tone control

[Kent S.]

Re: tone control

Put a .056 microfarad capacitor in series with the resistor. I am using a larger capacitor than mentioned above because the reistor has a smaller value.
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I assume that the cap value is also because of the difference in your pups having lower impedance than most pups ... actives don't count though as the preamp output impedance can dratically skew the test , unless the tone loading is done before the preamp ... just something to consider.

There seems to be a small difference, but I would not bet my life on it. I do not hear it every time I short/unshort the cap, so maybe I am imagining it. Artietoo, may be you have better hearing than I do and can be more definite about it.

Like I said the difference will be subtle at best, and I think it varies depending on pups ... It's just good to clarifiy that although the overall effect is generally similar to being the same, that it isn't the exact same and may vary depending on the pups used. That was really my point, also I would have to imagine that the larger the cap value (per a given Z of pup that is) that the differences in the effect would become a bit more noticeable ... I would think at least.

Kent, we agree on the series RC. When I say that the R hides the effect of the C, I just mean that changes in the impedance of the C with frequency have little relative effect on the overall series impedance when the R value is large compared to the C impedance. Just an intuitive way of looking at it, nothing more, and it only applies near the resonance because at really low frequencies the impedance of the C is huge.

I see what you mean, it kinda goes along with what I was saying, the lower the frequency the more resistance, and the less loading, the higher the frequency the less the resistance, and the greater the load. The minimum load will always be determined by R in this case plus the lowest Xc that the cap exhibits. It would appear that in this case both seem to be almost exact in their effect, although going about it differently. Still though, I tend to hear a bit more reduction in the high end with the RC rather than just the R alone, certainly (major opinion on my part mind you) the resistive approach seems a better way of controlling the amplitude of the pup(s)res Fc peak, after a certain point of course a standard tone control becomes much more productive and tonally agreeable, not to mention to the overall level is keep intact; even boosted a bit when the resonance shift takes place at extreme low resistve settings (tone at *0*).
I did notice that when the cap value was greatly increased per a given resistance that the load issue became a bit more evident, which I understand, but for some reason it seemed odd ... I'm probably not remembering some other thing that was going on in that simulation that made me think it was a bit odd. oh well ...

 

[Kent S.]

Re: tone control

Hmmm . . . thats interesting. I would have thought the difference to be more significant. However, its possible that you didn't get more noticable results because of the 100k volume and tone control. I've never actually heard of a guitar that used values that low. Its possible that you're pre-loading the pickup so much as to be beyond the level of effectiveness.

I'm going to repeat the experiment, but with using 500k controls. It'll still take me a couple days to get this together, however.

I'm picturing EMGs, Bartolinis, or some other such low Z out pups, although those are active (EMGs are like 2k or something aren't they? ), aren't EMG selects (I don't know of anyone that likes those BTW) relatively low in output Z as well, or no? Anyway, the lowered cap value and lowered control values would make sense for something on the low Z end (I thought the actives used like 525k or 50k pots, and the selects standard values).
However if a preamp was involved, see my earlier coment regarding where the R and RC loading had to take place.

 

[Kent S.]

Re: tone control

Artietoo, I would have preferred to do this test with a standard guitar, too, but this is what I have. The pups are not heavily loaded; they are quite bright. I made the pups lower impedance because I wanted a guitar that does not lose highs when you turn down the volume. Obviously one can do this by just winding less wire on the two coils, but there is more to it. The big problem with pups is that the inductance depends almost on the square of the number of turns, while the output level depends almost linearly on the number of turns. Suppose you replaced one coil with two in series, each with half the number of turns, and also suppose you keep the same core/magnet structure. Also ignore coupling between the coils. Then you have about the same output level, but half the inductance.

Sounds like one of Aron' Stompbox Forum guys has stopped by ... :laugh2:
Well, I'm glad you got a pup that you like, and I can see why not knowing the actual value of L, that you came to that conclusion, same with the output level ... you also need to toss in the distributed capacitance as that gets combined in series or parallel (series in this case), as the when Xc equals Xl that's your fc of res, the DCR only lowers the peak amplitude (bummer).
Hence the reason behing EMGs, design the pup for the tone you want, and then get the level you want from a preamp (with the added bonus of loe output Z to be less susceptable to cable L,R,and C) ... Anyway ...

Now in the real world, what you get is a four coil humbucker under a standard cover with less total wire because you have four cores taking up space (all use slugs, not screws). The impedance is lower than standard as I said; the output level is a bit less than a standard single coil, but the signal to noise ratio is better than standard with a solid state preamp, because solid state works really well with low impedance. These pups are not for tubes; I am trying to learn jazz, and a clean solid state sound is just fine. (Of course you could use an ss preamp with a tube amp in any case.)

Like I said, glad you got a pup you like ... Still a good tube preamp might perform just as well ... I don't rule out one or the other really, but it's your rig, and you know what works for you ...

Any way, I think the test is valid even with the different values, but I will wait for your results with patience, of course. (Actually, I have some heavy duty stuff coming up at work, and probably will not get here too much for the next week or so.)

As long as the issues of the preamp were addressed (regarding on-board only), then I think the test conditions were vaild as well, I still want to see what Artie comes up with so all notes can get compared as well ... :cool3:
Good luck at work, try not to let it stress ya .

 

[sanrafael]

Re: tone control

Kent,

Just a quick note; the guitar is completely passive. The goal is to drive the cable with a low enough impedance so that there is no loss of highs with the volume in any position without using a preamp in the guitar. One could do this with a preamp in the guitar; maybe next time.

I neglected to say that the correct resonant frequency is established with a capacitor, since it is quite high without a C. I did the test descried above with roughly a 5000 Hz resonance. Actually, the guitar tone circuit uses a switch to allow different values of C, and so different resonant frequencies, and a pot allows a resistance to be put in series with the C to adjust the damping.

 

[Kent S.]

Re: tone control

Kent,

Just a quick note; the guitar is completely passive. The goal is to drive the cable with a low enough impedance so that there is no loss of highs with the volume in any position without using a preamp in the guitar. One could do this with a preamp in the guitar; maybe next time.

Well that won't work per se', as in there will still be some loss, but the lower the output impedance the better. Plus pots have their own capacitive element that gets thrown into the mix as well...

I neglected to say that the correct resonant frequency is established with a capacitor, since it is quite high without a C. I did the test descried above with roughly a 5000 Hz resonance. Actually, the guitar tone circuit uses a switch to allow different values of C, and so different resonant frequencies, and a pot allows a resistance to be put in series with the C to adjust the damping.

Okay, so you are tuning the pup capacitively ... are you sure you aren't using an old Les Paul Recording Professional ... with those 2K pups ... LOL! :laugh2: The dreaded decade selector switch, and switchable low Z transfromer output ... ::::shudders:::: :saeek:
I see what your doing, it sounds a bit similar to something I've got as well ... But not used for quite the same purpose ... I think the test was valid, and I see your point with the R vs RC issue.

 

[sanrafael]

Re: tone control

Kent,
Well I had heard of the Gibson guitars with low impedance pickups, but nothing beyond that, so I found an interesting web page. A matching transformer! Not for me. Well, you are right, a 100K pot will still lose some highs, but so little compared to a 500K, I do not think there is a problem. There is plenty of output for an ss preamp, and maybe a good tube preamp would be OK as you suggest, and one probably could get the output up a bit. The pups use very weak magnets to prevent string mode splitting. It is easy to adjust the strength. I use a very small Neodymium rod or disk on each slug. They are cheap, and available in many sizes, so you can easily get any field strength that you want.

 

[Kent S.]

Re: tone control

Kent,
Well I had heard of the Gibson guitars with low impedance pickups, but nothing beyond that, so I found an interesting web page. A matching transformer! Not for me. Well, you are right, a 100K pot will still lose some highs, but so little compared to a 500K, I do not think there is a problem.

I don't underatnd here why a 500k would lose more highs, over a 100k, that sounds backwards ... however with a lower Z pup a 500k might be to bright, I musta missed something in the discussion ... :question:

There is plenty of output for an ss preamp, and maybe a good tube preamp would be OK as you suggest, and one probably could get the output up a bit.

I've often wonder if the input imedance is somehow modified, if one of those tube microphone preamps that are evrywhere now would work well in that situation. I think someone on this forum remarked about using one on a piezo equipped acoustic guitar, found it to be very nice ... I bet it would work good to on say an old Rhodes set of keys as well. I heard on used on a violin, and fund it very smooth and lively.

The pups use very weak magnets to prevent string mode splitting. It is easy to adjust the strength. I use a very small Neodymium rod or disk on each slug. They are cheap, and available in many sizes, so you can easily get any field strength that you want.

Must be the same reasonings behind their rapid and wide spread use in microphone elements as well, for all of the reasons that you just mentioned ... I believe they age rather well also (very stable).

 

[sanrafael]

Re: tone control

500K vs 100k pot: This is just the loading due to cable capacitance that causes loss of highs with the volume control turned part way down. Also, with the volume all the way up, the cable capacitance has less effect on the resonant frquency with the lower impedance pickup. (The capacitance of the lower impedance pup is higher for a given resonance frequency because of hte capacitive loading required to establish the frequency.)

In another week or so, I will see if I can put some numbers on the potential improvement in SNR uisng the lower impedance pup with an SS preamp.

 

[Kent S.]

Re: tone control

500K vs 100k pot: This is just the loading due to cable capacitance that causes loss of highs with the volume control turned part way down. Also, with the volume all the way up, the cable capacitance has less effect on the resonant frquency with the lower impedance pickup. (The capacitance of the lower impedance pup is higher for a given resonance frequency because of hte capacitive loading required to establish the frequency.)

In another week or so, I will see if I can put some numbers on the potential improvement in SNR uisng the lower impedance pup with an SS preamp.

With the volume up a the cable capacitance has less effect on a higher impedance pup also ...
I'm really not getting what you're saying here, a pot brings with it it's own set of problems, unless what your saying is that in YOUR case, because of the lower impedance that the pot value effects the loading of the pup less, And that you have reached a point in which that the series resistance added to the signal line from that section of the pot drives the source R/Z up and therefore interacts with the cables C to bring the cut-off Fc lower (high end loss), more so than would happen with a higher valued pot. A higher valued pot will still preserve more hi end on it's own; However in your case, if the above is what you are saying, then you may have a point. I never considered it from that point, merely because I still see the same thing happening on higher impedance pups.

 

[sanrafael]

Re: tone control

With the volume up a the cable capacitance has less effect on a higher impedance pup also ...
I'm really not getting what you're saying here, a pot brings with it it's own set of problems, unless what your saying is that in YOUR case, because of the lower impedance that the pot value effects the loading of the pup less, And that you have reached a point in which that the series resistance added to the signal line from that section of the pot drives the source R/Z up and therefore interacts with the cables C to bring the cut-off Fc lower (high end loss), more so than would happen with a higher valued pot. A higher valued pot will still preserve more hi end on it's own; However in your case, if the above is what you are saying, then you may have a point. I never considered it from that point, merely because I still see the same thing happening on higher impedance pups.

Right, I believe; here is one way to say it: The reason for going to a lower impedance pickup is so that one can use a lower resistance volume potentiometer and still avoid damping the pup too much and losing highs. The purpose the lower resistance volume pot is to avoid loss of highs due to cable capacitance loading of the pot when it is turned part way down.

One can think of lowering the impedance of the entire system connnected to the cable in order to prevent loss of highs due to cable capacitance loading.

Remember those little capacitors some people put between the top pot connection and the slider? They do not really work all that well, and with the 100K pot, you do not need one.

 

[Kent S.]

Re: tone control

Remember those little capacitors some people put between the top pot connection and the slider? They do not really work all that well, and with the 100K pot, you do not need one.

Personally I like the HPF system, for various reasons, Also, anyone ever hear of a Direct Box ... That's basically what you are doing ...

 

[sanrafael]

Re: tone control

Sorry, Kent, I do not know the HPF system, and for Direct Box I find a doubly shielded transformer, which does not seem to be what you mean?

 

[Kent S.]

Re: tone control

Sorry, Kent, I do not know the HPF system, and for Direct Box I find a doubly shielded transformer, which does not seem to be what you mean?

HPF ... High Pass Filter ...
Most direct boxes are transformer based (the passive ones, active is a different story) , converting hi Z to low Z, the lower Z would accomplish much of what you were referring to in terms of cable capacitance and what not ... it was kinda meant as a joke. Nevermind ...

 

[sanrafael]

Re: tone control

Kent, Sorry, I am running a big sleep deficit now; I will be alert again in about 6 days! But yes, you are right, one could transform down to do the same thing.