Monitoring Amplifier モニターアンプ P2: Tone Controls

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Hello, こんにちは,


In a previous article I wrote about a monitoring amplifier i want to build. This weekend i could continue with this and i built the tone control circuitry. It is a Baxandall type but the values are a little atypical as i made this tone control tailored for my needs.


I wanted controls that can help in a large format 2 way loudspeakers employing a crossover frequency around 1kHz. I need a shelving filter that can gradually bring up or down that range. Below is the schematic and the graph showing the maximum boost-cut levels.

Schematic of Tone Control Circuit

Schematic of Tone Control Circuit

Tone control range

Tone control range

The schematic represents 1 channel and it is not showing two 100n/63V polyester film capacitors used to decouple TL074 power rails.

List of Materials
# Component Quantity
1 TL074 1
2 C 100n/63V Polyester Film 2
3 R 10k 10
4 R 4k7 4
5 C 47n Polyester 4
6 C 10n Ceramic 4
7 C 150p Ceramic 2
8 Pot Dual 33k 1
9 Pot Dual 150k 1
10 Molex Connector 8 pin 2
11 6 pin header 1
12 Prototype Board 1

I didnt include the 3 pin Molex connector for input you will see in the pictures as i use it temporary to connect 2 RCA female plugs to it. Below you can see the picture of the circuit. It is a bit annoying soldering the SMD components on the prototype board but not a big problem. Since this is a high gain circuit grounding needs increased attention.

tone control circuit トーンコントロール回路図

tone control schematic トーンコントロール回路図


tl074 and caps TL074オペアンプ

SMD resistor

8 pin molex

Connection between boards will be made with a 6 wire shielded cable. This cable type is often used in home security installations like alarms systems and has each of the wires individually shielded.

シールドケーブル shielded cable


The shields are tied together and grounded to one side of the cable only as signal ground is carried on one or more of the six wires. Used thermoretractable tube to isolate the open shield cable end.

shielded cable molex connector シールドケーブルMolexコネクタ


Using the line input of the soundcard i could measure the response of the tone control circuit. As can be seen it is very close to the predicted response. At the bass boost you can see the line getting flatter towards the end because of saturation.

TL074とトーンコントロールオペアンプの周波数応答 Measured Tone Control Response


Here is a picture during tests:

Monitoring Amplifier LM3886 モニターアンプ


The bass control indeed it is just right, at low volume levels you can still get the deep bass without going through walls.

Thank you for visiting,


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