substitute for a 4009 in a EH Bad Stone?

[Marcos - Munky]

I need a 4009 for a EH Bad Stone I'm building. Thing is the 4009 basically disappeared from the (two) local parts store! And it's not like they're just out of stock for now, sellers from both stores told me they don't even have the 4009 registered on their parts system. Which is pretty strange, since I bought a 4009 from one of those stores once. Anyway.

I did a quick search, and saw the 4049 can replace the 4009 for a good number of applications. I indeed found the 4009 on a online store, but I don't really want to pay the full shipping price to order just this IC and I happen to have a spare 4049 on my parts bin.

While an easy answer could be "just socket the IC and and give it a try", it's a very tight build and the IC will be soldered to the traces side, so I have no room for a IC socket and can't easily remove it if it doesn't work.

What do you guys think? Link to the schematic. The 4009 is IC E.

[Kevin Mitchell]

I was wondering how a CMOS chip would supply ramping LFO voltages but after looking at the schematic in more detail I see the VDD pin is tied with the buffer input's supply so VDD matches the LFO and the buffers supply an inverted version of the LFO to the phase stages. I like seeing these kind of alternative designs 

You should be fine using a CD4049 as a pin to pin replacement in this case. Let us know how it works!

[anotherjim]

As I understood it, the CMOS is doing the same job as JFET's in providing voltage-controlled resistors. In the chip, the MOSFETs are already fairly closely matched.
The trick is to arrange it so the input gates are commoned and driven from the LFO, the N-MOS sources are internally common to the chips Vss pin and the outputs are the connections to each phase shift stage. No power is applied to the upper P-MOS transistors from the Vcc pin so only the lower N-MOS transistors drain is active at each inverter output.
Now, that said, the 4009 has differences from the usual 4049 which is simpler and doesn't have a power pin on pin16.

I can't read the pin numbers well enough on the schematic or the old 4009 datasheet I found, so I struggle to check if the 4049 can do the same job. I suspect it can, but I for one am not certain. It looks like power pins 1 & 16 are tied common to the gate LFO inputs.
For a 4049, I don't think you should connect pin 16 at all. That might be the only difference. Also, it must be CD4049UB. A CD4049B probably won't work.

[Marcos - Munky]

So, while I was searching for datasheets to write my repply, I found this post. Guess I didn't used the correct words when I google'd for info before asking the question.

Luckily, my spare 4049 is UBE. Hope to finish mine next week, and glad to know I won't have to bother with ordering a single chip.

Thanks for the replies.

[Mark Hammer]

There was a construction project for a 6-stage phaser, using a 4049 as control elements, in Electronics Today magazine in the late 70s.  Apparently it is necessarily a little noisy because the invertor sections clip easily, so you can't feed the first phase shift stage a hot signal.  It has to be attenuated a bit, and then the final result amplified in order to achieve effect/bypass volume balance.  That ends up achieving a slightly poorer S/N ratio.

[StephenGiles]

Didn't Mike Irwin offer a solution for making that ETI phase work a little better?

[Mark Hammer]

I think you're right, and I think I have a printout of that solution somewhere in my binder of modulation effects info and schematics.  I'll keep an eye out for it.

[Mark Hammer]

Pulled the binder off the shelf, opened it up and wouldn't you know it - it was the very first page in the binder!  Retyped it here (no OCR available).  Interestingly, Mike starts the note with "Hi Stephen", so I take it that his response was in reply to something you had posted; likely in 2000 or so.  I have a printout of a second post from MIke in 2001 (and reply from Rob Strand) that essentially provides the same information.  The circuit for the ETI phaser can be found in this thread: https://www.diystompboxes.com/smfforum/index.php?topic=124331.0

I miss Mike.  Don't know whatever happened to him.  If you're out there somewhere, please contact me.

"I've put together a number of phasers and BBD fx boxes over the past couple of years.  The two most recent use the unbuffered 4049 CMOS hex inverter chip.  Most of the different 4049's I've tried seem to work - the bias might need to be changed for different manufacturers.  Have obtained as good results as any by using  recently manufactured Motorola MC14049UB's.  Built the ETI phaser but modified the layout so regen is available.  Comments: very noisy - but nice sounding sweep.  The matching between the internal MOSFET's is probably quite good as the sweep sounds consistently even and intense with the regen turned up - moreso than with LDR phasers, where matching is difficult.  Trouble with the FET/MOSFET phasers is that the audio signal must be kept very small where applied to the FETs - around 100mV p-p max, in order to avoid excessively nasty sounding distortion.  The distortion results from the audio signal modulating the bias voltage on the FETs - hence is worst at "the bottom of the sweep" where the control voltage is smallest.  The ETI phaser attenuates the 1V p-p input to about 100mV p-p, applies it to the allpass chain, and then boosts the output back to 1V p-p with a 10x amplifier. (might have been x20, I don't have the circuit in front of me right now).  This x10 amplifies any noise already present.  Regen makes the noise more apparent.  The next PCB was for the same basic circuit but with drain to gate AC feedback on each MOSFET in the chip.  I will describe how it's done.  In the ETI phaser, all the gates are directly connected.  In my unit (this technique is used on the Aria and Pearl phasers), each gate is connected to its own 470k resistor, and the ends of all the 470k resistors are then tied together and connected to the bias/LFO circuit.  In addition, each MOSFET has a series 470K+4n7 connected between the drain and gate (in conjunction with an allpass capacitor value of 4n7 or 10n).  This configuration helps to reduce the distortion, approximately 500 mV p-p can now be applied to the allpass chain, with a 2:1 attenuator at the input and a 2x gain at the output.  Noticeably less hiss.  However, some distortion is still present at the bottom of the sweep.  This is most noticeable with buzzy, high-pitched synthesized string sounds when the regen is turned up.  I think part of this is due to the 1458's (or 741's) being operated at ecessively low voltages (from a 9V battery!).  Modifying the circuit to run on +/-9V or +/-12V *MIGHT* improve things a lot (that's the next step!).  Another thing I am not sure of yet is whether or not this technique makes the distortion come on fast and strong once the compensation is unable to correct any more, as compared to the basic ETI circuit.   Using 741's or 1458's seems like a terrible idea, with lots of new op amps out there.  Many of the old phasers used these chips.  But the allpass stages operate the op amp in unity gain, so there is lots of bandwidth available for the treble end, even with the 741.  Unity gain also implies that the noise contribution from the op amp is minimized.  Using quieter op amps for the gain stages would help reduce the noise further.  Faster op amps also like to oscillate at ultrasonic frequencies in the circuit - tried TL072's and NE5532's.  Being able to drive a capacitive load might be a factor here.

Regarding number of notches - they all sound good!  Except for single notch Phase 45 type stuff, where regen can't be used.  Tried 1 notch to 8 notches - 3 notches is my general purpose favorite.  More notches produce more of a "rippling" effect as the phaser sweeps, vaguely reminiscent of flanging.  Hope there is some useful info here - will send soe schematics later.  Regards, Mike"