Simple Tone control - how to modify for optimal response

[tnvijay]

This might be the simplest active tone control circuit, but is there a way to modify the gain and frequency response?
The circuit as given gives a gain of +/-20 dB which I think is huge and distorts given today's digital sources with 1vpp output.. Is there a simple way to modify the gain to +/-10 dB?

1. What is the effect of reducing the variable pots 100k to 47k?
2. What is the effect of replacing the Emitter resistor 1k and connecting to ground?

 

[rayma]

Here is some design info, use figure 12, which is a better circuit: https://sound-au.com/dwopa2.htm

Reducing the pot resistances would raise the frequencies where the tone action starts.
The range of bass adjustment would also be reduced a little.

You don't want to short out the emitter resistor, since the circuit would not work.
And the 1k is bypassed at signal frequencies anyway.

 

[tnvijay]

I have noticed that this tone control does a high midrange boost,which I don't like, If I want the bass boost to happen only below 100 hz and the treble boost only above 10khz, how to Modify for that...

 

[rayma]

Yes, look at figure 12 in the link.

The series resistors with each pot determine the amount of gain/cut.
Increase them all proportionately, until the gain/loss is what you want.
Don't change the pot values.

To change the frequencies as you describe, change the capacitors. Bigger for bass, smaller for treble.

 

[tnvijay]

Thankyou, Got the idea

 

[ejp]

Here is some design info, use figure 12, which is a better circuit: https://sound-au.com/dwopa2.htm

Rod‘s equations are incorrect. He notices himself that he gets wrong values. Use the equations in Baxandall’s original paper.

 

[tnvijay]

I see two variants of baxandall, one in which a single treble capacitor is connected to wiper and other in which two capacitors are connected on either side...Which one is preferred

 

[ejp]

I see two variants of baxandall, one in which a single treble capacitor is connected to wiper and other in which two capacitors are connected on either side...Which one is preferred

There are really four variants. On the bass side you can have one capacitor shunting the entire pot, or two meeting at the wiper. On the treble side you can have two capacitors, one leading to each side of the pot, or one capacitor in series with the wiper.

At this point I am going to refer you to the National Semiconductor Audio Handbook, 1976, pp 2-44 to 2-48, which you will find online, or the Tone Controls chapter in Douglas Self, Small Signal Audio Design, for a full discussion of the differences. They aren't great but they affect the calculations. The choice may simply come down to cost.

 

[ejp]

Rod‘s equations are incorrect. He notices himself that he gets wrong values. Use the equations in Baxandall’s original paper.

Using the correct equations, Rod's treble Ft is ~3700Hz, which is far too high, although not as high as his calculation of 13kHz. Changing the 560pF capacitor to 1nF reduces it to 2094Hz, which is still perhaps a bit too high.

 

[madis64]

I am pretty sure a simple LTSpice simulation would answer most of the OP questions.

 

[ejp]

Well not really. The equations show you what you can change and what it will affect. SPICE knows that, but it can’t tell you. For example, changing any of the four RIAA components will move the zero of the transfer function. That’s obvious from the transfer function itself, but only several SPICE experiments will show that, and it would be easy to miss.

 

[madis64]

Well not really. The equations show you what you can change and what it will affect. SPICE knows that, but it can’t tell you.

I reserve the right to disagree.
Use .step instructions and find out what the variation of each component results in.
But yes, LTSpice is not an optimizer so some manual work would be involved. 🙂

 

[ejp]

Rod‘s equations are incorrect. He notices himself that he gets wrong values. Use the equations in Baxandall’s original paper.

I communicated with Rod Elliott about this and he has now fixed the page.

 

[JMFahey]

SPICE is a powerful and very useful tool but it can not think or take decisions by itself.
You must first know the general principles behind anything.

 

[tiefbassuebertr]

here some advices:
https://learnabout-electronics.org/...line in Fig.-,4.2.,true bass and treble boost.
https://audiohertz.com/2020/09/09/what-the-fck-is-a-baxandall-eq/
https://www.duncanamps.com/tsc/index.html
the original article you will find in the attachment.
Luxman's integrated amp models L510 and L540 (so as several vintage Pioneer receivers) use an extended equalizer version with additional cut-off switches - check out last page of the attached service manual.
check out also this threads
https://www.diyaudio.com/community/threads/modified-baxandall-tone-control.398364/
https://www.diyaudio.com/community/threads/active-baxandall-tone-amp-design-ideas.394177/
https://www.diyaudio.com/community/threads/asymmetric-baxandall-tone-control-circuit.401494/
https://www.diyaudio.com/community/...entiometers-in-baxandall-tone-control.361027/
https://www.diyaudio.com/community/threads/baxandall-eq.40902/
https://www.diyaudio.com/community/threads/baxandall-differences.289173/

 

[kouiky]

I have noticed that this tone control does a high midrange boost,which I don't like, If I want the bass boost to happen only below 100 hz and the treble boost only above 10khz, how to Modify for that...

My main complaint with 99% of tone controls is the bass accentuation that was normally designed in above 100Hz. A few extra components plus a switch could have made it frequency selectable.

Feel free to check out Doug Self’s preamp from Linear Audio (volume 5) to get some ideas for a really interesting tone control. It’s frequency selectable using a potentiometer. At full boost the tone stack doesn’t clip until about 4.7V peak input.

https://linearaudio.net/douglas-self-preamp-linear-audio-vol-5