Vico Vibe Zener Diode Value Question

[Josemitejam]

Hi all,


I teach music at a middle school and I had my students breadboard a fuzz face based off of smallbear's directions last year, it went really well and the students loved it! I'm looking to add a Vico Vibe this year for them. The closest value that smallbear has is a 6.2 zener diode to the 6.8 zener diode that the parts list asks for. Would a 6.2 work?

http://tagboardeffects.blogspot.com/2012/04/jordan-vico-vibe.html

Thanks!


Joe

[Josemitejam]

Better yet, I might buy from stompboxparts instead because they have the transistors in stock, the closest values they have are:

5.1
9.1

would those work? One more than the other?

Thanks!


Joe

[antonis]

The closest value that smallbear has is a 6.2 zener diode to the 6.8 zener diode that the parts list asks for. Would a 6.2 work?

Add a Si diode (like 1N4148) in series with 6V2 Zener and you should be fine..



P.S.
Any Zener value higher than 6.8V should be fine (but a little bit harder to trim it) while any value lower than 6.8V should also be fine if you don't need full bias trim..

[EBK]

I have ten 6.8V zeners that I don't need. How many do you need?

[Josemitejam]

Awesome! Thanks! And EBK, I would need 3, maybe 4, to play it safe. But I don't mind using the 4148's - I have plenty of those around right now!

[Rob Strand]

As far as duplicating what is there, Antonis's recommendation is fine.

As far as critiquing the design,

- R5 at 39K is going to put hardly any current through the zener.   
   So the regulation isn't going to be that great.

- When the battery goes flat the regulation will get worse and the adjustment will go off.
  (because 6.8V is so close to a flat battery.)

- I seriously doubt you will need to adjust trimpot to full voltage.

Probably the best overall performance is using,
- a 6.2V zener.  (no diode)
- change the 39k resistor to 4.7k or 10k
  in the light of this being a low power device perhaps go with 10k
  it will actually work with 39k

You could use a 5.1V zener but you would need to drop the 39k resistor quite a bit (4k7 or less).  That's going to make the current draw of the zener somewhat more than the circuit.  The performance it likely to be worse although probably workable.

[EBK]

Awesome! Thanks! And EBK, I would need 3, maybe 4, to play it safe. But I don't mind using the 4148's - I have plenty of those around right now!

I'll defer to Rob and Antonis on the circuit analysis (I haven't looked at it).  If you decide you want to try the 6.8V zeners anyway (and if you are in the US--I forgot to ask), just send me a PM with an address to mail them to (free--pay it forward).

[Rob Strand]

I'll defer to Rob and Antonis on the circuit analysis (I haven't looked at it).  If you decide you want to try the 6.8V zeners anyway (and if you are in the US--I forgot to ask), just send me a PM with an address to mail them to (free--pay it forward).

Don't let circuit analysis get in the way of good deeds .

It will work with the 6.8V, I'm sure may people have built it that way already.

A 100k to 150k resistor in place of the zener would get it going.

[antonis]

A 100k to 150k resistor in place of the zener would get it going.

Together with a small electro cap, perhaps..

Don't let circuit analysis get in the way of good deeds .

BTW, particular circuit could be leniently characterized as "unusual"..
What it does is passive Volume dividing (max unity, min almost zero) so it inherently exhibits low output..
(of course, an output booster should settle amplitude issue but then Q1 should be redundant 'cause amplitude modulation could be applied directly on booster..)

[duck_arse]

it has one feature very rarely found in active circuits - input and output are interchangeable.

[Josemitejam]

Ha! That's pretty awesome duck_arse! Thanks for all the info everyone - I'll definitely toy around with this, and it'll be great to let the students experiment with some different options to hear how it changes the sound. EBK, I'll send you a PM in a few minutes!

Best,

Joe

[antonis]

I'll definitely toy around with this, and it'll be great to let the students experiment with some different options to hear how it changes the sound.

Good for all of us..!! 

[iainpunk]

I'll definitely toy around with this, and it'll be great to let the students experiment with some different options to hear how it changes the sound

maybe replace the input resistor with a capacitor so it works as a filter- instead of a volume-tremolo, and let the students experiment with values.
i suggest starting with 10n and experiment for the amount of bass, bigger capacitance is more bass, smaller capacitance is less bass

cheers