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Squeezing maximum gain from one dual op-amp?
Squeezing maximum gain from one dual op-amp?
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Old 2nd February 2018, 06:24 PM   #1
Eps is offline Eps  United States
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Default Squeezing maximum gain from one dual op-amp?

Hello,

I'm a beginner and working on a very simple preamp for a mono tape head.
I actually only need one side of the chip to since Im just using a mono head. Is it easy or possible to use the other side of this dual op-amp as an extra gain stage? If so what kind of rules do you generally need to follow?

Thank you!


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Last edited by Eps; 2nd February 2018 at 09:37 PM.
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Old 2nd February 2018, 08:45 PM   #2
rayma is online now rayma  United States
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Quote:
Originally Posted by Eps View Post
Is it easy or possible to use the other side of this dual op-amp as an extra gain stage?
Yes, as long as you use DC blocking capacitors at the inputs and the output.

Last edited by rayma; 2nd February 2018 at 08:48 PM.
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Old 2nd February 2018, 09:35 PM   #3
Eps is offline Eps  United States
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Originally Posted by rayma View Post
Yes, as long as you use DC blocking capacitors at the inputs and the output.
Thanks! Would you be able to guide me a little in the direction to make the second gain stage? Would it involve leaving the first stage as is and then removing the NAB eq from the second stage?
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Old 2nd February 2018, 09:40 PM   #4
rayma is online now rayma  United States
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Quote:
Originally Posted by Eps View Post
Thanks! Would you be able to guide me a little in the direction to make the second gain stage?
Would it involve leaving the first stage as is and then removing the NAB eq from the second stage?
Yes, the only difference would be the feedback network, which becomes just a resistor
instead of the tape eq. For example, short R1 and C1. Change R6 to 750R, for a flat gain
of x11, or +21dB.

Last edited by rayma; 2nd February 2018 at 09:48 PM.
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Old 2nd February 2018, 09:56 PM   #5
Eps is offline Eps  United States
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Quote:
Originally Posted by rayma View Post
Yes, the only difference would be the feedback network, which becomes just a resistor
instead of the tape eq. For example, short R1 and C1. Change R6 to 750R, for a flat gain
of x11, or 21dB.
Sweet! So does that mean when looping back in (say from left output to right input on to the second stage) I could also leave out C10 & C8? Or would it be better to leave them in as extra RF blocking?
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Old 2nd February 2018, 10:04 PM   #6
rayma is online now rayma  United States
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Quote:
Originally Posted by Eps View Post
Sweet! So does that mean when looping back in (say from left output to right input
on to the second stage) I could also leave out C10 & C8?
Right, only one DC blocking capacitor is needed for a connection, not two in series.
The C10 should not be necessary either.
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Old 2nd February 2018, 10:52 PM   #7
Eps is offline Eps  United States
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Quote:
Originally Posted by rayma View Post
Right, only one DC blocking capacitor is needed for a connection, not two in series.
The C10 should not be necessary either.
Thanks, and is there anything to know about how to avoid or even introduce distortion from this type of setup?
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Old 2nd February 2018, 10:57 PM   #8
rayma is online now rayma  United States
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Originally Posted by Eps View Post
Thanks, and is there anything to know about how to avoid or even introduce
distortion from this type of setup?
Careful construction, with a power supply bypass capacitor, should make it work well.
Clipping caused by too high gain would be the easiest way to add distortion.
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Old 2nd February 2018, 11:28 PM   #9
Eps is offline Eps  United States
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Quote:
Originally Posted by rayma View Post
Careful construction, with a power supply bypass capacitor, should make it work well.
Clipping caused by too high gain would be the easiest way to add distortion.
So if I added a pot in the feedback network of the second stage and then used a some value of limiting resistor in series with the pot I could obtain distortion correct? I will try it also later
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Old 2nd February 2018, 11:31 PM   #10
rayma is online now rayma  United States
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Quote:
Originally Posted by Eps View Post
So if I added a pot in the feedback network of the second stage and then used a some value
of limiting resistor in series with the pot I could obtain distortion correct? I will try it also later
Should work.
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