universal chip pre-amp project

[digi01]

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

[Atilla]

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.

[AndrewT]

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.

[digi01]

thanks for the suggestions,hopefully i can completed a backbone of schematic this week.i already have some pcb lay out ieads.

any suggestions?

[digi01]

here is the sch.extreme simple?
this is a balance/unbalance design,one gain stage with one buffer output.

[Ted205]

why have you used an output buffer ?

[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.

[digi01]

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...

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.

[Atilla]

Allright, that's good to know, thanks

[lgreen]

Why are R1,R2, R9,R10 at 950 ohms? Shouldn't they be more like 100 ohms?