new nurse quacky mod idea decay and attack

[fatfoohy]

Hello Internet, I got the idea that i wanted to build a nurse quacky for bass, but i want and attack as well as decay controls, however i have read that the attack messes with the decay mods.  However, I thought about maybe having a switch that would (A) switch between either a 68 ohm resistor or a 51 ohm resistor and 1k ohm pot{for attack control} and then (B) when the resistor and pot combo would be switched in,it would also switch in a resistor around maybe 150k in series with the 500k decay pot.  I was thinking this might cope with some of the issues that have been heard of with the altering of the decay that i have heard of. this probably sounds extremely obscure, if it wasn't so late, i would draw up a schematic, i'll try to put one up tomorrow.  However, until then, would this possibly work, or has anyone else had experience with using an attack and decay pot together? thanks in advance.

Fatfoohy

[Mark Hammer]

The difficulty with all the Dr Q-derived pedals is that the rectified signal (envelope) is not buffered in any way.  Since you are essentially driving the base of the transistor directly from the diode, the increased resistance you need to use to slow down the charge-up time of the capacitor also reduces the drive to the transistor.

Put simply, if you slow down the attack time with 1k in series, you will need to increase the sensitivity/gain of the op-amp that tracks the envelope.

Now, I realize that I was one of the most vocal  advocates of using variable attack, but I have to say that in retrospect this is probably not the pedal to do it with.  The cost in sensitivity is simply not worth the small difference in attack time you can produce.  You get far more mileage out of having a variable decay time.  Keep a 47R attack resistor to retain fastest attack time and maximum envelope sensitivity, and use a 47k/fixed + 500k pot to vary decay time.

[fatfoohy]

oh, wow thanks, that's exactly the type of answer that i was looking for, I have heard that a 68 ohm resistor does a good job for setting the attack time, is the 47ohm a better choice? Also, what would be a good envelope filter/follower that i could build that incorporates both an attack and a decay control, and is good for basses? Thanks for your answer

[Mark Hammer]

In the DIY realm (and I'm excluding the recent EHX Riddle and Enigma pedals), the MXR Envelope Filter has what is probably the best and most adjustable slow attack.  Please understand that this is NOT as slow as you would expect with a synth using an triggered envelope generator.  But it does have a pleasingly wide range of adjustment, and wider than I've found in many pedals.  This is the principle reason why I have been championing the cause of this thing since 1978.

For any of the Q/Quack/Quacky pedals, and those using a similar half-wave rectifier, the attack time is set by the joint action of the functional equivalent of the 51R resistor and 22uf cap shown here below.  The attack time is the time it takes for that cap to charge up fully.  If the cap value is bigger it takes more current to charge it up.  If the resistance is larger, it takes more time to accumulate that current.  So, you can shorten the attack time by opting for a smaller value cap, OR you can shorten the time by using a smaller value resistance (which is why the attack pot increases resistance), or you can do both. 

What I show below is a simple means for using a single SPDT toggle to go between slow and fast using both the resistance and the capacitance.  We have a 51R and 220-330R fixed resistor in series, going to a 10uf cap.  The centre lug of the toggle goes to their junction.  When the toggle switch is in one position, it bridges the higher value resistor so that the series resistance drops to the value of the smaller resistor.  Between the 51R and 10uf cap that a fast chargeup and discharge.  Flick to the other position and the series resistance is 51R + 330R.  Plus the 22uf cap gets added in parallel.  That gets you a noticeably slower attack and decay. 

There you go, slow and fast.

[fatfoohy]

ahhh, thank you, I am eternally grateful this actually gave me an idea, have two 3 way switches and have on one 3 resistors and have those values be 51, 150, and 330, to control the attack a little bit, and then have a 33uf, 22uf and 10uf cap on the other to mess with the decay, maybe this could keep some variability in the design without being too much. Thanks again

[Mark Hammer]

I don't know if you need that much control.  The gradations in attack time are actually not that noticeable, and 33uf is probably a lot more decay time than you'll want.  After all you do want the filter to settle before you hit the next chord.

[fatfoohy]

oh, alright thanks, i suppose that the KISS(keep it simple stupid)  method is the name of the game here, one last question, do you know of anyone having luck with a 4558 dual op amp in this circuit?

[Mark Hammer]

The Quacky has the Orman bias adjustment via the 10k/LED network.  That bias adjustment is intended to make most dual op-amps work properly in the circuit, not just the LM1458.

[funkxero]

mod bass?

[Mark Hammer]

The usual mod is to simply double the values of the caps used to set the filter sweep range.  In this case, make those .005uf caps (.0047uf, actually) both .01uf.  Done.

[vendettav]

this is interesting, i've found this little plastic enclosure, i'll try and put a NQ in there hopefully

any verified stripboard layouts?

[twabelljr]

http://www.home-wrecker.com/nurse-quacky.html

Not stripboard but a nice and simple perfboard layout and it is verified.

[Renegadrian]

There's a Dr. Q vero layout in my gallery, you can use that as a starting point to get the NQ on vero. After all the circuits are very similar, so I guess it would be an easy task!

thx for pointing out the mods for bass, I guess they work on Dr.Q and Dr. Quack too. I built the last one (pisotones) and I really like it!!! But I'd like to get it modded to get more filtering with bass!!!

[chemosis]

man this is exactly what I want a attack and decay parameters and heres why because u really cant get vtl5c optocouplers anymore so therefore no more clones of filters like the mutron 3 and lovetone meatball which means we can only build the ota style filters like maestro FH-1, baseballs,nurse quacky, and snow white auto wah and they all lack control for making experimental synthy sounds. us synthy guitarist need at least a AD envelope on our filter because there is no other way to get a ADSR envelope besides in a envelope filter pedal. envelope filters should have attack and decay anyways. don't keep it simple because then you are shorting yourself on sounds. mark u are a master but we need these attack and decay controls. im pretty upset that I cant hardly find any mods for the snow white auto wah or the nurse quacky.  there are hardly any mods for these filters. it sucks!! we can still build maestro FH-1 filters to because they don't use optocouplers but man we are getting very limited on options for filters here because of the extinction of the VTL5C optos

[anotherjim]

Maybe?....
After the range pot, insert another transistor follower (collector from V+). In between these followers, place an RC attack control. Optionally fit a reverse diode across the attack control so the envelope decaying also decays the attack.

[Mark Hammer]

The pedals you refer to don't require that specific vactrol to work.  The circuit  with all the specific values shown may need a vactrol with those specs, but one can always use other vactrols and simply adjust component values.  I made myself a DOD 440 using a homemade dual optoisolator.  Bought a bunch of 20-cent LDRs and glued two of them to the side of an LED.  Works fine, and sounds great.

Jim's suggestion about buffering the attack/decay components sounds reasonable, but my sense is that at this poinbt you would really like to be able to rely on the component values shown, rather than improvise.  Or am I underestimating your confidence?

[iampoor]

The difficulty with all the Dr Q-derived pedals is that the rectified signal (envelope) is not buffered in any way.  Since you are essentially driving the base of the transistor directly from the diode, the increased resistance you need to use to slow down the charge-up time of the capacitor also reduces the drive to the transistor.

Put simply, if you slow down the attack time with 1k in series, you will need to increase the sensitivity/gain of the op-amp that tracks the envelope.

Now, I realize that I was one of the most vocal  advocates of using variable attack, but I have to say that in retrospect this is probably not the pedal to do it with.  The cost in sensitivity is simply not worth the small difference in attack time you can produce.  You get far more mileage out of having a variable decay time.  Keep a 47R attack resistor to retain fastest attack time and maximum envelope sensitivity, and use a 47k/fixed + 500k pot to vary decay time.

Where would the decay control go? In parallel with the Cap after the 47ohm resistor?

[Mark Hammer]

Yup.

[iampoor]

Yup.

Cool, I will try this out! Just need to get my nurse quacky veroboard version working. The signal is disappearing around the envelope follower opamp. Its driving me nuts. And yes, I am using an LM1458. 

[duck_arse]

the signal is meant to disappear in the envelope section. voltages. what are yours? you should have signal at the sens wiper, dc on the non-inverting pin, no sig on inverting, gobs of distorted junk at the output pin. so, what voltages, all the way along to the 22uF cap.