Demystifying the MojoVibe

MWichni · Post by **MWichni** » 08 Oct 2010, 15:11

Bump! Any news?

madbean · Post by **madbean** » 08 Oct 2010, 16:08

I'll have more on this very soon. Just haven't made the time yet to do some video of the lamp in action. But, it will definitely get done within a few days.

MWichni · Post by **MWichni** » 08 Oct 2010, 16:12

madbean wrote:I'll have more on this very soon. Just haven't made the time yet to do some video of the lamp in action. But, it will definitely get done within a few days.

Great, thank you very much madbean for your effort!

Regards,
Mariusz.

gilmour_pugliese · Post by **gilmour_pugliese** » 08 Oct 2010, 16:45

Thank you Madbean!!!

candletears7 · Post by **candletears7** » 09 Oct 2010, 10:22

Sweet work, O Bean! Thanks for this mate.

coldcraft · Post by **coldcraft** » 13 Oct 2010, 13:37

very niace...

madbean · Post by **madbean** » 17 Oct 2010, 22:05

Here's a video of the bulb at different settings. The video is a little blurry, but good enough to understand what is going on. Here's the progression:

Low Speed, High Intensity
Medium Speed, High Intensity
High Speed, High Intensity
High Speed, Medium Intensity
High Speed, Low Intensity
Medium Speed, Low Intensity
Low Speed, Low Intensity

The bulb gets fairly bright at highest intensity but as you can see there is a large range of illumination.

I did this with my old Flip camera. If it isn't sufficient, I can redo it with my Droid, which has advanced features like the ability to focus...

The video: [/youtube]

JOHNO · Post by **JOHNO** » 17 Oct 2010, 22:36

Nice work Madbean and thank you.
Comparing the mojo to the neo the audio stage is almost identical, just some slightly different resistor values. I see that the audio section of the mojo runs at 18v but Q10 is isolated and only runs a 9v. Anyone have an explaination for this?
Johno

JOHNO · Post by **JOHNO** » 18 Oct 2010, 00:49

Does the switch connected to the led and the 4k7 (r47) just short the lfo to ground? So its not true bypass just like the original uni-vibe? I wonder if I can try this flashing led set up on the neo. Personally I think the cancelling of the lfo is better than true bypass on vibe pedals. The reason for my thinking is that with true bypass the bulb is flashing away all the time even when the pedal is bypassed. When you use the cancel option the bulb is turned off giving the bulb a longer life IMO.

JOHNO · Post by **JOHNO** » 18 Oct 2010, 02:32

JOHNO wrote: Does the switch connected to the led and the 4k7 (r47) just short the lfo to ground? So its not true bypass just like the original uni-vibe?

No it doesnt. The 4k7 is already grounded. So the led just shows the speed of the lamp? I guess the bypass switching just isnt shown on Madbeans schemo for clarity?

yeeshkul · Post by **yeeshkul** » 21 Oct 2010, 17:15

In the piece i reversed some time ago R13 was 100k, probably to get unity volume between chorus and phaser.
Also the input res was 22k (at least this is in my notes).
The thing didn't work as good as Neo (less prominent phasing), but cut through a fuzz box very nicely (unlike Neo).

yeeshkul · Post by **yeeshkul** » 21 Oct 2010, 17:50

By the way, did anyone here compare the Mojo Vibe and Neovibe with a fuzz/distortion unit placed before them?
I really wonder why is the fuzz sound so smooth and nice when you run it through the Mojo and so swashy when you run it through the Neo.

fuzzman66 · Post by **fuzzman66** » 22 Oct 2010, 23:33

Hi,
I recently repair my Univibe and i've done a lot of test and compare with a microvibe and a phase90.I remarked than the filtering of a fuzz signal was completly dependant from the overall filtering effect of ech phasing .If your effect is well present with a clean signal(not to wobbly)on the three machines ,there's always a difference beetween each phasingwith afuzz signal,because of the cells or transistor range ..On the micro and univibe ,the cells don't have the same rise and fall time ,and more it depends too of the frequencies you put in.Fuzz signal contains harmonics frequencies wich are prone to be affected more easiest than clean signal .Before i repair my Univibe the signal wasn't affected in the same values and it's worse with fuzz signal.The centering of the effect is very important too.I put a fresh four near matched photocells in place of the vintages ones,i tweak the centering pot(ligh level )and that's done .I tried with aclean signal:perfect breathe sound.so i engaged a 72 Fuzz face in it(front) a little tubedriver after to crunch and erradicate the bad frequencies(i think Hendrix had the same effect with cranked Marshall to avoid) ,unplug it from the hiwatt to the marshall and guess what? Perfect Woodstock tone!,it just let me to learn playing guitar!Haha!

Redhouse · Post by **Redhouse** » 25 Oct 2010, 03:35

madbean wrote:Here's a video of the bulb at different settings. The video is a little blurry, but good enough to understand what is going on. Here's the progression:

Low Speed, High Intensity
Medium Speed, High Intensity
High Speed, High Intensity
High Speed, Medium Intensity
High Speed, Low Intensity
Medium Speed, Low Intensity
Low Speed, Low Intensity

The bulb gets fairly bright at highest intensity but as you can see there is a large range of illumination.

I did this with my old Flip camera. If it isn't sufficient, I can redo it with my Droid, which has advanced features like the ability to focus...

The video: [/youtube]

That looks like a typical vibe bulb response to me.

Jaicen · Post by **Jaicen** » 25 Oct 2010, 17:28

When you say typical response, how light/dark variation is normal? Does the bulb turn off on the down swing?

Redhouse · Post by **Redhouse** » 27 Oct 2010, 04:03

Jaicen wrote:When you say typical response, how light/dark variation is normal? Does the bulb turn off on the down swing?

That always depends on how you set your 500-Ohm trimmer, and where you are running your Intensity pot. I just meant the "throb" looked normal.

Hey Madbean, can you take and post some nice close-ups of the PCB (both sides) ot of the box?

madbean · Post by **madbean** » 27 Oct 2010, 08:14

Yes, I will get some shots before it gets boxed back up (I've had it out of its box for a year!)

BTW: I got a build going on this, but the LFO isn't working. I'm going to double-check my work and see if I've made an error in how the Vactrol is laid out, and also get some voltages off the real one.

DrNomis · Post by **DrNomis** » 27 Oct 2010, 08:45

madbean wrote:I've got about 80% of this traced out. No big surprises so far, other than the use of a Vactrol for the speed control (http://www.geofex.com/circuits/ldrlfo.htm).

There is a switchable jfet input stage (modern/classic). The preamp and output stages are pretty typical except for a few value changes. Q1 is 2N5088, and most every other transistor is C945. The phase stages are standard, but I haven't gotten to the last stage or the speed control yet. There is also a charge pump. Haven't seen any regulator on the board, so the biasing voltage is maybe around 17v.

More later

I found out that the full type number for C945 is 2SC945,you should be able to find data on that,plus pinout info too...

DrNomis · Post by **DrNomis** » 27 Oct 2010, 09:09

I've got my UniVibe pedal lying under my bed somewhere,might drag it out one day and rebuild it....

MWichni · Post by **MWichni** » 27 Oct 2010, 11:48

2SC945 are pretty common and not highest quality transistors. They're just general purpose NPN's.

Demystifying the MojoVibe [traced]