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Old 25th September 2005, 11:18 AM   #1
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Question Preamp PCB layout.

Hey, just drew a pcb layout for a simple op-amp preamp. Any comments on how i can improve it or is it fine?
The thing in the upper corner is the pot with reinforced solder because it's gonna lift the pcb up.
Thank you

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Old 25th September 2005, 11:49 AM   #2
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Put a .1 cap from each supply to ground as close to the op amp as you can.
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Old 25th September 2005, 11:55 AM   #3
VT67 is offline VT67  Belgium
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Is C2 an electrolytic cap in the signal path???

Regards
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Old 25th September 2005, 12:02 PM   #4
rabbitz is offline rabbitz  Australia
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Have a look in the Chip Amp section as there's heaps of good info on pre amps and working with op amps.
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Old 25th September 2005, 12:06 PM   #5
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Aha okey thanks for your replies. Yes C2 is a Dc coupling electrolytic cap.
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Old 25th September 2005, 03:19 PM   #6
paulb is offline paulb  Canada
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The capacitor physical sizes don't look right. A 1000uF cap smaller than a TL071? Actually the capacitance values look a bit odd too. A 470 uF input cap into a 100K input impedance is much bigger than it needs to be. Where did the circuit come from and what is it for?
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Old 25th September 2005, 03:59 PM   #7
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The C2 could be 1 uF/ 63 V polyester, better than an electrolythics.

With 1 uF you will get 1.6 Hz corner frequency.
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Old 25th September 2005, 04:13 PM   #8
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Tack for your answer
I'll use 1uF instead.

I know the 1000uF size is wrong but it doesn't matter because i know t will fit anyway. Im currently reworking the pcb because i'll have a lm386 driving an headphone also from the same signal source.
Will uptade in a while
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Old 26th September 2005, 05:11 PM   #9
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Okey here comes some updates:
-Added filter caps for supply voltage
-Using +-12V for TL071
-Added a seperate headphone driver on board in form of a 386 (hence the 7812)
-Put the psu for the chips onboard
-Using seperate groundingcabling for psu gnd and signal gnd (they will however end up together when they hit the main reservoircaps ground)


Please feel free to comment if it sucks

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The opamp circuit is just a standard simple negative feedback circuit with a gain of ~25. The signal is splitted from the pot to both amps.
The schematic for the LM386 circuit is taken directly from the data-sheet (gain=50 version)

Thanks
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Old 26th September 2005, 05:23 PM   #10
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A couple more 0.1uF film caps on the rails by the LM386 wouldn't hurt, and if its driving headphones, then you could add some 100uF as well.

Why are you only regulating the + rail?
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