Magnavibe vibrato/tremolo blend mod for rotary speaker effect

[Ben Lyman]

As discussed before in some other threads, I've been trying to get some tremolo to blend in with the vibrato. I used to have a real Leslie rotary cab, modded for guitar amp of choice, of course. Anyway, it was cool and the sound cannot ever be reproduced in a pedal but I'm getting closer, With much help from, and a big thanks to, kipper4 and duckarse! 

I put a 10k pot after the cap coming off Q1c, right before the LDR/220nF. I think a trim pot will do for this but for the purpose of my demo vid I'm just using a 10k resistor to show max tremolo blending. A 100k pot could probably even be used for getting almost pure tremolo but I don't know for sure.

The more trem I add, the more output volume I lose so I added an LPB-1 booster stage at the end so I can turn the volume up as I switch back and forth between straight Magnavibe and tremolo mod.

EDIT: add schematic yo. Using 1 LDR app. 1M dark with 1 brite white LED facing app. 1/4" away. Second brite white LED is for visual and extra volts drop across the first to increase depth.

EDIT EDIT: parts values changed to reflect accurate BB layout and speed/depth pots adjusted/labeled for correct wiring

[robthequiet]

Just following to see how it unfolds. Sounds like you could push the boost stage after this to get a nice grit, too. Nice!

[Fndr8875]

nothing useful to add, but i just built one of these to. I didnt have 25k lin pots, tried 50k and 100k with all kinds of resistors across lugs 1 and 3 and some going to 1 and 2 and 2 and 3. Had massive volume drop no matter what i did. just had the photocell pack from radioshack but data sheet looks like theyd work in circuit. The vibe was really nice but i leterally had to turn 10 watt solid state amp to 10 to get what id normally get on 1 or 2. Needed 50k pots for a delay so i fmoved on.

[Ben Lyman]

Rob, you know if you follow long enough you will eventually see a completed pedal and a vid of me making a gawdawful racket with my hamfisted attempt to play guitar!
I have something very special in mind for this build so keep watching 

Fndr8875, I'm not sure why you had volume troubles, that's too bad. I used B50k pots with 51K resistors across both, kept one on the speed knob but eventually changed the depth to a B10k.
If I had to guess, I would think LED/LDR combo. I've spent a little bit of time with these, built 2 already and now this thing that I'm working on.
If you ever want to try again and you feel like you're having trouble with the vactrol, send me a PM and I can give you some pointers, see if we can dial it in. Or ask around here, there are some guys that really know how to do it, those are the guys that got me through my troubles.
Good luck!

[Ben Lyman]

I made some changes to the schematic. The main thing I am curious about is a good way to lower the input to the final stage. Rob, some OD might be cool but I kinda want to avoid it on this one, I might even try an internal trimmer for the output volume. That way I can set the tremolo/vibrato trimmer and then adjust the output volume trimmer, close it up and play.
So for now, as seen almost dead center, a 10k (R20) but is there another trick? Like changing R17 or something?

[Kipper4]

I've bread boarded it yet again with a few value changes. I'm using 2k2 for R10
Included are the Duck Arse trem mod (inc BAC) and the Lyman trem mod.
With my observations.




Errata.
I forgot the 10k input resistor on the LPB.

[duck_arse]

err. anyone interested in my take (add more parts!) can see a completed diagram here:
http://i.imgur.com/gkfvLAL.png

and anyone interested in a matching 20x10 game of tetris perf layout suited to 1/8W resistors flat, or all quarters standing, can look here:
http://i.imgur.com/GZRwo74.png

@kipper - did you get the BarseC mod to work?

@Ben - are you aiming for either vibe or trem, or both at once to some degree? is your C5 really only 10nF? I always find your 'ham-fisting' a good listen, you cover so much ground. (I haven't listened to the current demo yet.)

[Ben Lyman]

Thanks Rich, looks like I have some more experimenting to do!
I wanna figure out that choppy trem thing, everything I try either gets that ticking or just doesn't work at all.
I did try a 100K trimmer for my tree blend and it got much more intense without the ticking but not exactly choppy.

[Ben Lyman]

@Ben - are you aiming for either vibe or trem, or both at once to some degree? is your C5 really only 10nF?

Thanks duck! Yes, both at once, and just the right amount of each, nothing too extreme.
Also yes, 10nF. I tried the LPB 100n and thought I was losing a little too much high end, now I have 2x 10nF's in series right there plus that 10k to lower the LPB input. Do you think there is too much going on right there and can somehow be simplified?

Note also how I have used a 1k2 on my speed pot, it goes super-fast now without dying out. I couldn't do that before I added the second LED because superfast=LED always on. Now superfast=LED blinking superfast 

[duck_arse]

just for fun and S&G and curiosity, try putting a cap 47nF~220nF across R8 to ground, tell me wot it does ....... if anyting.

I put my gain at the front and used high Z buffer at the back for some sort of consistency, so I dunno how the loading at the mix point effects anything. and I switch the ldr to a proper shunt in my dia, if you can follow that bit. the trouble is, every throw of that mode switch gives a pop that can't be cured.

[Kipper4]

Always fashionably late to the party......
The Duck Arse mod referred to in my earlier diagram is with reference to this.

you blokes - yer mixing the DC from the collector wit der DC from the emitter. put a whacking big cap (to pass all freqs) in between the collector and the so-called L cap, then hang your Lyman resistor across the L cap, and report back.

[edit :] oh, and kipper - don't forget to "lard up" for your swim, to keep warm. I think the pro's favour goose fat.

and I saw pipporan, huddling under his umbrella, at the giro.

From another magna thread.
No offense Stephen. I was not putting words in your mouth.
The trem is choppy with this mod. As it was in my own earlier trem mod from way back.
Also IIRC the speed varies slightly turning this pot......

The Lyman trem/rotary mod was much more subtle. More desirable than anything I've managed to hack up.
I changed some PSO values to get the speed ranges I felt suited my needs. YMMV.

I haven't used the LPB mod yet, I just thought it needed including in the drawing.

Ps no goose grease needed. I have a wet suit. Only trouble is the fishermen keep shouting "whale ahoy"
It was a giggle of a day.
So many things to do especially now the concertina splitter is back on the BB.
I can get round to doing the cro experiment Stephen, sorry for the sattelite delay.

Carry on concertinaing guys. Smoke me one I'll be back for brecky.

[Kipper4]

More Vibe messing. Just a few value changes and notes

[DMichel123]

Have you thought about or experimented with a dual gang pot for the trem/rotary control and R15, biasing the stage hotter as you turn the effect up? You would lose some signal strength from the emitter of Q1, but maybe worth a try?

[DMichel123]

Or better yet, throw another LDR near the LED and wire it into part of a voltage divider with a fixed resistor and a pot to adjust the depth.

[Ben Lyman]

Sounds like some cool ideas Dmichel123, thanks... and welcome to the most awesomest forum on the infrawebs!

[DMichel123]

Like this:


Let me know if I should just shut up... I'm just sharing ideas I had when developing my vibe/trem pedal. What you're doing is mixing between tremolo and vibe, with both effects being less intense as they're mixed together. If you create the tremolo in another way, you will then be able to mix trem with full strength vibe.

[Ben Lyman]

on the contrary, please share more! this looks like a good idea. I will try it out before I take it off the breadboard, thanks!

[duck_arse]

hmmm. DMichel, also hello. you have as many likes as posts, a rare start indeed.

following from your trem idea, and what I put on a switch in my above circuit, and Ben's "Lyman pot"/kipper's "trem/rotary" control. that pot will work as the series resistance for a shunt trem, if you hang the tremming ldr between the rotary pot and the lyman cap to ground. it just might work.

and kipper - any bike races near your house ?

[Ben Lyman]

Yes, it does work, I tried it last night and I like it, very choppy trem at max turn of the pot (ugh, I hate more than 3 knobs on any pedal!)
I was hoping DMichel's trem would eliminate the need for the LPB but alas, it seems perhaps the curse of all tremolo circuits is a volume drop.
Oh well, I might have to incorporate this new trem idea on my next BB adventure into the magna vibe, for now I think I will stick with the plan and box it up as it is.

The bikers are hitting Folsom about 20 min. away from me before they go downtown Sac.
Russ posted this and I had to laugh, it reminded me that I was trying to navigate a piano moving truck through S.F. during the first ever "critical mass" gathering
http://www.diystompboxes.com/smfforum/index.php?topic=111745.msg1058757#msg1058757

[Kipper4]

Heres some cycle p.o.r.n for you D.A.
Lincoln Grand Prix no less.

http://www.lincolngrandprix.co.uk/site/


Plenty of prix on cycles the day before as you well know my friend.
Rant over.......