Rod Makes it very sketchy to how much power it can make in his article.
I can get MJ15003/MJ15004 's so that would increase the power alot over the 2955/3055.
Can the transister I have access to drive a 2 ohm load?
or... can I double the output stage then run a 2 ohms load?
and what sort of power output can I expect from it?
Thanks for your help
I can get MJ15003/MJ15004 's so that would increase the power alot over the 2955/3055.
Can the transister I have access to drive a 2 ohm load?
or... can I double the output stage then run a 2 ohms load?
and what sort of power output can I expect from it?
Thanks for your help
You can check out this P3A construction guide. It has a power calculator that should help you:
http://www.anidian.com/audio/construct/p3a_1.shtml
I really doubt this design is suitable for a 2-ohm load. You would at least need to double the output stage (use separate emitter resistors for each of the transistors).
http://www.anidian.com/audio/construct/p3a_1.shtml
I really doubt this design is suitable for a 2-ohm load. You would at least need to double the output stage (use separate emitter resistors for each of the transistors).
2 Ohm load
You can easily get more than 100W at 2 Ohm load with that amp, probably 200W (RMS).
You should think about a much bigger PSU, at least 300W per channel. This means more expensive parts as a bigger transformer, diodes and supply caps.
Also heatsinking will <b>need</B> to be increased.
About the output stage, just put a power transistor as those ones you got, in paralell with the 3055 and 2905 (two pairs at least, if you want a more reliable operation, three pairs), with a emitter resistor of at least 0.5 Ohm. It'll help to share the current, otherwise it will happen this: the hotter the BJT transistor is, the more current goes through it. The emmiter resistor will make smaller VBE so less current will flow through it.
I'd put a 10 Ohm resistor only in driver's emmiter, and would take off actual 0.47 Ohm resistor
You can easily get more than 100W at 2 Ohm load with that amp, probably 200W (RMS).
You should think about a much bigger PSU, at least 300W per channel. This means more expensive parts as a bigger transformer, diodes and supply caps.
Also heatsinking will <b>need</B> to be increased.
About the output stage, just put a power transistor as those ones you got, in paralell with the 3055 and 2905 (two pairs at least, if you want a more reliable operation, three pairs), with a emitter resistor of at least 0.5 Ohm. It'll help to share the current, otherwise it will happen this: the hotter the BJT transistor is, the more current goes through it. The emmiter resistor will make smaller VBE so less current will flow through it.
I'd put a 10 Ohm resistor only in driver's emmiter, and would take off actual 0.47 Ohm resistor
Is the only factor holding back this amplifier Heat/power usage of the transisters used?
This is what I've been figuring (correct where wrong plz🙂 )...
The transisters can only produce a certain limit to the amount of heat it can get rid of which intern only let you use a certain amount of power.
So If I had transister capable of 100w RMS I could run it at .5ohms for instance if it still was only producing 100w. Same if I was running at 100w into an 8 ohms load... I would just need to increase the voltage its running off.
Thats pretty much what i figured out after lots of thinking.
This is for a car amp btw. So If I make an output stage capable of 400w but have the rail voltage set for 150w/4 it would leave enough headroom for bridging into 2 ohms?
Any input would be great
This is what I've been figuring (correct where wrong plz🙂 )...
The transisters can only produce a certain limit to the amount of heat it can get rid of which intern only let you use a certain amount of power.
So If I had transister capable of 100w RMS I could run it at .5ohms for instance if it still was only producing 100w. Same if I was running at 100w into an 8 ohms load... I would just need to increase the voltage its running off.
Thats pretty much what i figured out after lots of thinking.
This is for a car amp btw. So If I make an output stage capable of 400w but have the rail voltage set for 150w/4 it would leave enough headroom for bridging into 2 ohms?
Any input would be great
2 Ohm bridged
You must take care of current limits of output transistors.
beta is very low when colector current is high, so you can also break the driver in that case.
100W with a 60% efficiency (max) means transitors can handle~80W, and means Vcc=~40V at 8 Ohm
With 0.6 Ohm, 100W means 14.2A, probably trasistors are blown since there were 7A.
100W at 0.5 Ohm also means V(load)=7V, so with 40V, you´ll get Vce=33V, and 33V*14.2A=468 W, a lot of smoke inside the car.
By making Vcc=10V, transistor would be either saturated (at a high curret Vce(sat) can get that higj and more.
So... You'd better not use a 0.5 Ohm load.
You must take care of current limits of output transistors.
beta is very low when colector current is high, so you can also break the driver in that case.
100W with a 60% efficiency (max) means transitors can handle~80W, and means Vcc=~40V at 8 Ohm
With 0.6 Ohm, 100W means 14.2A, probably trasistors are blown since there were 7A.
100W at 0.5 Ohm also means V(load)=7V, so with 40V, you´ll get Vce=33V, and 33V*14.2A=468 W, a lot of smoke inside the car.
By making Vcc=10V, transistor would be either saturated (at a high curret Vce(sat) can get that higj and more.
So... You'd better not use a 0.5 Ohm load.
ahh... thankyou for clearnig that up 🙂 much appreciated
I was just using .5 ohms as an example. Realisticly it'll never go below 2 (nominal).
So with a doubled (tripled even) ouput stage of MJ15003/004 it should be capable of 40amps and 400w into 4 ohms?
I was just using .5 ohms as an example. Realisticly it'll never go below 2 (nominal).
So with a doubled (tripled even) ouput stage of MJ15003/004 it should be capable of 40amps and 400w into 4 ohms?
fr0st said:
I know some car aduio freaks wh will work with 0,01 Ohm if it was aossible. 🙂
for getting 40A RMS and a realiable operation, you should use at least 8 pairs and a double driver. But yes, that's the way, output stage <i>is</i> the power. Its very easy to use Spice and calculate this more accurately.
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