Ibanez Flanger 301 from tonepad - No movement

[kevinrontel]

I've just finished the Ibanez 301 Flanger (aka trescientos uno) from tonepad (http://www.tonepad.com/project.asp?id=26).

I'm having a problem similar to what Pierre outlined here: http://www.diystompboxes.com/smfforum/index.php?topic=43404.0

I can make it flange by tweaking trim pot 101, but when I'm not moving the pot, there's no flange. 

I built it stock except, instead of the three TL022 ICs, I subbed two TL072s and a TL082.  I've swapped those ICs around.  It doesn't appear to make a difference.

The regen and width pots produce some effect.  The speed pot does nothing.

I'd appreciate any advice on where I might want to look for problems. 

IC105 and caps 125 & 126 appear to be the guts of the speed control.  Is that where I should focus?

Thanks! 

[PRR]

> IC105 and caps 125 & 126 appear to be the guts of the speed control.  Is that where I should focus?

Yes. This area should be wobbling several volts around 6V several times a second.

An old needle meter should wobble. Some digital meters are confused by wobble. You can tack 100uFd caps across C125 C126 to slow it down to a wobble every few seconds so a slow meter can follow.

Also of course wiring from that area over to Q107, which converts the voltage-wobble into some kind of loading on IC104. Since VR101 has effect, you should not need to trace past that point.

TL072-type is not really equivalent to TL022; for one thing, the '022 is NPN input not JFET input. I don't see why it would matter here (about any non-dead chip opamp is likely to work) but something to consider.

[kevinrontel]

Hi Paul,

I measured the area around IC105 with a needle-style meter and found no voltage wobble, which seems consistent with the problem.

I tested the tracing/wiring over to Q107 and found no problems. 

In trying to trace the signal with an audio probe, I'm having trouble following the signal thru the schematic and matching that to the layout on the pcb; this isn't straightforward like, say,  a tonebender circuit.  There are chunks of the board that aren't passing a signal, but I haven't yet figured out how to ascertain simple things like which direction the signal's traveling.  This is making it hard to know where potential problems lie.

Anyway, I think I've gone over my head once again.  I'll study up for a few months, though, and I'm sure the truth will reveal itself.  It always has (so far).

Thanks for your help.