100W Amplifier Help

[zak4000]

Hi, I was just woundering how i could get more power out of my amplifier, i have built the origanal (Orig 100W rms Schematic.JPG) and it works. My 'theory' schematic is 'New Schematic.JPG' - is it right?

View attachment 39063

View attachment 39064

 

[audioguru2]

Your "new" amp gives exactly the same output power as the original circuit.
Its 80V total supply voltage makes about 70Vp-p across the speaker at full output. 70Vp-p is 24.75V RMS. 24.75V RMS across an 8 ohm speaker is 76.6W.
If a 4 ohm speaker could be used then the amp's power would be about 130W.

You added additional darlington output transistors to supply more ouput current but they will overload the driver transistor if they are used. The driver transistor must also supply more current for a 4 ohm speaker to be used.
Also you didn't change the current-limiting parts so using a 4 ohm speaker to draw more current for a higher output power won't work. The power will be less into a 4 ohm speaker.

Additionally, the 4700uF supply filter capacitors are rather small and the power supply must be more powerful to use a 4 ohm speaker for a higher output power.

The amplifier must make 10 times the power to sound twice as loud. Doubling the power makes the sound just a little louder. Because your hearing sensitivity is logarithmic.

 

[zak4000]

Thanks , but how would you bridge this amp amd how do you work out the RMS and things? :-\

 

[audioguru2]

Hi Zak,
You can't bridge two of these amps without blowing them up.
A bridged amp must handle twice as much current as a single amp, for the same speaker's impedance.

It is easy to calculate the approximate power out of an amplifier.
Yours has an 80V supply. Its darlington output transistors and emitter resistors will create a loss of about 5V each when loaded. Therefore the max sine-wave signal is 70Vp-p.
70Vp-p is divided by 2.828 (twice the root of 2) to get its RMS voltage of 24.75V. Then 24.75V squared divided by the speaker's impedance (probably 8 ohms) equals 76.6W RMS.
It "peak power" or sometimes called "maximum power" is double which is 153W. Its "music power" is any made-up number like 1kW. 

 

[zak4000]

So the RMS and peak power across a 6ohm speaker would be:

V= Total voltage (subtracting 10V for the transistors + resistors)
R= RMS Watts
M= RMS Voltage
S= Speaker Impedance
P= Peak power
2.828= Twice the root of 2

M= V/2.828
R= M*M/S
P= R*2

RMS
M= 70/2.828
M= 24.75
R= 24.75*24.75/6
R= 102.1W RMS

p-to-p
P= 102.1*2
P= 204.2W Peak to Peak

 

[zak4000]

This might help someone..... ;D
(updated)

 

[audioguru2]

There is no such thing as "p-p power". You have calculated 204.2W as the "peak power" which is simply a number that is double the real continuous power.

Will the amp drive a 6 ohm speaker at high levels reliably? The current and heating is 33% higher than with an 8 ohm speaker.