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Old 28th May 2005, 02:37 PM   #1
madan is offline madan  India
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Default amplifier circuits

Hello,

I newer to this forum .Recently I'm trying to build an Amplifier .For this I have taken a circuit from http://sound.westhost.com/project27b.htm .But the thing is the PNP Transistor (Numbered BD140) which is connected to the MJ3055 is getting heat within few minutes whenever switch on the circuit.I can't find out the problem and proceed forward.So pls help me to complete the amplifier.Here I'm using the Power supply +/_30 volts railing.


Best regards
Madhu
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Old 29th May 2005, 01:17 AM   #2
anatech is offline anatech  Canada
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Hi Madhu,
Check the connections to the 2N3055's are correct. Bring the amp up slowly and watch the bias current.

-Chris
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Old 29th May 2005, 07:26 AM   #3
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Honey,

Have connected the BD140 and BD139 on the heatsinks , since these are CFB forming pairs, their temperature compensation must be adequately implemented..... apart from that is your connections are wired right , check the connections and proceed further.....
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Old 30th May 2005, 01:17 PM   #4
madan is offline madan  India
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Default Amplifier Circuit

Cris,

thanks for your sugession.I don't know how to measure the BIAS CURRENT .Rest of this every thing ok on my circuit.So please let me know how to measure the bias current .

Best regards
Madhu.
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Old 30th May 2005, 01:56 PM   #5
edl is offline edl  Hungary
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About measuring the bias current:
there are 1ohm rated power resistors between the collectors of the output devices and the output of the amplifier.
let's measure the DC voltage on these resistors.
you know, I=U/R
so, for example, if the voltage is 100mV-DC, then the current is: Ibias=0,05V/1ohm, so 0,05A=50mV
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Old 31st May 2005, 09:33 PM   #6
anatech is offline anatech  Canada
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Hi Madhu,
Yes, edl is correct. Let us know.

-Chris
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Old 1st June 2005, 07:14 AM   #7
madan is offline madan  India
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Hi All,

I'm trying to measure the bias current and ect...I'll come back you soon.


Regards
Madhu.
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Old 12th June 2005, 07:16 PM   #8
madan is offline madan  India
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Hi all

I went through that and measured the bias voltage across the resistor(collector to the out put ) is zero.And I observed that in the circuit Veb of the out put -NPN transistor (2N3055)as 10.2 Voltage.But the Vbe of the -PNP transistor(MJ2955) is 0.7 votage.Please let me know what might be the problem.


with regards
Madhu
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Old 12th June 2005, 07:44 PM   #9
anatech is offline anatech  Canada
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Hi Madhu,
Measure across the 0R1 resistors in the emitter lead. It sounds like the E-B connections are reversed biased (or open - ouch). The 220R resistor may be open, also the 0R1 resistors.
-Chris
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Old 12th June 2005, 08:07 PM   #10
madan is offline madan  India
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Hi anatech,

Ok I measurd the voltage as 0.2 voits.Tha resistor(220 ohms) working well .You said that"may be E_B reverse biased".If it is right what about complimentary transistor.I hope you will clarify my doubt.
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