ETI Magazine Guitar Note Expander

[edvard]

I've finished re-drawing this cool little circuit from a 1981 issue of ETI Magazine.
Makes novel use of the FET's in a CD4007 chip.
http://www.aronnelson.com/gallery/main.php/v/edvard/guitarnoteexpander.png.html

Enjoy!

[slacker]

That looks pretty interesting. Have you tried it?

[nick d]

              Hey , I remember building this way back! (about '82 ?) As I recall , the straight OD and compression were favourite , some of the other settings just variations on a theme .Could be a good tweaking exercise , have a go!

[caspercody]

Looks interesting. Kind of like the Catalinbread Hyper Pak. I have been looking into that pedal to build some day.

[edvard]

Nick, good to hear from someone who actually built the thing.
Glad to hear the OD/Compressor part works well, I currently have this project on the back burner but have put together a pcb with all the 'expand' bits eliminated.
Was the Expand function really all that boring?

I agree this circuit is ripe for mods though, as all the important bits are packed in the one IC.
Maybe add an oscillator for tremolo, wire up a jack for external control, tweak the 'expand' bit to be more like a noise gate, etc, etc.

I'll have a look at the Catalinbread too, never heard of it myself.

[nick d]

             Well , it was a LOOOOONG time ago.......I do remember a very valve-type sound with plenty of sustain , perhaps the other stuff wasn't to my taste at that time - it was the 80's!!!!
             Might be worth another go----when I finish these other 3 projects!!!!!

[StephenGiles]

I breadboaded it and found it to be quite useless I'm afraid.

[edvard]

Useless?  
Are you saying it doesn't work, it sounds bad or some combination of the two?
Did you try all the different variations?
Perhaps I made a mistake in the re-drawing (checking now)?

Oh dear, this won't do at all...

[jrod]

SW2a only shows 5 positions, while SW2b shows 6. 

[anchovie]

SW2a's pointer is on position 2 - look to the left of it.

[nick d]

                 Looking at the article , the switch positions are:-
                       
                        1) Overall overdrive
                        2) Overall compression
                        3) High-frequency compression
                        4) Overall expansion
                        5) Mid-expansion
                        6) High-frequency expansion

                         All variable (via VR 1)  except for straight overdrive ( 1)
                         
                         Hope this sheds a little light.

[kaycee]

Hi, I'm interested in having a go at this one, but I'm not familiar with op-amp schematics. Can anyone tell me what the circles at the tips of the op-amps mean? Other than that I should be able to breadboard this and progress to a vero.

many thanks for any help.

[edvard]

Those aren't op-amps, they're inverters.
http://en.wikipedia.org/wiki/Inverter_(logic_gate)

In this application, it's roughly equivalent to a standard op-amp wired in inverting mode.
http://en.wikipedia.org/wiki/Inverting_amplifier#Inverting_amplifier

Drawing the connnections as such makes it easier to visualize the circuit rather than showing connections to the legs of the pins.
If you end up breadboarding this, just make sure the pin numbers as shown on the schematic all go the the right places and you should be good.
If you have access to a library with back issues, there is a PCB pattern to accompany the article, I just thought I'd clean up the schematic to post for discussion here.

[kaycee]

Thanks Edvard, much appreciated

I suspected that they weren't op-amps, but didn't know what else they might be - thanks for the links, I'll take a look and edumacate myself a bit!

So, on IC1B pins 1 and 5 are tied?

Whenever I play with chips, it usually means the liberation of some of that magic black smoke....

[edvard]

Whenever I play with chips, it usually means the liberation of some of that magic black smoke....

Hehe, me too  

So, on IC1B pins 1 and 5 are tied?

Correct.
Technically, the 4007 chip is called a "Dual Complementary Pair and Inverter".
Looking at the chip schematic (link, page 2), we see that inside there are six transistors; 3 P-channel mosfets and 3 N-channel.
One N-channel and one P-channel arranged one on top of the other with inputs tied together makes an inverter.
In the 4007, one P-N pair is hard-wired as an inverter, and the others have the drains left separate.

Tying pins 1 and 5 together connects the drains of one of the free pairs, creating another inverter (IC1b), and only one transistor of the 2nd pair (IC1c) is then used in the Automatic Gain Control (the "compressor" part) of the circuit.

The 4007 is an odd duck of a chip, to be sure, but it's uniqueness is what makes it so useful.
Let me know if you build this how it sounds; I let the smoke out of the last 4007 chip I had before I could get around to this baby