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Old 18th February 2005, 06:09 AM   #1
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Default OP_Line Amp_02

Please comments on the attach simple IC line amp !

1) What will the performance, is it worth to build ?
2) The value of components ?
3)What will you think if the arrangement of U1 to U3 :-

a) opa 134, opa134, opa134
b) opa 134, op637, opa134
c)op627, op 673, op 627 (because the data sheet show 627 has better performance with no gain)
d) or any better choice ! (The price is great difference between 134 and 637 !!!!)

4) Can any one advise me some simple good O.P."Phono & Line" pre-amp schemtic & PCB layout !

Many Thanks !
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Old 18th February 2005, 06:38 AM   #2
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Simple? Most people would say a single opamp is sufficient for this application. Still, there is a benefit in buffering the volume pot and it certainly allows a very low value for the pot to be used.
But what is the third opamp for? I can see no reason...
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Old 18th February 2005, 09:05 AM   #3
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the third is an output buffer.To me,100k is enough for input resistor,need not 1M.The circuitry looks fine to me and sure it will work as it is a pretty standard circuitry.Just pay attention to layout and wiring during assembly
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Old 18th February 2005, 02:57 PM   #4
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Quote:
the third is an output buffer
Indeed it is. It also has absolutely no function.
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Old 18th February 2005, 03:13 PM   #5
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Default Output Buffer

Output Buffer is to deal with low-Z loads, since the 2-nd opamp has high GAIN /10-11/ and will suffer from higher distortion, because it's feedback is 10-11 times lower than the 3-rd opamp. Also it is good the 3-rd opamp to be a very fast Amp like AD811 or similar and OP2 and OP3 work with a common feedback loop, I've seen this on numerous designs of Headphone ams and pre-amps like this.
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Old 18th February 2005, 03:30 PM   #6
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Quote:
I've seen this on numerous designs of Headphone ams and pre-amps like this.
There is little doubt that what you say is true. I wonder how much distortion would suffer in real life and would actually argue that the loss of transparency due to an extra buffer is not really worth it
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Old 18th February 2005, 11:22 PM   #7
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Default Re: OP_Line Amp_02

Quote:
Originally posted by thomasfw
Please comments on the attach simple IC line amp !
With a gain of 11x?
And like analog_sa says, the last op-amp is not needed at all.
Avoid what you don't need.
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Old 19th February 2005, 01:31 AM   #8
jcx is online now jcx  United States
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if you want to improve on line amp performance with extra op amps you really need to read Walt Jung's composite Line Driver and Op Amp Audio articles:

http://home.comcast.net/~walt-jung/w...7s-20PDFs.html

noise performance is definitely an issue with the 1x buffer in front of the attn. if the headroom requirements premit with the sources you have I would move as much gain as possible up front to minimize noise
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