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Chip Amps Amplifiers based on integrated circuits

Making preamplifier...
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Old 29th December 2017, 08:52 AM   #131
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
Mooly,
the final two resistors setting the gain of the equal component value filter set the Q of the filter.
Setting the Q too high is the problem.
One should be setting the Q of the filter to a value that gives the Shape of the filter.

Gain of the signal is set elsewhere, as you surmised.

Here is Ti explanation.
Section 3 applies to the LPF sch shown. Note 3.1 and 3.4
Thanks Andrew. The details show that I overstepped the gain at which the combined phase shifts take the stage into positive feedback and oscillation.

The magic figure for a Wein oscillator is also a loop gain of 3 and so I tried plugging those values for gain into the circuit. Here we have a 1999 and 1000 ohm feedback network (gain of 2.999) and a 2001 and 1000 ohm (gain of 3.001). There was a 10mv excitation voltage applied to the input in each case.

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Originally Posted by diy1995 View Post
No, on the bass boost I set the gain of 2 (6dB) with 10k - 10k resistors. On original design it was 1k - 10k gain of 11. With gain of 11 it was distorting like hell. I don`t know why author of original bass boost circuit set gain so high. Maybe he used alot lower input signal or something.
Or is gain setted differently for NE5534 (and compatible IC`s) than for NE5532?
I'll change your circuit for a gain of 12db by applying the gain elsewhere.
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Old 29th December 2017, 09:00 AM   #132
Mooly is offline Mooly  United Kingdom
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You need to remove the feedback network and connect the opamp as shown. Then test it and see if you have enough gain for your application. If not then we can add gain around the middle opamp.
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Old 29th December 2017, 02:17 PM   #133
diy1995 is offline diy1995
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Quote:
Originally Posted by Mooly View Post
You need to remove the feedback network and connect the opamp as shown. Then test it and see if you have enough gain for your application. If not then we can add gain around the middle opamp.
I don't understand how should problem show up?
I would also like to use LPF without bass boost.
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Old 30th December 2017, 04:51 AM   #134
PRR is offline PRR  United States
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Originally Posted by Mooly View Post
...oscillator with the gain factor chosen.
It needs a rethink on gain....
You can set gain separate from Q if you use 3 low-value resistors in the NFB.

Your stimulator will tell you the "error of this way". Eyeballing, I think it goes 30dB down (15K/560r) and then eases-off one pole. For most audio purposes this is good-enough.

Yes, gain in the middle buffer works sure.
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Old 30th December 2017, 07:40 AM   #135
Mooly is offline Mooly  United Kingdom
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Interesting, thanks. This is the response with your suggested values. Doubling C5 removes the peak and shifts the turnover frequency down a little.

You could play around with this for hours to get what you want. Here is the original file if anyone wants to play.
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Old 31st December 2017, 12:10 PM   #136
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I fully tested my system with LPF, I didn't even used bass boost. Everything is shaking with 400wrms subwoofer, bass is strong, clean thru whole frequency range. It sounds really good.
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Old 31st December 2017, 01:29 PM   #137
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