Anyone got a lead on such a pot?
I am making a tone control and using linear pots makes more of an adjustable loudness control than a bass/treble control...
Cheers.
I am making a tone control and using linear pots makes more of an adjustable loudness control than a bass/treble control...
Cheers.
You might consider buying a 23 position switch and using resistors to create a log action taper. That way you will always be sure of reproducible cut/boost.
Another possibility is to buy a Danish Audio ConnecT pre-made step attenuator. They are not inexpensive.
You could purchase a kit for a 10-step attenuator from TubeCAD.com's Glassware store.
Finally, you might go to a thrift store and find used audio equipment with center detent pot. You may have to buy several pieces to find one with the right value (e.g., 10K, 100K, 500K) unless you are capable of scaling the capacitors in the RC circuit. That is something I would not be capable of doing myself, especially in a feedback-type tone control topology.
Another possibility is to buy a Danish Audio ConnecT pre-made step attenuator. They are not inexpensive.
You could purchase a kit for a 10-step attenuator from TubeCAD.com's Glassware store.
Finally, you might go to a thrift store and find used audio equipment with center detent pot. You may have to buy several pieces to find one with the right value (e.g., 10K, 100K, 500K) unless you are capable of scaling the capacitors in the RC circuit. That is something I would not be capable of doing myself, especially in a feedback-type tone control topology.
This one from Alpha suit? Alpha 100K OHM Dual MN-Taper Blend-Balance Potentiometer Center Click ~USA STOCK | eBay
The design is James... So apparently I need a log pot that's 30% at half way, rather than the usual 10%
Right now, it's built with linear and works for it's intended purpose - the fact is adds a "loudness" profile is actually a "feature" for the guy I built it for, but for myself I want a flatter response at centre.
I think I have some suitable pots, but they don't have a centre detent.
I have centre detent but they are linear. I've read about making a linear pot log by tying a resistor from pin 2 to 3 of about 1/4 the pot value. Anyone think that would work?
The MN taper pot works well for a balance control but not for a James. If it has a centre detent I might just grab a couple for balance though.
EDIT: Here's a link to the MN centre detent pot for balance if anyone needs one and doesn't wanna get ripped off by eBay guy. 10K OHM Dual MN taper Potentiometer blend-balance CENTER CLICK
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James is usually built with 10:1 ratios everywhere, so 10% taper.
It appears that James evaded this point.
https://www.talkbass.com/attachments/james-simple-tone-control-circuit-pdf.834665/
By changing all the parts you can build with 50% ("linear") taper, but you get barely 6dB of boost.
It appears that James evaded this point.
https://www.talkbass.com/attachments/james-simple-tone-control-circuit-pdf.834665/
By changing all the parts you can build with 50% ("linear") taper, but you get barely 6dB of boost.
1) Baxandall is he "Pro" type Tone control.
Hugely adjustable, can be set up flat easily and by definition, if Stereo, both pots track very well because Linear tracks are easy to make, easy to design, the works.
To boot, and because of that, it justifies making center detent pots for those who want to *guarantee* flatness, there is market enough for that ($$$$$ run the World).
2) James on the contrary is a "crude" type.
Not easy to achieve a great range of adjustment, doing so implies even higher losses (the only way you can go is down), log pots track worse, are not *real* Log by any means but two linear tracks joined at the center, etc.
I know, I actually manufactured Pots, including coating Pertinax strips with resistive paint, which was later oven cured.
3) there is NO guarantee that setting wiper on "5" (on a 0-10 scale) is exactly -20dB or same in different pots, or even in 2 halves of the same one.
4)
With due respect, if that happens, then top/bottom caps and resistors or Bass control capacitors are poorly chosen.
They also need to follow the 10:1 impedance ratio.
If you reached final values "by ear" , ok, you (or Customer) like them that way, but only by chance will meet the classic design.
Design and build a proper proportioned one for yourself.
And don´t worry about a detent, it will only offer "peace of mind" but actual design and balancing is more important.
Detent will add repeatability but not flatness.
If you "need" 30% pots, then it´s "wrong".
In the long run, this is not a "graduation project" (I guess) which will be critically analyzed by a team of Professors; if you like it, so be it 🙂
FWIW I commercially make Guitar amps and often use some variation of Jones tone control , often use Linear pots (if anything, out of lazyness) .... and nobody complains, ever. 😱
Of course, Guitar players have no use for Graphs, curves or plots, just turn knobs to a setting they like, chosen by ear.
The words "flattness" or "+/- X dB" do not even exist in their language 😉
Hugely adjustable, can be set up flat easily and by definition, if Stereo, both pots track very well because Linear tracks are easy to make, easy to design, the works.
To boot, and because of that, it justifies making center detent pots for those who want to *guarantee* flatness, there is market enough for that ($$$$$ run the World).
2) James on the contrary is a "crude" type.
Not easy to achieve a great range of adjustment, doing so implies even higher losses (the only way you can go is down), log pots track worse, are not *real* Log by any means but two linear tracks joined at the center, etc.
I know, I actually manufactured Pots, including coating Pertinax strips with resistive paint, which was later oven cured.
3) there is NO guarantee that setting wiper on "5" (on a 0-10 scale) is exactly -20dB or same in different pots, or even in 2 halves of the same one.
4)
Why?
With due respect, if that happens, then top/bottom caps and resistors or Bass control capacitors are poorly chosen.
They also need to follow the 10:1 impedance ratio.
If you reached final values "by ear" , ok, you (or Customer) like them that way, but only by chance will meet the classic design.
Of course, Linear pots mean boosted Bass and Treble when set to "5".
Design and build a proper proportioned one for yourself.
And don´t worry about a detent, it will only offer "peace of mind" but actual design and balancing is more important.
Detent will add repeatability but not flatness.
If you "need" 30% pots, then it´s "wrong".
In the long run, this is not a "graduation project" (I guess) which will be critically analyzed by a team of Professors; if you like it, so be it 🙂
FWIW I commercially make Guitar amps and often use some variation of Jones tone control , often use Linear pots (if anything, out of lazyness) .... and nobody complains, ever. 😱
Of course, Guitar players have no use for Graphs, curves or plots, just turn knobs to a setting they like, chosen by ear.
The words "flattness" or "+/- X dB" do not even exist in their language 😉
With respect, using Duncans Tone Stack Calculator, the James topology uses Log B pots which are described as having 30% at 1/2 way in the software. It looks like James but it has an extra 10k resistor (R3). B+ is not marked but it's 250V, and the tubes are 6N1. C5 is 100nF
The circuit I built is attached...
Attachments
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Ok. I think the Log B and Log A are backwards in my head or the help file I saw referenced online - my "help" doesn't work... I set the controls to linear and it's flat when the pot is at the 10% mark. JMF was right, I just need a "normal" audio pot and I found it.
Thanks for all the help everyone!
Koda
Thanks for all the help everyone!
Koda
I tried to find that before, and failed. After a nap, I found it in a few minutes.
"Linear uses a linear track where the resistance is in proportion to rotation of the potentiometer. Log A has 30% of the full value at half-way position, and Log B has 10% of the full value at half-way position."
I don't think Bax is "more pro". Excellent results are possible. More than 20dB "boost" (yes, an un-cut) makes little sense with <6dB/oct slopes. It tends to interact in the midrange but not a lot of dB. It is asymmetrical boost/cut but why must they be the same? And can't the user find a best fit? The "flaw" is the poor tolerance of tapered pots. In mono I have tinkered the passive parts to get flat at centered. Doing that in stereo is more than 4X harder. A Bax even with 20% *tolerance* (not taper) pots tends to wind up within a dB at "center". Which is never quite mechanical center, so if you truly need "flat" you switch-out.
Thanks for that, PRR. I knew I must have it wrong...
Yes, the centre detent is more of a convenience feature.
Long story short, someone commissioned a preamp and power amp combo but wanted tone controls so I designed one quick and dirty not realising it needed log pots rather than linear. I don't use a tone control so now I have 4 extra boards and just wanted to get the right pots to use with them to sell on as kits.
Now that I know more about it, I might use one in a preamp build myself but with different values, and I always bypass the tone control with a switch. In the case of the one I've already built, that "bypass" switch simply shorts input to output on the tone board.
Yes, the centre detent is more of a convenience feature.
Long story short, someone commissioned a preamp and power amp combo but wanted tone controls so I designed one quick and dirty not realising it needed log pots rather than linear. I don't use a tone control so now I have 4 extra boards and just wanted to get the right pots to use with them to sell on as kits.
Now that I know more about it, I might use one in a preamp build myself but with different values, and I always bypass the tone control with a switch. In the case of the one I've already built, that "bypass" switch simply shorts input to output on the tone board.