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My first experiments with CMOS started around 1980. I got a copy of the National Semiconductor CMOS data book which had a copy of AP Note AN-88 in the back. I posted a copy in post #4 of this thread:
https://music-electronics-forum.com/...in-the-circuit
I call this the Reagan Fuzz because he was elected President around that time. My first version used an opamp as a power supply regulator and a CD4007UB as the active element. The hard part was keeping the current draw as low as possible (250uA) so I used a programmable opamp, (LM4250 I think) and a reverse biased PNP junction as a low power zener diode. I still have that thing somewhere, got it back from the steel player I sold it to, but I'd have to trace out the schematic.
The next version came about after I moved to Texas in 83. It dispensed with the opamp and used a JFET current source and a big cap as a power supply for the CMOS. When you turn it on, it takes several seconds for the cap to charge up before it will pass a signal, kinda like a tube amp. For this version I used a CD4069UB and connected all the gates in parallel. Since I was using the CMOS at a very low current, I used a JFET Source Follower on the output to drive the real world since any load would reduce the gain of the CMOS. To protect the CMOS, I also used a JFET Source Follower on the input. The schematic is posted below.
The next version (also attached below) came somewhat later. I used the fact that all the MOSFETs in a CMOS chip match each-other pretty close so you can take one or two gates, tie input to output and that Voltage can be used to bias the other gates and you can run them without feedback. You can even stack the chips on top of each-other to up the gate count. More gates in parallel should lower the noise.
Some of the non-ideal characteristics of CMOS that you may have to deal with: The gain actually goes up as the power supply goes down. At 3V, gain for a single stage is around 300. At 5V it's around 100 and in the 10V to 15V range gain is about 30. The bandwidth also goes down with lower power supplies. It can go below 10KHz near 3V and up to around 5MHz at 15V. Noise is generally low, but can go up with big resistors in the inverting feedback configuration. Another thing is that when CMOS is banging rail to rail, the current it draws goes down. You can put a resistive load on it, but that will reduce the gain somewhat.
One problem I didn't solve is fizz. Under some circumstances, the CMOS fuzz can sound fizzy. I don't know if it was always there and I just didn't hear it, or if certain guitars that I don't own cause it. I have yet to hear it when I'm playing. Maybe if I recorded my playing, I would hear it in the playback.
My next experiments came around 2010. I wanted to use CMOS to more closely emulate a tube preamp. This was around the time I started using a scope in the X-Y mode to look at how a tube bends in guitar signal. I started looking at all the different ways a CD4007 could be used. I ended up using the 3 input NOR gate. With feedback it comes real close to a 12AX7. The 2 input NOR is pretty close, but I liked the 3 input better. A preamp was built, the 3 input NOR is the first stage followed by an opamp stage to boost the output of the CMOS. Next is a tweed style Volume and Tone control, then a three stage CMOS amp that I don't remember what I was thinking. Last is a bass cut control and an opamp buffer for the output. I don't think I ever sat down and tweeked that last part with a power amp connected.
Another thing that came out of all these experiments is what I call the "P Series N Series Inverter". It's a configuration of the CD4007 that isn't a normal configuration. Sort of like a NOR and NAND gate melted together. The advantage is it doesn't draw as much current as the normal inverter. At 15V, a normal inverter draws around 11mA. The PSNS inverter draws about 4.5mA, less than half. Clipping is a little softer too.
https://music-electronics-forum.com/...in-the-circuit
I call this the Reagan Fuzz because he was elected President around that time. My first version used an opamp as a power supply regulator and a CD4007UB as the active element. The hard part was keeping the current draw as low as possible (250uA) so I used a programmable opamp, (LM4250 I think) and a reverse biased PNP junction as a low power zener diode. I still have that thing somewhere, got it back from the steel player I sold it to, but I'd have to trace out the schematic.
The next version came about after I moved to Texas in 83. It dispensed with the opamp and used a JFET current source and a big cap as a power supply for the CMOS. When you turn it on, it takes several seconds for the cap to charge up before it will pass a signal, kinda like a tube amp. For this version I used a CD4069UB and connected all the gates in parallel. Since I was using the CMOS at a very low current, I used a JFET Source Follower on the output to drive the real world since any load would reduce the gain of the CMOS. To protect the CMOS, I also used a JFET Source Follower on the input. The schematic is posted below.
The next version (also attached below) came somewhat later. I used the fact that all the MOSFETs in a CMOS chip match each-other pretty close so you can take one or two gates, tie input to output and that Voltage can be used to bias the other gates and you can run them without feedback. You can even stack the chips on top of each-other to up the gate count. More gates in parallel should lower the noise.
Some of the non-ideal characteristics of CMOS that you may have to deal with: The gain actually goes up as the power supply goes down. At 3V, gain for a single stage is around 300. At 5V it's around 100 and in the 10V to 15V range gain is about 30. The bandwidth also goes down with lower power supplies. It can go below 10KHz near 3V and up to around 5MHz at 15V. Noise is generally low, but can go up with big resistors in the inverting feedback configuration. Another thing is that when CMOS is banging rail to rail, the current it draws goes down. You can put a resistive load on it, but that will reduce the gain somewhat.
One problem I didn't solve is fizz. Under some circumstances, the CMOS fuzz can sound fizzy. I don't know if it was always there and I just didn't hear it, or if certain guitars that I don't own cause it. I have yet to hear it when I'm playing. Maybe if I recorded my playing, I would hear it in the playback.
My next experiments came around 2010. I wanted to use CMOS to more closely emulate a tube preamp. This was around the time I started using a scope in the X-Y mode to look at how a tube bends in guitar signal. I started looking at all the different ways a CD4007 could be used. I ended up using the 3 input NOR gate. With feedback it comes real close to a 12AX7. The 2 input NOR is pretty close, but I liked the 3 input better. A preamp was built, the 3 input NOR is the first stage followed by an opamp stage to boost the output of the CMOS. Next is a tweed style Volume and Tone control, then a three stage CMOS amp that I don't remember what I was thinking. Last is a bass cut control and an opamp buffer for the output. I don't think I ever sat down and tweeked that last part with a power amp connected.
Another thing that came out of all these experiments is what I call the "P Series N Series Inverter". It's a configuration of the CD4007 that isn't a normal configuration. Sort of like a NOR and NAND gate melted together. The advantage is it doesn't draw as much current as the normal inverter. At 15V, a normal inverter draws around 11mA. The PSNS inverter draws about 4.5mA, less than half. Clipping is a little softer too.
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