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53 minutes ago, CWRNH said:

"0.1 Bypass caps on buffer stage lower pins"  Could you or anyone else please explain this to me?  I have everything done to this point and just need to know where these bypass caps connect....

Frankly, I am surprised the circuit works at all.  You have not provided a path for biasing the input stage of the LT1115.  You need a resistor from the non-inverting input to ground.  Pick a value to place the pole where you want to get your flat-band response.

Edited by LittleWatchShop
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19 minutes ago, LittleWatchShop said:

Frankly, I am surprised the circuit works at all.  You have not provided a path for biasing the input stage of the LT1115.  You need a resistor from the non-inverting input to ground.  Pick a value to place the pole where you want to get your flat-band response.

Thank you!

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21 minutes ago, LittleWatchShop said:

Frankly, I am surprised the circuit works at all.  You have not provided a path for biasing the input stage of the LT1115.  You need a resistor from the non-inverting input to ground.  Pick a value to place the pole where you want to get your flat-band response.

Not my design, I am making a modified version of this.  What value should I start with for the Biasing of the input stage?  Sorry I am new to this...  Not totally incompetent but certainly don't have a through understanding at this point.  Any help is greatly appreciated.   Here is the PCB so far, based on the schematic.  Will modify it once I get a functioning board.image.png.43e5ec29563003cd129ee1a8beec1f21.png

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29 minutes ago, CWRNH said:

Not my design, I am making a modified version of this.  What value should I start with for the Biasing of the input stage?  Sorry I am new to this...  Not totally incompetent but certainly don't have a through understanding at this point.  Any help is greatly appreciated.   Here is the PCB so far, based on the schematic.  Will modify it once I get a functioning board.image.png.43e5ec29563003cd129ee1a8beec1f21.png

Other than in the rail splitter, I do not see any bypass capacitors.  Poor practice.  You need to bypass every amplifier. 

For your input resistor, a 10k should work.

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Okay, I will put caps on pins 4 (V-) and ground on all amps and pins 7 (V+) and ground on all amps.   And will bias the main input with a 10k resistor between pin 2 (-) and ground of the first op amp.  Is this what you are talking about?   Again, thank you for your time.  I will post the updated board image when done.

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13 minutes ago, JohnR725 said:

How do curiosity the modifications purpose is to achieve what?

I want to first get a decent working preamp setup.  Then refine it a bit and I want to add a UART output, among other things.  The preamp is only a small part of the project.  There are many different schematics and ideas, I have tried a few.  I am also trying to learn how all this stuff works, partly for curiosity sake and partly to build a machine that does some very specific things that I will explain later on as I am working them out.  I have several commercially made timing machines so this endeavor is more of a hobby at this point.   Electronics have always been an interest to me, I have finally gained some of the knowledge and equipment to pursue this hobby.  There are many projects that I have built and am planning on  building.  So....  I am, right now, trying to find a good quiet preamp.. LOL

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2 minutes ago, svorkoetter said:

What I find interesting is to ask questions about the circuit with only a circuit board layout instead of an actual schematic.

 

2 minutes ago, svorkoetter said:

What I find interesting is to ask questions about the circuit with only a circuit board layout instead of an actual schematic.

I simply wanted to know where HE (the person who made the schematic, that I created the layout from) was putting the bypass caps.  I can share my schematic too if you wish.  If I am asking something that is foolish I am sorry.  You don't know what you didn't know until you learn that you didn't know it.  This isn't rocket science but I don't have as much experience with electronics as you fine folks.  Sorry for any misunderstanding.

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1 hour ago, CWRNH said:

Okay, I will put caps on pins 4 (V-) and ground on all amps and pins 7 (V+) and ground on all amps.   And will bias the main input with a 10k resistor between pin 2 (-) and ground of the first op amp.  Is this what you are talking about?   Again, thank you for your time.  I will post the updated board image when done.

Yup!

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Just now, LittleWatchShop said:

@cwrnh ...what layout tool are you using?  Looks like ExpressPCB.

Lately yes, Express.  I also have used Eagle but I am liking Express better.  I use Fusion 360 for most of my regular CAD/CAM nearly every day so I thought I would like Eagle but it is not as simple to use.  I used TINA do make the schematic and do some simulations.  Thankfully the tech school I teach at has a decent electronics department where I get some help.

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