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Thread: Tone Pots: Linear or Audio? Why?

  1. #71
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    Unfortunately if you need a split knurled shaft pot you can get them from Allessandro or antique radio supply. They are expensive. They will fit into smaller cavities like a Tele and you can solder to the back. Otherwise, the PEC's are a larger body , solid shaft and the back is hard to solder too, (stainless). You don't really need to solder to the back , it is just convenient. and $7.95 ea. Should fit most hollow body and les paul or strat style guitars.

    I believe you were talking about a Gretsch jet firebird. make sure you have about 2" diameter opening to work with around each pot. The pots measure 1.5 inches in diameter I believe. So 2" is tight but doable. And a knob that has a set screw, as I know vintage Gretsch's do.

    The PEC pots are 3/8: opening and 1/4" shaft diameter, same as CTS. Only the body is larger diameter.

  2. #72
    Old Timer J M Fahey's Avatar
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    I'm sorry but the example posted : Tone Control Circuit , a poor example in an beginner made page, is *not* a Baxandall type tone control (which is active), but a poorly designed passive James tone control.
    And in the passive type, the pots are not linear, but 10% logarithmic, to evenly balance losses in the high pass and low pass halves, and provide flat response on "5", (on a 0-10 scale), which is the reguar use.
    The real Baxandall one is:
    , which can be found at: Op-Amps as amplifiers and Tone Controls.
    For those who want the real thing:http://www.dself.dsl.pipex.com/ampin...y/ampartew.htm
    the *original* article by Peter Baxandall in Wireless World Magazine:
    1952
    Negative-Feedback Tone-Control Peter J Baxandall Oct 1952 p402
    ;
    a side comment on this article says:
    1950-59
    Baxandall, P J "Negative-Feedback Tone-Control" Article published Wireless World Oct 1952, p402.
    This is the famous article that introduced the Baxandall tone-control, which was for decades the universal choice in preamplifiers and mixing consoles, and is still by far the most popular arrangement where people feel they can permit themselves tone-controls at all.
    Before this article, tone-controls could be incredibly complicated, often involving switches and inductors. See Chapter 15 of The Radio Designer's Handbook by Langford-Smith; the currently reprinted 4th edition came out in 1953, but rather surprisingly does not mention the Baxandall concept; perhaps it appeared too close to the publication date.
    Apart from the payment for the article (which would not have been generous in 1952) I think I am right in saying that Peter got no financial return from this, his most famous idea.
    As an example of a properly-designed James tone control, just check the typical Ampeg tone controls, with its properly dimensioned 10:1 (20dB) attenuation appearing everywhere: treble capacitors: 4n7/47nF ; Bass capacitors: 10n/100nF; Bass resistors: 220K/22K; 10% Log Pots: 1M Log or Audio.
    This gives uniform attenuation (20dB) across the audio band (flat response), with pots set on "5", less attenuation (perceived as "boost") on higher values and the corresponding symmetrical "attenuation" on lower values.
    On the contrary, on the real Baxandall negative feedback tone controls, linear pots are used so there's symmetry on both halves of treble and bass networks, achieving flat response on "5".
    Mind you, linear pots are not the best choice, because then tone boost and cut is not uniform to our ears, but the required "S" curve one is complicated to make and very expensive.
    Common feedback type graphic equalizers also would need "S" pots, which is economically out of the question.
    Another reference to the original one, and by no less an authority than J. Linsley Hood:
    http://books.google.com/books?id=rn8...0valve&f=false
    Last edited by J M Fahey; 01-14-2010 at 09:03 PM. Reason: Forgot Link

  3. #73
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    BillyZ.... you said
    The best I have found are PEC available at Antique Radio supply. But others like the custom CTS pots from RS guitars and others.
    I called PEC - they're in Toronto, not far from me. Someone there helped me locate 2 options for pots...

    MIL Style RV4
    http://www.precisionelectronics.com/...tyle%20RV4.pdf - which he said was VERY close to the 500K solid CTS pots I have.

    and

    MIL Style RV2:
    http://www.precisionelectronics.com/...tyle%20RV2.pdf

    I'd like to know, what pots from them have you used? What model etc? Here's their page: Product Specs

    Much thanks again.

  4. #74
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    Quote Originally Posted by maltone View Post
    BillyZ.... you said

    I called PEC - they're in Toronto, not far from me. Someone there helped me locate 2 options for pots...

    MIL Style RV4
    http://www.precisionelectronics.com/...tyle%20RV4.pdf - which he said was VERY close to the 500K solid CTS pots I have.

    and

    MIL Style RV2:
    http://www.precisionelectronics.com/...tyle%20RV2.pdf

    I'd like to know, what pots from them have you used? What model etc? Here's their page: Product Specs

    Much thanks again.
    It seems this thread has broken into two separate discussions, ha ha.
    No problem for me, I find the other discussion interesting and far more technical.

    Well, I think I learned something. RV2 is a 1 watt rated pot and RV4 is a 2 Watt pot. And the RV2 is a Brass body meaning you can solder to it.

    The RV2 looks like exactly what you ( and I ) want. Most of mine are KA series or RV4 . KA is the commercial number, I understand it is the same pot.

    The RV2 looks like a 3/4 diameter opposed to the RV4 which is 1" diameter.

    By the way you can also order from Digikey.

    I would go with the RV2 500k A . let us know how it turns out.

    I have compared PEC to CTS , Alpha , Bourns an others. The PEC is only bested by some vintage Centralab Pots, equal to Clarostat A/B.

  5. #75
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    BillyZ, thanks again.

    You said:
    The RV2 looks like a 3/4 diameter opposed to the RV4 which is 1" diameter. I would go with the RV2 500k A . let us know how it turns out.

    I have compared PEC to CTS , Alpha , Bourns an others. The PEC is only bested by some vintage Centralab Pots, equal to Clarostat A/B.
    I'm trying to get pots that are the same size, body etc as my current CTS Pots. Really, those centralabs are hard to find, and very expensive. Ideally, I'd like to find a drop in replacement that's rated not only 500K or above for ALL pots (matched), but also pots with a taper of 70:30 or 65:35 (preferred).

    Billy, can these PEC pots be used "as is", or do they need to be tweaked somehow to be used as audio log pots?

    If I call PEC back, would it be correct to ask them, "what's the taper ratio of these pots"? - Thanks again Billy.

  6. #76
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    Quote Originally Posted by maltone View Post
    BillyZ, thanks again.

    You said:

    I'm trying to get pots that are the same size, body etc as my current CTS Pots. Really, those centralabs are hard to find, and very expensive. Ideally, I'd like to find a drop in replacement that's rated not only 500K or above for ALL pots (matched), but also pots with a taper of 70:30 or 65:35 (preferred).

    Billy, can these PEC pots be used "as is", or do they need to be tweaked somehow to be used as audio log pots?

    If I call PEC back, would it be correct to ask them, "what's the taper ratio of these pots"? - Thanks again Billy.
    The Taper of the PEC is the best you can currently find, I am not certain exactly what they are. I just know by my own experience. The just feel right.

    I only mentioned the Centralabs because I feel they were the Standard of what the best taper sounds like.() They are no longer made and are very expensive( also, The Tolerances are not as tight as the PEC). The PEC's are just as good ( if not better) and actually feel Smoother.

    The PEC requires no mods what so ever , They are right. Just get the Audio or LOG taper pot, NOT Linear.

    The diameter is only slightly greater than the CTS and should cause you no problem.

    As for matching, I don't think it is all that critical. The PEC's are very tight tolerance and MILITARY spec. But, for grins, measure them. I would use the highest ohms for the volumes and the lower for the tone. If you want to go further then say want a brighter neck PU, use the higher value there. OR use the lower value to compensate for a too bright PU.

    PEC does offer tolerances of 10% or 20%, ask about the price of each.

    I will be using the RV2 from now on. I suspect it what Allesandro has been selling all along at $40 a pop.

    Hey, If you don't like them , sell them me. You are no going to find a better current production potentiometer.

  7. #77
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    Hi all, thanks for the interesting info in this thread. I did post in the past but with college and stuff it's been a while. I was emailed and informed I was about to be "pruned" (doesn't sound too appealing) so I've just jumped back in. I tried to get the Peavey T60 schem that was ref'd earlier in the thread. Does anybody have one? The schem I mean. Cheers!

  8. #78
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    Hi, sorry if I haven't made any worthwhile contribution but I can't force something I'm afraid. Is it possible anyone here has a schem of the type referred to earlier in this thread for the Peavey T60. The original link doesn't seem to lead anywhere related to the guitar in question.

  9. #79
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    Quote Originally Posted by TriggerX View Post
    Hi, sorry if I haven't made any worthwhile contribution but I can't force something I'm afraid. Is it possible anyone here has a schem of the type referred to earlier in this thread for the Peavey T60. The original link doesn't seem to lead anywhere related to the guitar in question.
    Try this:

    http://natcade.tripod.com/schems/Peavey/t-40_t-60.gif

  10. #80
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    Quote Originally Posted by Glass Snuff View Post
    Thanks for the link. Sorry about the delay in getting back to you. Cheers!!! :-)

  11. #81
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    The link doesn't work.

  12. #82
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    This is a very, very, very OLD thread, but could not resist ..."resurrecting" it because I want to settle the argument once and for all about the human perception of sound.

    Our ear, all it "hears" is volume and indeed the perception of volume is not linear but logarithmic. But frequency response (e.g. coloration, EQ curves, etc.) is also heard as differences in volume at specific bands. Our ears emphasize the 1K - 4K (mid) spectrum (intelligibility range) because this is also the spectrum where human speech is usually produced.

    This means that for our ears to perceive different sound frequencies as of equal volume, the audio signal should have an SPL (sound pressure level) of 50 dB at 10K, 70 dB at 40K and 35 dB at 2.5K. Please follow this ---> https://en.wikipedia.org/wiki/Equal-...le:Lindos1.svg to see more about the "equal loudness contour". You will realize that our perception of tone, also depends on volume differences which is based on a logarithmic scale. And that explains why most stock guitars do use audio taper pots for tone controls.

    Of course I have to agree with and applaud Mark Hammer's comment that -ultimately- it all depends to ear of the ..."beholder" (or perhaps of the "behearer"? LOL).

  13. #83
    Supporting Member Steve A.'s Avatar
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    Each guitar (and guitarist!) is unique so I play it by ear. If I think that a linear taper tone pot gets too bright too soon when turning it up from 0 then one solution might be to replace it with an audio taper pot.

    As for volume controls I think it depends on whether you want more control when turning up from 0 or when turning down from 10. I prefer the latter, especially when told to turn down. Besides I never could do the Roy Buchanan volume swell with my pinkie.

    Then again I have a friend who wants to be able to turn the volume down quickly when switching from leads to rhythm guitar so he likes an exaggerated audio taper. Diff'rnt strokes for diff'rnt folks...

    Steve A.

    P.S. I have a theory that audio taper pots were invented - or at least became much more popular - in the 30's when you turned your radio on by turning up the volume control. For applications like that linear pots usually don't work that well...

    P.P.S. The imported PRS SE guitars usually come with just two pots, an audio taper volume control and a linear taper tone control which I thought was great because I could just switch them around...
    Last edited by Steve A.; 09-16-2017 at 07:03 PM.

  14. #84
    rjb
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    Quote Originally Posted by Steve A. View Post
    If I think that a linear taper tone pot gets too bright too soon when turning it up from 0 then one solution might be to replace it with an audio taper pot.
    Linear tone pots are for doing the Danny Gatton boo-wah.
    You rock the knob between 0 & 3 to oscillate between mud & clear with little rotation.
    It's a one-trick pony.

    Quote Originally Posted by Steve A. View Post
    As for volume controls I think it depends on whether you want more control when turning up from 0 or when turning down from 10.
    What about folks who use somewhere around 5 as home base?

    -rb

    PS - Don't mind me. I'm just taking a break from home winterizing.

  15. #85
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    A few things spring to mind with pot tapers;

    Most log or audio tapers aren't. This is why rotary switches are used in precision audio applications. I once had a volume control removed form an early Abbey Road desk and it had loads of precision resistors and maybe 100 positions on the large rotary switch. This gave a true (though stepped) log taper. Some hi-fi preamps use the same approach. Most, if not all commercial pots that I'm aware of use two or maybe three linear sections which form a transition 'knee' and don't have a correct taper.

    Different audio taper ratios are available and some work better than others with particular setups. This distinguishes 'audio taper' from 'log' pots. They're not necessarily the same.

    The pot taper doesn't sit in isolation; there's an interaction with the pickup resonance and in turn this is affected by cable capacitance and the tone circuit characteristics. This has a bearing on the perception of volume at various control positions that are outside the plotted DC taper characteristics.

    Amp distortion has a bearing on control perception; A heavily clipped amp or pedal will often not drop much in volume until the guitar signal is reduced below clipping level. I say often, because there are distortion setups that track the clean signal and apply the clean volume envelope to the distorted signal to give enhanced playing dynamics. But generally a pot taper can behave differently with a clean amp compared with a distorted one.
    pdf64 likes this.

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