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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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Old 6th May 2014, 05:15 AM   #11
PKN is offline PKN  Australia
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Quote:
Originally Posted by Zero D View Post
@ PKN

If you want to use a variable resistor/POT in both positions, you can. But as you showed only one in your initial sketch, i thought that's what you wanted !

Either way will work though.
Thanks mate you guys have been really helpfull. Sorry about the miss understanding.
I will try your circuit you designed for me and report back today.
Your design looks good and I will learn how to implement this in future projects.

Thank you
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Old 6th May 2014, 07:56 AM   #12
PKN is offline PKN  Australia
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@ Zero D

I have made the circuit you provided for me. It works
If i was to put a variable resistor on R5 say 5k or 10k this should increase the gain?
I know this works with DC voltages but i am not sure with line level inputs since it contains audio information

Thanks.
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Old 6th May 2014, 08:57 AM   #13
AndrewT is offline AndrewT  Scotland
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R5 & R4 set the gain of the first stage.
The gain for a non-inverting topology is 1+[R5/R4]
Change either R4 or R5 to change the gain, i.e. change the ratio of R4:R5.
You MUST use a unity gain stable opamp.
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Old 6th May 2014, 09:40 AM   #14
PKN is offline PKN  Australia
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Quote:
Originally Posted by AndrewT View Post
R5 & R4 set the gain of the first stage.
The gain for a non-inverting topology is 1+[R5/R4]
Change either R4 or R5 to change the gain, i.e. change the ratio of R4:R5.
You MUST use a unity gain stable opamp.
Thanks for your reply mate.
I will do some test on this part of the circuit tomorrow and see what happens.

Thank you
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Old 6th May 2014, 10:45 AM   #15
Zero D is offline Zero D  United Kingdom
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Quote:
Originally Posted by PKN

Your design looks good and I will learn how to implement this in future projects

I have made the circuit you provided for me. It works
Nice to hear

Quote:
If i was to put a variable resistor on R5 say 5k or 10k this should increase the gain?
Yes it will, but due to the limited amount of headroom you have running on 12V, you could easily clip/distort the signal. I doubt whether you will need much gain though.

R5 is the best position to replace the resistor. I would expect a 5k to give you more than enough gain, but if even you choose a 10K obviously you can still set it lower.
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Old 6th May 2014, 11:00 AM   #16
AndrewT is offline AndrewT  Scotland
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R5 can be lower than R4.
But the gain is still 1+[R5/R4]
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Old 10th May 2014, 10:08 AM   #17
PKN is offline PKN  Australia
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Ok Guys i have made the circuit on a PCB. Here are some pictures.

Just got to make the housing.
Attached Images
File Type: jpg rsz_low_pass_filter.jpg (183.9 KB, 110 views)
File Type: jpg rsz_low_pass_filter_circuit.jpg (170.3 KB, 106 views)
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Old 10th May 2014, 12:08 PM   #18
Zero D is offline Zero D  United Kingdom
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Hi, looking good !

Did you build it Exactly as in my Post #6 ? Also as i don't see variable resistors on the R5's, what value are the fixed resistors ?
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Old 10th May 2014, 12:30 PM   #19
PKN is offline PKN  Australia
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Quote:
Originally Posted by Zero D View Post
Hi, looking good !

Did you build it Exactly as in my Post #6 ? Also as i don't see variable resistors on the R5's, what value are the fixed resistors ?
Hey mate thanks. Yeh i used your circuit design. Did a test run today it works good.
I did not use the gain option I am running it on unity gain. It sounded fine with no gain. If i need more i will use the amplifier gain to boost it a bit.
Thanks for all your help. I will post pics of the housing once i made it.

Thanks
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Old 10th May 2014, 01:35 PM   #20
Zero D is offline Zero D  United Kingdom
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That's good to hear Looking forward to your compleated screenies.
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