GGG P45

[disabled_shredder]

Kipper idk if I said it In this thread or another but I built one for a bass player that was wah heavy (he plays metal) I know right, but he loved it and it sounds great. Nice option if you want a wah but don't think it fits also nicely as a jnivibe type sound on lower settings. I digress! When it comes to the trimmer I swear I find myself cracking the case open to make minuscule adjustments depending on whether I have the pedal fast or slow. Usually if the trimmer is set for good on slow I feel like the effect takes a somewhat dive when I crank it up. Maybe I'm over analyzing it. Either way play the heck out of it and have a good time w it after all that's why we build is to play and achieve that tone that makes us crazy when we can't hear it!

[bluebunny]

Next time i think i'll do a phase 90 for more of the effect.

Then you'll need to match *four* FETs!   

[Kipper4]

As pairs or all four matching?

[bluebunny]

All four the same.  Good luck.   

[Kipper4]

Thanks Mark I'm going to need it.

[duck_arse]

not necessary to match 4 fets for 4 stages. you can add 2, 4, 6, 22 .... unswept stages to what you already have, which help increase the thing. you'll have to search it though.

[Kipper4]

A little more detail please as this is as clear as mud mate
thanks if you will.
Rich
i got the bit about not having to match 4 but after that it got confusing.

[Mark Hammer]

1) The bias trimpot should be set and left alone, but you can vary the value of the (normally) 1M resistor feeding the gates of all the JFETs to move the sweep range up and down.  And yes, some sweep ranges sound better for slow than for fast, and vice versa.

2) Assuming all the JFETs are of the same type, you will still get phasing even if they are not all matched.  However, when they are unmatched (and remember they just might BE matched, even if you didn't check for it), there is the risk that one or more will simply grind to a halt and not change drain-source resistance any more at one or the other end of the sweep.  The effect is akin to a team of rowers on a boat, and one or more simply decides to stop rowing on their side at some point.  If they don't ALL row at once, you don't get smooth directional movement.  Similarly, if the JFETs are not all changing at the same time, the "turnaround" at the low or high end of the sweep becomes less musical, less graceful, even if those same JFETs resume resistance changeonce you move away from the extreme ends of the sweep.

So, matching is not critical to achieve sweeping, but it is helpful to achieve the most pleasing sweep.  The more JFETs there are involved in the sweep, the less any single one matters.  But at the same time, the more stages/JFETs, the greater the risk that more than one will decide to "take a rest" as you approach the top or bottom end of the sweep.  Matching will get you a more satisfying outcome.

[Kipper4]

Ok gottya.
Thanks for clearing that up Mark.
BTW Did you make that Burst box yet? Hahaha
I may not be able to acheive perfection in matching the fets but i'm sure i can get somewhere in the parish.
It may be a while until I do the phase 90 anyway. I'm still happy messing with the mini P45.
This will serve as a good referance point however when the time comes.
Cheers
Rich

[duck_arse]

it's got hammer's name on it.

http://www.diystompboxes.com/smfforum/index.php?topic=80111.msg662187#msg662187

[Kipper4]

Thanks Duck Arse for my night time reading for the next few weeks Hahaha.

[duck_arse]

well, mr kipper, I put this on the breadboard today, and I gotta say, to my uneducated ears, w/ my no guiter playing, it sounds like a tremolo. so far. I look on the cro to trim it, and it seems if I trim for the low setting on my audio sweeper, 200Hz, you get a different amount of "trem" then if using the mid setting, 2.2 kHz, and veesy versy. maybe this is exactly what phasers do, I'm uneducated, as I said.

I'm using the 2 extra unswept stages in the middle of the 2 swept stages, will be fiddling cap values tomorrow. and then rebuilding the oscillator, probably.

[Kipper4]

Let me know how it goes Sir.
Mine had a few errors once I ironed those out it has a nice swooshy sweep. A lot of the effect is kinda bunched up on the rate pot for my taste but I'm kinda fond of the tremolo effect .
It takes a bit of getting right. Especially the lfo and match those two transistors.
I must have tried 60 transistors before I did the right thing and tested and matched them properly. Bear in mind I still had the errors  in the ckt. It was not the easy build I thought it would be but I've learnt some. So I'm happy with it.
I hope you get it working soon Duck

[duck_arse]

well rich, I take it mostly back. I found the sweet spot, and boy! is it tiny, but sweet. (what does that remind me of?) with 1 10turn bias trim, watching the cro the waveform reminded me of hula girls dancing, and boy was I sick of that tone.

I rebuilt and musta had some error, and I used a diff bunch a fets, but was starting to sound like dead astronaut for a couple of chords. so now I'm going to add a third stage, dunno if swept yet, and use a quad opamp for the audio, and a dual comparator-integrator osc. I was nearly sick when I heard the vibe sound, so it looks like a blend pot as well .....