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Old 21st January 2005, 08:06 AM   #1
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Default Simple OCL AMP

here is schematic of mosfet ocl amplifier,not my design..
THD <=0.03% full output,I want to build one..
everybody had try this circuit?
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Old 21st January 2005, 08:17 AM   #2
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R5 and R15 should be the same value?
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Old 21st January 2005, 08:27 AM   #3
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Quote:
Originally posted by richie00boy
R5 and R15 should be the same value?
no!R5 and R15 at curent value is ok!,I had make some Simulation
..THD&phase offset is better than them at same value..

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Old 21st January 2005, 05:39 PM   #4
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What is the point of r3? It doesnt do anything at all.
Why not use a current mirror for the LTP. It will almost certainly lower THD and increase slew rate.

Doug Eleveld
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Old 22nd January 2005, 12:37 AM   #5
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Quote:
Originally posted by deleveld
What is the point of r3? It doesnt do anything at all.
Why not use a current mirror for the LTP. It will almost certainly lower THD and increase slew rate.

Doug Eleveld
Hi,deleveld:
somebody suggest R3 should be add,they said it will make the circuit work more balance...So I do..
as the title named "simple",this is the basic circuit of the complecity struture you say so..least device can be gain more fidelity..I think
and also suitable for the people who hated trouble like me,because it is much easy to do and don't need more component..
thanks!
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Old 22nd January 2005, 07:58 AM   #6
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Hi Darkhorse,

Don't forget the output stage Zobel network that will be necessary to stop a real world construction of this amplifier from chasing its tail.


Cheers ......... Graham.
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Old 22nd January 2005, 08:24 AM   #7
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Quote:
Originally posted by Graham Maynard
Hi Darkhorse,

Don't forget the output stage Zobel network that will be necessary to stop a real world construction of this amplifier from chasing its tail.


Cheers ......... Graham.
Thank you!Mr.Graham Maynard.
the output stage zobel network must needed!I miss..
and also input stage need shunts a small capacitor 100pF..
so sorry for my untight manner!forgive me please.
from now on,the schematic diagram I draw will be more serious..
happy!

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Old 22nd January 2005, 09:01 AM   #8
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Quote:
Originally posted by DarkHorse


Hi,deleveld:
somebody suggest R3 should be add,they said it will make the circuit work more balance...So I do..
as the title named "simple",this is the basic circuit of the complecity struture you say so..least device can be gain more fidelity..I think
and also suitable for the people who hated trouble like me,because it is much easy to do and don't need more component..
thanks!
Whoever told you that is wrong It *looks* more balanced, but in electrical terms it is not. There is no way you can get the currents in each leg of the LTP even remotely close with two resistors like that.

Take out R3 and then adjust R2 until the current flowing in each leg of the LTP is as close to equal as you can get it at idle.

You also need a small (22-220pF, determine experimentally) capacitor across Q3 base-collector otherwise you will see oscillation when you build it.

And I really think you need to make R5 and R15 equal. Simulation results are not always real
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Old 22nd January 2005, 09:13 AM   #9
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Q1 would benefit from a small base resistor.

A diode needs to be added from the collector of Q4 to the B+ rail to prevent gate damage.
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Old 22nd January 2005, 09:30 AM   #10
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Quote:
Originally posted by DarkHorse
somebody suggest R3 should be add,they said it will make the circuit work more balance...
I believe this is a common mistake. People think because it looks on paper to be more balanced, then it is. In the books I have read and amplifiers I have built they don't have a R3.

My understanding is it will still work with R3 but it will have more distortion.

EIDT: oops, a bit slow in hitting the submit button.
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