Zener Diode Question (for Phase 45)

[squeezer]

Hi guys,

having a problem with a Phase 45 build not phasing.

I used the schematic from http://www.generalguitargadgets.com/effects-projects/phase-shifters/mxr-phase-45/ but made my own vero.

The first thing i stumbled upon when debugging is that my voltages are lower than the voltages in the build instructions.
I have 3 Volts or less where it should be 4. Even directliy at the zener i only have 3 Volts which is the main reference voltage for the circuit.
I didn't have a 1n5230 and used a BZX85C 4V7 instead. Thought it's all about the breakdown voltage anyway.

Now i got suspicious and breadboarded the zener with a 10K resistor and a 9.2V source.
Just like:  +9V - 10K - Zener - Gnd
and measured over the Zener.
Well, i got 2.95 Volts, shouldn't it be more like 4.7 or a tiny bit less?

Edit: Did some more search on the forum and found a workaround. If i put 3 silicone diodes in seriss with the zener i get my 4.7 Volts.
Still wondering why the zener value is that wrong. I have some  BZX85C 9V1 here and they test fine with 9.05 Volts in the same config.

[PRR]

Welcome.

> used a BZX85C 4V7

That is a 1.3 Watt part. Rated 4.7V is tested at 45mA.

> the zener with a 10K resistor and a 9.2V source. ...i got 2.95 Volts

This is 6V/10K or 0.6mA. About 1/75 of the test current.

At 1mA test this part has dynamic impedance of <500, which is not an answer but does suggest over 1V difference when you get way off the 45mA test current.

Change your 10K to 1K. Is it better?

The drawback is shorter battery life. On power-supply, this may not matter.

(However if you use the way-small 1K LED resistor they suggested (in days when LEDs were dim), another 4mA for the Zener may be moot.

[squeezer]

Hey, thanks for the answer.

You're right, the BZX85C doesn't handle the low current very well.
With 1K i have 3.8V at 5.3 mA.
With 100R it's 4,55 V at 45mA.

Ordered some 0.5W zeners, will give them a try.

[slacker]

The zener is there to keep the bias voltage roughly constant if the power supply voltage changes, originally was so the effect would work the same as the battery went flat. If you use a regulated power supply for your pedals you can replace the zener with a 10k resistor.

[squeezer]

If you use a regulated power supply for your pedals you can replace the zener with a 10k resistor.

Yep, thought about that too. But I thought a zener would be the safer bet on whatever conditions.

Anyway, had some BZX55C 4V7 0.5W in my mailbox today. Tested one with 10K, gave me 4.07 Volts.
Soldered it in and pedal works as it should, nice and clean. 
This seems to be a proper replacement for the 1N5230.

[LightSoundGeometry]

I was never able to get my 90 going and thought it was a zener problem ..most likely i have oospec fets or testing them wrong. i may revisit today. Also today, I should be getting a madbean p90 board in mail. I have a mutron board from mb and love it!

I had just seen this a few days ago, not sure how they have been out but i want one!

http://www.jimdunlop.com/product/phase-95

I never use anything more than the 45 but this is pretty cool pedal for a traveling board..saving up for it now 

[squeezer]

According how the 4V7 behaves the 5V1 should give you around 4.4 Volts reference voltage with a 10K resistor (just a guess).
My JFETs are J201 with VGSoff -1.5, the trimmer is nearly in the middle.
I tried with 2N5457 VGSoff -0.5. Trimmer had to be all to the left and the effect sounded a bit bumpy.