GEOFEX Ramp up/down for Phase 90

[Gordo]

Hi all, this question is more directed at RG Keen but has anyone had any luck (or attempted) the ramp up/ramp down mods on a Phase 90.  I've been screwing around with this until I'm blue but no luck.  HELP!!!!  At this point I'm not getting anything out of the circuit.  The Phase 90 portion is working fine if I put the pot back in circuit, but I'm getting no LFO out of the ru/rd circuit.

[R.G.]

No LFO at all?

Did you use LM358 or LM2904?

[R.G.]

Reran the sims and checked it for component variation.

The thing that keeps this circuit from running is if the drive to the transistor to ground which switches the 51K resistor on the LFO opamp is not right.

The drive has to turn the transistor fully on and fully off. If for some reason the schmitt trigger opamp does not turn the transistor off by swinging close enough to ground, or if it can't turn the transistor on enough by swinging close enough to the supply, the oscillation never starts. That's why a single supply opamp is needed.

[R.G.]

Ah. Coffee helps.

Measure the pin voltages on the two opamp sections in the new LFO and on the new transistors and post them here. I think I can get you running.

Like I mentioned, it's probably that the transistor switch is not being turned fully off or fully on. I've used this VCO circuit several times and it always works if that transistor is switching. Well, OK, and the other stuff is per the schematic, too. 

[Gordo]

Thanks RG.  I'm spending the morning in my "frankenstien lab" tomorrow and will get some voltages posted.  I'm using the 358.

Gordo

[R.G.]

OK. Let me know what you find.

[Gordo]

Sorry for the delay R.G. it's crazy at work.  Anyway, the only noticeable voltage is on pin 8.  I tried replacing the chip and have swapped trannies as well but nothing.  Are you using 2/3 or 6/7 side of the opamp?  Not that it should make any difference...

Gordo