Hello all, this is my first post here.

I have designed a custom 12V battery, along with a LM386 amp circuit, which allows me to play my guitar through an 8ohm speaker fairly well

However, when switching pickups from humbuckers to single coils, the audio starts to clip and distort

How can I make an impedance matching circuit using a TL072 op amp?

All the relevant circuits that I found online seemed to be for applications much more powerful than mine.
My application is simply to have the electric guitar be clean when the default gain of the 386 is 20, and then distort ONLY when I manually increase the gain

From what I understand, a unity gain buffer must be made

This is the 386 circuit I am using:

 

The LM386 dates back to the early / mid 80s. I would have gone with something newer. However, what you have is close. The clipping is a result of overdriving. I would go with a 10K pot on the input. I would use maybe a 220 uF cap on the output. Not sure what you have going on with Pin 6 and your Vcc? The 100 uF decoupling cap is fine assuming a good clean DC supply. You may want to give this a read. Yes, you can add a buffer using any old chip like a TL072 for the buffer. A Google of "tl072 buffer circuit" will give you some examples.

Ron

 

How can I make an impedance matching circuit using a TL072 op amp?
From what I understand, a unity gain buffer must be made.

Suggest value changes on C4, C5 and add R4 in the LM386 circuit as well.

 

The LM386 dates back to the early / mid 80s. I would have gone with something newer. However, what you have is close. The clipping is a result of overdriving. I would go with a 10K pot on the input. I would use maybe a 220 uF cap on the output. Not sure what you have going on with Pin 6 and your Vcc? The 100 uF decoupling cap is fine assuming a good clean DC supply. You may want to give this a read. Yes, you can add a buffer using any old chip like a TL072 for the buffer. A Google of "tl072 buffer circuit" will give you some examples.

Ron

Unfortunately I was not able to find a 10k pot where I live

With the VCC, the positive 12V battery goes to pin 6, and in parallel is a 100uF capacitor connected to the ground

For the TL072 circuit, I had a doubt,
I am using only a single battery source, whereas the TL072 diagrams I see indicate 2 batteries, what can I do to make this work with a single source?

 

Suggest value changes on C4, C5 and add R4 in the LM386 circuit as well.
View attachment 357572

Thankyou so much for the schematic!

If I am understanding correctly, I have to use two TL072 chips in order to make this buffer?

 

No, the TL072 has two independent amps inside.
Or use a TL071.

 

No, the TL072 has two independent amps inside.
Or use a TL071.

Oh!

I did not read the 1/2 before the TL072

So basically, I have to connect that pin 1 to pin 5 and then continue, is that right?

 

Oh!

I did not read the 1/2 before the TL072

So basically, I have to connect that pin 1 to pin 5 and then continue, is that right?

Don't really need two buffers in series but not good practice to leave the unused amp "floating"
Another option.

 

Don't really need two buffers in series but not good practice to leave the unused amp "floating"
Another option.
View attachment 357580

Could I use the first circuit diagram you provided, but simply ground the pin 5 to the ground, while connecting pin 6 to 7, in order to disable the 2nd op amp?

 

It's recommended that the positive input pin be biased at half the supply voltage which is the reason for R4 and R5.
I suppose it would be OK to connect pin5 to pin3 and eliminate R4 and R5

 

It's recommended that the positive input pin be biased at half the supply voltage which is the reason for R4 and R5.
I suppose it would be OK to connect pin5 to pin3 and eliminate R4 and R5

So, directly connecting pin 5, to the two 1M resistors, R1 and R2?

 

So, directly connecting pin 5, to the two 1M resistors, R1 and R2?

Correct!

 

Correct!

Hello!

I built the schematic that you provided, by connecting pin 5 of tl072 to pin 1, and then taking the output from pin 7 through the 10uf capacitor and to the lm386

However there is a problem, when I strum my guitar, the audio distorts, and disappears for a second and then comes back.

What can I do to fix this?

 

The tl072 is a fet op-amp. I would design an extremely high input impedance pre-amp, almost infinite, that puts absolutely no load on your single coil or your humbucker coil. Under these conditions, your coil may develop some high voltages. This is a 30 volt device, and your coil may be producing 100's of volts. This is conjecture, but perhaps a impedance matching transformer, with an input winding that matches your pickup, and an output winding of much higher resistance, to match the input impedance of your op-amp.

 

I built the schematic that you provided, by connecting pin 5 of tl072 to pin 1, and then taking the output from pin 7 through the 10uf capacitor and to the lm386

Did you connect pin6 to pin7 at the output?

 

Did you connect pin6 to pin7 at the output?

Hello, yes, the pins are connected

And also, I tried another thing where I connected pin 5 to the ground, and took the output from pin 1

And that fixed the sputtering problem

But the distortion even at the lowest gain but full volume still persists

 

Clipping distortion is caused by driving a stage beyond it's linear range. Adding more gain in front of that stage will not solve te problem. Having the amplifier zero-signal output biased to other than the middle of the range will reduce the maximum amplitude that can be delivered without clipping.
Besides all of that, a low supply voltage will reduce the output voltage that can be delivered without clipping.