Magnavibe vibrato/tremolo blend mod for rotary speaker effect

[Ben Lyman]

Thanks for sharing Duck, I see some different cap/res values than what I'm using but I am going to have a go at adding a fourth stage.

Kipper, yes it will kill the LFO but (I think) I got around that by using a 4k7 on the depth pot, and adding the extra blinking LED was key to making it work, plus the 1/4" gap within the vactrol.

I am realizing that it all comes down to what each of us has mashed together for a vactrol and balancing the ebb and flow all around it. I have had such different results from what you guys got that I had to tailor it accordingly. Notice also that my speed resistor is 1k2 not 1k5, the difference was noticeable and when I went to 1k it killed it, that's how touchy it was.
Did yours go slower than what I got in that video on my slow channel? That's as slow as I can go without stalling out. I would like to go slower. But it just dies. If I try. With more than 54.7k.

[DMichel123]

Seriously... Dual-ganged 20k pot in series with 3.4k for two of the legs gives a perfect range of speeds.

Like I said, I've started selling mine commercially so I'm weary of sharing all my tricks at once. I'm new to the pedal building world, and I realize that there is a different code of ethics within this community than in the amp building community. Is it wrong that I feel like holding on to my schematic until my product has been on the market for six months or so?

[DMichel123]

Maybe mine isn't quite as slow as I thought... I accidentally ordered momentary switches, latching switches and panel graphics decals should arrive in the next couple days. I'm shipping this thing to Kid Andersen in San Jose for in depth demo videos as soon as it's done. You know him, Ben? My buddy Jon Atkinson is in Hayward and will be getting one too.

[Ben Lyman]

sounds great DM123. no, I don't know those guys, I used to live right by the Oakland Coliseum but I've been outta touch with the Bay Area scene for about 5 years.

[duck_arse]

DMichel123 - PLEASE! don't look .....



as for ben, well, I thought by now you'd realised, there ain't no way to hide those Lyman eyes ......

boom, tish. in the diagram, the right hand version will have resistance in line between the oscillator and ground at all times, the one left will have no resistance while swinging your poles. might be no problem, but there you go.

.... the extra blinking LED was key to making it work, plus the 1/4" gap within the vactrol.

funny. I told someone the other day I thought there was a difference when the led and ldr were spaced, I said about 3mm, tho. I wonder how real this effect is, or just the beam focusing from the led.

DMichel123 again - you don't have to show us anything you don't want us to see. I haven't yet listened to your clip, but I will. and as for
" ", what, too many parts?

[Kipper4]

I've yet to try the vactrol spacing thing. Later tonight I guess if i can find the drinking straws.
I posted a page where this was mentioned way back in february.
This is evolving nicely.
It must be me because if a 50k pot stalls the pso a 250k would reverse it, no?

Hows the Humpty Dumpty lumpy cap thing going D.A.?

[duck_arse]

gorn, kipper, that was days ago! double ldr/double led/inverting sine waves today. I thought I saw some easter eggs, but was sadly mistaken.

the values I've posted/schemmed all need to go together, or close to - one value up or down. you can't sling the big pot into the 3 stage pso (I tested, wouldn't run with more than 100k in the vari leg). the stop resistor for the led brightness also affects the stoppping, reducing the range of the pot both ends. and I'm using the different brightness wiring, so the part values in that string should affect the oscillator dyings less. should.

the resistor values in my schem should work with any string of caps, all the same value. maybe with 1 or 2 off by one value it will work, with flatter output level, but it might stall, too. and you could go a little higher pot value, but I found the slow end change with rotation is so small as to be un-noticable.

[Kipper4]

Yeppers I saved the drawing but my eyes are stinging. Forgot about the four stage PSO.
Forgive me for saying so but wasn't the triple pole PSO viable because of the 180 degrees out of phase?

So I need to match the Lyman cap and Humpty Dumpty cap values?

I'm always a day behind the Aussies. Some say retarded.
Edit. Does the straw colour have a bearing on the effect?

[DMichel123]

Hell, I'll just share it... The schematics I have are hard to interpret as one is made in LTSpice for simulating and the other in Eagle for board production, and I can't figure out how to attach them....

My main trick is using two phase shift stages rather than one. Also, as I said before, I also used a 2N7000 for bias-vary trem, with a 2N5457 as the variable impedance element.

[Kipper4]

Copy Copy breaker

I tried a blue and white striped 4mm straw spacer vactrol // with another led and it does make a small difference ( Note just using my little test amp, I'll do a big boy test tommorow.)
I tried 2x matched 100nf Lyman and Humpty Dumpty caps. I'm not sure if its overkill.

I'll probably keep the straw spacer vactrol//led
and the Lyman rotary pot B10k.

I'll have a crack at a mosfet concertina splitter before I clear the space on the breadboard.


Magnavibe Mission creep central over and out.

[Kipper4]

Its creeping back in.

I tried the mosfet concertina splitter and it sounds good.
I couldnt get the Lyman rotary pot (10k) mod to work perceptably well with it. I didnt faff about with the value though so it may work with a different value pot.

Try it DA and Ben. You might like it.

[duck_arse]

you and your bloody straws, kipper. the 3 stage caps provide 60 degrees shift* each, and the 4 stage caps provide 45 degrees each, they have to, because the collector is 180 degrees off the base, so the caps just divvy it up between them. I thimk vat's right.

so, the caps (3 or 4) in the oscillator phase-shift network are the ones for near matching. the lyman is by ear and to suit your ldr, so my circuits show 5n6. the cap that follows needs to pass the audio you want to hear, so big, like 220nF, unless you're some sort of add-more-parts dope, and have a follower following. and the humpty cap is just suck some values and see what they do (but not 100nF, too big).

I've dropped the mosfet as amplifier, it's now phase-splitting, and the follower is now a gain stage. so one transistor less, which might be going back in tomorrow as an extra stage .... or maybe I'll go long tail instead.

DMichel123 - you need to post your images somewhere on the mojo wires, an image hosting site, like imgur (there are others, I won't mention them). they (whoever) will provide you with a URL, which you copy and paste here, in the reply window, between the tags provided by the button. [imgur and others also provide a link with the [img] tags already attached.]

then we can set to work ripping off your designs mercilessly see what you've done.


* don't crucify my if it's not 60.

[Kipper4]

"* don't crucify my if it's not 60."

I tried the extra stage in the pso and yer its ok.
Thanks for correcting me Duck. I believe what you said is true about the 60 degrees thang.
I couldnt get the humpty dumpty small cap to work for me hence my value 100nf.

Theres one good thang about my straws.....

They suck.

I'm more your add-less-parts dope. It figueres a person of means is a cheapskate no?

Not sure if to use a mpf102 fetzer style make up amp?
Thoughts.

[DMichel123]

Here's what I have. The switches aren't shown here. On/off switch just bypasses the circuit, vibe/trem switch switches between shorting LED legs and grounding the gate of the 2N5457(connects to junction R13/R8). R3 can be changed to a higher value for a choppier trem(biases the 2N7000 further OFF on downswings). R16 and R17 are a dual-gang pot with each section in series with a 3.4k R. R7 is a 10k pot, series 2.4k. R13 is the trem depth pot, wired as a variable R.

As I said, these are kinda hard to interpret because they are drawn for simulation.

Duck, the wasn't about parts count... Just joking about looking when you said "for Lyman eyes only".

[Kipper4]

Thanks for sharing.
Quick couple of questions DM123.
Why the smaller 6k8 emitter resistor? I ask because Mark Hammer mentioned something of this ilk in a previous thread.

Are you using a 10k pot for R7?


I see now why it sounds like it does with 2x series concertina splitters.

[Kipper4]

Heres what's on my magnabread board right now.

[Ben Lyman]

This is great stuff guys, thanks for sharing.
Duck, I guess the way I wired my switches is not optimal because there is a brief moment when lifted off the ground, huh? I will try your other way next time, looks good, thanks.
I've been busy creating an OD/dist circuit and sanding/refinishing a church pew for my wife's dinner table but I think I'm ready to jump back to the vibe and try all these cool ideas.
Kipper, I like the mosfet idea, maybe double spitting 'tinas and a 4-stage coming up next. Throw in some tremolo blending and a 2-speed footswitch... 
DM123, thanks for sharing, your double 'tinas make the warble so much that my 2-speed box might need some depth control up topside after all... that should make duck a little bit happier 

[DMichel123]

Kipper: Yes, 10K depth pot(series 2.4k). I ended up with the smaller emitter R (and different bias R on the second stage) through simulations and adjusting for unity gain with the pedal on.

Anybody tried my "chorus" setting? It's just one extra C and R to implement it.... It isn't quite "univibe", maybe 50% of the way there?

[Kipper4]

Ok so what where you looking at in the sim to adjust the emitters R?
Gain comparison? Between emitter and collector outputs.
Sorry to ask so many stupid questions.

Thanks for the reply.
Rich

[DMichel123]

Comparing pedal input to pedal output.