Loudness stage

Today built up most circuits in this thread and settled on original Yamaha.
You would not think based on response plots.
But hooked up to a real amplifier sounded great.
I would say, even metaphysical.
Tweaked the input cap and resistor slightly but otherwise its the Yamaha circuit.
Best sound at various spl levels for me was between 5 and 6 on loudness dial.
 

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I used 10nF instead of the 8.2nF because can get 1% cheap.
The series resistor waiting for final test 4.7k - 8.2k, doing new pcb.
All other values same.


In the final app it is driven with opa1622 headphone amp.
It requires very lo-z drive. Otherwise weird peaking responses.

The driven output load load on my test ckt is a 20kA volume pot .

It cannot be driven from typical line-out.
 

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Guys, please help to find where is a mistake in the loudness control.
I used Alps RK09L series potmeter (100k log).

I think first mistake is that the potmeter wired reverse, according to the Freq. resp. measurement.
Questions:
- 10k log better instead of 100k log?
- Or I have to adjust the resistor size to 100k log?

Or there are another mistake?

Thanks
Laszlo
 

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R1 and C2 must be connected to loudness tap, not to wiper.

Edit: this is not usual loudness circuit, bass eq is mono?
Strange, with potentiometer without loudness tap I would copy some old circuit from old amps/receivers that use this standard potentiometer.
But I never saw connection like this. Volume pots are always connected to ground, your is summed to mono and that connected to cap and resistor to ground.
 
Last edited:
R1 and C2 must be connected to loudness tap, not to wiper.

Edit: this is not usual loudness circuit, bass eq is mono?
Strange, with potentiometer without loudness tap I would copy some old circuit from old amps/receivers that use this standard potentiometer.
But I never saw connection like this. Volume pots are always connected to ground, your is summed to mono and that connected to cap and resistor to ground.

I followed a wrong schematic. I designed based on Loudness stage
instead of
Loudness stage

the R1 location is wrong.