Nurse Quacky decay

[reeko81]

Hi guys! I've build my trafo Nurse Quacky, i want to get a faster decay, which cap i have to change?
I believe it's one of the electrolitic cap, but which one?

[Mark Hammer]

The 22uf cap shown after te Attack control determines how long it takes the envelope signal to charge up and discharge.  You can alter decay time by reducing that cap back to the 10uf that the stock Dr Q came with (at the cost of more ripple) or by sticking a 47k resistr in series with a 500k pot in parallel with the 22uf cap.

Actually, seems to me that we ought to collectively try and come up with a sensible way of varying sweep rate that continues the fine work Jack O did in improving the basic DQ design.  I'm thinking something like replacing the second LED with 2 1N4001s, the 22uf cap with 10, and then following that with a 3rd 1N4001 and another 10uf to ground.  The two cascaded cap sections should act like a 2-pole lowpass filter and remove more ripple.  The 2nd LED was included to subtract away what the LED on the input pin added, but 3 Si diodes should accomplish that too.  Dividing them up into 2 stages will still accomplish it.  Running a variable decay pot after thesuggested FIRST cap will likely have a very noticeable effect since i will also determine chargeup of the second cap.

[reeko81]

If i'm not wrong then...pick a 500k pot, then solder a 47 k to one of the three lugs , then solder a wire to central lug.
Now i solder the 47k res and the wire from the pot to a different pole of the cap.
Am i wrong?
Doing so i'll obtain the minimum decay possible (and of corse the maximum)?

[Mark Hammer]

Sounds correct.  Depends onwhether you want clockwise = slower or clockwise = faster.  For clockwise=faster, fixed resistor goes to + side of cap, and free end goes to wiper.  The pot lug that would be on your right with the lugs pointing down and the shaft facing you would go to ground.  That way resistance gets smaller as you go clockwise.  For the reverse, make the ground connection to the outside lug on the left.

Alternatively, since many folks have a hard time hearing variations in decay rate, just wire up a SPST toggle and use it to connect a 47k-68k fixed resistor between the + side of the cap and ground.  When the switch is open, it's stock.  When the switch is closed, you get faster decay.

Note that while varying the attack resistance will interact with sensitivity, varying decay resistance will not.

[reeko81]

It doesn't work....i don't understand...there's no effect in turning that pot on and off...

[Mark Hammer]

Read this: http://www.diystompboxes.com/smfforum/index.php?topic=45466.msg380664#new   bottom posting
My fingers hurt too much to type it over again.