built a magnavibe, not what i expected..

[nightendday]

Well, it's not working perfect, but it's working. First off I used 330n because i didnt have any 220 around. I swapped a few resistor values for what I had around.. and used the MPSA18 as suggested. What I'm getting is not seasick, nor does it even sound like vibrato. It sound like a sine wave style trem. It's very fuzzy as well, If I wanted to stop that, Would I need to change the bias on the transistors, or increase the resister on base? Seems like a fun little circuit to play with. 

[nightendday]

also, as it's not noted, I just ran lug 1 of both pots to ground...

[nocentelli]

The depth pot lug1 should be connected to lug2 or left disconnected: It's used a variable resistor between the +9v supply and the LED which leads to the Q2 collector, raising and lowering the brightness of the LED to adjust depth. If you connect lug1 to ground, it becomes a voltage divider instead. Speed1 is fine to ground (it should also be tied to lug2, but since this is ground anyway, it won't make a difference. I can't speculate whether this will cure the problem: How far away from the specified values are your substituted bias resistors? This is more likely the problem. A working magnavibe is definitely a vibrato (pitch wobble) and not fuzzy.  

[nightendday]

The depth pot lug1 should be connected to lug2 or left disconnected: It's used a variable resistor between the +9v supply and the LED which leads to the Q2 collector, raing and lowering the brightness of the LED to adjust depth. If you connect lug1 to ground, it becomes a voltage divider instead. Speed1 is fine to ground (it should also be tied to lug2, but since this is ground anyway, it won't make a difference. I can't speculate whether this will cure the problem: How far away from the specified values are your substituted bias resistors? This is more likely the problem. A working magnavibe is definitely a vibrato (pitch wobble) and not fuzzy. 

7.5 is 6.2
4.7 is 3.4
1.5 is 1

[nocentelli]

The 4.7 you've quoted should be 4M7, not 4k7 (just checking) so i assume you've got a 3M4 in there. Those values aren't too far away, but still might be far enough away to affect the bias sufficiently to make it fuzzy. You could try getting closer by putting combinations of resistors in series or parallel, although I can see how this is going to be a problem if you're trying to get it to fit them on an existing vero layout.

[nightendday]

The 4.7 you've quoted should be 4M7, not 4k7 (just checking) so i assume you've got a 3M4 in there. Those values aren't too far away, but still might be far enough away to affect the bias sufficiently to make it fuzzy. You could try getting closer by putting combinations of resistors in series or parallel, although I can see how this is going to be a problem if you're trying to get it to fit them on an existing vero layout.

The led and controls and everything work great, it just work as a trem, no pitch bending like I can notice.. What would effect that?

[nocentelli]

Is it fuzzy or not? If it's fuzzy, it's not working great. As for the trem/vibe thing, the LDR resistance wobbles up and down with the LED flashes: Wobbling resistance between collector and emitter gives vibrato, wobbling LDR resistance between collector and ground gives you tremolo - You can put this on a switch as an extra option (though you need to slightly lower the Q1 emitter resistor to compensate for the perceived volume drop) - And clearly hear the difference. Check your LDR is definitely connecting collector to emitter of Q1.

Afew other people who built this reported the vibe effect was dependent on the proximity and alignment of the LED/LDR combo: I found the greatest vibrato depth was to be found with them very close (with the LED facing directly onto the LDR surface) but not quite touching - Have a fiddle and report back.

[pipporan]

hello
i up this old post, because i have some troubles with this exact circuit
first i have to say that i'm  a complitely newbie in diy pedals, my experience is just 3 builded kits, and no more

well, i've followed the layout posted here, with all the same components with no ecceptions, the circuits run, the internal led works, the sound exit from output, BUT there's basically no effect...the led never flashed, it just stays on, in constant brightness...
the "depth" pot works (turning it the led rise in brightness)...the effect works, because touching the circuit makes the led oscillate sometimes, and in those moments you can hear the vibrato effect
all components are completely new, expect some capacitors...
can someone give me some hints, please??
P.S. i hope i explained well:-)

[Kipper4]

Check  for cold solder joints, bridges, cracks in the board maybe.
the biggest clue i can give you is

"the effect works, because touching the circuit makes the led oscillate sometimes, and in those moments you can hear the vibrato effect"

Check around the led?
Somethings only intermittantly touching where it should.

Welcome to the forum and to debugging.

[pipporan]

thank you very much kipper!!
im still not sure which is the element that cause electricity to come and go, because i still dont have soldered the pots ('cos i want to wait at the last to assembly them, to put it better in the enclosure), but it could be something else...
anyway, i'll check this more carefully ASAP, and let you know
thanx for the hints and for the welcome!!
greeting from florence, italy

[pipporan]

ah, last thing: i red in another post (about the same layout) to solder speed1 to ground and let depth1 unconnected, and so i did...should it be ok, shouldn't it?

[Kipper4]

looking at this schematic

http://s605.photobucket.com/user/pinkjimiphoton/media/MagnavibeSchemsmall.jpg.html

solder speed 1 and 2 together > to ground

solder depth 1 and 2 together> to the led - (anode )

Search the forum there's plenty of threads about the magnavibe. with notes and posts about how it works.
I hope you get it going.

[duck_arse]

thank you very much kipper!!
im still not sure which is the element that cause electricity to come and go, because i still dont have soldered the pots

pipporan - hello florence. what do you mean by 'don't have soldered the pots'? can you post some photos of what you have built?

[pipporan]

i used the exact layout posted at the top of the page: there's written where to connect speed 2 and 3, and depth 2 and 3, but not where to put depth 1 and speed1...anyway, i connected speed1 to ground (together with speed2)...i'll try to connect depth 1 to depth, even if i'm quite sure it will do no difference (because depth pot works perfectly: when you turn it, the brightness of the led increases and decreases)

for the photo, look at the photos: at photo nr2, you can see i just put the wires in pot's holes, without soldering them..it could be this the reason for the led to turn on and off sometimes (if you disconnect speed pot, led turns off)

right now i'll do some checks to the solders and will let you know...thanx for now...

[pipporan]

one thing i need to know (sorry for the stupid question, but my knowledge is veeeeery limited): WHAT part of the circuit should make the led flash and not stay on all the time? Q2? or the 1uf polarized caps? or something else?
because, if the led should flash for the effect to work properly, and the led DOESN'T flash, i have to check the problem in that part of the circuit, right??

anyway, i've just checked for unwanted bridges, and it seems to be okay...

[Ben Lyman]

Check  for cold solder joints, bridges, cracks in the board maybe.
the biggest clue i can give you is

"the effect works, because touching the circuit makes the led oscillate sometimes, and in those moments you can hear the vibrato effect"

Check around the led?
Somethings only intermittantly touching where it should.

+1 start here, reflow solder to be SURE everything is connected. Then cut between soldered spots with exacto, dremmel, tiny nail file, tiny screw driver, whatever you have, drag and scrape it between everything that should not be touching.
If R7 or R11 are too big/small (or shorted) it may cause the LED to stay on

[pipporan]

i've just soldered the wires to the pots,so the blinking is over, now the led always stay on

If R7 or R11 are too big/small (or shorted) it may cause the LED to stay on

the value is  what i red on the layout (the same of the schematic): R7 is 2.2k, and R11 is 1.8k...i used all the exact components written in the layout...they all brand new, except 2 polar-caps...the LED is a standard bright one

reflow solder to be SURE everything is connected

i'll do this right now, i'll reflow everything i can

EDIT
i'vejust reflowed everything, checked again with the multimeter for electrical continuty, and everything seems to be okay...i've just checked the resistors for proper values, and they are okay too...and the led is still fixed

[Ben Lyman]

Well that sucks. I'm trying to wrack my brain to remember when/how I had those issues when I built mine and that's all I can think of. I've built two now with pretty much the exact parts in that schematic so I know it works. I remember experimenting with those (R7/R11) and the pot values, if you go too deep and/or fast the light stays on but that's all I remember.
The fact that you can make it blink sometimes when handling the board is screaming "bad connection" somewhere.
But, if you've reflowed solder and lost the ability to make it work sometimes when handling, then it could be something else.
Can you post bigger, clearer pics? and a link directly to that layout you used?

[Kipper4]

It might just be my eyes and those photos are pretty sketchy.
I can't see the polarity protection diode and power filtering cap.
Are those secondhand capacitors working as they should? Can you check with the meter on capacitor setting?
It's a weird one.

[duck_arse]

pipopran -

you can see i just put the wires in pot's holes, without soldering them

this is not allowed. connections must be soldered, not poked. if you only want temporary, you can use alligator clips on leads, but just poking won't work. also:

you can see i just put the wires in pot's holes, without soldering them

this is not allowed. those holes you have the wires poked into are not for us to use. they are mechanicals for the lugs, and we solder the wires to the lugs so the mechanicals don't get loose - bad connections - useless pot. also, wires soldered all the way up there can short to the body of the pot, another bad thing.

start your buildings with confidence - I'll solder these bloody wires to this bleeding pot, and this pedal will bloody well work first go!

when you have pots with an outer lug (CW or CCW, sometimes called 1 or 3) not explictly connected to some nominated point, you are allowed to either leave it unconnected, or connect the unwired lug short to the wiper. this makes the potetiometer a variable resistance instead of a voltage divider.

so, now all your wires are soldered, and your led is flashing ....... you need to have your LDR completely in the dark. any light, even reflections off the BB will shift the vibeing to some extent. put a box over it, or a 35mm film can, something to block the light.