protection...

i may order some regulators in the future if i think the noise is too much ( i do seem to be getting increasingly picky) but for now i think i wil sort this filter as best i can and run with it for a while. (i will have 3, on on each chain/adapter)

i only really added the caps in parallel after the discussion i read in the link i posted earlier.
there was a guy who suggested different values remove noise from different frequencys...
also it seems common practise to have the large one and the small mylar/non polar caps at least, in parallel.

lastly. i measured for fun as you suggested..
the results seem to indicate the adapters are far from accurate to their labels!

the voltage doesnt seem to change too much with the filter connected but is about 14-18v on the 9v setting. 18-24v on the 12 setting and both come down with pedals attached.
i will measure the current tomorrow.

[rockin roy]

Hi Kepe, and Merry Christmas

I should be careful here. If you have a resistor in series with your peddles then that is a mistake.

If you tried using a 1n4001 in place of a zener that is also a mistake. A zener diode has a break down voltage targeted for a specific voltage. If your resistor is just in series with the diode and the pair in parallel with your load you are OK but your problem is you are dumping some current down the drain. This is not a problem if you have enough but it sounds like you don't.

14-18 volts is a big range. If it is 14 without the cap and 18 with then your power supply is unfiltered ( just a transformer and diodes). It happens. It is all some applications require.

Since you are not trying to kill 60 Hz hum but 120 Hz hum they may be betting you wouldn't notice.

Do you have any 18 awg magnet wire?

Try wrapping 10 to 15 feet (neatly) around your 1000 mfd cap, put the magnet wire in series to your load and the cap in parallel. It won't do much more then the cap by itself but it will look cool. If you want to use the Mylar cap it would do the most good across the primary of the transformer. All those windings produce a large RF spike when power is abruptly lost. I'm sure you have seen ceramic disc caps there.

[rockin roy]

Hey Kepeb,

Just out of curiosity what do you mean by you will have three on each chain.

I'm sure you know not to tie outputs of power supplies together. If you are using three caps you are building the wrong kind of filter. Believe me, no significant amount of rf made it through an iron core transformer. If you were using a switching supply, well, don't do that.