NEO-VIBE ...HELP + Mojo-Vibe parts INFO !!!!!

[KHStudio]

Hello,
I'm new here but not to electronics in general. I'm currently working on the Neo-vibe & have it tweaked just right... I love this thing (Thanks RG )

Anyway, my friend has a Mojo-vibe he let me borrow to use for comparison (which sounds KILLER  ) I opened it up as soon as he left my studio. More on that later.

PROBLEM:
I reduced the "speed resistors" to 1.8k to increace the speed, when I touch the speed or intensity pot it speeds up... when I let go it slows back down. What's going on here

Now, it's outside of a case... could it be the pots need better ground or sheilding? Please Help.

Mojo-Vibe Diferences:

No 22k x 2 on the input - just a single 10k x 1 input
1.2 megs are both 1 meg
the 6.8k is a 5.6k
output pot is 250k
input transistor is 5088
all other transistors are C945 (with pH45 under the C945) I looked these up and they are available but in different hfe's... not sure of the brand either but they have a white background under the #'s on the face.

MOD's I did to make the bulb flashing match the Mojo-vibe:

Using the 12v 25ma bulb from Radio Shack & the LDR's from Small Bear - I had to increase R49 from 4.7k to the "stock" value of 47k... the Neovibe show the 4.7k here - this slowed down how hard the bulb was BANGING on & off... much smoother & matched the Mojovibe VERY WELL. Next, I couldn't get the bulb intensity ow enough so I changed R48 from 68 to 120 ohm & with the trimmer maxed out it was there & the Neo-vibe was a new animal... smooth & musical just like the Mojovibe.

I was shocked to see that the Mojovibes bulb didn't ever reach full brightness even with the intensity all the way up... also, the VERY dim light almost never goes TOTALY out/off.  With the Neovibes STOCK components, the bulb was WAY too bright & FAST & turned off during the cycle.

I will have the Mojo-vibe for a few more days if anyone wants me to check out anything else but I can say it's pretty much the same except for the values I listed above + it uses the single gang pot/Opto-coupler (dual resistor) to control the speed. Info on how to do this can be found on RG's site.

Thanks,
Kevin

[SteveB]

....
Using the 12v 25ma bulb from Radio Shack & the LDR's from Small Bear - I had to increase R49 from 4.7k to the "stock" value of 47k... the Neovibe show the 4.7k here - this slowed down how hard the bulb was BANGING on & off... much smoother & matched the Mojovibe VERY WELL. Next, I couldn't get the bulb intensity ow enough so I changed R48 from 68 to 120 ohm & with the trimmer maxed out it was there & the Neo-vibe was a new animal... smooth & musical just like the Mojovibe.
....

Thanks for the info. I agree with you about the 4.7 giving the bulb too extreme of a swing. What value trim pot are you using, & what is the reading from the lamp driver to ground going through the resistor & trim pot?

R.G. had the 2 - 22k resistors in the design to stay true to the original Uni-Vibe, which had 2 inputs.

Steve

[KHStudio]

R.G. had the 2 - 22k resistors in the design to stay true to the original Uni-Vibe, which had 2 inputs.

Steve

I mentioned that change and the others on the pre amp section (along with the 250k out volume) because I THINK that's how the Mojovibe is squeezing out the extra volume in bypass... I could not find any other changes besides the ability to totaly switch a J201 buffer in/out.

And YES... the LDR's are flush to the board. (PM Question)

Anyone on the speed problem


Thanks,
Kevin

[KHStudio]

OK, the speed up/down problem happens the most:

when I pinch the wires of the speed or intensity pot.
Touch the top of the 3x 1uf caps in the speed section.
or any of the components (almost) in that section.

I also noticed when I run a jumper wire from the shell of the speed pot to the shell of the intensity it works almost perfect BUT ONLY WHEN THE INTENSITY IS 80-100% TURNED UP? It's almost like that section is either being pulled down or not enough power till I touch it with my magic hands 

PLEASE Anyone... I'm pulling my hair out.

I've been testing & swapping a few caps... nothing.

BTW, I'm using 3904's everywhere except Q1

Kevin

[R.G.]

Hmmm...

If I ran into this, I'd get out my ohmmeter and clip one side onto signal ground at the input of the board, then poke the other probe onto ground all over the board to see if it beeped every place, especially in the LFO section. If it didn't beep, I'd measure the resistance and figure out where the resistance was instead of the solid ground that should be there. Then I'd check the grounds on the wiring out to jacks/pots/switches to see if I could find an open. Pot shafts too.

There is another unusual thing that could be getting you. Things that change when you touch them are either very high impedance or RF sensitive. You might be in a high RF area and conducting RF into the circuit by your body-antenna, or causing a self oscillation at RF by touching your body-capacitor to the circuit. Putting it into a box would fix both of those, probably. But I'd look for the sloppy ground first.

[KHStudio]

Thanks RG,

I will do what you said & post back.

[KHStudio]

OK, I found it 

I simply took a ground wire off of the input jack and wrapped it around all of the intensity pot wires several times (like a sheild) ... that's it.

I'm guessing that if it was in the case it MAY do the same thing but I'm going to sheild those wires anyway.

BTW, I noticed there is a ground loop in the PCB 
Obviously it's not a problem after all these years but I did try to cut it so it didn't loop & it made NO difference at all.


Thanks for your help RG.

Kevin

[KHStudio]

I REALLY need some help here

I'm getting some hum & noise (pulsing) & sometimes a light tick

I can get it to completely stop if I touch the bottom of the circuit board in specific spots:
- Also, the speed almost doubles too (and seems to be correct)

SPOTs:
- the Darlington pair next to the SPEED control
- The speed control connectors on the PCB
- & a little bit of change  when I touch the Intensity PCB connectors

I can also still faintly hear a FAST pulsing when the intensity is all the way down



HELP!

Does it sound like a bad tranz or Cap?

Also, how am I suppossed to check the voltages of the Trasistors when the're oscilating up & down?


Thanks,
Kevin

[KHStudio]

OK,

Some decent progress

I changed Q11 & Q12 (LFO) from 3904's to 5088's & ALL noise went away. When I put NEW 3904's back in ALL the noise comes back
Could this be their drawing too much current??? My Power supply is 16v AC 300ma. This SHOULD be enough... No?

Now with the new 5088's, the pulse of the bulb doesn't have the same burst like it did before.
I had it sounding perfect even with the noise & now I can't get it adjusted to sound as good as it did with the 3904 (even with the noise) the FEEL was just perfect
... I've tried a few things.  I should mention that I like a 47k instead of the 4.7k right before the drive tranz. (this seems to be the stock value)
It totaly SLOWs down the FEEL & sounds more right but it also robs a little from the driver for the pulse.

Can I do the threashold MOD without making the Bulb Driver a Darlington

What it NEEDS is the bulb to get a little bit brighter but ALSO get LOWER on the low swing.

Maybe the power supply needs more BEEF & I could go back to the 3904's???

Thanks,
Kevin