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Hello,

I'm having a problem with the LFO in the Neovibe.  Here is what happens:  when the speed pot is all the way up, and the intensity pot is too, it has a nice deep pulse.  Touch the speed pot and the oscillation stops.

The intensity pot seems to be working well, although it is kind of useless up till the last 1/3 of the sweep.  I have a feeling there is something related to the speed control problem.

I used the pot from Small Bear, which should be the correct pot.  I have it wired just like the .pdf file calls for, unless the picture is a mirror image or something. (I cross checked it with the schematic.)  

When I started my debug, I didn't have any modulation, and I measured 18.2V on base and collector of Q12, which implied a short.  But,  with the transistor out, I measured the sockets and got 10.2V on the base.  I installed a jumper from base to emitter, and that got the oscillation to happen.  I tried a 2n3904, 2n5088, and BC108B in Q11.  They all have the same results.

Is there something that I am overlooking?

Thanks in advance.

Craig

The univibe, and by extention the neovibe has just enough gain in the LFO to start and maintain oscillation. It really needs the darlington connection of the two transistors in the LFO to work right.

Is it possible that you have one bum socket?

I am having the same trouble with my neovibe I finished last night. Is there a good higher gain substitute transistor to replace in the LFO circuit? I am currently using a pair of 2n5088's. I know very little about the options out there. Some guidance would be greatly appreciated. Parts avaliable through small bear or mouser would be best. Thanks in advance for your help.

RG,

I replaced the transistor socket with single-in-line sockets, and don't have the 18V on the base of Q12.  

I was able to get it vibing with 2n5088 and 2n3904 in any combination.  I also used a MSP13 Darlington in by itself and working with another transistor, and still have the same results - no slow speed.

I tried another dual gang pot from Radio Shack and tried that still has the same results - no sweep either.  I have double and triple checked that the wires are going to the correct spots on the board.  

Have any ideas?


Aruse,
Did you order your speed pot from Small Bear?  If yes, did yours come without the nut and washer?

Thanks for replying.

Hi,
What value is your dual pot?
Bruno

Both of the pots I tried were the 100K dual ganged.  The Radio Shack one is the same one that Dave Fox uses to retrofit a wah or rocker pedal to a 'vibe speed control.  (or he recommends it - I cross checked the model numbers a while ago.)  According to RG, this pot would act as a slowness control when its working, not being reverse log.  The first pot is the standard Small Bear Neovibe pot.

Aruse,

Make any progress?

I replaced the tranistors with similar combinations as explained above and ended up with a pair that worked about half the time. Seems like voltage is border line. Put the unit in box and am back to square one. NO SLOW SPEED! Sorry I don't have more positive news. Another observation; the fast speed of the neovibe is not nearly as fast as that of the sweet sound mojovibe I have. I am going to open up the mojo and see what that is using for its transistor selection.

Hmmm... something wrong with the pots, I think. The neovibe is just the same circuit as the univibe, after all.  I wonder if the diodes in the LFO are giving you problems. One shorted, maybe.

I'll try the pots and diodes tonight. thanks

RG,


I took out the diodes (socketed) and it was working exactly the same as it was with them in - anything other than full speed on the pot yielded no oscillation.  

According to your Technology of the Univibe:

QuoteThe two diodes across the center capacitor limit the size of the LFO output waveform. An oddity of this particular way of building a Univibe is that the LFO amplitude goes up with increasing speed, even with the diodes there.

So with no diodes, should whats happening be happening?  If yes, than I think something isn't connected in mine right - shorts are less likely because I have done real well in soldering and Dremel-ing out the traces.


Thank you for reading and/or replying.

PS.  Your Tube Amp debug page is VERY helpful.  I was having a problem with squealing, but I think you've narrowed it down to to a bad preamp tube.

Aruse,

What kind of diodes do you have in there?  The Neovibe file calls for 1n4148.  Are these what you're using?  Are they really small and orangish, or bigger and blackish?

Any improvements?

went through the LFO today and managed to get it to go slow as long as none of the pots or jacks ground touched each other. I think I blew the driver transistor in process. Would that stop the LFO from strobing? Diodes are small orange switching type as spec's call for.

Yeah, the driver transistor is pretty important to the strobe, or just getting the lamp lit in general.  This would be a good place to have a socketed transistor.

What kind of Lamp are you using in yours?  I have a Radioshack 12V/25ma in there right now.

Quotewent through the LFO today and managed to get it to go slow as long as none of the pots or jacks ground touched each other. I think I blew the driver transistor in process.

OK there's a clue. I've been trying to think of what's going wrong here, and I think I may have picked it up from that comment.

Do one or both of you supply power to the 'vibe circuit through a wall wart and use a metal-housing jack to connect it into the box? You can't (successfully at least) get that to work, because the board makes its own DC out of the incoming AC or DC through a bridge rectifier. That necessarily means that the negative end of the incoming power is two diode drops *below* the signal ground, and connecting the incoming power to the chassis is shorting out the negative side of those diodes, with various ill results. 'twon't work that way.

Verify that neither of your incoming power wires has continuity to the signal ground on the board or the chassis/box.

The original sidestepped this by putting the power transformer inside the box; we'd like to not do that, for obvious reasons.

RG,

I am using a plastic jack, and measured no voltage on the chassis, so I think the board is getting power correctly.  I have a DC adapter, so the bridge rectifier wasn't necessary (I think I got that advice from you months ago).  

I have the same results, no oscillation except when speed pot is full on, with or without the diodes in their sockets.  I measured fluxuating voltages in all of the sockets.  Is it possible to have too much voltage from the darlington section?

I don't even understand how I'm getting oscillation without the diodes.  From reading the "Technology of," I thought the diodes were the key element to create the necessary feedback.  Maybe the socket do it, LOL.

On a side note, I have been plugging this into my gear setup, and it sounds wonderful at the one speed.  The chorus mode is just awesome.

Thanks.

Drat.

The diodes don't really affect the oscillation other than to keep its amplitude (relatively) consistent. It should happily oscillate without them, just not at a consistent amplitude.

Is one of the caps isolating the depth pot perhaps shorted or backwards, so that the depth pot is siphoning off DC and stopping oscillation?

I've never run into this particular bug before and have hit a wall in counter-designing for what defect might cause it, which is why I'm acting so useless here.

Hi


  Try to desolder one side of C22 to be sure your LFO is well functionning without a charge  .Control the AC voltage at C22(meter on DC).If your LFO is OK,you will see oscillation on your meter even you pot is at slow speed .If you don't, the problem is really in the LFO part of the circuit ,try to debug it ,sold C22 and FIRST check your resistors values,it's possible to put the wrong value and this change the tensions in the LFO circuit (47k to the  place of a 4.7K ).If LFO is OK ,check for values of  R47,48,49,50,the trimmer pot,check the voltage on the transistor too,this one wich sets the right amount of mA  in your bulb
Bruno

Hello,


I desoldered C22, and took measurements - it was only oscillating when the pot was full up.  The problem lies in the LFO.  I have triple checked the resistor values, and all are correct, save for R48 (I used 10 ohm instead of 68ohm.).  

I measured DC voltage on the lugs of the speed pot - should this be happening?  I have always thought there should be no voltage on a pot.

What should the voltages of the LFO be around C22?  It seemed to only go to about 4.7 when it was oscillating.  

Thank you for your help.

Hi,
 I'm not actually at home for doing some measurements on my vibe ,but
i will take the voltage tomorrow morning.It's looks like a short .What pot did you use for the trimmer ?You never say if there's a small glow when the pot is full(speed pot)or slow.This could help a lot too.
Bruno

QuoteYou never say if there's a small glow when the pot is full(speed pot)or slow.This could help a lot too.

Sorry I didn't mention it before - it glows fine, and adjusting the bias trim pot (500ohm) adjusts the glow on it.

The entire rest of the circuit seems to be working correctly - I've crosschecked my voltages with a thread about the 'vibe a while ago.  It sounds really great when played, just at that one speed.

Sorry about that.

Hi,
Bad news, i've played with my Univibe to show it to my friend and truth me or not ,i played with the speed pot and i loose the LFO too.I took my meter ,check the three transistors ,one is burned,i change it but i loose the vibe at sloww speed tooo.It seem that the problem is due to low gain transistor,i'll debug it tomorow and i'll post you
bruno

Hi,

I've checked the two 2N3904, one was dead ,i think it's because the dual pot touch the chassis ground(my Univibe clone  box is little ).I've change the two's and now my bulb is blowing harder than before and the effect is more pronounced than before.It's sure the gain of the 3904 is very important to have a good vibe.Look at the JC Maillet website ,there's some good mods on the LFO .

Hey,

I went through and swapped out the LFO transistors with 3904's, and it's working!!

If you could, please describe the acutally intensity of the pulse as you change the speed.  It seems to have a really strong blink as the speed pot is at the extreme of the throw.

Thank you a bunch.  I would not have ever figured it out myself.  Thanks.

Hi,
Well i'm very happy for you :D .Well there's a lot of discussions about the Univibe cloning art and it's very difficult to know if you haven't got the stocks parts to tweak it like the original.Even in the stock Univibes there's some little difference beetween one model and another one cause the components had big tolerence at this time ,the current was not the same too .The cloning instruction text of JC Maillet is a good source for tweaking it .Some models sound like Hendrix style and some others are most Gilmour style.Since i swap the two's 2N 3904,i have a little difficulties to find the exact sound i had three day before because the like is blinking more  and even if i turn down the pot ,it's seems that the biais point is not the same and maybe there's too much current in  the bulb .It doesn't react as the same way!The cells and the bulb are the most importants things in the Univibe .
i have to go ,
Bruno

Hi,
If i tweak the pot to have the bigger effect possible at high speed, i lost something in the vibe even if the depth pot is at ten,and after 2 ,the effect is very hard,at full i ear the sound like hendrix in "Star Splangled Banner"
high notes sttaccato,but not so creamy and chorusing on the bass, too much "wobbly".I think i'm going to try some mods or to change one of the 2N3904,before the accident the effect was not so prounonced but the overall sound was better than now

Bruno

You might want to try to move the photocells around a little bit.  I can get different tones by making the cells face the bulb directly or on an angle.

Have you tried RG's trick to getting a better mix?  It's basically a 50k with pins 1 and three connected to R35 and R36 (change value to 82K) and take the output off of lug 2.  This is because the mix between dry and wet signal is crutial for a deep phase sound.

How useable is your speed pot?  Mine seems to be about 1 pulse/second at about half way up, and 4/second full up.  I want to try and get it to go faster, maybe.

Good luck, and thanks again.

Hi,
I've just finished to tweak my vibe,you're right about the cells and bulb position.This help me a little to be less tremolo sounding.I fine-tuning  the pot until i found  the sweet spot and  three solos later i decided to close the box  :D .This one is  a cool device again;My next project:a third Univibe with two choices for the speed control,slow or fast.I've seen this extention on the David Gilmour Rack,i've took some shoots,look at that:

ftp://zepfloyd93.no-ip.info/Photos/Mouving%20Vibe.jpg
ftp://zepfloyd93.no-ip.info/Photos/Gilmour%20Racked%20Univibe.jpg
You could see the marks on the intensity knob, good for tweaking!

Bye
Bruno

Thats an awesome idea.  I couldn't get either picture to load - do they work for anyone else?

Both worked for me.

Coudld a Resistor be used to dim the LED's ?
 A switch could be used for varying the some of the LED's intensity...[?]
 Or a mechanical bar/cam to bend the LDR's/LED's heat shrunk light shields when engaged...[lol]

Hi,
Ooooups ,sorry,my pc failed ,i try to degug this server problem,try again tonight if i have resolved it.
Bruno

So the end result was either a bad LFO transistor or low gain, in both cases? Replacing the two LFO transistors fixed the problem?

Yep, thats what did it for me.  Q11 was 3904 and Q12 was 5088 - replacing Q12 with a 3904 yielded good results.  Maybe it was burned out or just too low gain, although I tried more than one 5088 or 3904.

I was thinking of changing both to higher gains, maybe BC109's, to get faster speeds, but I'm afraid it not working lol.

It sounds fantastic.  Thank you sincerely for you help.  Now time to work on that other Neovibe from November which I could never get working.. remember that? haha.

Hi Craig,
Could  you tried again my FTP website? .Because everything seems to be normal now .
Thank you!
Regards

Bruno

It's still not working - do I need to do anything special to get into an ftp site?  I'm really quite internet illerate.


I was looking at your other website, and I must say you have quite a gear setup.  Those Hiwatts must sound great with FF's.

Hi Craig,
The only thing to do is to click on the link and if this one is restricted for you, it's because you're not load as an anonimous client.You must click on the link then right clicking  on the page ,and choose open an anonymous session and type anonymous in the name case. This should work.
Regards
Bruno

Hi,

I'm still unable - nothing happens with a right click on the page.  Maybe I have too old or too new version of Internet Explorer.


Back to the Univibe discussion, I think it's still not 100% working correctly.  I can only get from it vibeing when the pot is between 60-100%.  If I go lower than half way, the vibeing stops, and won't start again until I put it full up, then back down.  This means something is hogging voltage.  Or is this a symptom of weak transistors?  I have 3904's in there.

Thanks.

Hi,
No my vibe begins to be audible at 9 o'clock  but it is a litle too much effetc on the bass frequecies ,i think it is due to  my poor range cells. Maybe your problem is than the current for the lamp is smaller than the bias point ,try a pot at the place of the 47K in front of the  too. If the light doesn't bright so much ,it's because there isn't enough current try with the pot or change  the bulb for a smaller tension . It is says that the effect begin to be audible near nine o'clock,below the effect is lilited by the biais point.I just listen to Machine Gun and i could say that my vibe isn't so beautifull in the middle frequencies. My set-up is :Vox Wha,Univibe at 13 o"clock and speed 7 o'clock,then germ fuzz  and a  Garen Amp (6l6 powered). I'm sure that in my case there's a problem with the cells i had try everything ,or they are not so closed matched. This may be that too if the effect is only in a range of frequencies . And when i turn down the biais pot ,the effetc is changing on efficiency in regard of the frequencies
Bruno

Hi again

Send me your e-mail adress at bmpuig@club-internet.fr i'll post you the photo's
Regards
Bruno

Hey,

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

Thanks.

Hey,

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

Thanks.

double post.

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

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

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

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

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
 :D

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.

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

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?

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

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.

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

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.

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

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.

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

Hey,

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

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


Craig