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Old 19th June 2009, 09:36 AM   #1
digi01 is offline digi01  China
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Post universal chip pre-amp project

there are lots of wonderful opamp manufactured by nsc,ad and ti.i plan to make a universal pre-amp basis on the chips.

design goal:
1,simple configuration,
the unit will use 2pcs universal dual opamp.
2,pure dc coupling,
the unit will not include caps in the signal route.no high(low)-pass filtering,dc block.maybe setup some break points for unstable op.
3,diy friendly,
make the pcb compact,easy install,easy embed.

-zang
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Old 19th June 2009, 01:01 PM   #2
Atilla is offline Atilla  Norway
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It would be nice to be able to configure the opamps as unity-gain buffers in case you wanted a buffered preamp without gain.

Actually that's something I'm working on right now, but I plan to use dedicated buffer chips instead.
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Old 20th June 2009, 10:56 AM   #3
AndrewT is offline AndrewT  Scotland
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Default DC coupled pre-amp

DC coupling requires DC detection and some form of input and/or output muting if the detection activates.

Consider adding a DC servo to minimise the "normal" offset.

Ensure you have adequate RF filtering.

I have now done some smd assembly using To23 and 805 resistors/caps. Don't be afraid to use these sizes. It was relatively easy for my magnifying glass assisted old eyes.
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Old 22nd June 2009, 12:43 AM   #4
digi01 is offline digi01  China
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thanks for the suggestions,hopefully i can completed a backbone of schematic this week.i already have some pcb lay out ieads.

any suggestions?
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Old 22nd June 2009, 09:08 AM   #5
digi01 is offline digi01  China
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here is the sch.extreme simple?
this is a balance/unbalance design,one gain stage with one buffer output.
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Old 22nd June 2009, 09:26 AM   #6
Ted205 is offline Ted205  United Kingdom
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why have you used an output buffer ?
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Old 22nd June 2009, 03:41 PM   #7
Atilla is offline Atilla  Norway
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If you want to add a dedicated buffer after the opamp, you might want to consider to put it inside the feedback loop of the opamp. Look at the LME49600 application notes for example, I find it to be more beneficial.
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Old 23rd June 2009, 12:49 AM   #8
digi01 is offline digi01  China
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Quote:
Originally posted by Ted205
why have you used an output buffer ?
the buffer stage was setup for connection friendly,it can fix impedance problem of the after device such as connection cable,volume pot,power amp...


Quote:
Originally posted by Atilla
If you want to add a dedicated buffer after the opamp, you might want to consider to put it inside the feedback loop of the opamp. Look at the LME49600 application notes for example, I find it to be more beneficial.
this is a design case.the u1a,u2a voltage gain is isolated with the u1b,u2b buffer.
i have tested the overall loop configuration.it work good but it is no good for pre-amp.
if i make a headphone amp i will use overall loop.
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Old 23rd June 2009, 05:35 AM   #9
Atilla is offline Atilla  Norway
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Allright, that's good to know, thanks
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Old 23rd June 2009, 08:50 PM   #10
lgreen is offline lgreen  United States
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Why are R1,R2, R9,R10 at 950 ohms? Shouldn't they be more like 100 ohms?
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