500W PA amplifier with Limiter

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hadita

hadita

Member
Joined 2010
Sir, said apex B500 R27 (22ohm) I try to replace the previous 120 ohm load 4 ohm speakers at full volume and the final driver transistor hot enough after changing 120ohm & final drivers are not too hot, think about what effect the replacement of R27 is yes ... if the power is still stable at 3-4 hours usage, .. please guide

regard
 
apexaudio

apexaudio

Member
Joined 2010
hadita said:
Sir, said apex B500 R27 (22ohm) I try to replace the previous 120 ohm load 4 ohm speakers at full volume and the final driver transistor hot enough after changing 120ohm & final drivers are not too hot, think about what effect the replacement of R27 is yes ... if the power is still stable at 3-4 hours usage, .. please guide

regard
Click to expand...

Try this output stage
Regards
 

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D

Djnits

Member
Joined 2010
apexaudio said:
On R20/21(100R) you must have 0,5-1V, if don't replace R15/16 (1K) to get 0,5V (5mA thru VAS transistors MJE340/350), and use 1k pot instead R22(680R) for set BIAS (10mV on 0,33R/5W is 30mA per outputs)
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wow! What a nice advice thanks sir...sorry 4 late reply...i had made sir what you said..thank you sir apex sharing you talent all over the world..your awesome man and rare person..thanks sir GOD bless and more power...i share my project here in tread if i fixed it

regards
 
apexaudio

apexaudio

Member
Joined 2010
Djnits said:
wow! What a nice advice thanks sir...sorry 4 late reply...i had made sir what you said..thank you sir apex sharing you talent all over the world..your awesome man and rare person..thanks sir GOD bless and more power...i share my project here in tread if i fixed it

regards
Click to expand...

I measure DC offset on some old B500 amp, and I have 1mV on left 4mV on right channel (3 pairs outputs with +/-75V rail), I am sure you can get better DC offset than 150mV.
Regards
 
D

Djnits

Member
Joined 2010
apexaudio said:
I measure DC offset on some old B500 amp, and I have 1mV on left 4mV on right channel (3 pairs outputs with +/-75V rail), I am sure you can get better DC offset than 150mV.
Regards
Click to expand...
hello sir apex sory for the lated replied, anayway i had only -35mv on dc offset out put trns. why it's negative 35, it's normal?.... and bias .430mv and the left side ,350mv, but sounds Good very nice,, thanks sir apex for sharing this amp..

ragards
 
apexaudio

apexaudio

Member
Joined 2010
Djnits said:
hello sir apex sory for the lated replied, anayway i had only -35mv on dc offset out put trns. why it's negative 35, it's normal?.... and bias .430mv and the left side ,350mv, but sounds Good very nice,, thanks sir apex for sharing this amp..

ragards
Click to expand...

DC offset can be positive or negative it's normal. Where you get 430mV and 350mV (points). Transistor start to conducting at 550mV from base to emitter, and go from class B to AB, than BIAS current increase and base to emitter votage is still 550mV. Use 10R instead fuses and measure voltage drop on them (about 1V). Sound is good in class B it's normal for B500 and H900.
Regards
 
S

sekhar

Banned
Joined 2009
last but not the least i have also completed the B500. Its up and running , still in the testing phase but every thing seems ok . No heating , no buzzing just pure music , thanks a loads APEX . Will upload pics in a few days time.
i had a few queries
1. wat is the gain of this amp ?? And which set of resistors r determining them ?
2. if nsl 32 is nt used then wat value of resistor is to be used on the input side ?

regards
Sekhar
 
apexaudio

apexaudio

Member
Joined 2010
sekhar said:
last but not the least i have also completed the B500. Its up and running , still in the testing phase but every thing seems ok . No heating , no buzzing just pure music , thanks a loads APEX . Will upload pics in a few days time.
i had a few queries
1. wat is the gain of this amp ?? And which set of resistors r determining them ?
2. if nsl 32 is nt used then wat value of resistor is to be used on the input side ?

regards
Sekhar
Click to expand...

R12(1k) and R19(22k) determining amp gain, OP amp work as AC buffer and DC servo, first OP amp work with gain R1,R2 and R4 determining gain of this stage, and with different resistor value instead NSL32 you can detrmining amp input sesitivity (use 33k or any value from 1k to 100k).
Regards
 
S

sekhar

Banned
Joined 2009
as i type this msg i am currently asssembling the protection circuit for the b500. One thing came up to mind cant i use a single supply source for the protection board , may be a single 15-0-15 TF. Use a small sugar cube relay of 12V and drive 12V DC fans for cooling.
What changes need to done to incorporate a single TF.

regards
Sekhar
 
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