making the phase 90's LFO smoother

[nero1985]

i just wanna change it to make the sweep better cuz it sounds like it goes from phase to out of phase without any sweep, what should i do?

[markphaser]

it goes from phase to out of phase without any sweep

What u mean so there is no LFO sweeping?

To set the sweep of the LFO is the time constant or rate of change of the intergator which is a feedback cap. and a resistor to give a different rate of change or time constant

What are u looking for in a sweep?  most Phase 90's are linear what were u thinking about?

[nero1985]

I was thinking of a flager-ish type of sweep, i just feel like the phase 90 bumps in and out of phase. is there anyway to do this? thanks

[gez]

Always helps if you post a link to the schematic.  With the theme I use there aren't any links to the old schematics page etc, so I had to go through the rigmarole of converting to the Forum Default to access it (I've favourited it now).

Anyway, if it's the same circuit as RG's phase 180 thingy, then it's a relaxation oscillator - poor man's triangle - so you'd need to do some redesigning to get what you're after.  The bog-standard two amp triangle LFO would be best.

[nero1985]

here's the schematics to the script phase 90

http://aronnelson.com/gallery/Schematics-etc/MXR_Phase_90_Script

This is for the Reissue Block Logo schematics

http://aronnelson.com/gallery/Schematics-etc/MXR_Phase_90

[gez]

Sorry, but there's not a lot you can do Nero...not without a major redesign of the LFO.  As I metioned earlier, it's a relaxation LFO.  To get a better waveform, ie a triangle with nice straight sides, you'd need at least a two op-amp design. 

If your circuit is on a breadboard then this would be feasible, but otherwise there's no quick fix I can think of.

[lovric]

you may look at hammer.ampage for hypertriangular LFO. it transforms triangle waveform into a something that looks like full rectified sine wave. actualy a jfet stage with the diode to gnd before it resembling a stage in joe davisson's vulcan is added after the usual triangular LFO.

it is said to to keep the device longer in the low frequencies where it has something to modulate and the go briefly through the hi range where there's less harmonic content.

some call it swoosh.

[gez]

you may look at hammer.ampage for hypertriangular LFO. it transforms triangle waveform into a something that looks like full rectified sine wave. actualy a jfet stage with the diode to gnd before it resembling a stage in joe davisson's vulcan is added after the usual triangular LFO.

I'm pretty sure the waveform would have to be a proper triangle, and not the pseudo triangle from a relaxation oscillator, to get any sort of meaningful shaping.

I should think you'd need to set the thing up with a scope too - amplitude would probably be critical.

Either way, the LFO would have to be redesigned, there's no quick and easy fix.  Better to build something else like Ross?

[Paul Perry (Frostwave)]

I expect that to get an 'even' response, you would need to have teh fets matched. If they aren't, it isn't going to behave well.

[lovric]

oh yes, mxr has fets inside. they have to change their resistance according to the voltage changed by LFO. LFO may be perfectly allright but if fets don't listen...

there should be a trim pot between the power supply and gates of all fets, try to tune it to bias the fets.

you describe the change of sound as abrupt. it may be that LFO sends a square wave? check the connection of the cap in the LFO's opamp feedback. the cap in it's feedback makes it a comparator which is the generator of the triangle wave.

if all is set and phaser comes to life you may wish to change the LFO to hypertriangular one. incidentally ross and smallstone's LFOs generate hypertriangular waveforms. the schematic of electro-harmonix LFO shows a diode to ground on the LFO's output. whoever was playing with the distortion box would find an analogy here in what the diode to ground does to the signal or waveform. it limits half of its period.

happy hunting.