Quick thread about 9v power supply

[askwho69]

HI Again!!! I have "VERY QUICK THREAD QUESTION!!" ABOUT 9v power supply -. . .  i was cleaning my room and suddenly found a 9 v 850ma power supply! and i try it to my stomp box.. it hum a bit so i checked inside components are 4 diodes and 1000uf capacitor . . .  my question is how can i make it hum free and suitable for stompboxes? what can component can i add on it? thanks and hopefully someone can help me its a forever gratitude. .

[askwho69]

guys? 12 views no one left some food!

[darron]

usually we regulate the voltage after the capacitor and then add another capacitor after that. however, regulators usually need a couple/few more volts at the input than you want at the output, for example you'd be happier if you found a 12v DC power supply. if you measure the power supply with a multimeter you will probably find the voltage to be higher than 9v and maybe you could use a low drop out regulator as long as you only power a pedal or two....



without regulating it, you could just filter it even more than what the 1000uf cap is giving like this: http://www.muzique.com/lab/filter.htm
but that inductor could cost as much as a transformer.


you could build something similar to this:
http://www.beavisaudio.com/Projects/Huminator/index.htm
not as effective, but much cheaper. i'd make the caps much bigger though (1000uf and 100n maybe). the 100ohm resistor would have to be tuned depending on how many pedals you are running, but that is given as a general value probably.






here is an except off my website which will visually help your thought path out: (http://www.dazatronyx.com/support/quality/)



Power Supplies and batteries.

Typically we power our effects pedals off +9V DC from a battery or a 2.1mm DC socket with a negative tip. Some purists may argue that powering effects off a battery is the only way to go. Power supplies bring the potential (no pun intended) for problems, but are terribly convenient if you need to power a whole pedal board.

The first problem is that they can introduce hum. Your guitar signal is an AC signal - that is it swings from a positive voltage to a negative one, just like the power supply from the power point. If a little of the AC mains can find its way into your signal, you pick up the power point hum frequency and the harmonics it produces above that. This can be through capacitance or poor filtering. Australia's power supply has a potential of 230V240V AC @ 50 Hz (50 full cycles per second). Other countries can use 100V, 110V, 120V, 220V and 50/60Hz, but the principles are exactly the same.

The AC potential (voltage) is usually divided by a transformer. This converts electrical energy into an electro-magnetic field, then back into electrical energy, giving an electrical isolation. The output voltage of a transformer will vary however based on the voltage on the input and the load on the output. The mains potential from the power point can vary based on what the city is loading it with. If it's a hot day everybody might have their air conditioners and fridges running harder, meaning less voltage at the power point. Similarly, the more current you draw from your transformer, the lower the voltage it puts out. Less current means more voltage.

The output of a transformer is still AC, just lower voltage. This is then rectified with four diodes so that it only swings as either positive voltage or negative voltage, not both. This means that the power supply is now cycling at 100 peaks per second. You'll notice that through rectifying, the voltage goes up slightly.

To be made into useful DC for pedals, we need to be able to supply power during the low points of the peaks. To do this we attach a capacitor on the line. The capacitor quickly charges when the peak is high and supplies the stored voltage when the peak is low. This is now filtered DC. The larger the capacitor, the smoother the DC output.

There's still the issue of voltages not being stable. A pedal can respond differently at different voltages. The filtering capacitors may never give enough smoothing to eliminate all hum. You can also introduce spikes and pops from the mains AC, for example when someone turns the washing machine on. To overcome this problem you can then regulate the DC with a regulator IC. By supplying the regulator with a few more volts than the needed output, the voltage can be stabilized quite well.

There's also a potential issue with ground loops if you have multiple pedals sharing the same supply. Noise can also be transferred from one pedal to the next if you are sharing the same supply, especially for digital pedals. Pedals that work with positive grounds can not share the same supply as pedals with negative ground without a convertor, as they will short out the power supply. Generally only old PNP circuits have positive grounds though, and are often only run off battery anyway.

Here's a diagram visually representing every stage mentioned above.







Having a transfomer electrically isolates your pedal power supply Earth from your amp Earth, which diminishes Earth loop hum problems. Every pedal does not always needs its own individual isolated power supply and regulator. In most cases you can just have one high quality power supply daisy chained to every pedal without causing noise problems. This might assume however that every pedal has its own adequate filtering, which is not always the case with some older effects that were only designed to be run off a battery.

[askwho69]

WOW very nice reply! so i try to filter it more  . . . ill read this focus later . . .