CD4049UB... stages/inverters?

[Plexi]

I saw/build a few ones using this.
Never understand how it works.

What the deal with all the stages/inverters without use?
Almost every distortion use 3 of 6.






The only I found that use all the inverters is the ROG's Double D:



I've readed about it in another thread that I don't find at the moment...

[Mark Hammer]

The "spares" generally go unused, but their inputs should be tied to either V+ or ground in order to minimize noise.

[bluebunny]

^ What Mark said.  With a floating input, the output will be completely undefined and probably wandering around at random (and consuming current).  Fixing the input stops this happening.  BTW, check out ROG's UBE Screamer:



This uses five inverters (the Double-D is really two circuits, one using two and one using three).  Sounds pretty good too.

[anotherjim]

If the question is - "Why not use all of them"?

Self biasing the inverter into linear mode with feedback puts both transistors into some level of conduction, allowing some current to pass right through them across the power rails from Vdd to Vss. This is "shoot-thru".

Apart from being a waste of electricity, shoot thru causes heating of the chip which increases for every inverter in the package that is linear biased. This can easily exceed the power dissipation limits of the device.
There is a trick to reduce shoot-thru. By offsetting the bias with an input resistor to ground. It should cause one of the mosfets to be biased almost off reducing the current. This also gets some asymmetric distortion.

Although there is a "tube sound" effect with the inverters due to their soft clipping characteristic (which has no "step" point like diode clip op-amp circuits), how many do you need to get that effect? Maybe only one, or two. But they aren't very good at providing clean gain to drive the soft clip. Some designs keep things simple and use another inverter to get pre drive gain. The Hot Tubes uses op-amps for the initial stages. I'm sure I've seen inverters used in some solid state amps but only one per channel to provide soft clip. With the higher supply volts available in amplifiers, you have greater shoot-thru which really can burn the chip out. Some used the 4007 chip instead since the rest of the chip can do other jobs and not just tied out of use.

[Plexi]

Wow...thanks Jim! Clearer than crystal.

Mark and Bunny: checked both..thanks!
This one use 4 inverters:


I've read somewhere a thread about use the extra inverters to add some kind of active tone stack.


BTW: thanks ROG for exist 

[Kennt82]

I've been wondering the same with two projects I like using the CD4069, not the CD4049.  Your Tube Sound schematic allows the 4069 though, so I'll chime in.


The Stone Grey's first half is similar to a DOD250 (Ross GREY...etc), but with mosfet soft clipping driving two 4069 stages. It's marketed as a metal pedal that retains clarity with low tunings. I'd
be happier with a little more gain.




The ReezaFRATzitz uses more stages and sounds great, though can get quite noisy. I read about people replacing the CD4069 with TC4069 or HEF4069 for less hiss.

[Mark Hammer]

My own experience is that I like the sound produced when an op-amp is used to boost the signal before hitting the invertors.  However, I can understand why others look at the chip, think "I have all these extra invertor sections.  It's a shame to waste them.".

Ultimately, most designs will use at least two invertors so that the output is in phase with the input (invert twice and you're in phase).

The late Charles R. Fischer had a design in Electronic Musician using only a single invertor stage, governed by a current-controller to achieve a variety of tones from coloration through to full-on splat.  JD Sleep used to have the schematic posted on his general Guitar Gadgets site, but I can't seem to find it now since he redesigned the site.

[Kennt82]

useful older link:
http://www.diystompboxes.com/smfforum/index.php?topic=85798.0

[Kennt82]

Is this it? I found the images on Wayback and reuploaded them (the other 3 at this link):
http://imgur.com/a/5phGh



Here's the article:
http://www.generalguitargadgets.com/wp-content/uploads/em_fuzz.txt

[Plexi]

Good observation, Kennt82!
Stone Grey is very top on my list (you can check in my High-gain pedals thread  )

Which is the main difference between 4049 and 4069?

You're right, Mark.
It's our nature of use all the resources of that big CMOS 

[Frank_NH]

How about a rail-to-rail op amp stage made from four CD4040UBEs with a 5V supply?  Another CMOS tube screamer idea.   

http://www.edn.com/design/analog/4424461/A-true-op-amp-made-from-inverters

 

[Plexi]

That's awesome idea for a "stand alone" pedal for rehearsals.
I can use one of the many old 5v cellphone's power supplys that I have, inside an 1590BB enclosure.}

I'll try it on protoboard 

[Frank_NH]

Yeah, I have a big tube full of CD4049UBEs I bought a while back on eBay, not thinking about what I'd do with all the extra parts.  Now I have a project for those leftovers...

[Plexi]

You got it!
If not... you know where you can send a few ones! (I'm joking... I'm really far  )