4047 based slicer style circuit

[ragingben]

Hey, I'm having a bit of trouble with a part of a circuit I have been working on for a while and wondering if anyone can point me in the right direction.

Basically I am using a 4047 to drive a 4066, which in turn grounds my signal acting as a slicer style circuit. This is only a small part of a bigger project I'm working on. I was using a 555, but found it to be very noisy, which upon researching I have a few 7555's on the way under the impression they create less noise on the power supply rail. However in the meantime I have moved to a 4047 because it has a near 50/50 duty cycle, which for what I want is perfect, and a definate advantage over the 555. It also have an inverted output which is really helpful.

The circuit works, however, I get this 'popping' when the state of the 4047's Q output changes, which is getting into the audio signal and making it unusable. I found that running it at 5v by using a 7805 I can reduce the popping while the cmos chips are still happy, but the problem is still there. It gets worse as I play louder. My guess is that there is dc leaking into the signal path causing the popping as it gets released? I have tried adding a pull down resister to ground on the gate pin I'm uisng of the 4066 and this hasn't helped. I have added a 100nF decoupling cap beween the V+ and 0v pins of the 4066 and 4047 and this also doesn't help with the popping.

Can anyone spot anything obvious with this circuit that would cause the problem. I'm still a bit of a newbie to electronics, but love tinkering, although getting a bit frustrated with this now!

[scuzzphut]

Maybe a cap between the input and pin 1 of the 4066 ?  Just a guess, but worth trying.

[ragingben]

Cool, I'll give it a try later when I get back from work. Is that to stop the dc leaking into the signal chain? I'm guessing something like a 1uF electrolytic, with the anode towards pin 1 of the 4066?

[Fender3D]

^^
I think you should bias your 4066 either.
Check Geofex http://www.geofex.com/Article_Folders/juggler/juggler.htm

[ragingben]

Hi Fender3D, thanks for the reply that was an interesting read.

Here's a revised schematic, does this look to be correct to what you were implying?

[ragingben]

R5 and R6 should be 1M

[Fender3D]

You may avoid R6
Maybe 10uF for C6, just to be safe...
I'd use input and output buffers...

[PRR]

Pin 14 -Power goes to V-/Ground, yes.

Pin 2 switch O/I must go to Vbias +2.5V!!

R6 isn't doing that, because you also have it going to ground.

Otherwise, even with no signal, you are switching between the +2.5V at pin 1 and the Groound at pin 2, a 2.5V jump, a big POP.

Omit R6 and tie pin 2 directly to Vbias.

Circuit impedances should be smaller than source impedance. Taking 5K for guitar at lower frequencies, you want well under 1K, perhaps down to 82Hz. That suggests 2uFd for C6 and C5 together. I'd go 47uFd at C5, 5uFd at C6.

4053 (or two 4066 gates and the Q/Q lines from 4047) may be a "better" stutter. Instead of hard-grounding the signal, break the through-path and ground the amp input (SPDT). The single hard-ground may only cut signal to 1/10th or 1/20th, even less if driven from a strong source (active pickup or hefty buffer). The double-throw method kills signal two ways, and will reduce to inaudibility even strong sources. And now you don't need monster caps and switches.

Remove the LED for initial testing, it is bound to throw pops into the signal. On testbench, you don't need the LED after initial build. Get signal stutter working, then add-back the LED and work on those pops.

Go back to 9V. Boosted guitar can exceed 5V rail. Any peak outside the rail will be clipped; or worse, a "muted" peak may pop-through via the CMOS protection diodes.

[ragingben]

Thanks, for that reply PRR, a lot of food for thought. I'm moving to a 4053 after doing a bit of reasearch, what you have said makes a lot of sense. I'll get the the input and output buffers in there, get it on 9v, sort the switching as you have said and see where we stand. Thanks fgor the help guys, I'll post back when I have had a tinker!

[ragingben]

So, I have revised the circuit to a use a 4053 instead of the 4066. This seems good, I based it on this interesting article. The audio connection is both broken and the signal sent to ground which seems to work really well.

However, when I add in the 1M resistors with the 4.5v~ reference voltage I get a worse pop than when the pins of the 4053 have no + voltage on them - I guess because now there is 4.5v grounding! Removing these makes the popping less, but still present. Is R9 and that connection for the reference voltage to the output buffer needed as pin 15 on the 4053 already has a reference voltae connection? If I remove C8 I don't get any audio, so it appears that needs to be there even if this could be charging and discharging causing the pops. I have removed the LED to take it out of the equation, although when I add it back in I plan to do it like this article suggests.

Here's my updated schematic, including input and output buffers.



Any further help is much appreciated. CMOS switching seems to be troublesome for this kind of device wehere there is a hard on and off. Would it help If I somehow had a trapezoidal switching with sharp edges rather than a full square wave? Would this reduce the popping by having a less abrupt change in voltage? I read about square wave trmolos and the basic idea seemed to be that those that appear to be square wave are actually trapezoidal.

[~arph]

You could try an opto isolator, so the switching signal is separated from the signal chain.. Also, you can feed that with a low passed verion of the switching signal to round off the sharp edges.

[ragingben]

Cool, I'll look into opto isolators and try the low passed version, how low would you suggest going?

[~arph]

depends on how fast you want to slice things..  I'd say at least twice the max slice frequency you aim for. It's just to get rid of the sharp edges

[ragingben]

Sounds good. Would 4N38 be a suitable opto-isolator? Would that go in between the logic signal between the Q output (pin 10) of the 4047 and pins 10 and 11 on the 4053?

[~arph]

I'm no expert on them either, I've used a H11F1M with good results. It needs a fast switching time. Much faster than a vactrol.

You don't need the 4053 either. Just clock the opto isolator with the 4047 (put a series resistor to limit the current to the internal LED)
And connect the signal via a cap and a resistor to GND to the isolator in, and take the output from the isolator (also first a resistor to GND and a cap, so both ends of the isolator sit at the same DC level which minimizes popping sounds when switching) .No need to ground the signal, you can just disconnect it

Another idea is to use a 4066 in place of the optoisolator.. use the same cap and resitor to GND (vref) technique. There is an article on GEOFEX on switching using 4066's

EDIT: LOL I just realized you are using a 4066 already..

[ragingben]

Wow good advice! I switched back to the 4066 and used the vref technique on either side of the switch and it certainly knocked a lot of the popping out. It is still there but is much less audible. The hard shunting of the signal to ground wasn't necessary as it seems to work fine just cutting the signal between input and output. I think that's because there is no big change in voltage now, or there is less of one anyway. Tomorrow I'll post a schematic that's up to date once I've played some more. Is it likely any of the popping will be reduced whe, it's boxed up do you think?

[PRR]

> I get a worse pop than when the pins of the 4053 have no + voltage on them

Apologies for not being clearer.

ALL the switch leads must be at the same DC voltage, +4.5V (or 5V).

One gets signal plus 4.5VDC. Since your buffer is already biased to 4.5V, the signal is ready to go.

One gets NO-signal plus 4.5V. This is the Vbias node.

EVERYthing between in buff and out buff sits at 4.5V, with or without signal.

And then you can also lose many of the bias resistors. You need a cap and resistor to 4.5V at the front of the input buffer, and a cap (perhaps resistor) after the otuput buffer.



The double-pole (units X and Y) switching is not essential. The input buffer is quite happy not connected to any load.

The output buffer's input must connect to something, something at 4.5VDC. If connected to ground you get a 4.5V jump when you switch. This is 5X-10X larger than signal, so it POPs big. If loosely connected (via 1Meg) to 4.5V, it will tend to catch buzz/radio. So we connect to the Vbias node, which is 4.5VDC and also has a heavy cap to signal ground, to feed the out buff "no signal" (not even trash).

[ragingben]

Thanks for such a clear and concise answer, really appreciate it! I'm still really new to electronics and it takes a while to click, and then when it does it's hard to understand why it took me so long to grasp!

I've re-done the circuit with the mods on your diagram, I'm away at a wedding all weekend but I'll build it Sunday night and test it.



EDIT: Just noticed that pin 10 on the 4053 should go to +4.5v and not to the switch signal!

I've also done the circuit for a 4066. Does this look right?



By using the Q of the 4047 it turns on the second switch at the same time the first one is turned off, which disconnects the signal but as with the 4053 it is still at 4.5v. Is there any benefit to using the 4053 over the 4066 that you can see for this application? From playing with both I prefer working with the 4066 as the pinout is really simple and should be a bit easier when it comes to squeezing it onto a vero for a 1590B (I'm planning on having to oscillators and a selection of gates to combine the signals, so getting all the CMOS IC's in could be a bit of a squeeze!). With either switching method will it be OK for the brief time signal is between throws in the case of the 4053 or between states on the 4066, where there will be no Vref on the signal?

[PRR]

> Is there any benefit to using the 4053 over the 4066 that you can see for this application?

No.

In *general*, the 405x chips allow the audio signals to swing wider than the logic signals. At an extreme, the logic can be 0/+5V, while audio supplies and signals can be -9V/+9V.

However in a one-9V pedal, that's irrelevant.

[Jdansti]

I don't know if this would help in your case, but it would be easy to try.  I read something that Jon Patton recommended on one of the threads when I was playing with the 555 and it worked very well to eliminate the "popping" that occurred with each pulse.  The flowing component values are mine.  Place a resistor (approx 200R) in series with the voltage going to the 4047 IC, and place a "largish" cap (>/=1000uF) with the + lead as close to the IC as possible and the neg lead to ground.