Loudness stage

[jfetter]

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.

 

[toulou]

Yep, this simple circuit sounds good.
What values did you settle to, and what load is it driving? Cause there are many "original Yamaha's" with different values.

 

[jfetter]

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.

 

[gaszto]

Thus:

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

 

[jfetter]

Maybe replace the 100k pot with a 10k. Also are you driving with lo-z signal?

 

[gaszto]

Ok, first I replace 10k log type.
I just tested, and mesured with my Presonus AudioBox. Later I want to use with my tube amp. How should it be connected? Connect to the input siganal after the Volume pot.?

 

[jfetter]

What specifically is the problem with it?
If presonus has a headphone out use that for drive as a test.

 

[nironiro]

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.

 

[nironiro]

One example of loudness with standard pot is on Pioneer SX700 receiver, but it has only bass boost.

 

[gaszto]

What specifically is the problem with it?
If presonus has a headphone out use that for drive as a test.

I measured this freq. resp.

 

[gaszto]

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.

 

[nironiro]

I made a mistake too, sorry.
I was thinking that this is classic loudness on volume potentiometer, but this is Yamaha type of variable loudness, after the volume pot.

 

[sesebe]

The loudness circuit like this must be drive by a low impedance circuit and not by a variable impedance circuit as it is the slider of a potentiometer.

 

[gaszto]

I made a mistake too, sorry.
I was thinking that this is classic loudness on volume potentiometer, but this is Yamaha type of variable loudness, after the volume pot.

I changed the pot. from100k to 10k and according the original description I doubled the resistor values, and halve the capacitance, and it's working now. Thanks

 

[jfetter]

can you please put up the final schematic here? thanks

 

[gaszto]

I've attached the final schematic, and the pcb layout.

 

[jfetter]

Super!

 

[jfetter]

Here is the Dual CV40 loudness.
The pot has me wondering is it a special or drawn odd?

Its a discrete transistor design from 1968.

 

[nironiro]

You're right, that pot is a special one, with two loudness taps.
Same as Grundig amplifiers, up to 1/3 is double loudness effect, from 1/3 to 2/3 is just one loudness, and after 2/3 is linear.

 

[nironiro]

This is 5 pin volume pot in Grundig SV 2000 amplifier.
Many Grundig models use that double loudness.