Phaser problem

[Knas]

I've built a phaser designed by Robin Tomtlund (http://hem.passagen.se/robin2/im/phaser.gif) but it doesn't work..  Since i don't have any knowledge of phaser theory maybe someone here could help me. As i understand it, the "depth" pot is actually a mix knob inbetween how much original and phased sound you want. The problem is that no sound is coming out from the last op.amp. Actually, no sound's even coming IN after the 1K resistor on the top left. The signal i get there seems to be more or less a copy of the LFO which is by the way going suprisingly slow (about 0,4 - 4hz), is it supposed to be that slow?

thanks

Karl

[puretube]

maybe a wiring problem:
in the schematic, only the dotted wires should connect.
you possibly connected the 2 LFO wires left and right of the speed knob
to the phaser-output to the right of the depthknob/47k resistor?

just a first thought...

the LFO tempo is OK.

[Knas]

I do know that only the dotted wires should be connected and i checked my board several times, but no luck. I guess it is a wire problem though, cause that's what usually happends, but still... So, question; apparently there's a leakage of LFO into places there shouldn't be. Audio is first buffered and then travelling trough a 1K resistor, at that point it shouldn't be canceled by a signal that has to travel trough a 2.2M resistor. a FET and a capacitor, right? Something's strange...

[puretube]

somebody pleeze jump in here - got little time...

(all resitor values OK? FETs oriented correctly/pinout ?)

[gez]

Audio is first buffered and then travelling trough a 1K resistor, at that point it shouldn't be canceled by a signal that has to travel trough a 2.2M resistor. a FET and a capacitor, right?

Your 1k is either not connected so you have an open circuit, or it's shunting signal to ground due to a wrong connection.  This is the place to concentrate on as there's nothing showing after it.  Can't see your original post so is this on a breadboard or did you perf it?  If the latter, check/reflow your joint after the 1k.

The LFO signal you're measuring at the input might be feedthrough.  Is it reduced in amplitude compared to the LFO output?

PS I don't know how much longer our computer will hold out before I have to take it in for repair, so apologies if I suddenly stop posting.

[gez]

PPS  Check the pinout of that first FET, if you've wired it up wrongly then this might account for your problems.  Obviously, if it is wrong then you'll need to check the others.

[gez]

As i understand it, the "depth" pot is actually a mix knob inbetween how much original and phased sound you want

I couldn't be sure but I think it's supposed to be a trimpot and not a knob (personally, I'd make it a trimpot).  It looks as though it's there to fine tune the balance between wet & dry so that you get optimum phase.

[Claus H]

Maybe pointing the ovoids but something very important is missing on the schematic +/-15volt supply to the opamps

On the 4136 the +15volt go to pin 11 and -15volt to pin 7
On the 741 +15volt  to pin 7 and -15volt to pin 4
On 072  +15volt to pin 8 and -15volt to pin 4

And for best preforms match the FET's

Claus H

[Boofhead]

As drawn that circuit is operating off a dual/center-tapped supply of +/- 15V.  

Are using a dual supply?