Dropping 18v to 9v

[carboncomp]

If I only have a 18v plug left on my PSU, can I just build a voltage regulator like a LM7809 with a heatsink into the pedal.

Or, is it better to step down to 12v then 9v? (know the LM7809 is rated up to 35v, but guess 18to9 will be a little spicy heat wise?).

(A side question, will I still need to caps with a regulated PSU, and if so, what size uF should I go with each side of the regulator?).

[brett]

Hi
the heat will depend on current draw as well as voltage. Assuming the 7809 is good for dissipating 3 W with a little heatsink, 3W = 9V x 0.3A, so you could draw 0.3 A. ie. enough for most distortion/wah/phaser pedals etc, but not enough for some current-sucking digital devices.
Because there's no incoming ripple, only small caps are needed. Maybe 100uF on the input and output. On the output, add a film cap in parellel with the electro (for low ESR if you want to google/wiki it).
cheers

[DavenPaget]

I don't think you need the low ESR capability , i have gotten away not using a MKP and using purely electrolytics in the past .
I think a good ballpark is 1W without a heatsink , 1W = 9V x 0.1amps
What are you using it for anyway ? A normal pedal ? If so you can get away with just a 100uf on the input and 100uf on the output like he mentioned .

[senko]

You might also want to put some 0.1uF ceramic caps on both sides of the regulator.  I typically combine this with the 100uF caps and a decoupling cap close to the power supply leads of every IC I use. 

[carboncomp]

What are you using it for anyway ? A normal pedal ? If so you can get away with just a 100uf on the input and 100uf on the output like he mentioned .

using it on a SupaFuzz clone (3xOC75) just before a charge pump. +18V> LM7809> +9v> Pump> -9v> SupaFuzz.

[Pharod]

Hello, my first post on this forum and i gonna try to help:

The L7809 is one of the best methods of dropping down voltage. Simple description:

Look from above on the L7809 so you can read the letters. The left leg is there the 18v connect, middle is ground, the right leg is where you will get 9v. To stabilize a L780x regulator it is commonly advised to put a "big" cap between input and ground (maybe 100µF) and a "smaller" cap between output and ground (maybe 47µF), Electrolytic work just fine. Of course, you can use a film or even cheapo-ceramic cap on the output side in parallel to the electrolytic,( lets say 0,1µF on input), 0,047µF + 0,001µF on output. The film/ceramic has to be smaller (lets say 47µF electrolytic + 0.1µF ceramic). Thats all dependant on how much filtering you want/have to use.
In most commercial schematics and suggestions, a diode is placed between input and output, to protect the regulator from backward voltage, which can occur when you turn the unit off and some caps discharge suddenly. I drove some russian tube heaters with a L7806. They draw 500mA, so the regulator heated up pretty fast. Sufficient cooling is necessary. The backside of the L780x is always connected to ground, so you can nail it directly onto your hammondcase (or whatever housing you use) for cooling.

That article is in german, but the schematics will do: http://www.elektronik-kompendium.de/public/schaerer/ureg3pin.htm

[jongwong]

You can try LM2576ADJ,would be better than 7809,2576 have 3A max output .

[WickedBlade]

I have no opinion about the voltage regulators, but I have a thought to share:
before you commit to building a 18V-to-9V circuit, you may ask yourself if one of your pedals can handle a 18V input.

You are here, so you probably have DIY pedals, and you know exactly what is in them. It is my experience that many stompboxes are able to work at 18V. For instance, my latest build, a MicroAmp clone, can handle 18V because it's made only with metal resistors, an opamp and caps; and all my caps are rated for 25V or more, the opamp can handle a pos/neg 18V power supply (that means it can handle a 36V input), and the resistors are rated 0.25W, which is more than enough.

So before building something, you might find in your pedalboard a pedal that will gladly accept your 18V power supply, from the start or with a couple capacitor swaps (change 16V rated caps for 25V rated ones).

Just my 2 cents 

[lonewolf]

a 10 volt 1 watt zener diode/100 ohm resistor will drop the voltage...

[darron]

a 10 volt 1 watt zener diode/100 ohm resistor will drop the voltage...

that might be a good idea.

or maybe a size down 9.1/8.2