Neovibe Questions

[fretbuzz2003]

If anyone has built the Neovibe maybe you could help me with a few questions. I'm using the project from General Guitar Gadgets (which comes from GEO I believe):

1. The schematic shows R2 wired to the DPDT switch. The layout shows R1 wired to the switch. Which is correct?

2. What are pads P and O for? They aren't shown as being wired to anything.

3.  In the instructions it is mentioned that you can leave out R35 and R36 and wire a pot instead to find more exact resistor values. How exactly is the pot wired?

4. How do you add an LED to the pedal?

Any insight would be greatly appreciated. Thanks!

[Jason D]

1. Both. I believe the original Univibe had 2 inputs. So, both R1 and R2 are the same value. They both are at the input of the circuit. Use either one.

2. Pad O is ground. I don't see a P?

3. The idea is to get the right mix of the phaser signal and the non-effected signal. So instead of using the stock 100k for each, use a 200k pot. A wire running from C18 to one of the outer lugs of the pot. A wire running from the junction of C17 and R37 to the other outer lug of the 200k pot. And, the middle lug would go to pad N or the Chorus side of the SPDT switch. Of course for more precise tuning, use 2 82k (where the wires were) and a 10k or more pot. Which is what I did.

4. An LED for what? On/Off indicator, or pulsing with the lamp?

[fretbuzz2003]

Pad P is at the center of the board near the lamp, but it's not shown as being wired to anything.

I would like an LED that pulses with the lamp, but if that is too difficult I would settle for an on/off indicator. I'm using a 3pdt switch. I've only used LED's with pedals running off 9V, so I wasn't sure if I had too wire the LED differently with 24V coming into the board.

Thanks for your help.

[Jason D]

Don't know whay pad P is for right off hand.

It shouldn't be hard to use a LED indicator with the 3pdt. But, you will be using the 18V-24V, so you will have to use a larger resistor for the LED. Around 22k to 47k, probably.

Also, I would think that you could get away with using the pulses from the lamp. Run a resistor from there to the + of the LED. And, use the 3pdt to switch the - of the LED to ground or nothing.

Also, I think there is more info on that here:

//www.lynx.bc.ca/~jc/pedals.html

[saxtim]

I haven't got the schematic in front of me - so this may be wrong, but from memory when I built it P and O are for the cancel switch - the original had no bypass, only a switch that shorted the lamp to ground (which effectively killed the effect)- this is what P and O are for.  If you're building with a true bybass, don't connect them (that's what I did)

tim

[fretbuzz2003]

Actually X and I are for the cancel switch. O looks like an extra ground (I wired it to the 3pdt switch) and P is between C18 and R35. I can only guess it was added to wire in a pot to tune R35 and R36.

Anyway, I finished the pedal and fired it up. The lamp worked, but I only got sound in the chorus mode and it didn't modulate (only the dry signal?)
So I'm off to debug it.

[Jason D]

Good luck, and let us know what happens.

[fretbuzz2003]

Looks like I have several transistors that aren't working properly. I'll have to look at that more closely.

How should the speed pot be wired? Looking at the layout I can't tell if the third wiper isn't used or if it should be wired to the second.

[Craig V]

I have my speed pot wired in where both sets of the the 2nd and 3rd lugs are wired together, and then both sets connected.  The pic on the layout looks to be wired this way.

It shouldn't make a difference since they're wired in as variable resistors, I think...

[Jason D]

The layout is wrong on how to wire the speed pot. Use the schematic for that. The C pad actually goes to the middle lug.

[fretbuzz2003]

Pardon my ignorance, but could you please explain how to wire the dual pot? Thanks.

[fretbuzz2003]

I think I figured out how to wire the speed pot. I get sound through the pedal and the lamp lights, but there is no modulation.

I had put 100 ohm resistors instead of 100 k. Doh! Could I have blown out any of the transistors? How can I tell if a transistor is bad or not? Several of the transistors appear not to be working correctly (collector and emitter voltages the same, emitter voltage higher than the base voltage, etc.)

[Jason D]

Yes, it is very possible that one of the transistors has blown. When I built mine, I blew the lamp driver transistor several times. You should go ahead and get yourself a couple of those, in case this happens. Actually I think RG left room on the layout so that a larger size (the ones with the heat sink) can be used that can handle more current.

Anyway, check the transistors around the lamp (lamp driver, and LFO).

Do this by checking the voltage on each leg (C,B, and E) in reference to ground. Post them here, or compare them to what RG has on his schematic.

[Aharon]

What's a good larger (TO-220) transistor to use as a lamp driver?,any known to work prefered.
Thanks
Aharon

[fretbuzz2003]

I got the pedal working last night. Thanks for your help Jason. Turns out Q12 was dead. Then I fried all my spare transistors trying to hook up an LED that pulses with the speed (the LED kept burning Q12 out for some reason). Has anyone successfully hooked up a pulsing LED?

One thing I noticed was that the speed pot only worked though its full range when 2N3904 transistors were used for Q11, Q12 & Q13. I have 2N5088's in it now for Q11 & Q12 and the pedal will only vibe at the max speed. I saw a number of posts earlier on this topic.

[Chris Goodson]

Has anyone successfully hooked up a pulsing LED?

I hooked one in but it seemed to rob too much juice from the lamp.   I think something involving a transistor would do the trick.  But, that's all I know, maybe someone could throw us together a circuit for this.  I'm sure it's not very complicated, I'm just not sure which transistor would be best or what resistor values to use.  This is something a lot of people might like on there, it might would even be good to have it listed on GGG as a mod for it or something.