Tone Control/Sound Quality

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

I noticed something today that everyone should be aware of. The standard way of putting on a tone control is as follows: Run a "T" wire off of the output, or plus wire, of the pickup, to a 500K POT, which is wired as a variable resistor. Then come out of the POT, to a .022uf capacitor, then to ground. There is a real "BIG" problem with this approach that no one tells you about. Your signal is AC not DC, so it flys through capacitors, and is only limited by resistors. As you cut off highs with the tone control, you are losing signal. You lose signal needlessly unless the resistance the signal going through the .022uf capacitor sees is the same as the resistance on the plus line out of the pickup. Remember signal takes the path of least resistance. So, what is the resistance downstream on the plus line? That could depend on a lot of things. If you use a Pot pedal, that resistance is constantly changing. Then the input of your amplifier--pre-amp usually has a resistor to limit current. Now what I am getting at is that the signal sent through the tone control ,.022uf, sees less resistance to ground, unless you match the resistance on the plus line. This makes all the difference in the "WORLD" on tone quality, and a balanced sound out of the pickups. If you don't balance these resistances, your guitar pickup is losing tone quality. I suppose that is why many steel makers have quit putting tone controls on steels. The value of the resitor could not be determined,since so many guys use so many different hookup methods. The actual resistor value can only be determined when you know the resistances down stream. What really matters is the resistance to the first pre-amp, or the first active device.

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C Dixon · From: Duluth, GA USA

Keith,

I have read your post with much interest. But very respectfully, I do not understand what you are saying.

Could you possibly rephrase it in a different way? Maybe an example or two.

With a 500K pot and the wiper at its maximum, the input impedance of most any amplifier is only a fraction of that.

So I just do not see but very little tonal attenuation and/or "shift" at the maximum setting of the pot, except in only the highest of the highs.

99% of Emmons' PSG's have always had a "tone defeat switch". And even here, there is very little "audible" affect in switching the pot and cap in or out, if the pot is at its maximum "treble" setting. The only improvement in over all tonal quality it gives when switched out, is a small boost in the highest of the highs.

As one player I heard say incorrectly years ago, "Leave that defeat switch in the out position. It gives you a LOT more power!!" Wrong! Power is always measured at 1KHZ. The attenuation at 1KHZ can only be measured with the most sophistication of test equipment. And no one's ears could ever hear it.

Again, very respectfully, am I missing something here?

carl

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Keith....

That problem is what the "Myrick Mod" takes care of.

C.Dixon, What Keith is saying here is:

As you lower the volumne of your axe using the foot pedal, you are actually putting resistance beween the pickup and the 1st stage amp. This resistance has roll-off effect on the hi-freq notes. This in effect,makes the sound of the tone (depending upon the Imp of the pick-up) very muddy and/or bassy. Try playing your axe without the V/C pedal at a low level, then put the pedal in place. Big difference.

True, at max level on the pedal, there isn't enought difference to notice, but as you lower the volumne, you fade into the woodwork.

Keith...

I wasn't trying to answer him for you,(as I am sure you can do a much better job than I)just thought maby a novice approach here might suffice here..

Jack Stoner · From: Kansas City, MO

In most cases a passive type of EQ (Tone control) such as the type used on some guitars and steels will do what Keith has said. Some guitars/pickups are also noticeably affected by the volume pedal. On others, such as my Franklin with the Lawrence 710 pickups, the volume pedal affect on the overall frequency response is minimal and not enough to require buffering (some type of MatchBox or Digital sustain unit) between the guitar and the volume pedal. The Franklin does not have a tone circuit so that is not a factor on this guitar.

I personally noticed an obvious overall increase in the tone of the old 71 PP Emmons D10 with stock single coil pickups, that I had, when I added a buffer/impedence converter type device between the guitar and the volume pedal. I notice an additional increase in the overall tone when I used the "3 cord" hookup (guitar directly in to the amp input) on my Session 500 amp. When I first got the current Franklin it came with Lawrence 705 pickups. I immediately noticed an improvement in tone and frequency response with the new guitar compared to the Emmons. However, I still experienced an overall increase in apparent tonal quality using a MatchBox with the Franklin and the 705 pickups and using the 3 cord amp hookup.
However, when I changed to the Lawrence 710 pickups I noticed improved string separation, and the biggest difference I no longer needed the MatchBox type device or the 3 cord amp hookup.

All of this is strictly my ear interpretation. It is not scientific - backed by taking accurate electronic measurements.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

I think this information is really important, and I am excited to learn about it. Before I answer the questions that have been asked, let me rephrase the information for Carl. Respectfully--------Carl, I don't think you are following what I am talking about. Your pickup has a plus and minus wire coming off of it. On the plus wire, we "T" in ,and go to a variable 500K resistor. Out of the resistor we go to a .022uf capacitor. Out of the capacitor we "must" have a resistor before this line is hooked to ground. I am talking about the value of this resistor. If you don't have a resistor, signal from your pickup takes the path of least resistance. There will be resistance in the plus line going to your amps. For best results, you need to match the resistor you hook after the .022uf capacitor, to the resistance in the plus line. If you don't do this, signal rushes the line with the least resistance. This causes a really big suck or draw on our pickup. When this happens your pickup won't produce it's best sound quality.
I said this resistance value was difficult to determine with a pot pedal because resistance was always changing at that point. I suppose one could measure the resistance range he normally played in on the POT pedal, and use that value of resistor, or slightly higher. Something important was brought to my attention by E-Mail ,from a friend who has read this thread.
My friend said he had always wondered why the old Bixby pedals, that had tone controls, had a capacitor and a resistor. This thread had answered a old question for him.
How do you know what resistance to use?Besides your foot pedal, you must go to your first powered device. You must then find out what the input resistor value is. Most companys who build electronics plan on some guy walking across a carpet and generating 4,000 volts, then touching the device they made. My devices have protection just like PEAVEY does on their amps. I put a input capacitor and resistor for protection. I have no idea wheather or not Goodrich uses any protection. If you are first runing to a Goodrich box, you need to find out what the input resistance is. On my digital sustain, it is 10K. On my pedal it is 10K.
Actually ,there is a simple but messy way around not knowing what resistor you should use after the .022uf capacitor. You can put in another 500K variable resistor. Then you would have two variable resistors, one before the .022uf capacitor and one after. You could then experiment, and dial in the perfect resistance and balance on the pickup. Wonder why guitar makers don't do this. Well ,I can tell you why----one knob confuses many people, and a 2nd knob would be even worse.
I wonder what resistance the old Fender standard Guitars and the Peavey standard Guitars have on their tone controls? I would suppose these standard guitars were designed for a straight guitar cord run to a amp first.
Now ,to the questions: Bill,it is obvious you understand what I am talking about. Several people have tried to explain the Myrick Mod to me. Several sent me diagrams. I really don't know if the people sending me these diagrams really knew exactly what this Mod was. I do know one thing, when I tried the diagrams they would not work. I suspect the diagrams were wrong. I can understand how a capacitor and a resistor could be arranged and sound good. I really can not see how just a capacitor alone would ever work. The diagrams I saw of a Myrick Mod just had a capacitor and no resistor. If there is no resistor after the capacitor, I see real problems.
I know Jack understands what I am talking about, although he got off on pickups and the Goodrich Matchbox. Jack, respectfully--- If you don't have a resistor of some kind on the tone control after the .022uf capacitor, you are losing sound quality. Jack, I think very few of the newer guitar builders install tone controls on their guitars. For those who used to install tone controls, wonder if any were aware of this problem??? This goes for steel guitar builders and standard guitar builders. It is obvious that Bixby Company was aware of this problem, because they had a resistor on their tone contorl. Does your guitar have a tone control? Is there a resistor after the capacitor, before it goes to ground? As you can probably tell, I am excited about finding this snake that kills sound quality.

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[This message was edited by Keith Hilton on 09 July 2000 at 02:15 PM.]

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Keith..

You stated..
"The diagrams I saw of a Myrick Mod just had a capacitor and no resistor. If there is no resistor after the capacitor, I see real problems."

This is true !! A Capacitor of any kind isn't involved in the "Myrick Mod". Such a device would completely null the whole reason for the mod. It only consist of two(2) pots wired up in a manner that the pick-up is at all times seen by the 1st stage input section as tho it was at the max impedience. This is accomplished by:

As the VC is rolled toward the off position, the pick-up is rolled toward the max gain position also. This demands that a dual pot control be used. A passive resistive device only.

If I can find it around here somewhere, I will e-mail you a copy of it.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Bill, now I am really confused. I am not saying you are wrong. I had about 5 diagrams of the Myrick Mod sent to me and everyone was different. I can't remember any mention of a dual pot. Anyway, what you said about keeping the resistance the same, and maxed out sounds good. A pickup likes to see high resistance. Bill, this would not solve the problem of putting the resistor after the .022uf cap in the tone control. If the pickup always sees 500K ohms with the Myrick Mod., then that value, and the input resistor of the first powered device ,added, is the value of the resistor you need from the .022uf tone capacitor to ground. Next question: If a single element pot now costs from $22.00 to $28.00, what in the world does a dual element pot for steel cost?

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Jack Stoner · From: Kansas City, MO

All the "Myrick Mods" that I did involved two separate pots. The regular volume pedal pot and then a second 500K pot for the "tone" control.

Keith, sorry I got off of the tone circuit in my previous response. But, I thought you were leading toward using a buffer amp between the guitar and the amp.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Thanks Jack! I'm not really interested in the Myrick Mod at all, or the pre-amps hung on the leg of a steel guitar. What I am interested in is tone controls, and finding out what companies put resistors after the capacitor.
Thus far we know Bixby installed a resistor after the capacitor.
Jack one other thing; Bill says the Myrick Mod had no capacitor. I thought all tone controls had a capacitor. Is it the capacitance in the 2 pots that is causing the tone change in a Myrick Mod.
I assumed everyone knew how to make a tone circuit, maybe I assumed to much.

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[This message was edited by Keith Hilton on 10 July 2000 at 07:36 AM.]

Jack Stoner · From: Kansas City, MO

Keith, the second pot, and the way it was wired produced a "tone control".

I did quite a few of them, including one for Terry Bethel back in 72.

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Keith...

Quote:
"Thanks Jack! I'm not really interested in the Myrick Mod at all, or the pre-amps hung on the leg of a steel guitar. What I am interested in is tone controls,"

O.K.

Now, With that said, This is true. Any kind of passive resistance placed beween the pick-up and the pre-amp stage, wheiter it be in series and/or to ground IS going to change the characteristics of tonal freq generated.

So, with that in mind, What the "Myrick Mod" attempts to do is keep the full impedience of the pick-up as seen by the amp. As the resistance of the V/C approchases the value of the pick-up, the second pot, in effect, has little effect, BUT as the V/C droppeds below the value of the Pick-up, the second pot begins to direct the "HOT" lead of the pick-up more toward the 1 st stage amp. This keeps the impedience of the pick-up (as seen by the amp) at it's full value. As the the V/C is lowered below the value of the pick-up, ONLY the current(Microamps)output of the pick-up is changed as the DC resistance of the pick-up and the 1st input stage of the amp are both lowered to ground together. Thus NO voltage change is seen beween the pick-up and the 1st stage amp. Only a amptitude change is seen, as I/E is the determinng factor here.

I am still looking the print of the mod, I will post it here, when I find it.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Well...this is certainly interesting. I'm not a sound engineer, but I would like to bring up a couple of points. First, someone made a statement, something to the effect that "when using a tone control, you lose signal". This is EXACTLY what happens in any passive tone control. They ALL "cut" frequencies. There is NO WAY a passive tone control can "boost" anything. What these controls do is to cut out what you DON'T want, and then you boost what you DO want with more volume. (A "passive" tone control uses no power, and therefore can't "amplify" anything.) Look at it this way...your whole signal (highs, mids, and lows) is a dollar. You can't take thirty cents away from that dollar, and still have a dollar! When you roll off the highs, OF COURSE you are losing signal! That's a fact of life.

I've also heard many steelplayers say "When I turn the volume down, the tone goes away." NOT TRUE! MOST of what's happening is this...your ear's frequency response isn't as flat at low volumes. When you lower the volume, your hearing "linearity curve" goes out the window. We can't hear low frequencies as well at low volumes. Old "Hi-Fi" amplifier manufacturers recognized this, and they added a "loudness" control to their amplifiers. What it did was to boost the low frequencies at low volume levels.

A good amplifier, one with an active graphic equalizer, can work wonders. Why so few instrument amplifier manufacturers use graphic equalization is probably a matter of dollars and cents. I will say this, I don't think you'll find very many stereo systems without one!!! (Am I the only one who notices?) Say all you want about parametric, and shelving tone controls, the fact is that they just don't give you the control you have with a graphic equalizer. In my opinion, we shouldn't be buying amplifiers that don't have them! But they're not available, so we buy what they make, and then go to endless extremes to try and make them sound good.

Also, one other point I would like to make. Most amplifiers sound best when the gain controls are at the maximum. Your amp has more signal to "work with". Try this...turn you amp all the way up, and then use your volume pedal to play at the level you want. I always run my amps "wide open", and find that I have more tone and sustain than I would if I ran the amp at half volume, and then pushed down further on the volume pedal.

And no, this doesn't make you play loud! Learn to USE the volume pedal! (You don't put a block of wood under you car's accelerator pedal to keep you from going fast..do you?)

[This message was edited by Donny Hinson on 11 July 2000 at 09:06 AM.]

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

I like all of you guy's ideas! Everyone seems to be avoiding my real reason for this post. The real reason for this post is a resistor between the capacitor and ground in a tone control. I say it has to be there to keep from milking the pickup. Bixby used to use it in their pedals with tone controls. Emmons guitars never used one. I say the Emmons Guitar tone control would of worked much better with a resistor after the capacitor. I am not putting the sound of a Emmons down. It is one of the greatest sounding guitars ever made. The real questions is wheather or not the Emmons guitar would of sounded better with a resistor on the tone control? Naturally this assumes a guy uses the tone control when playing, and it is not turned off. I say the guitar would sound better with a resistor. I think I know what value to use, even if you use a POT pedal. I talked to Bruce Zumsteg about this yesterday, and told him the range of resistors to try. If you make a post please stay on one thing---the resistor between the capacitor and ground on a tone control. Thanks!

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[This message was edited by Keith Hilton on 11 July 2000 at 09:36 AM.]

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Well Keith, I guess some sort of resistor (for isolation purposes) would have made the tone control more useable. I don't think the value would have to be that critical, as long as it stopped the majority of signal voltage from reaching ground. A quick check of amp schematics shows that these values vary widely.

However, the point remains whether most players would use these controls, and to what extent each player would want to "roll off" the highs. Remember, these passive controls reduce the amount of signal, and we don't have that much to spare anyway! I suppose that's why most players eventually bypass, or renove these controls, and then use the controls in the amp. While the controls in most all amps are limited, they offer many times the amount of variation you can get with one passive control.

When you get technical, like audiophiles and some players do, even the brand of coupling capacitors makes a slight difference. That's right...same capacitance size and voltage, but different sounds! Materials used, as well as physical design, all come into play. When I would modify guitars for friends, I would use a resistor of 30-50k with the Cap., and I would change the Cap. to .05, or sometimes even .1uf for more tonal variation. This topic is so "subjective", it's hard to nail down what all of us want in any one design. Which is why I believe it is all the more important to have graphic equalizers in amps. A controller for the harmonics (overtones) would also really be nice!

By the way, I think most lead players prefer a little overdrive for the purpose of sustain and compression. You see, they usually don't use volume pedals like we do, so they have to get that "sustain" from somewhere else!

Terry Downs · From: Wylie, TX US

The series resistor Keith is referring to acts as a limit to the minimum resistance placed in series with the capacitor. It is the same as NOT turning the tone control all the way down.

Something awful happenes with a tone control circuit. A simple tone circuit driven with a zero ohm impedance and received with a infinite impedance makes a 6dB per octave tone shelf. With a magnetic pickup as a source impedance however, the pickup inductance is significant when the tone pot resistance is low. This creates a 12dB per octave response. As you begin turning the pot down, you get a pretty smooth gentle high frequency rolloff. When the total impedance of the tone network gets near the value of the reactance of the pickup inductance at a specific frequency, you begin the sharp 12dB rolloff. This sounds terrible since string harmonics rolled off that sharp are displeasingly dull. Keiths idea keeps this from happening, but is no different that just "don't turn the tone knob down so far". That is hard to do. I advocate the series resistor as opposed to a smaller cap.

I my opinion, I think passive tone controls should have stayed in the 1930's where they belong. And don't get me started on capacitor brands that sound different, unless the happened to stick a polar electrolytic in there.

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Terry Downs
http://nightshift.net
terry@nightshift.net

[This message was edited by Terry Downs on 11 July 2000 at 06:47 PM.]

Blake Hawkins · From: Florida

Donnie and Terry have pretty well nailed it!
You can put more resistors in and modify the
range of frequencies affected by the tone control circuit.
Keith, I think you are saying that the resistor has to match the impedence of the pickup.
Since we are dealing with high impedence circuits that is not critical. The tone control pots have generally been 250k to
500k.
Remember, when you "match" the impedence of the pickup to the load you lose half the signal anyway.
With a high enough input impedence at the amplifier input (10 times the impedence of the pickup) you are "bridging the pickup" and
not drawing current from it, therefore getting a better frequency response.
There are lots of ways to "improve" a single capacitor circuit as Terry mentioned but it still does the same thing.
If your tone control pot has enough resistance, the pot is effectively out of the circuit at the maximum "treble" position.
Engineering theory can only go so far....you have to finish the job by ear.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Here is another thought to ponder; Is there a sound difference in the different arrangements. The first way I suggested was to "T" off the plus pickup line, then run to a 500K variable resistor. Then run to a .022uf capacitor, then to a resistor, then ground. What "if" you were to "T" off the plus pickukp line, then run to the .022uf capacitor first. Then run to the 500K variable resistor, then to ground? I am sure there would be some capacitance in a 500K pot wired as a variable resistor. The whole point being, wheather or not there would be a difference in sound in these two arrangements? Naturally, with the separate resistor, the tone control could never be taken below a value set by the resistor. I would think there would be a sound difference when using the resistor after the capacitor. What do you think?

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Terry Downs · From: Wylie, TX US

For ideal components you can connect any number of resistors in series with any number of capacitors and still get the equivalent of one resistor and one capacitor. The parasitics of a typical potentiometer used for tone controls in musical instruments have negligible parasitics at audio frequencies. The pot cover is far away from the composition wafer. The closest ground "plate" to the composition layer is the flange below the threaded bushing. It is generally 20-30 mils from the wafer. This results in no more than 2-5pF of capacitance max. Since the pole setting cap is usually 0.022uF, the parasitic is roughly 1/10000 or -80dB of the dominant component. With this said, there is NO difference in how you connect it.

It is VERY important how you wire it from a noise perspective. It is common to use the pot cover as a ground point. NEVER NEVER EVER rely on the pot cover shield as a ground without the backup ground wire. If the pot bushing becomes loose, you have a faulty noisy ground. You should solder to the pot cover as they are usually tin/lead plated for solderability, but always use a wire in addition in case the pot mounting bushing comes loose.

Another important connection issue is with the tone control pot as a rheostat. Always connect the vestige pot terminal to the wiper.



INCORRECT








   >------///////--


            |         


            +-------------<





CORRECT





  >---///////--------+---<


            |         |


            +---------+

Imagine a dirty pot... the wiper lifting and disconnecting from the composition surface. The resistance of the network transients from its fixed value to infinity. With the unused end of the pot connected the the wiper, the transient resistance only goes from the wiper value to 500K. The reduces noise when the pot becomes old and scratchy.

In conclusion, you can do more for the instrument quality with proper grounding and wiring techniques than you can ever do by worring about the component parasitics in the audio band.

Regards

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Terry Downs
http://nightshift.net
terry@nightshift.net

Terry Downs · From: Wylie, TX US

I should also mention that you should NEVER rely on the output jack bushing for ground. Run that ground wire to the jack terminal. If the pot becomes loose, you have a major noise problem. It is not a question of IF a pot or jack nut comes loose, it is WHEN. This also applies to the ground on the volume pot. Always use a wire to connect ground as a mechanical conection will fail you.

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Mr. Downs has nailed this thing down far better than anything I could say or do !!

I completely agree with all he saids. while realizeing that the main gender of this thread may have shifted a bit, his thoughts are text-book perfect.

Keith.... I know you were thinking of "Tone Control" and how best to achieve it, I must appolize for I feel I may have mistakenly thought you were trying to keep the most signal from the pick-up from being lost due to roll-off of the V/C pedal. After reading a few of your post responces, I get the idea that you wish to alter the freq magnitude before it ever leaves the guitar. To this idea, I must agree with the other folks,

1) Attempt to get the maximun signal from the pick-up to the 1st stage amp.

2) Don't attempt to modify the tone before it gets to the amp.

3) Freq shapeing is best done via EQ process after the 1st preamp section.

All this stated, I understand that a bit of buffering/shapeing of signal may be desired due to chacteristics of pickups and/or V/C pedal design is needed here to compansate for the loss of signal. (Which is what your pedal achieves most greatly.)

As for which to put first, the cap or the resistor, I don't think it makes any difference due to the fact,

To the laymans ear: (PSG player)
Current lags voltage, or vice versa, the overall results is the same. He will never notice the difference. This difference in phase shif is ONLY detected by electronic eqipement(sp?) and most players arn't aware of it.

To me, most of us are looking for that "SOUND" we hear from the masters of our instrument. Whatever means we use to achieve this is subjective. In general, ( as I am a novice player) I find that if you can get the max signal to the amp, you can enhance it in a veraity(sp?) of ways. Your Pedals achieve this splendily. While I do not own one at this point in time, I have played a set or two with it. You do have a great product to enhance overall sound we look for.

Keith Hilton · From: 248 Laurel Road Ozark, Missouri 65721

Thanks Bill. I guess you know that my pedals are cast in Goodlettsville, where you live. I think they do Franklin, Fessenden, Emmons, and a bunch of others. Their castings cost a little more, but the guy does good work.

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[This message was edited by Keith Hilton on 13 July 2000 at 09:09 AM.]

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