--I used the search and either found threads trashing this pedal or posts saying you can make it work but not clearly--
Recently I had the urge (aka GAS) to have an envelope filter. Things get reeaaalll costy here in Brazil, so I was considering the chaper options. Bassballs costs around $200 here and the Doctor Q Nano is the cheapest of all, costing around $100.
I looked around and found some advice in a couple of forums (DIY Stompboxes and some others I don't remember now, maybe The Gear Page) so I had to give this a try.
This might be interesting for people that don't like the sound of the dual filter of the Bassballs. Some people say the Bassballs is actually 2 Dr. Qs in parallel.
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Doing it:
Usually there are 4 problems people point out in the Doctor Q Nano:
1. No effect comes out, regardless of the setting
2. Only a hissy swoosh sound comes from the output
3. When you get the effect going, it is too trebly / lacks lows
4. It is too "subtle"
From what I learned, this pedal needs a lot of gain to trigger the filter, so the bass itself plugged in won't do it. Any booster will work for this purpose. I have a LPB-1 and the VT Bass; both do fine before the Doctor Q.
Now that you can hear the effect, it is awful, isn't it? The hissy swoosh you get is the filter acting in a range that is beyond bass (I guess it is supposed to work high up in the neck of guitars thou). So flip up the BASS switch and forget it exists. Seriously, you don't want it off. NEVER.
When you turn on the BASS switch, you might get no or little effect again. So here's the trick with the internal trimpot that people usually do to get it working:
That trimpot circled in pink controls the amount of signal that it takes to open the filter (I guess):
That's the guy up close:
It took me about 15min to fool around with this trimpot and get a good result out of it. I don't know
exactly what it does but turning it clockwise the filter takes more gain to open and turning counter-clockwise the filter opens even with the lightest touch. Sounds to me that it changes the frequency response as well, but my ears could be mistaken. This trimpot is really sensitive, so a minimal tweak will change much of the way it responds to your playing.
Looking closer, you see in position "1" where the trimpot was when I first opened the case. Position "2" is the spot I found that works best with my rig/playing:
Now it is just a matter of finding the sweet spot that will work for you.
The RANGE knob also will help to get it bassy enough to get the quack tamed. I'm using it at 9:00. When I want it to quack a little more, I bump it to 10:00. After 12:00 it is back to "guitar mode", so you might get hiss and very trebly quacks.
I plug my bass in the EHX LPB-1, run it to the Doctor Q and then to VT Bass in front of amp (I have other time-based effects in the amp's effect loop too). After you tweak it you'll notice that this unit is very sensitive to your playing dynamics and to the level of the input, like I said before. This way I showed here I have the Doctor Q set up so I can kick it on and control the trigger with my dynamics. I can do fingerstyle without opening the filter, and just dig in harder to get the effects (harder you play, more the filter sweeps up to the highs). And it isn't "subtle" at all!! Diggin' hard and slaping get some serious Bootsy-style funk out of this
cheap box!!
This is the way I'm using it before the other effects:
Electro-Harmonix Doctor Q: Make it work on bass! 
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