How about a ducker?

[sean k]

I've wanted something to duck for a while now and after making the clari(not) and the uglyface where we're using the 386 to drive an Led and use it with an LDR to create an envelope I thought it might be time to build a ducker. Previously I'd be looking at current control amps, 3080's and suchlike but this looks to be a much easier way to implement things. Little bass paralooper, little doctor quacky and a little clari(not) all thrown together.


So basically the master signal gets rectified and then a range of caps( on a 2 x 6 rotary) set the decay, which may or may not be enough to hold the LED on, and the 1k pot, which could be dual or two separate pots.  sets the level. Should work eh?

[doitle]

What does it do? Sorry if it is obvious and I'm just being dense. I've never heard of a "ducker" before.

[trixdropd]

What does it do? Sorry if it is obvious and I'm just being dense. I've never heard of a "ducker" before.

A ducker is like a parallel fx loop that has it's mix control adjusted depending on how hard you play. TC electronics has a famous "Ducking delay", so you have a delay on all the time, but the only time you hear  repeats is when you stop picking or pick lightly. You can hit a heavy note knowing it will repeat over what you're playing.

Does this make sense?

[Mark Hammer]

A "ducker" allows a radio announcer to talk over music.  When the ducking input gets stronger, the volume of the main input signal is turned down.  Once the announcer stops talking, the music signal gets louder again.

[sean k]

I've got multiple instruments that I often play at the same time and it can be tricky turning one down and another up in a time that makes sense to the music around me. Specifically I've got an instrument that I use lots of delay on and I also have a simple theremin. Using the ducker with the delay'd signal into the slave and theremin into the master then when I come in with theremin it'll automatically cut the delay signal. My thinking is that by rectifying the signal from the 386, I forgot to put a cap on the output, oops, and charging caps I can use the cap charge and discharge times to control how much overlap occors... hopefully.

So if the slave is on a 100nano it'll drop out quickly whereas the master on a 100uf is going to charge up on signal before it discharges into the LED. Well thats the plan.

[earthtonesaudio]

Looks cool, but a couple suggestions, to make it work more predictably or save on parts count:

[Ben N]

ETA:
'splain?

[R.G.]

Alex hit most of them.
The most crucial is the resistor before the LDR in the slave signal path. Most opamps are perfectly capable of driving a few K to normal output, so the expected voltage divider action of the LDR shunt to ground won't happen without some series resistance. Series R needs to be about 10x the high-light resistance of the LDR.

The second most important is the reconnection of the output in the opamp at lower right. As is, it won't have any output when the 1M feedback resistor is over a few K. I think that was a simple error in drawing, not a design error.

The JFET follower is not needed because the first opamp also acts as a buffer; in fact, leaving the JFET out improves things by placing less loading on the input signal.

The resistances between the 386 outputs and the caps will help keep the 386s stable and limit the instantaneous current. The 386 self limits current, but driving a pure capacitive load is hard on any voltage-feedback amp.

One I didn't see there is that I think that one 386 is not needed. With buffer resistors, one should be able to drive both capacitors. If the 386 had a bipolar supply or if you tinkered with a DC blocking cap and a reset diode, I think you could drive one LED from positive half cycles of the signal to the 386 and the other one from the negative half cycles.

[StephenGiles]

http://www.rolls.com/pdf/M_DU30.pdf
http://www.rolls.com/pdf/M_DU30b.pdf

How about a Rolls Ducker!

[sean k]

Thanks chaps, much less on the parts count. I didn't want this to be an exact ducker as such, like with radio guys, but something a little more musical and interactive between parts. So if the high light resistance is about 1.5-2k then 15k-20k on the output of the first opamp in the slave section? And maybe 100 ohms or so on the tail of the 386's?

And oops, indeed the cap off the - input was a mistake as I didn't change it after it was a direct connection and decided it needed some extra oomph. I've gone back to direct in the interim so it would have been correct.

I'll draw up another schematic to clarify things... then get etching!

[Cliff Schecht]

PAiA makes a pretty darned nice ducker. Not to push any sales on you but give the kit a looksie and see if it does what you need. This could save you a lot of headache and maybe some money. A lot of studios like these because they're simple but still have a lot of functionality for what you pay (we usually get orders of 5-10 at once). Link: http://www.paia.com/proddetail.asp?prod=9209K

[sean k]

Thanks Cliff but with our dollar about half what yours is then I'm looking at a hefty investment compared to what I'll pay in parts if I build my one, though I'll keep it in mind for the future, the functionality looks awesome..., if I ever finish my fatman kit 

So heres number 2 version and I hope the 4001's will isolate the two legs for capacitor choices.

And I decided to put a mix/balance control in there.

[sean k]

Cliff, I found this.

Is this the one you mean or has the kit been updated?

[ech0es]

I bought the rolls du30b for my pedalboard and it works perfectly

[petemoore]

  Dang good lookin' deal Cliff.
  Was thinkin' the same thing, 10 ducks but not in a row, more like forming a line, only one or two ducks out in front at a time...
  M.R.2.ducks !
  No, M.R. Not 2 Ducks !
  Drum ducker is what I need, so when the drummer hears a guitar solo building and starts pounding twice as hard, instead of knowing a lead was supposed to stand out right there, the lead stands out !

[Arn C.]

ECHOES,  how do you hook it up and how do you use this?  I am assuming you use this with guitar since you have it in your pedalboard......

Thanks!
Arn C.

[Ben N]

I am imagining up a looper-based pedalboard for use with acoustic or electric, and I could see a ducker having its uses there (along with a compressor-limiter, mic preamp/splitter/line-driver, mixer, pan pedal, acoustic sim and octave divider).

[sean k]

My thoughts were that duckers are a much overlooked method when dealing with lots of fx and only one signal but it took me a while to get my head around what they do. Simply put they gate out another signal when the key is playing. So if you've got a drone going on in the side chain that will gate out then when the key signal plays it'll drop out the drone so like the guys says above that if his drummer was in a side chain then he'ed have the key signal and when he plays the drummer gets gated.

In a studio situation it's a handy tool to get some very funky rythyms going by doing stuff like having the bass duck out the kick drum or having the kick drum key in the bass by ducking itself out and letting the bass in or having a rythym guitar key the cymbals etc.

I did a project file of the Paia to wake up this morning and I don't know if publishing it is kosher or not. It's out there as fair use so I suppose this is fair... I'm intending that its fair (because it might be wrong and work in a way that the original designer bypassed because he is knowledgable to a degree that far surpasses me... I just do it to wake up!)
http://artyone.blogtown.co.nz/other-stuff/

[StephenGiles]

My thoughts were that duckers are a much overlooked method when dealing with lots of fx and only one signal but it took me a while to get my head around what they do. Simply put they gate out another signal when the key is playing. So if you've got a drone going on in the side chain that will gate out then when the key signal plays it'll drop out the drone so like the guys says above that if his drummer was in a side chain then he'ed have the key signal and when he plays the drummer gets gated.

In a studio situation it's a handy tool to get some very funky rythyms going by doing stuff like having the bass duck out the kick drum or having the kick drum key in the bass by ducking itself out and letting the bass in or having a rythym guitar key the cymbals etc.

I did a project file of the Paia to wake up this morning and I don't know if publishing it is kosher or not. It's out there as fair use so I suppose this is fair... I'm intending that its fair (because it might be wrong and work in a way that the original designer bypassed because he is knowledgable to a degree that far surpasses me... I just do it to wake up!)
http://artyone.blogtown.co.nz/other-stuff/

I remember that the bass player & drummer of the Hank Wangford Band in England managed to keep the bass and bass drum together most of the time. When I spoke to the drummer he told me that it just evolved out of playing together over 4 years, and gave a very powerful sound. 

[andrew_k]

Just to throw another ducker schematic into the mix...

http://www.thatcorp.com/datashts/dn102.pdf

Less parts, but an expensive chip