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Hello all just worked on a Doctor Q and got it running and ran into a rather weird deal with the circuit. I noticed when I use just the pedal by itself the “quack” doesn’t begin to occur until 10-11 o clock and even then you gotta attack the strings pretty hard. Seems as if the circuit wasn’t being driven hard enough for the range to do much as far as having a versatile range. Sure enough when I switch on the Alembic booster on my strat the effect seems to quack with ease at 10-11 o clock where without the booster I’d have to really attack the strings for it to make the effect occur. Was it just a lousy design? Because I seen a modded schematic on the web where a JFET stage was added on the input of the effect.

http://www.muzique.com/schem/doctor-q.gif

Thanks in advance.

It's an input level-sensitive effect, so a guitar with beefy output humbuckers will trigger at a lower sensitivity setting then a strat with lower output single coils. A booster in front of the pedal will help, but although the signal at the envelop detector will be boosted, so will the signal to the filter itself and you might notice some unpleasant clipping of the filter stage.

If you lower the 47k after the sensitivity pot (e.g. with a 22k in parallel) or raise the 2M2 in the envelope section opamp feedback loop (e.g. to 3M3) you'll get more sensitivity without affecting the signal to the filter.

Hi rambozo,

Try to mod your unit according this schematic, that have some improvements: http://www.muzique.com/schem/quack.gif

Cheers,
Jose

ppluis0 wrote:Hi rambozo,

Try to mod your unit according this schematic, that have some improvements: http://www.muzique.com/schem/quack.gif

Cheers,
Jose

1-10M pulldown resistor before 1st decoupling cap to eliminate possible pops.
Also consider replacing sensitivity pot with a controllable gain stage.

plush wrote:1-10M pulldown resistor before 1st decoupling cap to eliminate possible pops.

Agree !!

The main improvement of this design is the inclusion of a couple of red leds in the envelope detector to reduce the threshold. Otherwise the audio section is identical to classical Dr Q

Cheers,
Jose