Zener or Transistor to regulate dual input voltage?

[fretzburner]

Hi I'm combining two effects in one enclosure and my problem is one effect is strictly 9v and the other is dual voltage 9v-18v.My goal is to use this effect  dual voltage either 9v or sometimes 18v.Is it okay to use 9.1v zener for the 9vFX(input 9v-18v) or use 78L009(input 9v-18v)?Biggest concern is when input is only 9v if those zener or transistor will work.What i have in mind is to use 8.2v zener and place 33ohm resistor in series with the zener.By the way the 9v effect is mxr noise gate clone.Need some knowledge from you guys.
Thanks

[PRR]

> input 9v-18v
> 8.2v zener and place 33ohm resistor in series with the zener

Do math.

18V in, 8.2V Zener, 9.8V must be dropped across the 33 ohm resistor.

9.8V/33= 0.3 Amperes current. That's a lot in pedal world.

Zener dissipates 8.2V*0.3A= 2.5 Watts. Resistor dissipates 9.8V*0.3A= 2.94 Watts. Your common half-Watt parts will NOT work.

If you have over 0.3A available in your 18V supply, and find 5W Zener and resistor, it works. Though the heat from over 5 Watts in a small box may soften decals.

Let's check the 9V input. Say it is 9.0000V. 8.2V Zener, 9.000V=8.2V= 0.8V dropped in resistor. 33 ohm resistor, 0.8V/33= 0.024A or 24mA resistor current. If your load approaches 24mA, the Zener current approaches zero. When you exceed 24mA load, the Zener is useless and the "8.2V" drops; at 50mA you really have 7.35V output.

> the 9v effect is mxr noise gate clone.

Ah, well....

1) that probably draws under 5mA

2) that can work just-fine with 18V. All fussy nodes are referenced to a 5.1V Zener. The chip will blow-up somewhere past 36V. The worst-spec Q1 could quit at 30V, though 45V total is more likely. The JFET does not feel supply voltage.

[fretzburner]

Thank you very much PRR for the clarification.
So it's okay to use this circuit(mxr noise gate) 9-18v.I will just use 25v electrolytic caps at the supply section which is a single 10uF. One more question,is it safe for the 5.1v zener of the mxr gate to operate properly without heating?
Thanks again
fretz

[PRR]

Yes.