Neovibe Tremolo Mod

[SonicVI]

I searched and didn't find this info posted before.   The Shin-Ei RT-18 Resly Tone is basically the same as the Univibe/neovibe with the addition of tremolo and a 6 position speed control rather than pot.   Here is the schematic for the RT-18 in which you can see a 3 position switch for chorus/vibrato/tremolo.   
http://www.freeinfosociety.com/electronics/schematics/audio/shin-ei-rt18.pdf

and the project file for the Neovibe for comparison.
http://www.geofex.com/FX_images/vibeschm.pdf

This mod is to add the tremolo selectrion of the RT-18 to the Neovibe.  It does actually sound like tremolo, not just a variation on the vibrato that Shin-Ei decided to call tremolo.
What you will need are a:
2P3T rotary switch
100K and 47K resistors
.068uF and 1uF caps.

As you can see below the mod adds a third switch option which for throw one of one pole adds 100K/.068uF to ground after C5. For the other pole throw one ads a 47K resistor to ground and a 1uF cap off the emitter of Q5 (Q5 and C5 are neovibe component designation). I wired the 1uF cap directly to the lead of R17 at the point shown in the diagram.   One thing to be careful of is the labelling of the switch throws in the RT-18 schematic. One set of throws should be reversed numerically, the tremolo additions need to both be on the same throw number. They are on opposite throws in the schematic. If you follow the schematic the mod won't work properly.    The diagram below should be easy enough to follow.  I actually used a 3P3T switch and used the third poles throws as ground points for the new components that are grounded.
Here is a page with sound files of an actual RT-18 so you can hear the tremolo setting.
http://tonepedia.com/index.php?page=category&cat=1&subcat=2&sample=118
 

[John Lyons]

Muy interesante!
I can't check out the clip here, how strong can the trem get?
Amp (fender blackface) like?
The Vibe is kind of blah usually.

john

[SonicVI]

It's not the deepest trem you'll have ever heard, but it's probably not the shallowest either. About as deep as a blackface on 6 or 7 maybe? That could be variable depending on your bulb intensity though.    Put it this way, you probably wouldn't replace a dedicated tremolo pedal with it, but it's a relatively easy mod that adds another mode to the Neovibe. It's a worthy addition in my opinion.    I'll try to record a clip late tonight or tomorrow.

[SonicVI]

Here's a quick and dirty demo at a few speeds from slowest to fastest (will vary with your build) at max depth (followed by a little chorus and vibrato)
http://homepage.mac.com/sonicvi/neovibetrem.mp3

[R.G.]

There have been a few versions of the Neovibe that didn't make it out to public consumption.

One was an all-tube phase line version; another was an expandable four/eight/12/... stage version. Another was the Omnivibe.

The Omnivibe contained the RT18 tremolo mod as well as single-pot speed control, stereo outs,  and a few other tricks on a board that was smaller than the original Neovibe board. I didn't release these primarily because when they were ready I was afloat in a sea of "I can't get my Neovibe to work" debugging requests and despaired of anyone able to make an ordinary Neovibe, let alone the Omni.

[dr]

RG-I would love to see and build that Omnivibe!..I'm still loving the Neovibe I built of yours from a long while back............dr

[John Lyons]

The tremolo sounds good.
Nice and smooth, good depth.
Thanks for that clip!

john

[Lithium_Grim]

Hi SonicVI,

Do you have a schematic/drawing using your 3P3T instead of the mentioned 2P3T?
In the diagram below, there is always a 1uF/47k to ground behind R17 even when position 1 is not chosen. Will that not affect the working of the vibe? Or is that how you use the 3rd pole by lifting ground in position 2 and 3?

[Lithium_Grim]

Is this a good representation for the mod? Note I cut out the normal vibe/chorus part of the schematic and altered it to include the new switch options and I cut out the first part of the LFO and added the trem mods. Can someone please tell me if I'm correct? I've  marked the alterations in red.

[Lithium_Grim]

Bump... anyone?