Another quasi-complementary design

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#601
Lars Clausen said:
Ravslanka: Remember to consider what happens if one rail fuse blows, but the other one doesn't. In some designs you get full DC on the output terminal, which can damage your speakers, and even start a fire.

Best regards

Lars Clausen
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hi

Lars Clausen

i already had taste of smoke with this amplifier.i will be very carrefulll this time.what about the questions in my post.

thanks


ravs





be a vegeterian,
 
#603
Sorry Ravslanka, i dont think i should be the one to answer the questions. I looked at the circuit, and it looks ok. However the high gate capacitance of the MOSFET's paired with the 330 Ohms, tells me, that you will have problems with high frequencies. The feedback loop can compensate for some of it, until the phase shift of the closed loop collides with the anti-oscillation capacitors' cutoff frequency. I think i'd have placed a buffer before the gates, to speed things up a bit, and get a good bandwidth of the amplifers.
 
#604
Lars Clausen said:
Sorry Ravslanka, i dont think i should be the one to answer the questions. I looked at the circuit, and it looks ok. However the high gate capacitance of the MOSFET's paired with the 330 Ohms, tells me, that you will have problems with high frequencies. The feedback loop can compensate for some of it, until the phase shift of the closed loop collides with the anti-oscillation capacitors' cutoff frequency. I think i'd have placed a buffer before the gates, to speed things up a bit, and get a good bandwidth of the amplifers.
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hi Lars Clausen,

this circuit is already discused over here and many amps have been build the circuit is proven.i myself have one running for about 5-6 months.i was just askng if this pcb layout gona work.

thanks


ravs




be a vegeterian.
 
#605
ravslanka;

You would do well to heed Lars Clausen's advice regarding driving the IRF mosfets - take a look at Nelson Pass's redesign of the HK Citation 12 for an example of using a buffer transistor. Also, take a look at how QUAD use a buffer transistor in their 405 current-dumping amplifier.

No offence, quasi, I like your design a lot !!!
 
#606
hi quasi,

this is my new to be completed actrk600 pcb.right now mounting the components.any suggestions.


ravs




be a vegeterian,
 

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#608
hi quasi and others.

i have made a new board of actrk600.iam testing the board with only
one pair of output and +-44 vdc.i can set the bias but i could not get down the dc offset to 0 volts the last i can set is 96 mv..i have changed the trimpot and have checked t1,t2 and t3 they are ok.do you guys have any idea whats wong with it


http://www.adam.com.au/cgpap/QuasiWeb/pdf's/Actrk Nmos600 schematic.pdf


i will be posting the pics tommorrow.


thanks


ravs





be a vegeterian.
 
#610
danieljw said:
Hi Ravs,

it might be the earth connection is bad or perhaps another power supply issue. 96mV should not ruin a speaker but it is nice to get it to <25mV



-Dan
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hi danieljw,

i didnt find anything wrong or earth missing in the board.i modified the output stage pcb layout but didnt altered the predriver layout below is the pcb layout.setting 0.35 volt across 10 ohm resistors iam getting

r32=7.1mv r33=10.8mv

r19=2.28 volts r17=3.85 volts and diffrential on r7(18k)=32.5 volts

removing the output pairs and checking the dc offset its 5 volts which could not be vared through vr1.

pcb layout


thanks



ravs




be a vegeteian
 

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#612
i am not sure ravs,,,, usually the input stage sets up the offset perhaps a resistor is slightly wrong or perhaps the input pair has a transistor in the wrong spot or the gain of the input pair could be too different to trim out....

- just a few ideas to check

-Dan
 
#613
hi danieljw,

i added one more output pair to the board and powered up. now threres another problem.rebiased it.around 0.60 volts across 10 ohm resistor.powering the amp of and then on.the reading goes to 15 to 18 volts.i again set the bias and do same thing the reading also comes to be the same 15 to 18 volts.changing the trimpot doesent make any difference.but when i set bias to around 0.44 volts it doesent happen anymore the same.the reading stays around 0.40 to 0.44 and dc offset can also. be set to 3-4mv.all the arts i used are new.

quasi

please help me out.iam stuck with it.


thanks


ravs





be a vegeterian.
 
#616

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