Converting a Doctor Q into a Nurse Quacky

[rousejeremy]

I have a Doctor Q that I despise and cannot sell.
How could I convert this to a Nurse Quacky, part by part if possible? I like the sound samples I've heard of it.

[edd29]

I have a Doctor Q that I despise and cannot sell.
How could I convert this to a Nurse Quacky, part by part if possible? I like the sound samples I've heard of it.

take a look at this.

[rousejeremy]

Perfect, Thanks edd29

[edd29]

Perfect, Thanks edd29

You Welcome!

[Thomeeque]

 Hmm, Nurse Quacky sounds sweet!

Most delicate autowah for my ears is Xotic Robotalk2, but this Nurse is not so far! And since there's no Robotalk2 schemo available (right? ), I may give it a shot.

Does somebody see simple way how to add there:

• RESONANCE pot and
• ENVELOPE POLARITY (or how to call it) switch (to reverse the way how the filter reacts to input signal envelope)?

Thanks, T.

[Mark Hammer]

Resonance is relatively easy.  Simply increase the feedback resistance in the filter stage to increase the gain around that stage.  The Seamoon Funk Machine used a near identical filter stage and does the same thing. 

I have to say that there are several caveats that come with it, though.

1) You're increasing the gain, so an output volume pot will also be required if you intend to have effect/bypass volume balance.
2) The transfer function of the filter depends on the interaction of the various components around that stage, such that increasing the feedback resistance will also change where the resonance is applied.  Typically, as you turn up the gain, the filter appears to shift its' focal point downwards.  One more reason to want to include other tweaks like a volume level, and moving the tuning trimpot to a panel control.

As for downward sweep, check some of the ideas at Tim Escobedo's Circuit Snippets page.  Note, however, that while it may seem easy to have a circuit change that simply reverses the direction, usable downward sweep can sometimes be a little more complicated than people think.  First, there is the decision about where the starting point of the downward sweep should be, then there is the decision about how far downward it should sweep to be useful.  Then there is the issue of the time constants.  You'll find that attack and decay times which are pleasingfor a sweep that goes up and down may not always sound that great when the sweep goes down then up.  I'm not saying to abandon it.  I'm just saying that the aesthetic aspects make it a little more involved than the electronic aspects.  Other than that, go for it!

[Thomeeque]

 Thanks, Mark! You gave me a lot to think about!

[Mark Hammer]

One or two additional comments.

• The posted schematic for the Funk machine shows a 5M resonance pot.  IN practice, I don't think this is necessary or even advisable.  If you reduce the feedback resistance to 330k fixed resistor in series with a 2M pot, that should cover all your variable resonance needs.
• Time constants in simple half-wave rectifiers can be tricky to optimize.  You have the series resistor (usually in the 68-330R range) and the cap to ground (anywhere from 1uf to 22uf, typically).  Although you can extend attack time by increasing the value of the series resistor, it takes a lot of resistance to produce what might be describable as a wide range of attack times.  Once you start to get over 270R or so with the Dr/Nurse, you start to lose significant current-drive to push the transistor base.  This, in turn requires adjustment of the sensitivity control (maybe even more gain on top of that), and perhaps an adjustment of the tuning pot/trimpot.  So, as much as I'd love to have variable attack, there is just too much involved to aim for anything other than degrees of fast.  So, consider simply using a toggle switch to select between 51R and something a little slower (220R?), and avoid the frustration and nuisance of the larger-value attack pot.  Instead, I think you'll find greater payoff by installing a variable decay control.  Unlike the attack control, this does not decrease current drive to the transistor (at least not as much), and provides what I think you'll find to be a more useful control.  To implement it, put a 33k fixed resistor in series with a 1M variable resistor, and stick that in parallel with the 22uf cap.  To isolate the new decay time control from the trimpot, stick a GE diode between the trimpot input and the attack/decay components.  One of the neat things about being able to get faster decay is that it sounds more synth-like.

[Thomeeque]

 Great! Thanks again, Mark!

[adf]

Does somebody see simple way how to add there:

• RESONANCE pot and
• ENVELOPE POLARITY (or how to call it) switch (to reverse the way how the filter reacts to input signal envelope)?

Thanks, T.

Hi, I built this recently, and found this topic in my searching:
http://www.diystompboxes.com/smfforum/index.php?topic=11187.0

A J176 in place of the bipolar will sort of reverse the sweep. It's not exact but worth a play with...

[Thomeeque]

Does somebody see simple way how to add there:

• RESONANCE pot and
• ENVELOPE POLARITY (or how to call it) switch (to reverse the way how the filter reacts to input signal envelope)?

Thanks, T.

Hi, I built this recently, and found this topic in my searching:
http://www.diystompboxes.com/smfforum/index.php?topic=11187.0

A J176 in place of the bipolar will sort of reverse the sweep. It's not exact but worth a play with...

Thanks, Al! I'll definitely check this topic, sounds interesting!

T.