A few Neovibe mod ideas/questions...

[Isaiah]

Hi,

I'm going to order components to build two Neovibes. One for a friend, and one for myself.
I'm going to use the GGG PCB and the GEOFEX schematic available here:
http://www.generalguitargadgets.com/projects/20-modulationecho/121-neovibe

I plan to implement a few simple mods that I've seen (I think they were by GEOFEX and VIVA ANALOG, correct me if I'm wrong).
*Using 10uF for C6, C8, C11, C14, C17, C18.
*Changing R3 for a 2M2 resistor for increased input impedance and unity gain.
*Pulsing LED mod.


I have a few more interesting ideas and questions:

*TREMOLO
One way I can think of doing that is to have DPDT switch to disconnect C5 from the Base of Q4, while connecting the output jack to a decoupled output (Emitter of Q5 decoupled by 10uF then pulled down by a resistor, maybe 100K-1M).
That way, you're only taking the output from the first phasing stage, and it is only acting to modulate amplitude.
Does that sound about right?


*EXTERNAL CV INPUT / BIAS CONTROL
This will allow interfacing with my modular synthesiser, using CV signals (AC, not DC) to control the lamp's brightness.
I'm thinking about also adding a decoupled LFO output, seems a shame to let it "go to waste" if the Neovibe is being controlled by CV, might as well use it as an interesting, "flawed" LFO in the modular.
The way I think I'd do this is to feed the CV input to pad X on the PCB via a series resistor and capacitor, maybe a pot wired as a potential divider for control of Depth.
Or, instead of adding an extra input to the lamp driver, use the existing one as follows. The connection between C22 and point G on the Depth pot, could be cut and wired to switched jacks that are normalised to each other, so plugging a jack into the LFO output, or CV input breaks the internal connection.
It would also be nice to add an input for DC CV, so I could sweep the filters manually with a pedal.
Also, I think replacing R47 and R50 on the lamp driver with a pot to allow manual control/offset would complement the external CV input mod.
Any thoughts or opinions please?

*MIX CONTROL
Remove R37 and R38 and replace R35 and R36 with a 250K pot for continuously variable mixing between "Dry" and "Vibe", with different shades of "Chorus" in between.
Does that sound worth implementing?

*CAP VALUES / RATIOS
C5, C9, C12 and C15 could all be replaced with the same value, which would give a more phaser-like tone in Chorus mode, but how would that effect the vibe setting?
What about repeating the same decade ratio, for example 470pF, 4700pF, 470pF, 4700pF?
I know I could add a few switches to select different values, but I don't want to construct something that has too many controls (says the man with the modular synth and proposing the above mods!)
I'm not particularly precious about the Hendrix/Gilmour Univibe sound at all, but equally I don't think I'd like to implement a straight phaser.
I guess I'm after Beatles meets David Lynch soundtracks (which I realise make heavy use of tremolo, no vibe, hence the above mod).

I think those are all my questions/thoughts for now...
Any thoughts or opinions would be greatly appreciated!

Cheers!

[ChristoMephisto]

Finished up a Neovibe with the Tremolo mod, here's a link to how you can do it easily with a rotary
http://www.diystompboxes.com/smfforum/index.php?topic=76157.0

Playing around with the caps (c5,c9,c12,c15) you could switch it from the univibe vibe/chorus to the reisly tone vibe/reisly
univibe's caps are .015,.22,470pf,.0047, and the Reisly's is .0047,.0033,.0022,.001
you could use a 4pdt switch to drop in caps parallel to change the lfo

[Isaiah]

Thanks for the reply and link!
Would be great to see and hear your Neovibe!

Looks like the Resly-Tone Tremolo mode is very similar to the implementation I described. Nice to know it should work!

After some thought, I'm not sure I see the point in a Mix control when including the Tremolo mode,
since it requires an extra switch, and I'd like to keep the control interface fairly minimal.
By using a rotary switch, and fixed resistors to mix the all-pass and dry signals, you only need one control to access the three modes (Chorus, Vibe and Tremolo).
Though, using a resistor chain for mixing, extra Chorus modes could be implemented:
1- Chorus I - 25:75 (?) mix of Dry : All-pass
2- Chorus II - 50:50 mix
3- Chorus III - 75:25 (?) mix
4- Vibe
5- Tremolo
Would there be much difference between Chorus I and III?

Any more thoughts, ideas and feedback would be greatly appreciated.
Cheers!

[Isaiah]

After even more thought, I think I plan to keep the Mix control for dialling in different shades of phase,
and use an extra footswitch to simply switch between Tremolo mode and Phase (Chorus - Vibe - whatever) mode.
Both my friend and myself will find being able to switch between Tremolo and some variation of Phasing more useful,
than only being able to switch between the Univibe-standard Chorus and Vibe modes.


I'm still not sure where to start with the cap values/ratios.
Perhaps something phaser-like.
I'd like something that would sound good on keyboards and vocals as well as guitar...

[Isaiah]

Bump!