Dr. Q x 2 layout?

[RickL]

I built this (two Dr. Quacks in parallel using one envelope detector, outputs mixed via 100 volume pots into an opamp mixer) using a hand-drawn layout marked DR.Qx2. I'd like to post a review and ask a question about a minor problem but I don't remember where I found the layout (I used a printed copy).

I had no luck with the search function using several variations of Dr. Q. Does anyone recall this layout? My remarks and question would make a whole lot more sense if you could see what I was talking about.

Rick

[j.frad]

well, never heard of that one! sounds interesting though, does it have any problems of distortion? Thats what happened to my nurse quacky an I'm still looking for a envelope filter that doesn't have this problem... Don't you have any way of scanning the printed version?

[puretube]

http://www.diystompboxes.com/smfforum/index.php?topic=23334.0 ?

[Mark Hammer]

Got it...at home.  t was contributed by one of the more recent regulars, whose name I plum forgot. 

Personally, I was eager to use a layout for a cascaded filter arrangement.  I tried some experiments using one DQ plugged into another, and I very much liked the sound - over the top resonance.  The shortcoming was that the envelope of the second depends on the output amplitude of the first, so the ideal arrangement would have been to extract the envelope once and use it to control two cascaded versions of the same filter.  The fitlers would be the DQ filters with the same component values.  The drive circuit would be more like the Bass Balls.

[RickL]

I thought that might be the one but the link for the layout/schematic is missing for me. In case someone has a copy of it I'll give my comments anyway.

First my question, which I managed to answer on my own. I was having trouble with the volume controls. If either one was turned below about half way the effect started to distort and eventually completely cut out. I added 1uF coupling caps between the wipers of the 100k volume pots and the resistors going to the mixer and it solved the problem.

There is a discrepency between the schematic and the layout around the sensitivity and attack pots and a diode. One wire connection is shown going to one side of the diode on the schematic and the other side on the layout (I'm going by memory here, my copy of the schematic/layout is at home and I'm at work). I wired according to the schematic and it works.

The layout is a bit crowded, the pot connections are only shown for one 'side' of the double quack and there are a couple of awkward jumpers that aren't shown on the layout. The traces and pads are there but you'll have to reference the schematic to realize that the jumpers are required and where to put them and how to wire the pots for the other side. With the noted corrections and cautions the layout works.

As Mark speculated it sounds a bit like a Bass Balls. With both filters mixed equally it sounds vocal in the same way that the BB does but it doesn't have the option of varying the filters frequency like the BB. Note that the two filters *are* tuned differently. I suppose you could use a pair of dpdt centre-off switches to get three choices for each of the filters, giving a total of 9 combinations. I should do that.

Having the option to mix the outputs of the two filters is nice. Changing any one of the three controls for either filter makes a noticable difference in the combined sound (i.e. short attack on one filter, long attack on the other). I was happiest with both volumes all the way up, both sensitivities all the way up (it might not hurt to do the common gain increasing mod) and adjusting the attack times. With the volume of one filter all the way down, it's a plain Jane Dr. Quack.

Combining two (or more, I've done a BB with four) envelope controlled filters in parallel gives some nice sounds. It might be worth trying the same thing with some of the other standard EFs. I need a new project. Maybe I'll try using the Craig Anderton EF to control two Super Tone Controls. Now there's a batch of knobs...

Rick

[Mark Hammer]

Okay, now its coming back to me.  Wasn't the modus operandi of this dual DQ supposed to be something that used a pair of filters governed by two different sets of envelope parameters so as to produce a more vocal sound?  The idea being that real speech moves formants at different rates, hence syncing the filters together via one envelope follower would/could not "nail" a vocal or talking sort of sound.

[RickL]

This schematic may have come as a result of that discussion but I'm not sure. I don't even know if it came from the thread that puretube referenced since the image is missing when I go there. It may have been as simple as someone wanting to combine two Dr. Qs to see what it would sound like.

Any comments by me today until I get home are complicated by the fact that I don't have the schematic/layout in front of me.

Rick

[Mark Hammer]

If its the hand-drawn one that did come from that thread, then you should see an attack pot on one of the sidechains going to one filter, but not on the other one.

[RickL]

It doesn't look like it. The buffer goes to an inverting op amp through a  100k trim pot, then splits into two side chains, each with an attack pot and a range pot (500 ohm and 25k), one for each filter. It specifies a 2n5457 for the JFET but I used a J201 with no problem. I also used 1k pots for the attack controls.

Rick