Neovibe LFO Problem

[Craig V]

You 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.

[Gearbuilder]

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

[Gearbuilder]

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 .

[Craig V]

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.

[Gearbuilder]

Hi,
Well i'm very happy for you .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

[Gearbuilder]

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

[Craig V]

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.

[Gearbuilder]

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   .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

[Craig V]

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

[RickL]

Both worked for me.

[petemoore]

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]

[Gearbuilder]

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

[R.G.]

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

[Craig V]

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.

[Gearbuilder]

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

Bruno

[Craig V]

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.

[Gearbuilder]

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

[Craig V]

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.

[Gearbuilder]

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

[Gearbuilder]

Hi again

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