Single gain stage transistor amplifier.

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#62
As I can see from the video at 7:18 this circuit runs on 12V which is reasonable, but uses two transistors - I am not too confident in using two transistors connected to each other - is it straightforward or does it have feed back distortion issues that are hard to correct?

Actually, my requirements can be specified as follows:

1) Power source : standard power supply/adapter. The lower cost ones - are they good enough?

https://www.amazon.com/LEDMO-Power-...ywords=12v+power+supply&qid=1607392385&sr=8-3

2) Power output 70 dB at 1 metre, which works out to 1.2 to 2 Watts is fine

3) Lack of audible distortion (lets find a distortion meter online and sort this one out)
 
#63
#64
Scheme No. 61 - composite emitter follower (Darlington). It amplifies the current, but does not amplify the voltage. Any low gain transistors can be used. The last transistor is powerful.
To amplify the signal, a 10Ω 5W load must be connected to the collector of the last transistor, from which a bias through a 100-510kΩ resistor is applied to the base of the first transistor. A 1-10 kΩ resistor is connected in series at the input. It determines the voltage gain. A 0.5 ohm resistor can be added to the emitter of the last transistor to reduce distortion. It will be a different OK-OK-OE scheme.
 
#65
Scheme No. 61 - composite emitter follower (Darlington). It amplifies the current, but does not amplify the voltage. Any low gain transistors can be used. The last transistor is powerful.
Click to expand...

Post # 2

In the early stages of power amplification, we need to increase the 'pressure' of the signal. So we use small devices, which don't draw much current and which produce little heat, to amplify the voltage at low current, or, put another way, to amplify the pressure at very small flow. This is voltage amplification.
Click to expand...

Current amplifying vs. voltage amplifying.

Not sure I understand that, heading on over to falstad circuit simulator to examine this a little.
 
#66
I need something explained : a transistor circuit like the one I am using works like this: there is a voltage applied across the transistor. When the transistor is off, this voltage is zero. When a power supply is connected to the base, say for example a battery, the current flowing into the base turns the transistor on at a certain input base voltage, allowing current to flow from the collector to the emitter.

I have demonstrated this using the transistor as a switch. A load such as a light bulb connected in series with the transistor, and requiring 5 V to light up, will increase in brightness as the input current to the base of the transistor is increased.

With a varying signal such as a sine wave, or rapidly increasing and decreasing the input current rapidly, will cause voltage swings between 0 and the maximum voltage across the transistor. So it can be seen that amplification of a sine wave signal or an varying electrical signal will be amplified by the transistor circuit.

What I do not understand about the Darlington pair is this: there is a maximum voltage swing possible with the Darlington circuit, how is this voltage swing greater than the voltage swing of one transistor?

Unless of course, the base current supplied is very low, and much lower than could be boosted by the transistor. Looking at transistor specs should help next.
 
#70
I reconnected this circuit yesterday and got it working. Output is very low. The YouTube videos that I watched showed the components directly connected to the transistor, without any wires. Could this affect the output?

Checking the resistance of wires showed that a 10 cm length of copper stranded wire has a resistance of 0.5 Ohms. Other connecting wires with joining wires show a much higher resistance. This could be it, so I will have to follow some advice I got asking me to use the short wires.
 
#71
After sorting out some defective wires, and checking each wire before use, I was able to get the circuit working again. The HTC Explorer does not put out enough of a signal so I used the M01 which at least let me hear some music. Connecting a CD player with higher line output gave me listenable sound volumes, just barely, at 83 dB at 1 metre from the Sony ES 333 speakers.

As someone said, I have reached the limits of this sort of an amplifier. It may be useful later on to build a small PC desktop speaker with one of these transistors but for now I need something more powerful.

What are the options? The TIP series seems a good candidate, running off 12 Volts. There are these videos on building a simple TIP based amplifier, one in stereo, using 12V. How would these simple circuits sound?

How To Make Mini Amplifier Using Only One Transistor || Cheap Amplifier - YouTube

Mini Amplifier tip41 | Super Bass - YouTube

Mini Amplifier TIP41 Stereo - YouTube
 
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#74
Lots of information - thanks. The TDA7297 sounds good, even great, and is available locally for less than $5 including delivery in 2 weeks.

I will have a look at the YouTube transistor and amp videos.

That headphone amp looks good, I always wondered what the need for a headphone amp is since headphones play loud enough. Headphones typically have high impedance 16 Ohms or so, so will connecting 8 Ohm speakers affect the characteristics of the output sound and how?
 
#76
OK, so let's look at the options, taking into account the original poster's remarks from 2010.

So I want to find/ develop a circuit that uses a single gain stage single ended transistor amplifier. I had a darlington amp work...but not enough volume. I'm trying to stay away from mosfets- I always come up with more distortion on the simulator with mosfets...and seems to give me a headache when played...awsome transparency though...just too sharp on the highs.
Click to expand...

The Zen amp in post #2 is too complex for me, and requires too much voltage.

In post #4 the DIY Class-A 2SK1058 MOSFET Amplifier again requires 24V.

In post # 60 OldDIY suggested a TIP 102 Darlington transistor.Requires 16V.

BC945 transistor: not enough volume max of 83 db at 1 metre on a 90db speaker, with distortion

BC2050 IC. Question is, how much voltage will it require to run? I want to use 9-5V and that with an AC/DC adapter.

So the winner is:

This one uses 12 V for stereo on TIP41.

Mini Amplifier TIP41 Stereo - YouTube

So I will get one and start experimenting. It is supposed to be a single transistor, a power transistor at that.
 
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#77
Well, at least, following OP directions, some power is needed. A 20 W figure keeps everything safe and clean; when you surpass It (a 30-50 W woofer and a 10W tweeter as a load) you'd expect clipping.
So to respond to Basic HiFi :snoopy:
A TDA 2050 is the minimum for the duty
At 15+15V supply (read 30 V)
Double the figure to stay safe (and clean).
At that point, the speakers would be the weak point, just to say: most of the power goes to heat
Given the fact that a TDA 2040 contains about 20 transistors...and that not all speakers are easy loads (another chapter...then there's the big volume about the systems) and that 300-400 V operating tube amplifiers would put you in the figure, I'm asking where the 5-9V supply comes from....
😕
 
#78
Ok, giving credit to what I heard during car trips-a car stereo works at 15 V- the level is loud enough. But that is obtained with low Z speakers and distribution -front&rear- which makes some loudness augmentation
In a little cabin...now expand that to a room, eliminate the rear speakers, make the speakers [perfect], make the source [perfect], then return to the amplifier, trough a cable, and ask again: what do I Need..?!!
 
#79
And yeah! the recording...
Now you have the crest factor
The sinus Power
The decibel wars
The violins that are unhearable because too low but when orchestra explodes that's too loud
...and distorted.
'You have to allow 5-10 dB( some day someone would ask what do you extract those numbers from when ballparkin') headroom for managing the peaks'
 
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