300w rms amp

Looks pretty straight forward to me. R10 is DC offset, R22 controls the amount of current biased through the outputs. Measure Vout DC to ground and adjust R10 until it is as close to 0V as possible. Measure the voltage across the emitter resistors on the output transistors and adjust for the current bias you want....V/R=I.;)

Might want to adjust output bias first...
This is of course if it is constructed properly.:rolleyes:
 
Adjust R22 to maximum resistance. Attatch a millivolt meter to measure over one of the emitter resistors (R33-R40). Adjust R22 until the millivolt meter reads 20mV (for 55mA idle current in each transistor)

Attach millivolt meter to speaker output. Adjust R10 until output offset is as close to 0mV as you can get it.
 

leander

Member
2005-08-26 1:23 pm
Thanks for your replys people .

The specs says 300w rms with +/-70 volt rails

Do you think the amp will hold up if I add other 2 power transistors and give +/-80 volt rails ?

do I need to change something else in order to do this modification or I just add two power tansistors and resistors in parallel with the others. Do I need to change the resistors value for example?


Thanks

Leander

Malta
 

leander

Member
2005-08-26 1:23 pm
I checked out the mj15003/4 specs and there maximum voltage Vceo are 140v therefore I guess that higher voltage than +/-70 will destroy them.

May I replace the 0.39ohm 5 watt resistors, with say 0.22ohm resistors for an increase of power output ???


Note these transistors have a very high current capability
Ic = 20A
 
leander said:
I checked out the mj15003/4 specs and there maximum voltage Vceo are 140v therefore I guess that higher voltage than +/-70 will destroy them.

May I replace the 0.39ohm 5 watt resistors, with say 0.22ohm resistors for an increase of power output ???


Note these transistors have a very high current capability
Ic = 20A


Replacing the 0.39 ohm resistors with 0.22 ohm will give you around 0.5 (1/2) extra volts to your speaker. This is something that you will not hear. This substitution though will affect the current sharing amongst the output transistors by 40% and this is less safe.

I would concentrate on the power supply. Improving the power supply will have the biggest affect on the power cabability (and sound quality) of your amp.

Cheers
 
Or you can get 350V transistors.

MJL4281/MJL4302 350V, 15A, 230W

Amp I'm building with 5 pairs of those transistors I'm going to run on rails that peak at 70V with a 50-0-50 transformer.

If you parallel enough devices, you could easily run rails over +/- 80V. Also MJL21195/21196 are 250V 16A 200W and would work too.