Some help understanding a tone filter circuit

sasukenebe

New Member!
Jul 30, 2022
1
Indiana
I am new to audio circuit building, and I am using existing schematics to try and make a very simple amplifier circuit with tone control as well (consisting of a single potentiometer). I am not concerned with audio quality at this time, as I am just trying to learn, before moving to more advanced circuits. I want to construct these circuits and get them working so I can scope and test them and learn.

I have an existing LM386 based amplifier circuit (Figure 1 below) that I would like to add a tone control circuit to (Figure 2 below, with one potentiometer for sweeping).

I would really appreciate guidance regarding the following:

1) Is the tone circuit (Figure 2) a standalone tone circuit that I can just tack on to the output of my amplifier circuit (Figure 1), say after C6, before the speaker?

2) I think R45 (1milliOhm) in Tone Circuit (Figure 2) would typically be a potentiometer to control gain? This makes me wonder if this circuit is more than just a tone filter and everything at and before the op-amp is just an amplifier circuit similar to figure-1. Is the tone filter in Figure 2 then just the R/C network and potentiometer after the op-amp output?


Thanks for your time,
Greg
 

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NewUser619

Strat-Talk Member
May 28, 2022
54
New Zealand
1- yep.

2- yep. The tone pot is the big muff tone control meaning that one way on the pot is a high pass, the other is a low pass, centre is neither. It's basically panning between those 2 filters, which as you correctly stated are RC networks so you're cutting bass or cutting treble.

Before that is a simple gain stage with soft clipping and high pass of 723hz like a TS. It states a dual op amp, but only uses a single so a tl071 would work the same otherwise you'd need to tie up the other op amp, or use it as a gain recovery stage to make up for the insertion loss of the tone stack (about 20db).

You could make the 1m resistor variable without much trouble, but you might want to add a resistor in series with it so at minimal gain (all the way left on the pot) there's still signal. Otherwise you'll mute everything when you turn right down.
 

Triple Jim

Guy Who Likes to Play Guitar
Silver Member
Feb 27, 2018
8,265
North Carolina
The LM386 amplifier IC in fig. 1 is a relatively high power device that can drive a speaker. The TL082 is not, and the circuit it's in has a relatively high impedance that wouldn't drive a speaker even if the TL082 could, so no, you can't just tack fig. 2 onto fig. 1 and get something that would drive a speaker.

R45 in figure 2 is a 1 megohm resistor, so 1,000,000 ohms.

Welcome to the board, Greg!
 

CB91710

No GAS shortage here
Double Platinum Supporting Member
Feb 24, 2019
10,860
SoCal
Typically, the tone circuit follows the volume control, so a passive tone stack would go on the noninverting input of the LM386

Here's a drawing that I found back in the 90s... I think this circuit used 741 Op amps

FednerPre.jpg
 


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