Bigfoot FX Magnavibe

pinkjimiphoton · Post by **pinkjimiphoton** » 06 Apr 2014, 12:18

nocentelli freakin rocks like that.

dbat69

do you have a breadboard yet? if not, get TWO or three.. them pocket sized ones are wicked handy.

you can play with the cap values some and get it to go a bit faster, but as it goes slower it'll lose depth and like he said become unstable and stop.

that said, if ya find a couple cap values in the timing part of the circuit that work for you, just put your caps on a dpdt switch... i like them on/on/on dealios for this... solder your normal value across the middle, and two bigger caps, or a bigger and a smaller one, on the outside lugs.

take your input and output from the same terminals as the cap across the middle poles. this way you have stock cap, and either larger or smaller depending on the size of the caps. remember, caps in parallel act like resistors in series. so you can kinda ballpark the sizes to the closest standard values you have on hand and get some good results.

this trick also works great anywhere you need to change cap values.

you can also do it with a spdt, or a 3pdt.... in the 3pdt case, you can even use a tri color led if ya want

works great for inputs on fuzzes. i often put stuff like this on what i call "phat" switches, make it like a stompbox. in this case, you may need to add some big freakin resistors (i like 4.7m cuz i have like zillions of them) to ground from some of the nodes of the switch. sometimes i set it so it changes the input and output caps at the same time... you can really get on top of tones that way.

if ya use a spdt, same deal, but just tie the free ends of the 3 caps together. that will be fine, too.

experiment with the led's too if not using a vactrol... different sizes, colors and orientation to the ldr can make a big difference. i liked a 10mm jumbo ultra clear white one in mine, but i imagine orange yellow or green would probably work better.

i haven't tried it yet, but i'm gonna have a play with some of them little 3.5mm xmas bulbs... they have wire leads and are incandescent, and i've been curious for a while if it would change the way the effect sounds. if ya gotta breadboard... you will become triumphant. most of the time.

sorry for the slight OT hijack.... peace

dbat69 · Post by **dbat69** » 06 Apr 2014, 14:21

Jimi

Thanks for your comments.
I have a couple of different Vactrols and was also going to experiment with the LED/LDR option (might as well as I have loads of bits). Hopefully will find something that fits what I'm after. I also read that the distance between LED and LDR can be influential on the effect parameter too.

I'll try a few different values on the breadboard first ad see what happens - it might be useful to add a switch if some values alter the effect but these can't be replicated with other values. The fun of DIY

dbat69 · Post by **dbat69** » 25 Apr 2014, 19:55

Well after a bit of tinkering I've a few results which may help anyone building this. I am still waiting for a selection of LDRs (from China - so may be a while

), I'll then have a go with different LDR values to see which may be best with the different colour LEDs.

I had a few vactrols to try (acquired for other builds) and found the VTL5C2 to give the best result overall.
VTL5C1 was shallower but smoother in vibe wave, perhaps slightly slower (but that might just be me after much testing)
VTL5C2 was a bit deeper and more 'wobbly' perhaps a little choppy at times
VTL5C4 was too shallow and didn't give much vibe wave

I also tried a Tayda LDR with a few LEDs (red, yellow, white, blue, green and uv) in shrink tube at various distances. (Sorry I don't know what the light dark values are for this LDR - hence wanting to try different ones).
The blue was possibly the best at about 6mm

Tried various values for the 1k8 resistor to increase the depth. Although it seemed the changes were very subtle, a value of 820R worked best for my build. I would like more depth than I achieved though - it still needs more

.

The speed was the next thing to try and change - I wanted it slower. For this build I retained the three 1uF capacitors (next build I might try 2.2uF). So I was limited to the adjacent resistors and tried Madbeans suggestions.
A reduced value from 2k2 to 1k5 gave a bit more range (faster)
A reduced value from 27k to 10k gave the speed pot more control, but it resulted in the loss of some of the slower speed. I ended up increasing the value back to the 27k. (next build may try a slightly larger value if the increased cap values don't do the business).

Hopefully this may be useful

dbat69 · Post by **dbat69** » 06 May 2014, 13:58

OK my consignment of LDRs arrived from China - and testing is complete

I kept the changes previously made to the 1k8 - reduced to 820R, 2k2 - reduced to 1k5, retained the 27k parallel with the pot. I also changed the transistor in the audio path to a slightly higher gain (but I didn't seem to notice a difference to the depth) (hfe = 770)

I made a little test rig to help speed up the process

I tested the Vactrols, Tayda LDR, GL5506, GL5516, GL5528, GL5537-1, GL5537-2, GL5539 and GL5549
I used LEDs - red, yellow & green diffused - red, yellow, green, blue, white clear
I tried them at 10mm, 6mm and 1mm

The combination I found to give me the best sound (particularly at slow vibe which is what I am after) was the GL5528 with red 5mm diffuse LED at 1mm from the LDR.

Now to box this thing before I wreck the board anymore and I can get on with another build.
I hope this is useful for anyone else building this useable circuit

graemey · Post by **graemey** » 10 May 2015, 20:39

I have just built the buffered version from the vero layout on this thread (unverified).

The effect works, but is low in volume.
I used an audio probe to listen between guitar and buffer to amp, and volume levels were good, so I'm assuming it's not the buffer.

I used 2N 5089 transistors, and the pinout is double checked and correct.

I have used the only LDR I had in my stash box. I think it read around 400k max on my multimeter.
If I source a larger resistance LDR, will that bring the volume of the effect up? I believe between 2M and 20M is recommended?

Any help would be great guys!

Nocentelli · Post by **Nocentelli** » 10 May 2015, 21:11

Is it unity without the buffer? The LDR resistance shouldn't make much if any difference to the output level.

graemey · Post by **graemey** » 10 May 2015, 21:40

Hi,

No, there is a drop in volume without the buffer (and with it).
The probe test I did only proved the the buffer on it's own was unity or above.

Nocentelli · Post by **Nocentelli** » 10 May 2015, 22:21

Check all the resistor values around the wobbled stage, it should be unit.

graemey · Post by **graemey** » 11 May 2015, 18:07

Nocentelli wrote:Check all the resistor values around the wobbled stage, it should be unit.

Yes, had one wrong! Thanks for the leg-up!

warioblast · Post by **warioblast** » 23 Sep 2015, 00:14

I just built one using Nocentelli's layout.
Using stock values, MPSA18 transistors, a 10mm clear red LED facing a 20k - 2M LDR. The effect was very subtle. I tried other LEDs; 5mm clear ultra violet, 5mm bright blue and a 3mm red diffused. And also I tried to cover the LDR/LED with black tape. All of this didn't change a thing.
Then I remember those brand new MPSA18 had a strange low 250 hFE. So I swapped them for 2 MPSA18; hFE around 500; I had salvaged from an old crybaby. This made a big difference. It now sounds close to this

It still lacks intensity compared to this but it's in the right way.
I still can't hear any difference between LEDS. I'll try to lower 1k8 and see how it goes. I hope the 20M dark photocell I'm expecting will make it sound right.

So my conclusion, don't overlook transistors in this build.

hopdybob · Post by **hopdybob** » 11 Feb 2020, 13:05

hello all
i have listened to this vid
https://youtu.be/uE6lj29CJsA

and i would want to try to build it.
i have build some overdrives and boosters before with veroboard so technical i could build it but.!?!?!
here and on tagboard https://tagboardeffects.blogspot.com/20 ... mment-form the discussion go all the way with the parts like the LDR and other stuff so i loose track now.
(i think both veroboards are not the same, so i want to stick to this one here)

the MPSA18 can be found so that's no problem, but the LDR ?
i don't understand the values so make a choice so could someone please help me with that?

hopdybob · Post by **hopdybob** » 12 Feb 2020, 07:53

well, i made a choice on what i have read on both site's and ordered a LDR 5-20K (light) 20M (dark) (type9203) (RLDR9203) together with the MPSA18 Hfe 400-1500
so hope i have the right parts

hopdybob · Post by **hopdybob** » 13 Apr 2020, 06:43

hopdybob wrote:well, i made a choice on what i have read on both site's and ordered a LDR 5-20K (light) 20M (dark) (type9203) (RLDR9203) together with the MPSA18 Hfe 400-1500
so hope i have the right parts

and i have a winner!!

its alive and works fine.
did some test with different LED and the on that did the trick was a 3mm clear yellow (although it seems green from the side)
because of the very little space is made a separate LED/LDR print with a piece of pencil shaft

here is the led flashing controlled with the depth pot
https://youtu.be/23F7uA604_Y

now i am thinking about if i will put 2 boards in one unit so i can set two settings and switch them, ore is this possible to use another set of pots and switch between those?

Nocentelli · Post by **Nocentelli** » 14 Apr 2020, 08:33

Two sets of level + rate controls and a DPDT toggle switch to choose between them is perfectly possible. Can provide a diagram if you need further advice.

hopdybob · Post by **hopdybob** » 14 Apr 2020, 10:58

Nocentelli wrote:Two sets of level + rate controls and a DPDT toggle switch to choose between them is perfectly possible. Can provide a diagram if you need further advice.

if you could, please do.
i have thought of rebuilding a volume ore wah pedal, but these are mostly very expensive ore have opto regulation i think.
if you could make a diagram, than i would opt for a extra footswitch.

but you have made a great sounding magnavibe vero

i had a great volume and treble loss at first but someone gave me the hint to connect pin 1 to pin 2 on the speeds knob and than the volume drop was gone.
don't understand if that was the reason of my problem but it works!

Nocentelli · Post by **Nocentelli** » 14 Apr 2020, 12:33

Here is how you could wire the two pots to a DPDT (e.g. toggle switch)

: magnavibe settings swithc.jpg (23.39 KiB) Viewed 1185 times

If you want an LED to show which speed is selected, you could take the DPDT scheme and use a 3PDT with a two colour/bicolor LED

: magnavibe bicolor for 3PDT.png (2.6 KiB) Viewed 1185 times

or a 3PDT with two separate LEDs:

: magnavibe two LEDs for 3PDT.png (19.89 KiB) Viewed 1185 times

hopdybob · Post by **hopdybob** » 14 Apr 2020, 14:48

Nocentelli wrote:Here is how you could wire the two pots to a DPDT (e.g. toggle switch)
magnavibe settings swithc.jpg
If you want an LED to show which speed is selected, you could take the DPDT scheme and use a 3PDT with a two colour/bicolor LED
magnavibe bicolor for 3PDT.png
or a 3PDT with two separate LEDs:
magnavibe two LEDs for 3PDT.png

your a wizard, thank you so much

Bigfoot FX Magnavibe [traced]