Dr. Quack - popping and muting sound.

[Darthf]

So i was about to build Quack for my friend from the kit that he delivered. It was based on this schematic. After putting everything together i get highly compressed attack with annoying cliccking/popping sound.

Doublechecked for bad soldering, wrong values of components etc.

Quack is supposed to work with bass guitar.

Sound samples are in here.

Thanks for any help!

PS. Lower then all the way up values of 100k pot make that Q doesn't quack at all.

[GibsonGM]

We'll need some more info before we can offer suggestions!
Read this:  http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

[Darthf]

I will post voltages as soon as possible.

Battery Voltages:

Unplugged - 9.02V
Plugged - 8.7V
Voltage at the circuit board end of the red battery lead = 8.61V
Voltage at the circuit board end of the black battery lead = 0V

Q2

C = 0V
B = 0V
E = 0V

Q1

G = 4.07V
S = 5.39V
D = 8.58V

D1

A = 1.68V
K = 0V

D2

A = 1.47V
K = 0.18V

D3

A = 0.18V
K = 0V

U1
1 = 1.47V
2 = 1.43V
3 = 1.7V
4 = 0V
5 = 4.3V
6 = 4.31V
7 = 4.3V
8 = 8.45V

Any changes/mods/substitutions were made to original schematic i posted before.

[Darthf]

Anyone can help?

[strungout]

Oi, I can't see the schematic you linked and the only 3 clips on your soundcloud seem to be quacking pretty well! I'm guessing that's not the Dr. Quack.

It's been a while since I built a Dr/Nurse Quacker (had experimented a lot with it) and it's been since scavenged for parts, but if Q2 is the control element, the voltages seem to indicate the problem (to be sure, use the search function, I'm sure someone has posted voltage readings for Q2). I'd recheck my wiring, that's always a weak spot for me. I checked my wiring 10+ on the EQ I'm working on and the 9th and 10th time I found a wrong cap connection and an ungrounded IC! 
Build and/or use an audio probe. That was you can follow the signal through every component and hear where it dies. That'll narrow down the faulty connection/component.

It's really hard to be of any use if we can't see the schematic.

[R.G.]

Remove Q2 temporarily. Connect one end and the wiper of a 100K pot where the collector and emitter of Q2 used to be.

Play and listen while turning the pot. Although it won't quack, it should act like a wah pedal as you turn the pot. If it does not, something is wrong with the filter section. If it does, something is wrong with Q2 or the circuit that drives it.

[Darthf]

http://img600.imageshack.us/img600/6721/4zco.jpg Here you have the schematic. I guess Q2 should have 0V with no input signal. Tomorrow i'll replace both transistors and IC and see if it will change anything. It's possible that it'was damaged when my friend tried to solder it on his own.

[GibsonGM]

Maybe...I'd do what R.G. suggested.  He has a very good track record!  *hint hint*

[Mark Hammer]

Finally listened to the sample.  That, my friend, is the sound of a very fast excessive sweep.  It's exactly what I'd get on a Dr. Q with the "wrong" op-amp chip (i.e., not a 1458).  If it swept less, you likely wouldn't hear it and if it swept slower, you likely wouldn't hear it.  So, we know it is sweeping, which means both the envelope follower portion and the filter portion, as well as the input buffer, are working.

So, since the Dr. Quack employs Jack Orman's nifty little biasing scheme to make use of any dual op-amp feasible, I have to ask the following questions:
1) Did you use RED leds where it shows to use leds?
2) If you did use red leds for both, does it seem to behave properly when the sensitivity is turned way down?
3) Does it behave better when the 25K trimpot is turned down?

[Darthf]

1) Bth LED's i used are red ones.
2) When 100k pot is turned down D2 isin't flashing at all and there is no wah. Wah starts to appear when sensitivity is turned to about 1/3. and it comes with this popping sound.
3) Turning trim pot down gives more wah. Turning it up above 1/2 gives no wah , d2 still flashing.

[Mark Hammer]

The LEDs might flash, but they do not need to.  If you are using superbright LEDs, there is a good chance a peak will be enough to light it up visibly, but the biasing will work just fine, even with "old school" 300mcd LEDs.  Indeed, they are simply a convenient way of having a specific voltage-drop (one red LED = 3x1N4001, more or less), so don't focus on whether or not the LED lights up in a visible way.

the gain of the op-amp in the rectifier circuit is based around the expected level of the guitar signal.  A 2M2 feedback resistor is used, but some find the need to go up to 2M7, and occasionally higher, because their guitar signal output is too low.  When it comes to bass,however, output levels can be very high sometimes.  Is this an active bass?

[Darthf]

I have Maya Rickenbbacker with Rickenbacker High Gain pickups.

[amz-fx]

Darthf,

I would get a new battery. It may not be the cause of the problem but the voltage measurements are too low for a prime battery, so eliminate that.

Also, Q2 needs to be the lowest gain transistor that you have. Find a 2N2369 or something along those lines with a low hfe.

The RV2 trimpot is a critical adjustment, and can be difficult to dial in. The sweet spot on it is usually quite small so you will have to work with it.

D1 will be illuminated. D2 should flash (maybe quite briefly) as you play. 

The voltage on the gate of Q1 should be slightly higher...  4.5v with a 9v supply but your V+ is low at 8.58v so it should around 4.29v. Not sure what is causing this unless the jfet is oriented wrong.

Best regards, Jack