Here is the 'dirty' version of the schematic.
Note, it is correct, but hard to understand maybe.
http://www.cdupload.com/files/42436_wdrak/Preamp%20Draft%20SCH.pdf
Sorry the values are not on the schematic, all the values are on my paper diagrams at the moment.
Rhys
Note, it is correct, but hard to understand maybe.
http://www.cdupload.com/files/42436_wdrak/Preamp%20Draft%20SCH.pdf
Sorry the values are not on the schematic, all the values are on my paper diagrams at the moment.
Rhys
Hi Rhys,
The most significant problem is decoupling. You have no decoupling capacitors on the 5V rail at all. This will mean there is lots of noise on it.
There should be a bulk decoupller of 100uF at least. then 100nF caps shoudl be placed close to the micro controller and the 5V supply to the pre amp chip. I would also use an inductor to reduce noise from the Micro controller getting into the pre amp chip via the PSU.
I recomend re-reading the 7805 data sheet you should have some input and output decoupling on this part, however I can't remeber the optimal parts.
I'd recomend an input filter on the opamps to reject RF noise say 100pF to GND. However this is one of those value judgements as in a sirtuation where these is very little RF noise the system may sound better without them, however if there is noise about it will upset the input to the opamps.
I would recomend much more decoupling on the +/- 15V rails to ensure all th opamps and the output of the preamp as completely stable. 4.7uF to 10uF for each chip would be optimal with a seperate 100nF cap for each chip as well. However there is clearly some decoupling alread there and this will rpobably be ok.
I can't see where the +/- 15 comes onto the PCB it doesn't seem to have a connector, but I may have just missed it.
Regards,
Andrew
The most significant problem is decoupling. You have no decoupling capacitors on the 5V rail at all. This will mean there is lots of noise on it.
There should be a bulk decoupller of 100uF at least. then 100nF caps shoudl be placed close to the micro controller and the 5V supply to the pre amp chip. I would also use an inductor to reduce noise from the Micro controller getting into the pre amp chip via the PSU.
I recomend re-reading the 7805 data sheet you should have some input and output decoupling on this part, however I can't remeber the optimal parts.
I'd recomend an input filter on the opamps to reject RF noise say 100pF to GND. However this is one of those value judgements as in a sirtuation where these is very little RF noise the system may sound better without them, however if there is noise about it will upset the input to the opamps.
I would recomend much more decoupling on the +/- 15V rails to ensure all th opamps and the output of the preamp as completely stable. 4.7uF to 10uF for each chip would be optimal with a seperate 100nF cap for each chip as well. However there is clearly some decoupling alread there and this will rpobably be ok.
I can't see where the +/- 15 comes onto the PCB it doesn't seem to have a connector, but I may have just missed it.
Regards,
Andrew
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