Author Topic: Dr. Q/ ECF Help (repost)  (Read 4855 times)


Dr. Q/ ECF Help (repost)
« on: August 17, 2003, 08:08:52 PM »
Jack, yeah I realize that the Dr. Quack was around a while before (nice circuit by the way).  I tried the original values and it seemed like the filter didn't go high enough towards treble...when I switched it, it sounded great.  I'll try the lower gain again though and see if I get rid of the pop.

Aron, the same guitar was used.  I thought about what you said also and tried to hear it on the other amp but it just wasn't there.

Thanks guys,


Dr. Q/ ECF Help (repost)
« Reply #1 on: August 17, 2003, 08:45:36 PM »
it seemed like the filter didn't go high enough towards treble

Are you tweaking the trimmer before the transistor?  You should be able to get plenty of sweep by adjusting it, even with the original resistor value.



Dr. Q/ ECF Help (repost)
« Reply #2 on: August 18, 2003, 09:42:06 AM »

Yeah, I was tweaking that.  Still didn't go as high as when I increased the gain...weird.  I also forgot to mention that I increased the AC coupling cap in the sidechain to .1uF b/c it seemed like the bassnotes weren't triggering as well as the higher strings.  Do you think that might have messed anything up?

ps, I now realize what you meant by "not".  When I said "Dr. Quack project (really a Nurse Quack with input buffer)" I didn't mean to say that the Dr. Quack IS a Nurse Quack with an input buffer, I meant that MY pedal is a nurse quack with an input buffer.  Sorry for the slight confusion

Thanks again,


Dr. Q/ ECF Help (repost)
« Reply #3 on: August 18, 2003, 12:28:42 PM »
Mark Hammer posted on the old one asking if one amp is brighter than the other.  My reply:

The amps are both pretty bright. So Mark, you've never encountered the "popping" sound in an ECF? In the "new" forum Jack suggested that I have too much gain in the sidechain hitting the bipolar and the signal is somehow "folding over." I'm not quite sure I understand that, but I consider it a definite possibility.

Mark, there's a couple things in the circuit I don't understand. How does the bipolar's collector get biased? It looks like at DC it's at ground, but then it won't be operating in the linear region. Is it not supposed to? What does that collector resistor do?

The reason I ask is, if I wanted a stronger envelope signal, could I decrease the closed loop gain of the opamp, and increase the 47k resistor going to ground at the collector of the bipolar so it doesn't source as much current? I might be looking at this the wrong way though.

edit: I also wanted to mention that I'm using an LM833 Dual Opamp.  Has anyone had problems with this guy?

Thanks for your help,


Dr. Q/ ECF Help (repost)
« Reply #4 on: August 20, 2003, 02:48:13 PM »
Ok, so I have an update.  I built another one on a breadboard again and it sounds great through both amps.  I used the same component values as my other one also (high sidechain gain).  I had the chip socketed, so I tried swapping that...didn't help.

The next thing I'm going to look at is the bipolar.  I'm using a 2N3904 in there, has anyone come across bad ones?  It's going to be a little harder since I didn't socket it and I'm using perfboard.

All my electrolytics are the correct orientation.  The bias points all look ok.

Does anyone see anything I overlooked?