Neovibe LFO Problem

[Craig V]

Hey,

If you don't mind, would you tell me the voltage on the base of Q11?

Thanks.

[Craig V]

Hey,

If you don't mind, would you tell me the voltage on the base of Q11?

Thanks.

[Craig V]

double post.

[Gearbuilder]

Hi,
Yes ,sorry i'm a very busy man ! My scope is out of order then i take the voltage with my meter on DC current
Here my results
The voltage on Q11 is :
                       Intensity : Full               Slow  Speed   Fast Speed      
                                                           8.4V to 9V   7.4V to 10.3V
                       Intensity : Mid               Slow  Speed   Fast Speed      
                                                           8.4V to 9.2V  5.8V to 11.8V
                       Intensity : Low              Slow  Speed   Fast Speed      
                                                           8.4V to 9.6V  4.7V to 12.6V

                  on Q13 (bulb driver)           All at full  11v to 23v
                                                          (biais 17V)
I hope this help you !
Bye
Bruno

Bruno

[Craig V]

Thanks for taking those measurements for me.  Sorry about not getting back to you sooner - it's been really busy times around here.

Do you mind if I as about how fast and how slow do you get it vibing?  The slowest I get it is about 1.5/second up to about 3/second.  I had it set to the slowest setting last night, and it was sounding incredible.  Should I be able to get it to go much faster?

Thanks.

Craig

[Gearbuilder]

Hi,
You're welcome I understand   ,sometimes i'm too busy too .Your speed seems to be limited ,if  i remenber mine is vibing more slowly and faster than your .Slow speed is 1 pulse per  3 seconds and fast speed  is 5 per second
What pot did you use a 220K or a 100K ?
Bruno

[Craig V]

100k dual ganged.  Did you use the same one?

[Gearbuilder]

Hi,
No i use on all my vibes 220K without prblem ,i'm going to try 100 just for compare the difference . On my next project (rack Univibre clone with 2 speed controler ) i'll take the best of two's.
Regards
Bruno
 

[Craig V]

I read some archived posts, and I found out that when I plug power into the box, at a slow setting, the circuit will oscillate about twice then dies down into nothing until I turn the speed pot way up.  

This would indicate low gain?  I have been putting 3904's and 5088's in there and seem to be getting the same results.

Thanks.

[Gearbuilder]

Hi,
 
I had this problem yet with one of my clones ,it's sure it's an LFO problem often encountered . I had the same  it could be  gain or ground mistake .Check the ground and if it's ok try this ; put your finger on the transistors darlington if the lamp is lighting more than without your finger it's possible that your transistors don't have enough gain and the feedback
current doesn't allow to regenerate the LFO (LFO is caps charge and discharge in resistors or pots ),check the solder too on the LFO part of the PCB ,if you've got a cold solder or bad contact this produces  the same
effect on LFO;
Regards
Bruno

[Craig V]

Hi,

What should the voltage reading be at the R40/Q11 junction?  I am reading 3.4V.  

The .pdf file calls for 11.6V on the other side of R40, and I am measuring 10.6 there.  This is the 2M2 resistor.  Do I need to decrease this resistor?

[Gearbuilder]

Hi,
If you increase or decrease the 2M2 resistor you're going only to change the range of the LFO ,the total resistance of the pot with the 2M2 is important in the LFO speed (R/C time ) and the resistor is a limit to the pot ,  then  the speed limit is limited by this one . If you want to change voltage at R40 it's R41  that steps the voltage here in conjonction with the base of the darlington ;check darlinton R41 .Maybe the other side of the circuit pump too much current then the LFO is sensible to the move pots  pair ? I'm sure you havent got enough gain with this darlington . why don't you use a MPSA 13 to the place of the two 2N3904?And are you sure about the bulb ?And Q13?Send me a shoot of your PCB if it's possible  and maybe i could see some problem on the traces
Regards
Bruno

[Craig V]

Hi,

I've tried the MSPA13 and got no oscillation at all.  

Maybe my power supply is too weak.  I have the Dunlop 18v 150mA.  Do I need more current?

Thanks for all your help.

[Gearbuilder]

Hi Craig,

I don't know exactly how much   current needs  this device to well functionning ,ask to  RG or JCMaillet . It's seems that 150mA is small but i think that if you don't get enough mAmps ,you'll ear it in the audio .
Maybe you've got a short in another place than the LFO ;Sometimes we look at one place where appears the problem but the solution is at another place (even the last we could mind)
Bruno

[Craig V]

Hey,

Did you notice that the layout and the schematic on the .pdf file don't match?  Look at pad C and then look at the schematic.  

I still have it wired per the layout, and it seems to work better than it used to.  I may need to try the schematic method.

[Gearbuilder]

Hi,
Yes,it's seems that the layout is different of the schematic.To copy the schematic wiring reverse the wires beetween C and E . If it's wired like the layout ,the two wires  are always connected together by the pot's lugs,it could be a bug from RG .What's about the LFO now?
Regards
Bruno

[Craig V]

I'm not sure if I want to put it the correct way.  I seem to like the sound of it, and the problem with the sweep is probably caused by the pot.

[Gearbuilder]

Hi,
The best way is to wire the pot in the same way of the original schematic of Univox Univibe .Maybe that's the trick .Be carefull with the chassis pot ,this one should be grounded and if you touch only one of the lug with it, your LFO driver will be history!For my part i've always put electric tape around ,this trick  avoids an "LFO" transistor accident.Does your LFO run correctly now ?
Regards
Bruno

[Craig V]

Hey,

I switched the wires, and now its 100% functioning correctly.

Thanks for all you help for the past month.  This pedal rocks.


Craig