Neovibe Mods - my build completed ( so now tweaking begins )

[pedrocortez]

First post so be gentle on my naivety...

I've just finally completed a Neovibe I started and abandoned 18 months ago.  I'm in Leeds in Uk so parts weren't easy to come by, but all is well after much searching and parts subbing.

The NEO  sounds wonderful - though I was hoping for some more depth at slower speeds , and yes, Ive now read up on that a lot....

Firstly - much thanks to RG for such a wonderful way players can access the magic tones of the Univibe.  I'd longed for that sound since being a kid.

Presently mine is going from my Tokai LS150 into my self-built  Park 1210 replica and my 4x12. It sounds wonderful.  I finally worked out all the parts to Day of the Eagle !!

Now,  I HAVE read as many of the posts on the Neovibe as I can find,  but I wondered what tweaks I should go for to get the deepest sweeps at the slower speeds ?

I also got interested in JC's offsett mod after reading RedHouse's Forum-vibe document too, but I'm not sure how to implement this in my neo build ( ideas / examples ? )

I am decided that I will build a second vibe now - using the forum-vibe as a platform.  I'll still cherish the Neo though.

So any thoughts on how I could implement the offset bulb driver idea in my existing NEO ? Any other good mods to focus on ?

Best rgds all - great creative forum.

Pete C

[SteveB]

Hi Pete,

I recently did a mod that I guess could be considered a simplified offset mod.

I wired a 100k trim pot in series with the 100k resisitor (R47). The higher the resistance, the darker the dark side of the bulb swing will be. Use the bias trimpot to get the bright side of the phase swing where you want it.

I guess a 50k trimmer could be used, because I didn't increase the value of R47 all that much. I had a 100k lying around, so that's what I used.

I have never been more please with the sound of mine as I have been since I did this. I can get more phase cancellation now, & this does much more than the mix trim pot ever did.

Steve

[pedrocortez]

Many thanks Steve,

thats getting modded today !
I'll let you know how I get on.

I worked out last night how I can mod the Neo board ( with off board trimmers )  to apply the JC offset as well , so I'll try your simplified method first, and try the JC darlington and trimpots later.

Cheers
Pete

[Crawf]

Hi Pete,

I recently did a mod that I guess could be considered a simplified offset mod.

I wired a 100k trim pot in series with the 100k resisitor (R47). The higher the resistance, the darker the dark side of the bulb swing will be. Use the bias trimpot to get the bright side of the phase swing where you want it.

I guess a 50k trimmer could be used, because I didn't increase the value of R47 all that much. I had a 100k lying around, so that's what I used.

I have never been more please with the sound of mine as I have been since I did this. I can get more phase cancellation now, & this does much more than the mix trim pot ever did.

Steve

Hi,Steve do you have a diagram on how to do your mod? Crawford.

[pedrocortez]

Hi again,

thanks SteveB - good mod !  cant wait to try the full JC mods too. 

so, I super-glued the end of a blue 100K multi-turn trim pot to the board next to the 47K, so I had an upright trimmer, and lifted one end of the 47K from the board and soldered to the middle leg of the trim pot. the far end I just put a link down to where the 47K was lifted from t board.

I also found a few 2N5088's on an old board and soldered one in as the first in the LFO darlington pair.   What a difference - I must have had a weak 2N3904 in there before - the thing has come alive and I have much better sweep depth especially at the lower speeds ( which I prefer and couldnt get before )

So very happy, all bugs removed and now tweaked nicely - couldnt stop jamming along with my EZ Drummer in Cubase earlier tonight. 

Have decided to try the Forum-Vibe build too as next vibe.   Also A Chicken Dano turned up in th mail today ( ! )  ready for re-housing.

I am truly bitten by the Vibe bug at the moment. Thanks all.   

Any tips and advice on the Forum Vibe - especially off board power supply ideas would be most welcome.

Rgds
Pete

[SteveB]

Hmm, I'm very curious to hear what yours sounds like! My offset trimpot is connected to R47, which is a 100k resistor.

Steve

[SteveB]

Hi Pete,

I recently did a mod that I guess could be considered a simplified offset mod.

I wired a 100k trim pot in series with the 100k resisitor (R47). The higher the resistance, the darker the dark side of the bulb swing will be. Use the bias trimpot to get the bright side of the phase swing where you want it.

I guess a 50k trimmer could be used, because I didn't increase the value of R47 all that much. I had a 100k lying around, so that's what I used.

I have never been more please with the sound of mine as I have been since I did this. I can get more phase cancellation now, & this does much more than the mix trim pot ever did.

Steve

Hi,Steve do you have a diagram on how to do your mod? Crawford.

It's really easy: Unsolder one leg of the 100k resistor(R47). Solder that leg of the resistor to one of the outer legs of the 100k trimpot. Solder the middle leg of the trim pot to the hole in the PC board where the 100k resistor used to be.

Steve

[pedrocortez]

Steve

Doh ! I of course meant the R47, not the 47K !        Too excited obviously !

Rgds
Pete

[vince76]

Hi all,
only to report some tweaks..
I tried the R47 100K trim series mod to have better depth response to slow speed settings as suggested by SteveB.  Think it's very effective. I had to set the trim near 50K so I don't reccomend to use a 50K trimmer.
I also tried the mod suggested by JC to have more speed at max setting ( the same you can find on several thread)... it worked fine for me.
The  JC mod on the 2M2 Bias Feed resistor in the Oscillator part to provide an extended low Speed range doesn't worked because it stopped the oscillator...

[Eb7+9]

The  JC mod on the 2M2 Bias Feed resistor in the Oscillator part to provide an extended low Speed range doesn't worked because it stopped the oscillator...

what the mod will do is effectively reduce the usable top SPEED resistance level before the oscillator gain drops too much ... try a resistance like 3M3 or 2M7 so that the LFO still works at minimum rotation (max dual resistance) - this won't affect the top speed mod ... I've gone up to 10Meg with some transistors and got the LFO to run around 0.2Hz - which by then is probably way too slow for any serious application ... I shoot for a 0.3Hz minima in my builds

[R.G.]

I tried the R47 100K trim series mod to have better depth response to slow speed settings as suggested by SteveB.  Think it's very effective. I had to set the trim near 50K so I don't reccomend to use a 50K trimmer.
I also tried the mod suggested by JC to have more speed at max setting ( the same you can find on several thread)... it worked fine for me.
The  JC mod on the 2M2 Bias Feed resistor in the Oscillator part to provide an extended low Speed range doesn't worked because it stopped the oscillator...

I guess I need to make up a page with the word "MODS!!!" in it. 

A really simple thing to do to extend the range of that LFO without worrying too much about hand selecting transistors so you can raise the series resistance is to replace the first transistor with a low-VGS-off JFET. The input impedance of a JFET in that position is a few orders of magnitude higher than the input impedance of even a darlington NPN, especially a discrete darlington made from two normal transistors. A J201 should do fine. Then you can go to 10M, 22M, etc and get much more range. For even more range, replace the two transistors with a JFET or MOSFET input opamp set up as a gain-of-one.

I posted a bunch of stuff on this particular issue in this forum a ways back, including both of those observations.