Opa1632 gain in 5630evm circuit

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brighter

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Joined 2011
#1
Hi,
I have to increase gain in this circuit by 12dB:

photo%206_zps4lwwbham.jpg


Anyone know how to do it?
Tried increasing 10k feedback resistors to 40k but this reduced gain and/or added roll off in freq response.

Thanks in advance for any info!
 
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#2
We would need to see the circuit to make an informed decision. Sounds like the 10k isn't what you thought it perhaps was. The opamps could actually be configured as unity gain with all the resistors simply forming an active filter. That's not easy to change without hacking the board about.
 
#6
Guess we all have different ideas on this. I would leave the input side of this alone and raise the four 10k feedback resistors to get the gain you need (say to 20k), with appropriate reduction of the two 150pf (82pf would be very close) caps.
 
#7
well; it`s depend on what tools and parts you have; if you have a rework smd station and 0603 resistors is better to replace the 10k resistors; if you have just a letcon and your not familiar with smd soldering put some 22-47uF caps and short the 2.2k resistors
 
#8
why would the 10k to 40k change reduce gain then and next if original 10k created 80khz low pass (given), how is it possible that 40k give instantly audible rolloff, so probably 10khz or lower low pass, I understand it drops (would guess to ~40khz) why so much more ?
 
#9
irribeo said:
why would the 10k to 40k change reduce gain then and next if original 10k created 80khz low pass (given), how is it possible that 40k give instantly audible rolloff, so probably 10khz or lower low pass, I understand it drops (would guess to ~40khz) why so much more ?
Click to expand...

Quite possible that the resistors you changed were not the gain resistors. If you changed the resistors on the input side instead that would be compatible with reduced gain and reduced bandwidth.

These boards are a pain to figure out!

Jan
 
#11
Spreader said:
well; it`s depend on what tools and parts you have; if you have a rework smd station and 0603 resistors is better to replace the 10k resistors; if you have just a letcon and your not familiar with smd soldering put some 22-47uF caps and short the 2.2k resistors
Click to expand...

I have soldering station with narrow blower and it is not too much trouble to resolder anything.
The only problem is that I don't have any experience with opamp circuits.

Thanks to all for trying to help!
 
#14
Spreader said:
if you short r63,r65,r69,andr71 you will have double the gain; but half of the input impendace; you will need to increase 10uF capacitors to a bigger value
Click to expand...

Doube meaning double the voltage or double gain factor?
If double the voltage than, unfortunately, it is not enouh.
I need at least to quadruple voltage to achieve even half of adverised power. When stock, I'm measuring 5w@4ohm, input via bluetooth, all maxed (phone and amp potentiometer) to maximum, and that is with 48v psu. Input via rca, same thing.
 
#16
Hi brighter,

That circuit looks like it has 12dB already in it, are you sure you need an additional 12dB? Might be useful to download ti filter pro and simulate a 1st order multiple feedback (MFB) fully differential circuit. Free from the TI website.

This process should only take a few minutes to download install and sim. Simply set the filter order to fixed 1 order. After that change the feedback resistors to 10k and the program automatically calculates the capacitance and gain resistor values. If you ignore the passive 1st pole input filter you should be close enough to the original filter response but with your desired increased gain.
 
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