Hex inverter chips

[HamishR]

Lately I've been building Red Llamas with the CD4069 chip - because I was given a bunch of 4069s by a friend. It probably sounds exactly the same as a 4049 but at least the 4069 is two pins smaller! The two-knob version seems to sound better to me and it really does sound good with the 4069. Such a great boost, if a little noisy when used as a boost.

But it makes me wonder why these pedals use a hex inverter when they only use two stages - is there no such thing as a dual inverter chip?

 

[jwin615]

CMOS circuits are generally at least a dozen chips if not dozens so you rarely need one or two of something. Also, they're super cheap to produce anyway so no sense in making multiple varieties of the same thing.

 

[HamishR]

It rankles with the minimalist in me! I would rather that the pedal either used a dual inverter IC or used all of the stages! At least having six of exactly the same stages gives you options in your layout.

 

[Robert]

There are single inverters if you want to be super efficient and don't mind working with SMD.

https://www.mouser.com/c/semiconductors/logic-ics/inverters/?mounting%20style=SMD%2FSMT&number%20of%20circuits=1%20Circuit&output%20type=CMOS

 

[mckillacuddy]

Lately I've been building Red Llamas with the CD4069 chip - because I was given a bunch of 4069s by a friend. It probably sounds exactly the same as a 4049 but at least the 4069 is two pins smaller! The two-knob version seems to sound better to me and it really does sound good with the 4069. Such a great boost, if a little noisy when used as a boost.

But it makes me wonder why these pedals use a hex inverter when they only use two stages - is there no such thing as a dual inverter chip?

CD4007 is three. Quieter too

 

[MattG]

As Robert said, there are dual- and single-inverter chips, but they are all in SMD format. I've searched, and can't find any through-hole versions with fewer than six inverters. Edit: clearly I overlooked the CD4007!

If it makes you feel any better, the unused inverters, assuming they are wired correctly (input tied to V+ or GND, output floating), won't waste any power (maybe a few micro amps of leakage, but negligible even on battery).

I've never personally tried to use more than three inverters, but both RunOffGroove and @Chuck D. Bones have reported that three seems to be the upper limit before the noise is too much. See the RunOffGroove Double D, Chuck's take on the Double-D, and Chuck's CMOS Overdrive for good discussions on using these inverters in analog mode as gain stages.

An interesting experiment: the inverters can be paralleled for more current-driving ability. I wonder if running them in parallel has any effect on the noise? I used to build DACs from the old tda1387 chips, and running them in parallel was a common trick for improving noise characteristics.