Question about Zener diode...

[Govmnt_Lacky]

I have a pedal (chorus) that will work just fine with a battery BUT, it will not modulate (create the wet signal) when I plug in my PS. Now, my power supply is rated at 9V but.... it is unregulated (puts out more like 14V)

So my question is.....

Could I install a 9.1V zener between the power path and ground in place of the polarity protection diode to "regulate" the power input so that the circuit is getting 9V instead of 14V?

[R.G.]

my power supply is rated at 9V but.... it is unregulated (puts out more like 14V)...
Could I install a 9.1V zener between the power path and ground in place of the polarity protection diode to "regulate" the power input so that the circuit is getting 9V instead of 14V?

You could, maybe. However, it's also likely that you would have problems with that. Here's why.

Zeners don't regulate, as such. They just don't conduct at all up to some voltage, then they conduct all the current they can get, even if that's destructive. It's that "even if it's destructive" that makes zeners tricky. The first rule of zeners is **you have to limit the maximum current through them somehow if you want them to live**.

A zener regulator is actually a fairly complex design. You have to know the min and max voltages of your incoming voltage over all the load variations it will see. You have to know the min and max currents the load will pull. From those, you calculate the maximum current the load needs, the difference between the minimum voltage and the maximum zener voltage, then from this calculate a resistor to put in series with the zener. This ensures that the load can suck it's maximum current. If the load is removed, then the zener eats all that current to keep the voltage constant. If this current times the zener voltage is more than the zener's power rating, it goes up in smoke. Oh, and you have to assume that the raw input power has simultaneously gone to its maximum value to see if the zener survives. Not too simple.

I feel called on to say that you have the *ideal* setup for using a 7809 three terminal regulator. 14V in, 9V out, self limiting, thermal shutdown, able to handle up to an amp with proper heat sinking. What's not to love?

[Govmnt_Lacky]

I feel called on to say that you have the *ideal* setup for using a 7809 three terminal regulator. 14V in, 9V out, self limiting, thermal shutdown, able to handle up to an amp with proper heat sinking. What's not to love?

Thanks for the input RG. Unfortunately, what's not to love is the fact that there is no board space to install a 7809 regulator. There is no feasable way to insert it into the circuit without having to create some gaudy off-board wiring disaster.
I was hoping that I could insert the Zener a-la the CE-2 from Boss. They used an 11V Zener directly from power input to ground in order to regulate the voltage going to the BBDs so it would not go above threshold.

[Ice-9]

I'm not sure if i'm missing the point here, but would it not just be more practical to use a 9v PSU that is regulated to 9v.

[Hides-His-Eyes]

Make a little power board and use a regulator. Put it where the battery would go or something. two 100n film caps and a regulator, it'll be fine.

[Govmnt_Lacky]

OK. I think we are not staying on point here.

I'm not sure if i'm missing the point here, but would it not just be more practical to use a 9v PSU that is regulated to 9v.

Yes it would however, it would be cheaper and easier for me to just be able to implement the 9.1V zener that I already have.

Make a little power board and use a regulator. Put it where the battery would go or something. two 100n film caps and a regulator, it'll be fine.

In my above post, I stated that I really do not want to modify the board. In addition to that, I do not want to add another board as the space is not accomidating.

What I do not understand is why Boss got away with implementing the 11V zener in the CE-2. Why can't I just follow that same practice in this chorus? (a CE-3 modified to CE-2 spec but using the MN3207/MN3102 BBD set)

The max voltage ceiling on these BBDs is around 11V vice 18V for the MN3007/MN3101. So why not use the 9.1V zener in the same spot as the CE-2 uses the 11V zener?

[PRR]

> So why not use the 9.1V zener

**you have to limit the maximum current through them somehow if you want them to live**.

> What I do not understand is why Boss got away with ....

They know the current-sag/limit in their source. You don't.

Here's example. I have a 12V battery in the truck. Internal impedance is about 0.01 ohm. I put your 9V Zener across it. The Zener sags the battery to 9V. That is a 12V-9V= 3V drop. 3V in 0.01 ohms is 300 Amperes. The Zener must dissipate 9V*300A= 2,700 Watts. By comparison with half-watt resistors and 1,400 watt room heaters, you might guess that your Zener is good for a half or whole Watt but not hundreds or thousands of Watts.

I can build a 3KW Zener. Next problem is that a sustained current of 300 Amperes is bad for the battery and its wiring. The battery has sagged 3V at 300 Amps so has 900 Watts of heat in it.

Yes, the numbers are less frightening on wall-warts than on car batteries. Maybe just a few Watts of heat in Zener and wart. Maybe a slow-cook death instead of instant shatter.

Characterize this "unregulated power supply". How much does it sag for zero to large current? How much current does your pedal really need? How hot does the power supply get after a long night when delivering much more current than the pedal needs?

> we are not staying on point here.

Your path needs much more study or risks a stinky meltdown. R.G. Mick and HHE are suggesting similar paths they feel are more likely to be happy-trails. But do what you like do what you like do what you like .....