A Darlington type audio amplifier idea.

[Analog_Fan]

I was plying around Darlington type of transistor arrangement for logic and driving leds in the simulator.

Than this idea came up to build a amplifier with this type of Darlington transistor arrangement.



I went to local shop to buy some power transistor and the guy sold me BD137 and BD140, rated for 1,5 amp.
I also got some (NOS) 4700uF capacitors for 0.40€ each, ROE, EGM-D (made in Germany), 7815, 7915.

With a little fiddling you can reduce or eliminate the zero cross over distortion.

Since i never build such things that consume high "power", I'm wondering about R1, R2, R3, R4.
The simulator shows 1.7 amp with 1 Ohm for each.

What more to consider?

More or less according to Falstad simulator, what you put in is what you get out.
10 V.p.p results in about 10 V.p.p., but it delivers power.
What the goal of a amplifier to drive a random 4 or 8 Ohm speaker?
Deliver the power or amplitude?

 

[Analog_Fan]

I have refined the stuff a bit (in the simulator), even the HFE of the trannies and removed R1, R2, R3, R$ and reduced the input currents on the base of the 2SC945, 2SA733.
It would take like 37,5 x 0.4 Watt resistors in parallel coping with 1 amp @ 15V, Bad Idea.

i changed the input signal to 3 V.p.p. (approx line level) and output is almost 6 V.p.p. @ 1.1 Amp on the power rails and 600 mA over the 4 Ohm load.

 

[JohnRoberts]

Not sure what you are trying to accomplish. There are many published schematics of modest output power amplifiers.

The topology you show for mixed npn/pnp darlington is called a "Sziklai" configuration. You can do a search for pros/cons.

I saw it used years ago, before robust PNP power devices were widely available to oppose a normal NPN power output device, with a quasi-complementary PNP darlington output stage composed of a small PNP driving a robust NPN power device.

JR

 

[Analog_Fan]

Not sure what you are trying to accomplish. There are many published schematics of modest output power amplifiers.
The topology you show for mixed npn/pnp darlington is called a "Sziklai" configuration. You can do a search for pros/cons.

I saw it used years ago, before robust PNP power devices were widely available to oppose a normal NPN power output device, with a quasi-complementary PNP darlington output stage composed of a small PNP driving a robust NPN power device.

JR

Thank you for your time.

Yes, i found the "Sziklai" more or less via youtuber, called: IMSAI Guy

I was working on circuit from someone else, who used a PNP in parallel of a led, bypassing and using (5) mA's in idle doing nothing, pretty stupid from someone that has a known biznis in Barcelona.
so i replaced the circuit with Sziklai. the current going in to the base is less the using a simple NPN.

I figured out the PNP version of the Sziklai myself and from there i came up with the above circuit.

The multiplier came from here:


I don't know what is pro or con.
I build many synth modules and they are accept for the first one all perfect apart from cosmetic things, even the first one with a botch.

I recently got 2 x 15V transformer, although they differ in windings / V output, 1 x 40VA & 1 x 10VA.
New Old Stock, just 7€

I have refined the design even a bit more and eliminating the zero cross over distortion completely.

I recent got 2 x 15 Volt transformer, although not both windings are the same.

The Dartzeel NHB-108 uses 2 x 55 Volt psu.
I can't buy such transformers locally.
But this amp circuit is tested by a German using power resistors (and measuring over it) and it's over 200kHz before it starts to drop.

My "circuit" is cheap to build and wanna give it a try .... on veroboard.
Maybe it serves to replce my 5€ computer speakers, the guy around the corner has some speakers lying around
According to the discussed but easy to use "Falstad" simulator says it's stable.

I have broken set of pc speakers, it contains the known mass produced speaker, witch do pretty well for what they are, This will be the first Ginny pig.

I learned the math a long time ago, but never used it professionally, let alone audio.

Just wanted to see if the people here see things that need to better, different.
I'm pretty much a total newby in "audio amplifiers" to drive speakers.

I still don't know if the speaker just want current from the amplifier or also voltage.

Currently i have almost twice the input amplitude.

 

[Voyager10]

I don't want to be the bearer of bad news, but there are a number of ... issues here.

• There's no voltage gain. You would need to drive it from something capable of +/-15V output swing to achieve full power.
• There's no reliable control over the output DC offset, looks like it'll depend on transistor gain and will drift with temperature.
• There's nothing like enough current flowing through the 75K resistor chain to turn on the first 2SC945 transistor. What's is supposed to be doing in your circuit?
• Resistors R1-R4 waste power, which could be delivered to the load.
• The 100K input pot is too high a resistance to drive the output transistors properly.
• The diodes mean there won't be any source of current to drive the 2SC945/BD140 output pair, once the input gets over +7.5V or so.

...and much more besides. Sorry, but it's a terrible circuit. Please don't waste time trying to make it work.

 

[Analog_Fan]

I don't want to be the bearer of bad news, but there are a number of ... issues here.

• There's no voltage gain. You would need to drive it from something capable of +/-15V output swing to achieve full power.
• There's no reliable control over the output DC offset, looks like it'll depend on transistor gain and will drift with temperature.
• There's nothing like enough current flowing through the 75K resistor chain to turn on the first 2SC945 transistor. What's is supposed to be doing in your circuit?
• Resistors R1-R4 waste power, which could be delivered to the load.
• The 100K input pot is too high a resistance to drive the output transistors properly.
• The diodes mean there won't be any source of current to drive the 2SC945/BD140 output pair, once the input gets over +7.5V or so.

...and much more besides. Sorry, but it's a terrible circuit. Please don't waste time trying to make it work.

I stepped over to opamps rather being full transistor amplifier.
Now i have lots of methods of controlling currents and where.
One tiny value change can make it go out of control, far beyond the limits of the components and get very hot.

I was thinking about some shunt (power) resistor, since i don't have an accurate voltage meter, but i do have a scope.
Indeed waste of time if you don't know what is going on. not knowing the formula including the transistor setup.

I have now twice amplitude (theoretical).

The guy round the corner has some NOS (old stock) 1, 2.2, 3.3 ohm power resistors and even some 10 Watt.
What value would be suitable?

These are the parts i got.


adding voltage followers to above circuit also provides a lot of help.
the 75K was 2 x 150K, that's what i saw in a circuit, another circuit showed somewhat similar to the 75K.

 

[Analog_Fan]

I'm using the same mount of capacitance as the darTZeel NHB-108

I have chosen 4 x 10uF + 1 x 6.8uF = 47uF.
parallel delivers more juice.

What are these big capacitors in the darTZeel?
Do they belong to the PSU or amp circuit?

I have some IRZL44N & IRF4905 for power supply, allows to make it any voltage using zeners up to 50 amps.

How it's done in "aftermarket" car amplifiers?
How does that "link" with the others amplifiers using voltages like 55V.

Some Chinese company cloned darTZeel NHB-108 and it's perfect.
But quadrupled the output transistors in parallel.