Magnavibe question

[Kipper4]

love it.

[duck_arse]

Thanks for all the help here guys, especially you kipper, this pedal is so quick and easy to make and it sounds great. I used 1 yellow superbrite, filed flat, super glued to an LDR from Tayda and heat shrink tubed. Both transistors are 2n5088's and a couple of very minor resistor changes.

EDIT: I forgot about my most notable change  I used a 10n on Q1c instead of 100n, I think it made it sound better, more shimmer, less thump

it's "the Lyman cap!" I listened to both the vids, and I've been fiddling w/ the magna today. my bb'd circuit now sports a modded sho frontend and an emitter follower backend [and depth pot diffs, indicator - led a diagram is available for those interested/brave enough], but I reckon the lyman cap could be a useful switched addition.

I found the stock 100nF would/could only vibe the low strings, but w/ 10nF it shimmmered the whole lot. and, it can compensate to some extent for your choice of vactrol led. a lower value cap gets more shimm from a dim led, if you follow my drift.

and millions don't.

[Ben Lyman]

I follow exactly your drift Duck, I experimented further with that cap when I made my second pedal and determined the 10n sounds way better but it might be because of my Tayda LDR. Kipper pointed out to me that these LDR's are probably 500k dark while a 1M might work better with the 100n cap, possibly different LED colors too.
Whatever the case, I like the combo I came up with for both these pedals, the only difference in my second was to use a flat top clear LED and I scuffed the surface with sandpaper so it didn't get too bright. Second pedal seems to have a little more depth to it but almost identical in a back to back test.

[Kipper4]

How you like them onions.

Modified magnavibe. Tremolo and Vibrato mode.

[Groovenut]

Sounds great Rich!

Very nice!

[Ben Lyman]

Yes indeed, sounds great Rich! Now I wish I explored further the tremolo mod... maybe next time

[Kipper4]

Ta very much guys

[Plexi]

Hi everyone!
I'm starting this vine now.

I'll se how it goes... and looking for reduce the speed

[duck_arse]

hey plexi - how much slower do you want?

[Plexi]

As low as possible without losing the atmosphere.
Remove the 27k speed resistor, and replace the 10k for a 15k one, 2.2k for 4.7k.
I will try to increase the 1uf caps to 2.2 and see how it goes.

I'm experimenting with the vibe/tremolo mod: using some pot/resistor and 100nf/220nf cap in the ldr junction.

[duck_arse]

it looks to me there isn't a schem posted in this whole thread. can you post the schem you are working/starting/modding with?

[Plexi]

My bad!


I confused the threads:
http://www.diystompboxes.com/smfforum/index.php?topic=114118.140
http://www.madbeanpedals.com/forum/index.php?topic=9958.0

[Kipper4]

I'll have a look at my schematic I used.
I think I altered R 7 ,8, 9
Or the lfo caps I can't remember now. To alter the speed of the lfo (PSO. Phase shift oscillator type lfo). The PSO transistor can be any common or garden bjt. E.g. 2n5088

The phase stage (Q1 etc) will work nicely with a common bjt too.


There's some neat tricks to do with this circuit. More later

Such a great little platform circuit for experimenting.
Ask Duck.

[Kipper4]

Seems I settled on the same values as the above schematic except I changed R10 1M5 to a 2M2.

I know I did a lot of experimenting with the lfo speed mods.

Try a bigger speed pot too. eg 50k

[midwayfair]

Slower speeds decrease how noticeable the effect is, so "slower without losing the atmosphere" is pretty much the bottom of the existing control. You really need multiple stages to get a decent slower vibrato effect.

That said, you can shift the entire range downward by half by doubling the values of the 1uF caps in the phase shift oscillator.

While it's possible to also increase the value of the resistors to ground in the PSO (including the speed pot, which is variable), above about 100K (pot) / 22K (R9), it will simply conk out. You can get a tiny bit more range by using a dual gang 100K pot with 220K resistors in parallel and limiting resistors of 2.2K. You can go up to around 60K on the speed pot before it will conk out with the current capacitors.

There are limits to how slow a speed you can get out of a phase shift oscillator, period. If you truly need even incredibly slow speeds, an op amp oscillator can probably get you to a 15-second cycle!

Rich, a bigger speed pot won't do much if you leave the 27K in parallel.

[Plexi]

Thaks both, Kipper4 and midwayfair!

So, I tried what you say, and speed go down: remove r8, increase R7, R9, C5 and C6.
But, the effect is very very subtle. Even with the LPB pushing in the front, or increasing volume in the end.

Some additions:
- I use a 10k trim in R11: tryed a few values there, and I don't know why, the depht pot never work as it should.
- ON/OFF swithc between C3 and LDR: 10k resistor in one side, and direct another. With 10k I have some kind of tremolo, and some vibe without it.
Again: I try with pots there... but they act strange, so I prefer that value.
More or less than that value, back to "vibe"

So, that's my small contribution.

If I use dual gang pot, can I go really fast and medium slow?
Maybe I prefer this pedal for fast leslye settings

[Plexi]

Here's the vibe beast (¿)

From the beginning is in tremolo mode, at 1:30 start vibe mode.

What if I wan the opposite: more speed?
I have to take the inverse way?
Reduce caps, increase resistors, both?

Any experience about that? (I've changed so many components in the pcb, that's complicated to continue doing so  )

[PRR]

> There are limits to how slow a speed you can get out of a phase shift oscillator

I don't think there are. (However start-up and stabilization time is proportional to period, so it could take an hour to start.....)

The resistors are usually picked for good _DC_ conditions. Do not change the resistors (except very slightly for exact tuning). The caps have no effect on DC conditions, only frequency. Those three 1uFd caps, change them to 2uFd, it will run half the rate.

OK, there is a practical limit how slow you can go with a 1-transistor phase-shift LFO. The capacitor values get too large for film caps. If you use electrolytics, the leakage upsets the DC conditions. (Also at least two of them need to be bi-polar.) With good modern e-caps you can probably go to many seconds.

[duck_arse]

I quite like to add the fourth phase cap and its resistor, and up values all over. also run the led parallel with the collector resistor, but that's just me. here are two variants I worked up for Mr Ben Lyman, who wanted more and less of everything.

http://imgur.com/Gjo7Fuf
http://imgur.com/6tGyf1a

[Plexi]

Thanks PRR and Duck!

Duck, that's great, let me know if I understand:
- 3pdt
- you jump both 470nf caps and remove R4 and R5 for high speed
- In low speed you have 1.47uf

What happen if y reduce 1uf to much more less? Wild super fast leslye?

..warming the welder to try... I hope copper doesn't come off