How to Modify 150 Watt ocl power for the subwoofer so that the sound is more jarring

How to Modify 150 Watt ocl power for the subwoofer so that the sound is more jarring

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The 150 Watt ocl amplifier circuit is one of the phenomenal power amplifier circuits, because of the popularity of this circuit, many electronics hobbyists create and modify this amplifier circuit.

In general, any power amplifier circuit c...

The 150 Watt ocl amplifier circuit is one of the phenomenal power amplifier circuits, because of the popularity of this circuit, many electronics hobbyists create and modify this amplifier circuit.

In general, any power amplifier circuit can be modified and used as a special subwoofer amplifier. No exception to this 150 Watt ocl amplifier kit. Then how do you modify the 150 Watt ocl power for the subwoofer so that the resulting sound can be more jarring and optimal? let's look at the explanation below.

Overview of the 150 Watt ocl power amplifier circuit

The 150 Watt OCL amplifier circuit or kit has a fairly simple circuit construction making it easy to build at a fairly affordable cost. For audio enthusiasts, this is one of the strongest advantages for novice audiophiles who are learning to assemble electronic circuits.

There are many 150 Watt ocl power amplifier kits available with different PCB layouts and shapes. However, in principle the circuit schemes are not much different and relatively the same. Usually what makes the difference is the quality of the components, the type of final transistor (final) and the PCB layout which is wrapped in an attractive and neat packaging.

The following is an example of a 150 Watt amplifier kit.

150 watt amplifier kit

150 watt amplifier kit 2

Definition and use of a subwoofer in an audio system (sound system)

Before modifying the amplifier that we have into a subwoofer amplifier, first we know more closely what a subwoofer is. In general, there are 4 types of sound produced by speakers. Namely twitter, medium, woofer, and subwoofer.

The subwoofer is a device that can produce the lowest tones in the audio spectrum. Typically subwoofer tones range from 20 Hz to 200 Hz. Because the subwoofer produces a low tone, of course the sound that will be produced is only the bass tone.

The subwoofer device in question can be a subwoofer loudspeaker, subwoofer amplifier, subwoofer filter and so on. In audio devices, the subwoofer tone will help increase the bass boom so that the resulting sound will be more blaring and booming.

High-power subwoofers are widely used in audio devices or field sound systems because they have to cover a wider radius, while low-power subwoofers are widely used in room audio devices, home theater and others.

But in principle, it is the same, namely both producing very low bass tones. The difference lies in the amplification power of the amplifier to reach a certain radius.

In the context of this 150 Watt ocl amplifier circuit or kit, it can be categorized as a field subwoofer device with a medium radius distance. However, it can also be used indoors with the note that the volume level is not set too high.

How to modify 150 watt ocl power for the subwoofer

This 150 Watt ocl amplifier is a multifunctional amplifier. This means that this amplifier kit can be used for any purpose related to amplification, such as an outdoor amplifier with a not too wide range, or a home theater to produce blaring multimedia with a booming bass effect.

In order for the 150 watt ocl amplifier kit to be used as a subwoofer amplifier, there are a number of things that must be modified to create a really solid bass sound and reduce sound frequencies other than 20 Hz to 200 Hz.
Use a good quality subwoofer kit / module

The 150 Watt OCL Amplifier is just an ordinary power amplifier that when used without any filters will produce a flat sound, which tends to produce a dominant vocal tone compared to the bass tone.

Therefore, to be able to produce just a bass tone that is amplified through this amplifier, it is necessary to use an additional circuit called a subwoofer filter.

This subwoofer filter can be in the form of a ready-made kit or module so that it can be used immediately. The function of this subwoofer kit is, of course, as a filter, more precisely, it is a low pass filter that can pass lower frequencies and block medium to high frequencies. Thus, after the audio signal passes through this subwoofer filter, only low frequency bass signals will be amplified.

There are many different types of subwoofer kits or modules in various designs. Some use transistors completely, some use ICs. In fact, not infrequently the subwoofer kit / module consists of a combination of IC and transistors. The following are some examples of subwoofer filter kits on the market.

150 watt ocl amplifier circuit ready to be modified

There are many types and types of subwoofer filters or pre-amps. Ranging from simple to quite complex. But usually even the best subwoofer filters don't really have a complex circuit. The best option is to use a subwoofer filter or pre-amp that uses a MOSFET IC such as TL084, a metal resistor that has a tolerance of 1%, and a special audio mylar capacitor.

However, the selection of component quality is only one aspect that determines the quality of the resulting audio, it is not the best guarantee because there are other aspects such as circuit design, audio response measurement results, and the experience of listening directly to the resulting audio.

Modify amplifier components

Here you already have a benchmark for choosing the best subwoofer filter or subwoofer pre-amp. Next is the modification of some components of the 150 Watt OCL amplifier. The purpose of this modification is actually to adjust the desired gain value with the voltage from a given supply.

In general, the 150 Watt OCL power amplifier uses a symmetrical DC power supply voltage between ± 25 Volt to ± 35 Volt, depending on the type of final transistor used. Basically, you actually don't need to modify any passive components in this amplifier circuit. What you have to modify, or rather "replace" is the driver transistor component with a higher power. The goal is to produce a higher thrust to the final transistor, so that the output power generated can also be optimal.

But there are some people who replace some passive components which according to the experience of some people who have tried, modifying the passive components get better audio results. However, if you want to modify some of the passive components, which will be described later, it is advisable to measure the frequency response and the resulting distortion level, before and after modifying the value of the passive components in the 150 Watt OCL amplifier circuit which will be used as a subwoofer.

speaker protector kit 2

Actually the 150 Watt ocl amplifier circuit as shown in the picture above already has a pretty good design, therefore if you don't really understand how this amplifier circuit works, too many component modifications don't need to be done.

From the components above, you can see an arrow that you can modify without changing the audio frequency response much. This component modification will only help to strengthen the power that will be released by the loudspeaker, especially the bass tones which usually require more power than the amplification of high or medium tones. So it is hoped that the modification of this component will make the resulting audio more stable.

The following is a modification of the 150 Watt ocl amplifier circuit components to be used as a subwoofer amplifier:

Replace all resistor components with a resistor that has a tolerance of 1%, is usually blue and has 5 colored bands.
Replace all elko with a special elko brand audio or higher quality. Usually the built-in 150 Watt ocl amplifier kit is fitted with passive components that have makeshift quality to reduce production costs. For capacitors other than elco, you can use the mkt type capacitor.
Replace the 100nF capacitor component value as shown in the arrow in the circuit with a value of 220nF. And replace the 47uF capacitor as in the arrow with a value of 100uF.
Then you can replace the BD139 and BD140 transistors with the values ​​D313 and B507. Both transistors of this type have higher power and are more heat resistant. By replacing the default driver transistor, it is hoped that the audio signal can be more "push" against the final transistor (Final).
If necessary, replace the 2N3055 and MJ2955 final transistors with better quality such as the Sanken brand. Because there are several brands and qualities of transistors in circulation. Usually the inferior quality final transistors will not last long. Especially when working at maximum voltage.

One more thing to note is the aluminum cooling fins used. Often times the built-in 150 Watt OCL amplifier kit or module is only provided with a makeshift aluminum cooler. When the amplifier works at maximum, it is feared that the thin aluminum cooler will not be able to withstand the heat dissipation generated by the transistor. For that you can replace the aluminum cooler with a thicker cooler.

Modify the power supply for the subwoofer amplifier

The power supply circuit for the amplifier, in principle, is the same and the difference is not too far away. However, because the amplifier circuit must produce a clear sound without any hum from the power supply. then use elko with a value of 10.000uF / 50V and above. Or you can also use elco 10.000uF / 50V which are parallel as many as two or 4 pieces.

For the recommended transformer is a transformer with a minimum of 5A pure or using a toroidal type transformer. The greater the amperage of the transformer used, the better and minimizing the voltage drop when the amplifier is working at its maximum.

Especially for the subwoofer filter power supply, you should use a separate transformer from the Amplifier transformer. Since the subwoofer kit does not require large currents, a transformer with a current of 1A is more than sufficient. However, the thing that must be considered in the subwoofer filter power supply is the type of regulator used. It is recommended to at least use the 7812 IC regulator to minimize hum and noise.
Selecting the Loudspeaker Type for the subwoofer

An ordinary amplifier can be used any type of speaker, as long as the power specification of the loudspeaker is able to accommodate the power output from the amplifier. However, unlike a subwoofer, you must use a subwoofer type speaker because this type of speaker will be optimal for the bass tone that will be issued.

In addition, special type subwoofer speakers usually have a thicker type of diaphragm rubber so that they are more elastic. There are many brands and variations of subwoofer type speakers. In this case, you can buy them according to your power and needs, from the cheapest to the most expensive. The 150 Watt OCL amplifier circuit that is used as a subwoofer can push the subwoofer speakers up to 12 inches properly without any problems.

Use a speaker protector circuit

How to modify the 150 watt ocl power for the subwoofer will not be separated from the speaker protector kit. A power amplifier circuit can work at a maximum voltage of up to +/- 35V. Even for amplifiers with higher power, for example 500 Watts or 1000 Watts requires a higher supply voltage of up to +/- 50 volts.


The OCL type amplifier circuit has an output circuit that is directly connected to the loudspeaker via the transistor leg without capacitor coupling. This makes advantages and disadvantages. One of the drawbacks is that when a part of the transistor is damaged and short, the DC voltage will immediately come out through the output section connected to the speaker.

As a result what happens is the speaker with a resistance of 4 to 8 ohms will be energized by DC voltage. And of course this is very dangerous and will immediately damage the speakers. To prevent this, a speaker protector circuit is used.

In addition, the speaker protector function is to prevent burst voltage (DC) when the amplifier is turned on. So that by using a speaker protector kit or circuit, the loudspeaker will last longer. That's how to modify the 150 watt ocl power for the subwoofer.

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