How to amplify audio linearly with a few transistors

How to amplify audio linearly with a few transistors


This is for beginners and interested people. Here you see how to create a simple amplification stage with one or two NPN transistors, usable for audio and HF, most suitable for audio. The transistors are in a grounded emitter figuration. You can give every individual stage its own amplification factor by turning the variable resistor on the emitter. The right values of the resistors connected to the basis are the key to success. When you home-brew on the basis of this schematic, always use a variable resistor on the basis of each individual transistor (25 K to 50 K, try 25 K first) to set every transistor to the own correct working range. I cannot stress this enough, some schematics cannot be successfully reproduced because the author had a certain "luck" in designing these resistors. When the amplifier works correct (check it with the scope) take out the variable resistors, measure them and replace them by fixed value resistors. This schematic is usable for simple high frequency stages up to maximum approx. 10-15 MHz. The BC547 b (hfe = 300) is usable up to 8-9-10 MHz. The 2N2219 is usable as typical HF transistor, up to 15 MHz in this schematic. For higher frequencies other types of schematics and specialized HF transistors work better. The schematic is very good usable for audio applications (20 Hz-20 KHz) for instance as a microphone amplifier. In that case often 1 stage is enough. You can set the amplification between 2 and approx. the maximum that the transistor can give. Example: stage 1 = 10, stage 2 = 100 (supposed both transistors amplify (hfe) more than 100). Total amplification = 1000, one microvolt AC in will be 1000 microvolt (1V) AC out.
It is possible to put a third stage in.
In most cases not necessary, given the fact that a modern NPN transistor amplifies approximately 300 and 300 x 300 = 90000. If you use electrolytic capacitors the + should be to the "most positive" side in the schematic (=the point with the highest potential READ MORE...

How to amplify audio linearly with a few transistors

How to amplify audio linearly with a few transistors


This is for beginners and interested people. Here you see how to create a simple amplification stage with one or two NPN transistors, usable for audio and HF, most suitable for audio. The transistors are in a grounded emitter figuration. You can give every individual stage its own amplification factor by turning the variable resistor on the emitter. The right values of the resistors connected to the basis are the key to success. When you home-brew on the basis of this schematic, always use a variable resistor on the basis of each individual transistor (25 K to 50 K, try 25 K first) to set every transistor to the own correct working range. I cannot stress this enough, some schematics cannot be successfully reproduced because the author had a certain "luck" in designing these resistors. When the amplifier works correct (check it with the scope) take out the variable resistors, measure them and replace them by fixed value resistors. This schematic is usable for simple high frequency stages up to maximum approx. 10-15 MHz. The BC547 b (hfe = 300) is usable up to 8-9-10 MHz. The 2N2219 is usable as typical HF transistor, up to 15 MHz in this schematic. For higher frequencies other types of schematics and specialized HF transistors work better. The schematic is very good usable for audio applications (20 Hz-20 KHz) for instance as a microphone amplifier. In that case often 1 stage is enough. You can set the amplification between 2 and approx. the maximum that the transistor can give. Example: stage 1 = 10, stage 2 = 100 (supposed both transistors amplify (hfe) more than 100). Total amplification = 1000, one microvolt AC in will be 1000 microvolt (1V) AC out.
It is possible to put a third stage in.
In most cases not necessary, given the fact that a modern NPN transistor amplifies approximately 300 and 300 x 300 = 90000. If you use electrolytic capacitors the + should be to the "most positive" side in the schematic (=the point with the highest potential READ MORE...

Homemade transistor from a photocell

Homemade transistor from a photocell

Like many of us, Nyle Steiner has long aspired to building a homemade transistor. While considering possible way to achieve this, he stumbled upon the interesting idea of building a FET transistor from a cadmium sulfide photocell.

Normally used to detect light, the photocell is pretty close to what one would need to make a transistor. The device consists of two pieces of metal that are separated by a very thin layer of a cadmium sulfide semiconductor. The semiconductor is normally an insulator, which means that no electricity can flow from one of the metal legs to the other. However, when light (photons) hit the surface of the semiconductor, they knock electrons free, and allow some current to flow across the semiconductor. To make a transistor, though, the device needs to react to electricity, not light. Nyle realized that the photocell could be used as a transistor if an insulated gate was added to the top of it. A bit of scotch tape and water later, and he claims to have a working transistor.

Of course, this isn’t a truly homemade transistor, it’s more of a DIY transistor conversion. The device appears to be functional, however it requires fairly high voltages to work, and only acts as a power amplifier instead of a voltage amplifier. Even so, it looks like an interesting way to experiment with transistors at home. I’d like to build one, and vary thickness of the insulator (scotch tape) to see what the results are. Anyone else have experience with this? READ MORE...

Homemade transistor from a photocell

Homemade transistor from a photocell

Like many of us, Nyle Steiner has long aspired to building a homemade transistor. While considering possible way to achieve this, he stumbled upon the interesting idea of building a FET transistor from a cadmium sulfide photocell.

Normally used to detect light, the photocell is pretty close to what one would need to make a transistor. The device consists of two pieces of metal that are separated by a very thin layer of a cadmium sulfide semiconductor. The semiconductor is normally an insulator, which means that no electricity can flow from one of the metal legs to the other. However, when light (photons) hit the surface of the semiconductor, they knock electrons free, and allow some current to flow across the semiconductor. To make a transistor, though, the device needs to react to electricity, not light. Nyle realized that the photocell could be used as a transistor if an insulated gate was added to the top of it. A bit of scotch tape and water later, and he claims to have a working transistor.

Of course, this isn’t a truly homemade transistor, it’s more of a DIY transistor conversion. The device appears to be functional, however it requires fairly high voltages to work, and only acts as a power amplifier instead of a voltage amplifier. Even so, it looks like an interesting way to experiment with transistors at home. I’d like to build one, and vary thickness of the insulator (scotch tape) to see what the results are. Anyone else have experience with this? READ MORE...

BC107B NPN Silicon Transistor

BC107B NPN Silicon Transistor

Discription
BC107B are widely used "Industry Standard" NPN transistors in a TO18 type case designed for applications such as medium–speed switching and amplifiers from audio to VHF frequencies.

Features:
Low Collector Saturation Voltage: 1V (Max)
High Current Gain–Bandwidth Product: fT = 150MHz (Min) @ Ic 2mA

Absolute Maximum Ratings:
Collector–Emitter Voltage, VCEo 45V
Collector–Base Voltage, VCBo .50V
Emitter–Base Voltage, VEBo .6V
DC Current Gain Hfe (Ic=2mA; VCe=5V) .Min 200, Max 450 Typical 290
Continuous Collector Current,Ic .. . 100mA
Total Device Dissipation (TA = +25°C), Pd. 300mW
Derate Above +25°.. 2.28mW/°C
Operating Temperature Range, Tj  –65° to +175°C
Storage Temperature Range, Tstg .–65° to +150°C READ MORE...

BC107B NPN Silicon Transistor

BC107B NPN Silicon Transistor

Discription
BC107B are widely used "Industry Standard" NPN transistors in a TO18 type case designed for applications such as medium–speed switching and amplifiers from audio to VHF frequencies.

Features:
Low Collector Saturation Voltage: 1V (Max)
High Current Gain–Bandwidth Product: fT = 150MHz (Min) @ Ic 2mA

Absolute Maximum Ratings:
Collector–Emitter Voltage, VCEo 45V
Collector–Base Voltage, VCBo .50V
Emitter–Base Voltage, VEBo .6V
DC Current Gain Hfe (Ic=2mA; VCe=5V) .Min 200, Max 450 Typical 290
Continuous Collector Current,Ic .. . 100mA
Total Device Dissipation (TA = +25°C), Pd. 300mW
Derate Above +25°.. 2.28mW/°C
Operating Temperature Range, Tj  –65° to +175°C
Storage Temperature Range, Tstg .–65° to +150°C READ MORE...