Ultra Flanger debugging

[Michael Allen]

I modded the Ultra flanger to use the MN3207 (BL3207) instead of the MN3007. Details and such here: http://www.diystompboxes.com/smfforum/index.php?topic=68806.0.

I'm getting no flange at the output. Opamps biased to 4.9V with the extra trimmer on the GEOFEX board. LFO biased to 3.8V and working. BBD biased through added 100k trimmer between +V and GND to the diodes on MN3207 pin 3.

The effect sound is only straight signal. Audio probe takes me to signal at pin 3 of the MN3207. Pin 7 and 8 give me a much quieter distorted signal that vibrato-wobbles. When the signal decays, the distortion cleans up. This is working as it should, giving the vibrato effect right? It's just very faint and distorted.

Voltages on MN3207:
pin1 - GND
pin2 - 4.36
pin3 - 4.9
pin4 - GND
pin5 - 8.95
pin6 - 4.36
pin7 - 2.59
pin8 - 2.59

Pin 3 is biased to give the best sounding output on pin7/8. It's a little more than 1/2V+.

The weak signal off pin7/8 disappears when it gets to the lowpass filter U1B. U1B has some funky voltages going on:

pin1 - 4.95
pin2 - 4.95
pin3 - 4.95
pin4 - GND
pin5 - 2.57
pin6 - 3.17
pin7 - 1.35
pin8 - 8.95

I checked the values of the 100k's and 47k's on the lowpass filter and they're the correct measurements. Any ideas on these voltages? I'll try replacing the caps first.

The LFO is working and controls the wobble coming off MN3207 pin 7/8. So the LFO and Clock are alright.

Any ideas why the BBD has no strong output? The 47k resistor on pin7/8 goes to ground now, not V+ as for the MN3007.

[Michael Allen]

Several things:

1) The lowpass filter 100k resistor and 1n capacitor that go to 1/2V+ now go to ground
2) Lifting the Vgg pin 4 of the MN3207 from ground

these fixes allow for some flanging to happen with the MN3207 in the Ultra Flanger. There's a lot of LFO and clock noise and the flange is not very prominent.

Still needs some tweaking but I'm getting closer. I'll try implementing a bias trim on the Vgg pin as shown in the Zombie Chorus that was adapted for the MN3207.