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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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55 minutes ago, CWRNH said:

Could you or anyone else please explain this to me? 

Bypass capacitors should be place from v+ to ground and from v- to ground.  Placed as close to the package is possible with the shortest possible leads.

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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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24 minutes ago, JohnR725 said:

How do curiosity the modifications purpose is to achieve what?

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

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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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9 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.

The schematic was posted a few posts back.

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5 minutes ago, watchweasol said:

Hello and welcome to the forum     interested to find out how you get on 

THANK YOU!  It is fun stuff.  Tell me what you think....  LOL

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If one never attempts anything nothing will get done and there are always those who know more than you do  who will hopefully share that knowledge to make your path easier. Thats what we are all here for, good luck with the project.

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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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26 minutes ago, LittleWatchShop said:

Yup!

Okay I added caps and biased the input.  Does this look correct?  If so I will add these to my layout.  Anything else you can see that I have wrong?image.thumb.png.d00d51f318b154ed91974ac0db4ca142.png

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7 minutes ago, LittleWatchShop said:

Once you are done, please share the ExpressPCB schematic and layout files.

So far......  Not very tidy. Please check it over if you have time.  I will share when it is finished and tested.image.png.5cef97346f1b198fb8d36227512aa037.png

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