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Variable Loudness modification
Variable Loudness modification
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Old 4th October 2021, 06:05 AM   #1
presscot is offline presscot  Thailand
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Default Variable Loudness modification

I'm going to build my own preamplifier. I plan to use a variable loudness function from Nakamichi 410 where the circuit is shown on attachment. The brochure exposed the characteristic curve as shown in attached as well. It said that the circuit reduced frequency of 3kHz to make the contour curve. I'm wondering that If I were to change the point to any frequencies, which parts should be varied and how much values? Are they only capacitors to be considered?
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File Type: jpg S__15302674.jpg (19.0 KB, 194 views)
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Old 4th October 2021, 08:33 AM   #2
nironiro is offline nironiro  Croatia
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Capacitors and resistors both make that loudness curve.
Upper RC, above the wiper make treble boost, and lower, under wiper make bass boost.
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Old 4th October 2021, 09:20 AM   #3
presscot is offline presscot  Thailand
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Quote:
Originally Posted by nironiro View Post
Capacitors and resistors both make that loudness curve.
Upper RC, above the wiper make treble boost, and lower, under wiper make bass boost.
Do you know how much values if I were to change the sagging point to 3.5kHz or at least the formula to calculate myself?
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Old 4th October 2021, 12:55 PM   #4
nironiro is offline nironiro  Croatia
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It is posible, but hard to calculate because all depends on the wiper position.
Maybe easiest would be to measure upper and lower parts of potentiometer resistance in 10 positions, and than calculate frequency response that relates to that positions of potentiometer.
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Old 4th October 2021, 05:10 PM   #5
Brinkman is offline Brinkman  United States
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Variable Loudness modification
I’ve seen more than a few loudness controls that boost the high frequencies and this is wrong. Nothing about the Fletcher Munson curves or ISO 226:2003 indicates that this is necessary.

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Old 5th October 2021, 02:47 AM   #6
presscot is offline presscot  Thailand
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I try to draw the circuit myself as shown on attached. I cannot find the symbol of loudness pot (4 pins pot), so I use a typical pot (3 pins pot) series with a resistor. Please advise me is it correct?
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Old 5th October 2021, 09:15 AM   #7
nironiro is offline nironiro  Croatia
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Of course pot is not correct.
Is it logaritmic pot, or antilogaritmic?
Pot is important part of that circuit.
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Old 5th October 2021, 05:20 PM   #8
PRR is offline PRR  United States
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Variable Loudness modification
Quote:
Originally Posted by presscot View Post
Do you know how much values if I were to change the sagging point to 3.5kHz or at least the formula to calculate myself?
Leave the resistors alone. Change the capacitor(s) bigger to shift frequency down, smaller to go up.
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Old 6th October 2021, 02:20 AM   #9
presscot is offline presscot  Thailand
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Originally Posted by PRR View Post
Leave the resistors alone. Change the capacitor(s) bigger to shift frequency down, smaller to go up.
This is similar to what I am thinking.

Could you or anybody derive the formula for the capacitor values?
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Old 6th October 2021, 03:40 AM   #10
PRR is offline PRR  United States
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Variable Loudness modification
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