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Old 1st June 2005, 08:31 AM   #1
kpero is offline kpero  Croatia
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Default Output stage on amp

Ok. First and only question is about output transistor. This shematic is orginal and has only one pair of output transistor. It's drive about 120 W in 4 ohms but it also can drive 160 W in 2 o.hms.
Now, is it posible to add one pair of output transistor. Power disipation wil bee far lower on every transistor and there will be little more gain on output. Which modification must be made ,if this can be done?

Thanks

Sory on bad English
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Old 1st June 2005, 09:28 AM   #2
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Default Re: Output stage on amp

Quote:
Originally posted by kpero
is it posible to add one pair of output transistor.

sure, but it would be safer if emitter resistors were increased from 0.1 to 0.22
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Old 2nd June 2005, 08:37 PM   #3
kpero is offline kpero  Croatia
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Ok. I put two transistor in shematic. Blue line.
Is this good or I must conect diode on colector like D213 and D214 on firs pair.

Thanks
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Old 3rd June 2005, 06:31 AM   #4
AndrewT is online now AndrewT  Scotland
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Hi,
I don't know what the diodes are doing.
But they are connected to the power rails.
So so do not need to duplicate them.
I just ran an SOAR for one pair MJ15003/4 and your amp is struggling with this loading. For 2 ohm resistive you need about 15mF+15mF smoothing to keep the ripple low enough and must keep the output case temp below 28degC to be right on SOAR limit.
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Old 3rd June 2005, 07:06 AM   #5
kpero is offline kpero  Croatia
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This is car amp so power capacitor won't be so big. Output transistor are 2sa1673 and 2sc 4300. I don't know is this change thing?
You say it is struggling with one pair. If i put two pair will thing be better?
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Old 3rd June 2005, 07:12 AM   #6
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We have laws against LOUD car amps here and my past experience of driving in Bangkok ( dodge-em-cars/drag racing no rules) daily are much more relaxed and 'in control' with milliwatts of distraction from the horrible drivers.


Sorry , can't help.
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Old 3rd June 2005, 07:26 AM   #7
AndrewT is online now AndrewT  Scotland
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Hi,
I don't have SOAR data on 1673.
2 pairs will share the load and get you much safer on current draw through each transistor.
Since it is current that produces heat then you are reducing heat stress.
BUT car amp!! What temp are the transistor cases running at? (Tc).
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Old 3rd June 2005, 07:53 AM   #8
kpero is offline kpero  Croatia
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From data-shet Tc is 25 C with 80 W power. Is that what you looking for?

Temperature range is -20 ,+150. I don't know on which temperature will operate in because i don't have technical info
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Old 3rd June 2005, 08:12 AM   #9
Duo is offline Duo  Canada
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It appears that the diodes are there to prevent forward biasing of the CB junctions in the driver transistors.
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