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rhinson wrote:just built one of these and it's sounds pretty much like a small old magnatone amp i worked on a few yrs back. i was just wondering how to increase the depth on this circuit. are there any values in the circuit to change or is it pretty much dependent solely on the ldr and led combo? thanks. rh

also any reason to use a mpsa18 or would any other bjt type be fine (2n5088 or 5089, etc).... thanks

x2 any way to get a little more depth aaaaaand....

I need to slow this thing down a bit - even at it's slowest setting it's still a tad too fast for me.

Where would I go to decrease the speed ?

Thanks.

Lower the value of r8 for more depth. The total resistance of r7,r9 and the speedpot will determine the speed. The bigger the slower the speed. You can start to remove the resistor paralel to the pot( r9). If thats not enough you can raise the value of the speedpot.

Sorry i made a mistake. For more depth reduce r11 to 1k2 or even 1 k.

It won't go very much slower before it stops oscillating altogether. It's a very simple design for an LFO, hence it's limitations.

hi!

it's been a while since i posted... stopped building for 3 years, but i'm back to it and enjoying it a lot.
just build a magnavibe+ vibe/trem
it all works fine. the trimpot does a great job at keeping enough gain on the trem.

as stated before, the speed could be slower, but i know what to do to try and achieve that.

the depth isn't what i want it to be yet...
as i measured you get maximum depth when the depth pot is at 0 ohms.
does this mean more depth will be achieved if i lower the value of the 1.8k resistor from the 9V?
(yes... just saw the post stating that changing it will increase depth)
i'm still wondering if it wouldn't be more advisable to just use a 2K pot though... the range on the 25K is in the last 2 mm of the swing...

thanks for tracing and making the layouts! great jobs.

nk

well... just went ahead...
1k instead of 1k8 increases depth, but on vibe i'd still like some more.
a 2K pot works fine, but 5K might be better for people who want a really subtle effect.
i personally like a trem or vibe to be there...

I'd advise fiddling with the alignment of your LED and LDR in the optocoupler - Mine is stock, as per that vero exactly and has plenty of depth: It goes from almost no effect, right up to super seasick at max depth. I don't think the LED/LDR pair need to be right up against each-other, a slight gap seems to increase the depth. However, there must be several other variables including the type and colour of LED and the datasheet specs of the LDR. I slipped both LED+LDR into tight-ish fitting heatshrink, whacked the depth up full, and tweaked the alignment til I got the strongest effect, and heat-shrunk it at the appropririate spacing. A bit fiddly, but quite possible.

thanks for the tip!

i gotta revisit mine.

but i gotta ask.... this is basically an escobedo wobbletron, isn't it?

seems to have about as much in common with a magnatone as the "ep booster" has to do with an echoplex (i own 2 plexes, and they most definitely aren't "boosters")

Hello people, my first post. I've built the magnavibe successfuly using dimebugg's PCB. Sounds great. I only have one problem. When using it with a 9v battery the pedal is great, but when using my clea power supply, built from the project at General Guitar Gadgets, the LFO gets into the audio path and there is a ticking sound. How could I solve this problem? It's the only pedal that does this. I've built a phase 45, a phase 90 and a little angel chorus and none of them have this ticking problem with the power supply. Maybe a resistor to limit the voltage getting to the circuit? Yet would this mean that when using a battery the sound would change?
Thanks in advance for any help you could give.
Andy Hooper

Also built a Heartthrob tremolo and no problem with the power supply. Just remembered that.

You could try a small resistor (like 100r) in series with the power line to the audio transistor, followed by a cap to ground (100uF) before the 7k5 collector resistor if you don't already have this. You could try the same on the power line to to LFO transistor as well.

You could put these filtering components on a separate little daughterboard, and just hook up the new connections to the power jack and the original board.

I've built a couple of magnavibes from my vero layout and had no noticeable ticking, so bear in mind these are suggestions based on standard advice and general practice, not actual experience with this particular circuit.

Thanks for the reply! I haven't tried the 100ohm resistor and dimebugg's layout already has the filtering caps. The strange thing is that I tried the magnavibe alone, with no other effects connected to the power supply and it was dead quiet. It only started making noise when I connected the rebote delay. So I connected the little angel chorus and it also made noise. With other effects it is quiet as well, it only ticks when those pt2399 effects are connected to the same power supply.

Hi! I just placed the 100R resistor and the ticking is completely gone. Amazing effect. Thanks!!!

I built this circuit using Nocentelli's vero layout with the tremolo switch, thanks for putting that together, it works great. At first I wasn't getting quite as much depth as I thought I should. I used a high-brightness, water clear blue LED and an LDR that measured about 5M dark resistance. I tried out a few other LDRs from my Radio Shack bundle and ended up going with one that measured about 7k light and nearly 40M dark before it went out of range on my DMM. Not sure if that dark measurement is accurate but it seems like a higher dark resistance gave more depth. I noticed the Small Bear has these Silonex NSL-7530 high dark resistance LDRs now, wonder if they're the ones used in the original unit, they look similar.

http://www.smallbearelec.com/servlet/Detail?no=712

on mine, i took the resistor across the speed pot off and went with 50k, at slowest setting still there.

took the 1.8k resistor out, put in a 1k trimmer in series with a 470r resistor. to me, seems best somewhere around 800r total.

I made the LFO section on breadboard and raised the caps from 1uf to 4.7 and it is a lot slower, but it doesn't go to the faster speeds as with 1uf. Any ideas on how to add a switch to change between the fast 1uf speeds and the 4.7uf slower speeds? I've noticed many lfos get slower by raising the caps (tremulus lune, vox repeat percussion for example). Earthquaker devices hummingbird switches between caps for example.

Just remembered I changed all the caps and not each cap...dumb me...I'll try individually and see if that slows the speed. That would make adding a switch to change just one cap easier

Thank you for the information. I'm in the process of putting one of these together, so will be interested in your results. I was looking at the caps but also read here that changing a couple of resistors would also lower the speed.

The type of LFO used in the Magnavibe is very simple, but has a few drawbacks, the biggest being the limited range of speeds available before the oscillator becomes unstable and stops.

There's a thread over at DIYSB discussing the issues and suggesting some possible solutions -

https://www.diystompboxes.com/smfforum/ ... c=106566.0

Many thanks Nocentelli for the link. There is some very interesting and well explained information - useful for someone like me who isn't an electronics expert (far from it ). Helps explain what is going on within the circuit.

I might try a couple of things just to see what happens while building mine.