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What does this IC do in the circuit?

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  • What does this IC do in the circuit?

    The integrated circuit in question (IC4 on the attached schematic) is a CD4007UBE CMOS Dual Complimentary Pair Plus Invertor. What does it do in the circuit?

    Attached Files
    Last edited by Axtman; 01-14-2021, 06:08 AM.

  • #2
    Look at the data sheet for the part, it is just a logic gate used as a gain stage. It has three push pull stages wired in parallel. As long as it has power supply, it should pass signal.
    Education is what you're left with after you have forgotten what you have learned.


    • #3
      The use of the CD4007UBE begs the question, why? The preamp is full of opamps so they could have used one of those to get the gain of three, same as the 4007UBE. I think the clue is in the data sheet. Take a look at the plot of Vout vs Vin:

      Click image for larger version

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      You can see that at as the output voltage approaches the limits, the plot is very rounded. In other words, when driven hard the output doesn't clip hard but is rounded so arguably produces a pleasant sounding overdrive sound. Also note that at higher supply voltages the the supply current increases quickly and that is likely why they chose a lower supply voltage.
      Experience is something you get, just after you really needed it.


      • #4
        There is an old ap note from National Semi about using CMOS gates as linear amps. The 4007 just gives you some access to the individual MOSFETs inside. You can use NAND and NOR gates too, they will give you more asymmetry.

        In the Sunn Beta Lead amps they use several inverters in parallel to drive the reverb tank.

        Attached Files
        WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
        REMEMBER: Everybody knows that smokin' ain't allowed in school !


        • #5
          Check SUNN SS amps, they were heavy users of CMOS logic gates used as amplifiers, Fender may have picked the idea from them.
          After all they bought the Company.
          Laney was another heavy Logic Inverter amp stages user.
          At one time, they were supposed to "distort like tubes" or some other nonsense.
          Not rue, but they still give you some unique distortion.
          Loved by "Stoner" rockers, go figure.

          Sunn Beta Lead Digital CMOS Technology
          Now you know what that means

          Juan Manuel Fahey


          • #6
            The last of the HH guitar amps also used a CMOS inverter IC in the audio path in the drive channel. I always assumed it was there to give tube-like overdrive, similar to the Craig Anderton Tube Sound Fuzz that uses CMOS inverters in a CD4049 to give a really nice characteristic to the clipping.


            • #7
              Thanks for your answers!

              With the amp littered with 4558 op amps, I wondered why they would bother to use a different IC. Making the solid state amp more tube like makes sense to me. From what I see on my scope it does have soft clipping.


              • #8
                These amps seem to be very highly regarded and perhaps great "sleepers."


                • #9
                  Well I can attest that the amp is does have a nice sound. The overdrive does not sound harsh like a typical cheap ss amp. Now if I can only get the reverb to work.


                  • #10
                    Apparently the Catalinbread Supercharged Overdrive (or SCOD) was built on the CD4007UBE. Sounds pretty good to me.


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