Single TIP41A Power Transistor Amplifier

Update November 24 2021

The amplifier is now called N2, running in mono mode, however with the two RCA inputs joined to a single input using two resistors on the left and right channel wires. The inut RCA cable is faulty, so it does not combine the signal properly. With the ES speakers, however, the sound is nothing less than amazing, I could listen forever. Smooth and detailed, distortion free as far as I can tell. I am obtaining at 1 metre 85 dB with the ES, however with the other speakers, the Realist 40-1011 about 80 db and 72 dB with the DOB1.

It is time to package this in a case of metal and get it working on the desktop. Two amplifiers would set the sound level higher running in mono block mode.

I am looking into using the Darlington transistor package as demonstrated by John Audio Tech, although his MOSEFET amplifier puts out about 300 to 600 mW, the Darlington package allows 1 Watt or more, which is substantial Costs are not much higher, going at Rs. 50 at Scion electrics. All my amplifiers will be class A I think.

The other development is the use fo 4 AA Envelop batterer running at 1.2 V each for a to tal of 4.8V, which give sufficient current under load to tun the thing to acceptable levels. This set up has been running for a few days now with o loss in IR. I have a charger ready just in case. THe plan i sto hook up two sets in series for a totla of 9.6 Volts which should allow higher input volume without distortion, Heating i minima in this set up. Altogether amazing fortuitous,

The Falstad and other circuit simulators continue to be almost useless for designing except for basic electrical theory.

Update November 15, 2021

The amplifier is connected and working, at 6V DC, it amplifies music at 85 dB at 1 meter and is relatively distortion free as I can tell. There is a low pitched hum in the background, probably power line. Yesterday it was running for about 4 hours an the transistor got almost too hot to touch and keep a finger on for a minute, this is with the heat shield that was hastily manufactured yesterday.

Update November 11, 2021

After a few more rounds of circuit sim, I have had enough. I was not able to determine the turn on current of the amplifier by using the circuit simulator, for whatever reason. I know this: in reality, the amplifier worked, it worked with the speaker in the collector path, it worked with a transformer connected across the 9V + and the collector, and a speaker connected to the other side of the transformer. The caution to use an audio grade transformer made me abandon the project, in any case the audio transformer was bulky and I needed a 'specially made' transformer.

I decided to build the circuit on a sheet of corrugated cardboard and lay it out over a wider area for ease of connection and troubleshooting. In half an hour I had half the circuit connected, and it was clear how hit should be connected. I could even make notes on the cardboard sheet.

How do I test this circuit? First of all, the measurements from an audio output mini stereo connector of a laptop showed a voltage (potential for current, that is x Amps given a R resistance ), of 100 mV using a 1 kHz tone, and using the multi-meter in AC voltage mode. Using the volume booster on the computer, I was able to get this to 380 mV. Both these outputs were sufficient to power a small speaker audibly and enjoyably.

The next step will be to test the amplifier circuit with DC current. The power supply will be initially a 9V battery, depleted to about 4 volts. Once the power is connected, and the circuit is closed, I only have to connect the input to a tone signal and check the voltage across the base and emitter, and the voltage across the collector and emitter. When the transistor is turned off, this should be the full voltage. Lets see if I am right. Then I have to check the voltage across the speaker terminals, without the capacitor. If there is an amplification, the voltage across the speaker terminals should be higher than 100 mV.

The current ratings for 424 mA for the laptop output but this rating seems suspect, so further testing across a set resistance is needed.

Update November 10, 2021

After some help online from friends, I have a better understanding of the working of the amplifier. The circuit diagram shown is from the Falstad circuit simulator applet, which I have learned to use better now, after a few months.

The circuit shows the original "November 1" amplifier which is base on a simple amplifier based in the circuit in : which seems to say the amplifier will work. The amplifier worked without the capacitor attached, however a capacitor was added to the circuit to prevent a continuous DC current from passing through the speaker, which may damage the speaker and push it forward during operation, push it forward past its resting point.

The simulation shows that the amplifier works, but that the amplifier output is distorted, and the signal reduces in ampliftude after a while due to the capacitor charging up. A large 3F capacitor was used, however there seemed to be leakage from the capacitor as it was rated at only 2V. The capacitor heated up, and so did the transistor, however music was clear and pleasant. The set up was not sustainable.

The next picture, based on a suggestion, was to remove the speaker from the path of the 9V line that runs through the transistor, and to replace it with a resistor of 4.7V. This resistor would have to be a 5W or 10 W resistor as it would heat up as a lof of current would pass through it. I used the circuit sim to create a circuit with this arrangement, and it seems to be workable.

You Tube is filled with videos of amplifiers powered by a single transistor. The transistor is the TIP41 power transistor as seen in this video:

https://www.youtube.com/watch?v=j_4QzDttn9E

The D718 NPN Power Transistor has also been suggested. What are these transistors like?

TIP41C is a low cost general purpose power transistor that can be used for amplification and switching purposes in your electronic circuits. It can drive maximum 6 ampere of load.

https://www.componentsinfo.com/tip41c-transistor-pinout-equivalent/

The transistor is available at this site, along with the D718.

https://nilambaraelectronics.com/product-category/components/transistors/

As far as a parts list and circuit diagram of the amplifier circuit used, I was able to compile the following list from the you tube video (which was suggested on the DIY Audio forum)

TIP 41 x 2

1 K Ohm Resistor x 1

1000 uF 16 V Capacitor X 1

100 K Ohm Potentiometer

Heat Sink x 2

Inductors (Unspecified) x 2

this video describes a stereo circuit. It may be simpler to test out a mono (single channel ) circuit which is described in another video.

This single transistor circuit, using an unspecified transistor, equivalent to the TIP 42, is listed at this Russian site. Suggested by a post on DIY Audio:

https://usamodelkina.ru/10249-prosteyshiy-usilitel-zvuka-na-odnom-tranzistore-za-15-minut.html

The next step is to order the components for the simpler mono circuit and test out the sound quality. Order 2 transistors and 2 heat sinks just in case?

Parts List:

TIP41 Transistor x 1

Heat Sink (Not used but necessary)

100 uF 16V capacitor

Variable Resistor 4 k Ohm

here is another video from DW TECH for a single channel amplifier.

https://www.youtube.com/watch?v=85OfUHw-jWg

Read all about transistors here:

http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P2.html#Vbe