Ultimatest Passive Tone Control Network based on James-Baxandall's topology wanted - diyAudio
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Old 5th September 2011, 06:15 PM   #1
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Default Ultimatest Passive Tone Control Network based on James-Baxandall's topology wanted

Ultimatest Passive Tone Control Network based on James-Baxandall's topology

Arround James-Baxandall's topology there are a very extrem amount of proposals about google - thus this don't help me.
here some examples and a basic article (overview)
Tone control circuit - Wikipedia, the free encyclopedia
The James-Baxandall Passive Tone-Control Network
http://home.comcast.net/~stphkeri/Ne...edbackTone.pdf
Baxandall Tone Control Using CA3140 Op-Amp | Circuit Diagram
http://www.ti.com/lit/an/sloa042/sloa042.pdf

There are two basiclly topologies:
1) passive version between two line gain/buffer stages
2) active version - i. e. in the negative feedback loop (frequency dependend NFB) from an inverted mode amplifier and from a non inverted mode amplifier - both in voltage amplifier gain stages (preamp) and power amplifier stages in cases without separate preamp line stage.

I need the best circuit topologies for both applications. The most important features for me are follow:
1) the insensibility (immunity) against electromagnetic hum sources and against microphonic effects.
This means, low impedance character (i. e. the contrary of such circuits, where the variable resistors/pots have values between 5 meg-ohm and 10 meg-ohm, often to find in tube amp/preamp stuff and vintage tube audio devices).
2) the establishing of any cutoff frequencies for the lower and upper aera

Where I can find such circuit topologies both here on diyaudio and by commercial devices?
Thank you for your advices

Last edited by tiefbassuebertr; 5th September 2011 at 06:20 PM.
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Old 5th September 2011, 06:24 PM   #2
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You can build a classic Baxandall circuit using opamps and switched low value resistors.

He used pots that are really not easily found today and was limited to high impedance valve circuitry.
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Old 5th September 2011, 09:07 PM   #3
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Quote:
Originally Posted by simon7000 View Post
He used pots that are really not easily found today and was limited to high impedance valve circuitry.
low impedance pot is the smallest issue. Here I intend to use a rotary switch like ELMA (Switchable Attenuator/Rotary Switch) or an relay controlled solution.
A selection can be found under
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Potentiometer Overview - Alps, Penny+Giles, TKD and Vishay and more, what's your fav?
Quote:
Originally Posted by simon7000 View Post
You can build a classic Baxandall circuit using opamps and switched low value resistors.
Unfortunately only by using of power op-amps.

Last edited by tiefbassuebertr; 5th September 2011 at 09:12 PM.
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Old 5th September 2011, 09:20 PM   #4
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Try this. You can use almost any opamp as the current requirements are not too severe.
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Old 5th September 2011, 10:38 PM   #5
forr is offline forr  France
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Almost by definition, the Baxandall tone circuit can only be active. Using a virtual earth input, it enabled very low distorsions compared to all other tone controls of the time.
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Old 6th September 2011, 01:08 AM   #6
Zero D is offline Zero D  United Kingdom
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@ tiefbassuebertr

Hi, your title is misleading, as you then go on to say you're looking for active too

I've always known him as Peter Baxandall, now i know his middle name

You might like to take a look at Page 27 of Doug Self's Precision Preamplifier Tone control circuit in here Self_on_Audio_Second_Edition.pdf

This should be available from his www, i think !

It's what i built & use in my PreAmp, which i've had for many happy years. You can change the caps around the pots to suit the centre frequencies you desire, i did.

Use high quality BiPolar OpAmps for low impedance work

You should place a buffer on the output as well.
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Old 6th September 2011, 01:23 AM   #7
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Some time ago I looked at non inverting Baxandall type tone controls, and after some searching, I found these. The idea isn't new, it was used in the Crown IC150 pre amp of the early '70's.

The non inverting type have gain (I've set it at 2, Crown used a gain of 11 I think), and a high input impedance, so they don't need to be driven from a buffer stage. With the values I've shown, the boost is twice that of the cut, which some people might not like, but I think it is probably more useful than similar cut and boost values. A simple DPDT switch will defeat the tone controls and give a flat response.

Note that the two attached drawings have different R&C values. The schematic is shown with 100K pots, and the curve drawing with 50K pots (both linear).

Paul Bysouth, Sep 2011
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File Type: gif Baxandal-Non-Inverting.gif (50.1 KB, 1036 views)
File Type: gif ToneControlResponse.gif (47.7 KB, 998 views)
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Old 6th September 2011, 10:29 PM   #8
mlloyd1 is offline mlloyd1  United States
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search on this site for the APT Preamp schematic or manual. When I used to use tone controls, I was happy with this one. You could also look for the (now expired) patent.

mlloyd1
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Old 7th September 2011, 04:51 PM   #9
banat is offline banat  Serbia
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Tiefbass check the Luxman integrated Amps for `` Duo Beta `` tone control circuit !

Best Regards
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Old 7th September 2011, 05:14 PM   #10
mlloyd1 is offline mlloyd1  United States
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oops, sorry my comment is not appropriate after all. i missed the header about passive. the APT uses an active version.

mlloyd1

Quote:
Originally Posted by mlloyd1 View Post
search on this site for the APT Preamp schematic or manual. When I used to use tone controls, I was happy with this one. You could also look for the (now expired) patent.

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