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You are making a simple preamp for the guitar pickup. Since the circuit has no distortion diodes to reduce the level and has no volume control then you should use low gain in the circuit to prevent the output of the opamp from producing massive clipping if you play the guitar loudly.
My observation of the distortion diodes in the "overdrive opamp circuit" is that they limit the level of the signal at the output of the opamp to 0.7V peak. Then the signal has no dynamic level changes that occurs in all other music.
My observation of the distortion diodes in the "overdrive opamp circuit" is that they limit the level of the signal at the output of the opamp to 0.7V peak. Then the signal has no dynamic level changes that occurs in all other music.
With a guitar pickup feeding an opamp with a gain of 201 times and with nothing (no gain control) to limit the opamp output voltage then the opamp output will be severely clipped squarewaves with a level so high that the speaker amplifier volume control might be difficult to turn down.
If the speaker amplifier plays the guitar well without an added preamp then your new preamp needs no gain (use the gain of 2 times) until you add the distortion diodes.
If the speaker amplifier plays the guitar well without an added preamp then your new preamp needs no gain (use the gain of 2 times) until you add the distortion diodes.
Still working on this build. It's been slow because there's a few other things going on.
This question occurred to me. Given that some op amps are dual, what would happen if you used both of the? In other words, what if both outs were streamed to the Out jack and the In jack let to both + Ins? What would the result be?
This question occurred to me. Given that some op amps are dual, what would happen if you used both of the? In other words, what if both outs were streamed to the Out jack and the In jack let to both + Ins? What would the result be?
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- Nov 17, 2011
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You mean connect them in parallel? "+" to "+", "-" to "-", "out" to "out"?
Please don't. As no two amplifiers are 100 % identical this will result in stray currents and unpredictable behavior.
You can do this if you use current balancing resistors in the output circuit. But:
In this circuit there's nothing to gain from the parallel connection of the opamps.
Please don't. As no two amplifiers are 100 % identical this will result in stray currents and unpredictable behavior.
You can do this if you use current balancing resistors in the output circuit. But:
- The resistors will increase the output impedance, thus reducing the available output voltage (depending on the impedance of the load).
- The gain will not increase (as you may expect).
- Max. output current is increased (limited by the current balancing resistors), but current is usually not the limiting issue in an application as yours.
In this circuit there's nothing to gain from the parallel connection of the opamps.
Squarewaves sound like squarewaves don't they?
I think the small difference between all the opamps is caused by their different input resistances.
The diodes in the negative feedback produced "soft" distortion and the diodes at the output of the opamp to ground and the opamps themselves (when the input volume control was turned down) produced the "hard" distortion.
I think the small difference between all the opamps is caused by their different input resistances.
The diodes in the negative feedback produced "soft" distortion and the diodes at the output of the opamp to ground and the opamps themselves (when the input volume control was turned down) produced the "hard" distortion.
I built the circuit using the gain 2.0 version, and it does not work.
I popped in the 4558D op amp, and yes, I did buffer the second op amp.
Here are my PIN readings:
PIN
1 8.25. (OUT)
2. 4.10. ( - IN)
3. 4.16. (+ IN)
4. 0. (GROUND)
5. 4.16. (second op amp + IN)
6. 4.55 (second op amp - IN)
7. 4.55. (second op amp OUT)
8 9.02. (VCC +)
I also connected pins 7 to 6 and I ran a wire from the biased half/ voltage to Pin 5 to silence the second op amp
Not sure why I am getting no sound.
I popped in the 4558D op amp, and yes, I did buffer the second op amp.
Here are my PIN readings:
PIN
1 8.25. (OUT)
2. 4.10. ( - IN)
3. 4.16. (+ IN)
4. 0. (GROUND)
5. 4.16. (second op amp + IN)
6. 4.55 (second op amp - IN)
7. 4.55. (second op amp OUT)
8 9.02. (VCC +)
I also connected pins 7 to 6 and I ran a wire from the biased half/ voltage to Pin 5 to silence the second op amp
Not sure why I am getting no sound.
The voltage of pin1 is as high as it can go but should be at half the supply voltage. Here is my guess why:
Attachments
I installed the capacitor and the circuit works!!!!!
I typically use a very small guitar amplifier for testing purposes. It is a very small Orange amp that sits on my desk.
When I plugged the guitar through the circuit and played, it did not sound like I had any sound. At that point, I was playing through the amplifier clean (in other words- the guitar amp did not have its distortion dial turned up- it was set to just play the signal cleanly).
When I turned up the distortion dial on the guitar amplifier, I heard the guitar signal.
To get the circuit sounding louder, do I now build it with the 201 gain?
I typically use a very small guitar amplifier for testing purposes. It is a very small Orange amp that sits on my desk.
When I plugged the guitar through the circuit and played, it did not sound like I had any sound. At that point, I was playing through the amplifier clean (in other words- the guitar amp did not have its distortion dial turned up- it was set to just play the signal cleanly).
When I turned up the distortion dial on the guitar amplifier, I heard the guitar signal.
To get the circuit sounding louder, do I now build it with the 201 gain?
Please show a schematic with all parts values. Maybe the input resistor value is too low and reduces the pickup output.
The 220nF capacitor to ground in series with the 10k resistor at pin2 cuts 73Hz at -3dB (half the output power). Use 470nF for -3dB at 34Hz. If the resistor from pin2 to the capacitor is 1k then the capacitor value must be 10 times higher.
The ratio of the resistor values between pin 2 and the pin1 output, and from pin2 through the capacitor to ground, determine the voltage gain.
The 220nF capacitor to ground in series with the 10k resistor at pin2 cuts 73Hz at -3dB (half the output power). Use 470nF for -3dB at 34Hz. If the resistor from pin2 to the capacitor is 1k then the capacitor value must be 10 times higher.
The ratio of the resistor values between pin 2 and the pin1 output, and from pin2 through the capacitor to ground, determine the voltage gain.
Hi AG
I have attached the schematic and values. Please note the following:
I have not shown the voltage divider. It is exactly built from the original schematic. So the 1M resistor that carries the haled voltage is not shown, but it is part of my circuit.
I circled another component that I missed - (see red circle). I forgot to install the 1uF capacitor that comes just before the Out.
I will install that, once I hear back as to next steps.
Thanks
I have attached the schematic and values. Please note the following:
I have not shown the voltage divider. It is exactly built from the original schematic. So the 1M resistor that carries the haled voltage is not shown, but it is part of my circuit.
I circled another component that I missed - (see red circle). I forgot to install the 1uF capacitor that comes just before the Out.
I will install that, once I hear back as to next steps.
Thanks
Attachments
I don't know if you could hear this, but this is what it sounds like through the Orange small desktop amp. I get no sound at all if I keep the amp clean. Once I dial up some distortion, I get sound (as in the linked to audio). And I'm using a Gibson Les Paul guitar, which, on the best of days sounds like it woke up pissed off -).
https://drive.google.com/file/d/17bZTD6ZnpBGUemgkvRfx5yMYzoX3TeIF/view?usp=sharing
https://drive.google.com/file/d/17bZTD6ZnpBGUemgkvRfx5yMYzoX3TeIF/view?usp=sharing
Hi guys....now that things are starting to show signs of working, I plan to do a build from scratch. Mainly because I slapped the current build together and it's sloppy.
So....I think I;d like to take the current approach whihc means building the voltage divider and the op amp portion, and making sure it works prior to installing diodes.
However, because I want to go for it again, I'd prefer to start with a design that contemplates going full blown. So, should I be using the 201 Gain design that AG posted?
So....I think I;d like to take the current approach whihc means building the voltage divider and the op amp portion, and making sure it works prior to installing diodes.
However, because I want to go for it again, I'd prefer to start with a design that contemplates going full blown. So, should I be using the 201 Gain design that AG posted?
The gain of the opamp is needed to overdrive the diodes for them to produce clipping of the signal or so that the output of the opamp produces clipping. Use as much gain as you want. You might like the sound of the opamp clipping like crazy without the diodes.
ok..so if I understand you correctly, I can go with the 201 gain and this will better facilitate the diodes addition and clipping. In that schematic that I am working with (which now is a mix of that schematic and yours), can I use LEDs as diodes, or does it have to be the IN4148s?
Not entirely related question.... I've seen some guitar stomp box circuits start with a buffer stage where they use a transistor to achieve buffering. What does buffering mean in this context? Why utilize a transistor driven buffer? This is prior to the signal proceeding to the op amp stage.
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