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Op Amp Substitute?

bertus

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Nov 8, 2019
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Hello,

The replacement of the opamp with an 4558 would not be a problem.
You can also run the circuit on 9 Volts, as the CD4093 will work upto 12 Volts.

Bertus
 

Audioguru

Sep 24, 2016
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The circuit in the video produces noises, not theremin music. The squarewave output will sound like a variable-pitch buzzer.
A theremin hand-distance volume control is missing.
I think static electricity in winter will destroy that very simple circuit.
The output volume control badly has DC in it because the output capacitor is in the wrong location.

The very old 4558 opamp needs a 10V minimum power supply but the newer MCP602 uses a 5V supply.
You can power the 4558 and CD4093 with a 10V or 12V DC power supply.
The unused opamp in the MCP602 dual opamp and unused gates in the CD4093 are not properly disabled.
The resistor values used with the opamp are low enough that any opamp can be used.
 

Audioguru

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The minimum supply for your Japanese NJM4558 is 8V which a 9V battery will soon drop below.
Texas Instruments recommend a minimum of 10V for an RC4558.
 

SparkyCal

Mar 11, 2020
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I was going to attempt this, but there are two problems:

1. I only have one 4093 chip, however, it came in a kit that has one 4093 chip and one 4094 chip. I am not sure if the 4094 can be used in place of the second 4093?

2. I also note that his data sheet calls for 2 10K potentiometers. but the schematic seems to show a 100K pot (TM2) and a 10K pot TM1. I wonder if the 100K is a typo.
 

VenomBallistics

Aug 30, 2018
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I was going to attempt this, but there are two problems:

1. I only have one 4093 chip, however, it came in a kit that has one 4093 chip and one 4094 chip. I am not sure if the 4094 can be used in place of the second 4093?

2. I also note that his data sheet calls for 2 10K potentiometers. but the schematic seems to show a 100K pot (TM2) and a 10K pot TM1. I wonder if the 100K is a typo.
sounds like you need a deeper parts mine and you may have a sketchy project too.
Get a few different schematics so you have a plan B.
Personally, I've been gathering parts for an exotic PT2399 delay ... Like yourself, I'm coming up a bit short on a few things.
Power supply is interesting. 9V in ... +18/+4.5/-9 out for the analog rails. +5 to feed the digital.
PIC micro for the brains of the operation .... should make some nice smoke.
 

Audioguru

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The Instructables circuit does not use a CD4094 and needs only 2 of the 4 logic gates in one CD4093.
The 2 unused gates in the CD4093 are not properly disabled.
 

SparkyCal

Mar 11, 2020
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Sounds like this can’t happen unless I has two of those chips. Thanks for the advice.
 

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The perfboard photo in the Instructable shows one CD4093 IC with 14 pins and 4 logic gates in it but only 2 of the gates are used. It also shows one dual opamp with 8 pins but only one of the two opamps is used.
 

VenomBallistics

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I think I remember that bundle from way back.
You will need ghostscript to view many of the files in that archive ... but that tube overdrive looks like a potentially interesting springboard.
 

SparkyCal

Mar 11, 2020
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Thank Bertus. Yes, I see there are a few files with theremin schematics and explanations. I have a growing list of potential projects that I'm not sure I'll ever get to lol. But great to have choices.

I think my next venture, is to try to use everything I learned about pedal building, and try for a final build. This is because I have now received three steel professional looking pedal boxes, that come with a PCB, a step drill bit and templates. But before I =do that> I plan to breadboard the stomp box switch. I have never used the 9 pin switch that is found on cost all boxes, and so I plan to wire that on a breadboard first, along with a LED. I may need help figuring out what step down resistor I need for a blue LED. I know most boxes use red LEDs, but I think a blue one would look sharp- especially since the case are silver.
 

VenomBallistics

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I may need help figuring out what step down resistor I need for a blue LED. I know most boxes use red LEDs, but I think a blue one would look sharp- especially since the case are silver.
be a bit open minded about color choice. Blue looks lovely, but it also has a lot of glare. This may prove annoying depending upon your lighting situation.
 

SparkyCal

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The LED is basically used by the guitarist to take a quick glance to make sure the box is working and activated. I suppose if you look at anything too long, it will be annoying. You may be right however. If it turns out to be an issue, I can always swap it out.
 

VenomBallistics

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The LED is basically used by the guitarist to take a quick glance to make sure the box is working and activated. I suppose if you look at anything too long, it will be annoying. You may be right however. If it turns out to be an issue, I can always swap it out.
I was thinking more along the lines of why so many amps are still built with 1940's style "chicken head" knobs.
In most live venues, light is at a premium. Chicken heads, most often can be glanced at to confirm settings.
pedals are at the far end of the visibility spectrum where we are blessed if we can make out the knobs at times. Add enough glare and that can become a write off.
 
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