Forum Vibe advise...

[Pierre]

Hi !!
I'm just about to start putting together a "Forum-Vibe", for now I'm planing to build just one but I'm not sure which version will be...I'm tempted to do the modern version, as I allready build (and sold) a NeoVibe, but then, I don't know...
Maybe somebody can help me to decide telling me the mayor sounds differences between each version...

Many thanks !!

Pierre

[Ummagumma]

Hey Pierre,
I did "forum" (modern) version first, to find out that it sound to sterile. so I reworked it to vintage (mainly the caps part is most important),
left trimmers except for mix,  and added darlington for Q10. I found that this combination sounds the best (for me).

Cheers

[Pierre]

hi Ummagumma ,

Did you experienced any volume drop ?, I had this issue with the NeoVibe...What kind of resistors did you use, metal film or regular carbon film ? And what about caps ?

Thank for you answer !

Pierre

[Ummagumma]

I've used some old tranies (B)C548, carbon resistors, caps are mkt/wima (carbon where noted as vintage), 1uF are all electrolytic (I think this is mojo).
I didn't experience any volume drop, volume knob is on 60% all the time, beyond that it's booster.

[jasperoosthoek]

I had some difficulty building the NeoVibe. Some people report problems with getting the LFO working as the transistors sometimes don't have enough gain to get oscillation starting. My LFO worked fine from the start as I used transistors with a gain (Hfe measured in a cheap DMM) of 280.

There was a big problem in the input buffer though: it oscillated with a 9Vp/p square wave at 300kHz. This was simply caused by the same transistors as used in the LFO. I swapped them for lower gain transistors (Hfe=190) and it worked fine ever since! The reason it oscillated is that they used 3 transistors for a unity gain buffer even though 1 or 2 would have sufficed. And back in the day the transistors had somewhat lower gain anyway.

So I can safely recommend for your next build to use high gain transistors for the LFO and low gain transistors for the input buffer.

[Pierre]

thanks for the opinions !!
...but now I just realize that the Forum Vibe file was updated this year, a few weeks ago...and I have made my pcb's with the old file !
Apparently the only mayor pcb update is regarding how C14 connects to Q10...I'm not sure if I miss something...I guess I'm going to use the old pcb anyway...hope it works.
By the way, I think I will build the Vintage one and maybe try Red Hose's mods...

[Pierre]

...to be more specific...

this is the project file that I used for making my PCB's
http://basicaudio.net/univibe-ForumVibe-final.pdf
...and this one is the updated file...
http://classicamplification.net/forumvibe/.%5CForumVibe.pdf

[jasperoosthoek]

Oh btw, my Neovibe has a little bit of volume boost. I'd have to change that output resistor one day.

[Talon5051]

I built the neovibe and searched through the forum for the mods and I feel adding the darlington pair for Q10 really brought the pedal to life.

[Pierre]

well, I think I'm going to do some PCB's of the updated project after all...and, because I really can't decide I will do both versions at the same time...