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Post by JohnH on Aug 18, 2006 21:23:25 GMT -5
Here’s one for those of you with a scientific frame of mind. In most of our wiring designs, we take care to try to avoid shunting coils, ie, making coils inactive by bypassing them, such as in coil cutting a humbucker for example. The concern is that this locally shorts out the bypassed coil, allowing it to generate currents internally, sapping power from the strings. This is a good and true theory, but is it significant in practice? I decided to investigate……. On my ToneMonster2 guitar, I have three single coil pups, which can individually be switched on and off, and all put into system series or parallel. My way of switching the pups off in series mode is to bypass them, hence risking the coil shunting issue described above. In parallel mode, there is no coil shunts. Check out the schematics page to see the circuit: guitarnuts2.proboards.com/thread/3121/tonemonster2-series-parallel-sssSo the option exists to listen to one pup, with the other two off, with system series or system parallel engaged. In series mode, the two off pups are shorted out, while in parallel mode, they are fully disconnected. To test this, the best option to listen to is the bridge pup, with neck and middle off, since bridge picks up relatively more treble, and middle and neck are subject to larger string movements. Before testing, I decided to raise the stakes a bit higher. I have a pair of powerful ceramic single coil pups, each with twin magnets, and one is reverse wound. I arrangement them together like a humbucker, and shorted out each of the coils to itself, for max current generation. I call this the ‘Tone-sucker’In the following testing, the parallel sound are of the bridge, with no coils shunted. The series sounds are bridge, with neck and middle shunted, plus the Tone-sucker held as close as possible over the strings, at about fret 20. Hence the difference is no coils shunted, or four coils all shunted. Here’s the sound – alternately shunted, not shunted, shunted, not shunted: I tried to be consistent strumming, but of course could not be totally so. The Chord is Em, played all on open strings. people.smartchat.net.au/~l_jhewitt/circuits/shunt1.mp3And here’s a picture of the wave form: Another try, as above: people.smartchat.net.au/~l_jhewitt/circuits/shunt2.mp3And the waveform: Who can hear, see, smell (or imagine) a significant difference? I can’t – but I’m interested as to whether or not you can. In a further post, I’m gonna think about the maths of this, so beware. regards John
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Post by JohnH on Aug 18, 2006 23:20:18 GMT -5
Further to previous, here’s some numbers. Its all to do with power dissipation, damping and decay. There are proper mathematical ways to consider such issues, and the following is not one of them.
The energy going into making the strings vibrate comes only from the initial pluck. Consider just one string; I’m guessing that a reasonably strong pluck could be about 1/2 kg of force (= 5N), deflecting the string by about 3mm until it is released.
Energy in = 5N x 0.003m x ½ = 0.0075J (the half comes from the fact that the average force while deflecting the string is ½ of 5N)
From the waveforms, the signal amplitude appears to decay to about 70% in about a second after the end of strumming. The energy stored in the string at this time is then the square of this, ie 50% of the initial energy from the pluck. Hence 50% of 0.0075J has been dissipated in one second, a power loss of 0.0038W, due to sound output, damping to the body and all the reasons why strings do not sustain for ever.
The particular loss we are interested in is loss due to electrical energy induced in the pickup. Normally, a pickup feeding a high resistance produces a voltage, but very little current, so not much power is drawn from by the pickup. When shunted, it has a lower resistance in its circuit (its own impedance), hence current and power dissipation can be more.
Lets guess that the voltage output from a pickup, with a string strongly plucked is initially 0.3V. lets say the impedance of the pup is 10k.
If the pup is shunted, the power induced in the pup, which can only be drawn magnetically from the strings, is:
0.3V x 0.3V / 10,000 Ohms = 0.000009W.
The above numbers refer to the initial part of the sound, but further down the decay, they would be expected to be in similar proportion.
Comparison: the string is initially losing power from all causes at the rate of 0.0038W, but that due to electrical induction in a shunted pup is only 0.000009W, ie, only about 0.2% increase in string damping, which is too small a difference to hear. That why you can’t hear it, even with four of them including the Tone sucker!
Now I respect the fact that several esteemed members of this forum are sure they have heard this effect. But how and what?
cheers
John
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Post by seventh string on Aug 20, 2006 10:13:13 GMT -5
Okay, i understand a bit , so if i wire too many cable or too many routing, the sound will be affected because of the energy loss then? GBU.
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Post by JohnH on Aug 20, 2006 15:55:11 GMT -5
These tests were about just one aspect of wiring, which could cause an energy loss, which is when we disable a coil or a whole pickup by shorting it out using switches. This can be a convenient way to change the saound - its not really to do with having too many cables or pickups. Shorting out a coil should cause an energy loss, but my tests suggest that this is too small to be heard.
J
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Post by ChrisK on Aug 20, 2006 22:27:11 GMT -5
Regarding a previous thread: This previous post states that the primary effect of a shorted coil is a harmonic one and not a sustain (decay) one. There IS additional loading from a shorted coil, the issue is how much. I believe that 1 N = 1 kg m/ s2. Are you sure that you have both the magnitude and units correct? This would indicate that there is about a -3dB decay in PER SECOND in string amplitude. This does indeed correlate to 0.0038 J (w seconds), but only for the first second. Since this is a ratiometric decay (as most are), over the next second 0.0019J will dissipate. My point is that the energy decay is a power (as in exponential) function. This does not take into account the frequency dependency of a complex (internal) load that includes resistive, inductive, and capacitive components. This is a STATIC statement of power (time independent) being compared to energy dissipation (time dependent) which is not correlated in this example and hence meaningless. Before I induce any chomeric responses (which I DO NOT wish to do), I would like to point out that once the units of measurement/reference are properly correlated, there still exist a fundamental issue with the means of energy induction into the string as well as the means of precise measurement. Sustain (1/decay) is an amplitude measurement issue, which our human ears are NOT well equipped to discern. Only the use of a proven constant energy induction method coupled with a digital storage scope (12 bit input resolution please) can discern the actual effect (of which there absolutely WILL be one of some value). I would also encourage, once such means are perfected, that single notes be analyzed, and not chords which will be much more difficult to measure. Now, as to the discerned effect, a harmonic difference was observed aurally between the tone of a pickup while another one was switched rapidly between open and shorted (in both case the switched coil was not in-circuit). Since this was occurring, the harmonic energy was going somewhere, and hence being dissipated. Since the human ear is most sensitive to frequency (as opposed to amplitude), quite minute variations in such (harmonics) are discernable. In fact if these were not discernable, there would be far fewer variations in musical instruments. While this is aurally discernable, it is more difficult to measure in a definitive manner. For harmonic component variation measurement, once a constant energy induction method is perfected, a spectrum analyzer would have to be used, or a DSO with data exporting means and a math package that can run FFTs or other frequency component determining calculations. Now, in all fairness, some component of this harmonic effect may well be based on the ratiometric location of the energy thief. This goes to the harmonic’s peak points along the string. If such a load were to be placed at a null point along the string for that harmonic, in theory less effect would occur, again for that harmonic.
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Post by JohnH on Aug 21, 2006 6:33:42 GMT -5
Chris, don’t look too hard at the maths! – its dead crude. My main purpose was to share the sound results. The numbers were just to think around it on the back of an envelope. That being said, I think they are OK as back-of-envelope calcs.
No problem there, that IS the question. In referring to a harmonic effect, do you mean that,with shunting, the higher harmonics decay faster than they normally do? - or that the overall tone (mix of harmonics) is different throughout?
I wish it did (my day job would be easier), but the force due to gravity acting on 1kg is 1x g = 9.81N (=kg m/s2)
No problem with that bit either. My simple maths only looks at the initial decay, but it is a mostly exponential decay, both for the string vibration, and the electrical output, so as a first pass, the ratio, in a given time period, between the total energy loss from the string, and that due to this electro/magnetic effect is roughly constant, both diminishing with time. The idea of the numbers was only to get a rough ratio between total rate of energy loss, and that due to extra damping caused to shunting. I think if this ratio is very small initially, then the ratio will stay very small through the decay period.
True it doesn’t, but 10,000 it’s a reasonable ballpark figure for an example. e.g. , by my maths, at 440Hz, the impedance of a 7k coil with 2.5H inductance, ignoring the capacitance is 9837.
I think it is valid, the numbers are just for a comparison at the initial decay, but both equate to a rate of energy dissipation, in Watts, being J/s. Smaller numbers, but with a similar ratio would apply at a later time. The numbers are crude, but support the hypothesis that the effect of shunting may be too small to hear, which is what I find to be my experience so far.
Well, I’ll leave that to someone else with a white coat! There’s no doubt that with the right equipment, it could be measured. But I’m more interested in whether this effect can be heard. If it is significant, it should be possible to set up real-world a test that demonstrates it in a recording, and my intention was to have an excess of shunted coils to provoke some audible difference. A test with single notes is a good idea, and I might try that.
I’m not biased one way or the other, just interested pragmatically. Avoiding shunted coils is a PITA on some wiring designs, and I want to be convinced one way or the other if it is important. If we cant find an effect outside of a lab, then I say it is not important. You have noticed an effect with your guitar, but I have not been able to reproduce it - and I really thought this test would do so.
regards
John
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Post by RJB on Aug 21, 2006 10:58:31 GMT -5
Well, I'll pipe in here, seeing as I believe I was the one that started this originally. Based on the cheap PC speakers here at work I don't hear anything significant. Keep in mind I design audio circuits for a living and I'm "trained" to listen. I actually hear more variance in strumming than "tone suck". In fact the most muted sound is from one of the unshunted strums. I'll try and listen at home with the HiQual headphones.
someone (maybe John) tried a similar experiment before, and came up with similar results. I'm inclined to say myth-busted.
Ron
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Post by ChrisK on Aug 21, 2006 21:02:09 GMT -5
John, Thanks for responding to my post. It was a "put", in fond hope of a challenge. Yes, your analysis is indeed most adequate . Again, the compulsive analyst in me analyzes everything always (it's what I do). The harmonic content has the higher harmonics somewhat muted when compared to an unshorted thief coil. Now, again to be fair, this was in a Nashville Telecaster, with single coil pickups, with an ebony board and a fairly dense alder body. It do twangeth a bit. If I ever get around to testing it again, I'll also compare the piezo output as well, which should best capture the different harmonic contents. Uh, fer sure, like OK. However'ith, just exactly how does gravity apply here (other than the gravity of our interchange)? Are you dropping the guitar adjacent to a fixed pick and generating the strum therewith? Compared to the tension on a guitar string, gravity certainly deserves its moniker here as the " weak force".
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Post by RJB on Aug 21, 2006 23:46:24 GMT -5
OK I'm back. Well after further review with the Bose headphones, and rechecking which was shunted and not, I'm going to have to reverse my previous statement. The shunted coils DO seem to suck a bit of the high frequency content. Just that little bit of jangle or shimmer is missing. Just proves how crappy those speakers at work are.
Now if I were to only hear one strum I don't believe I would be able to tell whether it was shunted or not. The effect is very subtle. IMHO if you HAVE to shunt to get the combination desired I would, but I would still avoid it if possible. Again I'm looking for significant/definitive changes, and without a side by side comparison I would not be tell.
John, Thanks for a great test. Your time is greatly appreciated Ron
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Post by JohnH on Aug 22, 2006 7:51:06 GMT -5
Chris - The gravity bit is not fundamental to the calc. What I wanted was to get a value for the force used to pluck a string. I did this by estimating the plucking deflection, then found something that, when hung on the string, caused the same deflection, then I weighed that. The SI unit of force is the Newton, and the force in Newtons due to gravity is weight in kg x g. Once the force is determined, gravity is out of the reckoning.
Rons critical listening seems to have revealed the lost suckiness of shunt. That’s great and it confirms 150 years of electromagnetic theory. A very subtle effect, barely discernable with ‘phones, but nevertheless identified. For myself, I still cant hear it, but I do not have decent headphones to listen with.
That test was with the 4 coils shunted, so stepping back to a more normal situation with just two shunted, then the implications are further reduced. So the conclusion would seem to be confirmed, that shunting is worth avoiding if you can, but not too critical if you can’t .
Further comments are invited.
I think there is one further test needed, to investigate shunting a Humbucker to cut to a single coil. Doing that can be convenient, such as when an 0n-on-on switch is used to provide series, single and parallel wiring of a pup. Shunting a coil of an HB has some different implications, with the possibility of changing the magnetic fields around the active coil (unlike the current tests, where shunted coils are remote from the active coil, and shunting only acts on the strings). Again, when I tried this once before I did not notice an audible effect, but it is worth testing a bit more carefully. It is a slightly more involved test, since I don’t have a guitar where you can switch this in and out, but I think something could be set up.
cheers
John
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Post by ChrisK on Aug 22, 2006 11:41:00 GMT -5
Doing this test with a dual-coil humbucker should be easy. Use a 4 wire pickup, use the screw coil (since I believe that it is the brighter structure), and short/open the slug coil. This probably will be best way to test since it, in theory, removes the thief coil from ANY electrical contact with the actual circuit. BTW, if you're using a 4 wire humbucker, the traditional DPDT ON-ON-ON (SP3T) switch can select series/parallel/single coil without any coil shorting. IMHO this is the proper way. I'm building a new pickup test bed using 2 pole 6 position slide switches (2 each per wire) on a PCB. This gives a significant speed advantage over the last one that I built. It had used single pole 10 position thumbwheel (as in like) switches that had an up and down button. It took too long to reconfigure and I had trouble doing A:B testing. It will probably use an alder pool route body blank band sawn to a Tele upper profile (for good neck coupling) and a rectangular lower profile for the switches. The ToggleCaster, as implemented in a MIM Nash Power Tele might be a good place to try some tests. Of course, this means that I actually have to get the Tascam digital recorder out of its box and turn it on. I have an idea for a "struminator". A long-throw solenoid with a knee joint mechanism would realize a relatively (we'll see) constant pluck.
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Post by Mike Richardson on Aug 22, 2006 12:15:11 GMT -5
The one issue I have with all of this is simply that the magnet is always pulling on the string(s), regardless of whether that pickup(s) is in the circuit. Other than that, it looks very interesting.
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Post by sumgai on Aug 22, 2006 15:53:54 GMT -5
Like M.R., I too have an issue. This is extremely interesting from a "hard science" standpoint, I like getting my hands dirty on things like this. But..... There comes a time when we have to sort of justify how our results will affect our future performance. In this case, both John and Ron have stated what they have observed, but they very carefully stated the limitations on their observations - Ron was using high quality headphones, and John was in an otherwise quiet room (presumably with at least good quality speakers). In both cases, the differences were hard to tell, or not discernable. Now I ask you, if the difference is just a smidgen in a quiet environment, then what difference can you possibly note when playing on stage, whether it be in a chamber setting, or in an arena? The obvious answer, if you'll let me, is that you can't. Mike is right, the magnets are already present, and in themselves, they are altering the sound. That alteration is accepted, isn't it? And that's compared to "if the magnets weren't present", which of course is not acceptable. So did the added magnetic field due to electrical energization really suck so much more tone out of the signal? I think not. For me, the litmus test is not in a pristine environment, it's when you're out in front of a crowd (even if that crowd is in your living room). An added note to all this, apropos here...... The very air itself changes under many conditions, and seeminly conspires to suck tone right out of our ears. The fact that a small room is vastly different from a set of 'phones should be a significant indicator of what can happen to tone on its way to your year. Chris's idea of a 'struminator' is beautiful, it controls one important aspect of being able to repeat this experiment. But if we can't control the very atmosphere, and repeat the conditions at will, then we're still stuck with variables that may skew our results. If the results reported so far are this small, I'd be leary of investing any more time into it, short of an astounding discovery (which will crop up right after I post this! ;D). But by all means, carry on. After all, it's nearly the dead of winter for John, so I don't mean to deprive him of his escape from dreary (or freezing?) weather. sumgai
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Post by ChrisK on Aug 22, 2006 16:30:32 GMT -5
There isn't an added magnetic field due to electrical energization (except in an electromagnet).
If you spin the armature of a DC motor with rotor windings and field magnets, it will slow down due to the magnetic coupling between the rotor core and the field magnets. If you short the rotor thru the brushes, the rotor slows down much more rapidly since additional work (energy) is being performed by the rotating mass of the rotor.
On my MIM Nash Power Tele, played thru a decent PA system (which I use to A:B all new guitar purchases) this effect was easily discernible. I would estimate that the tonal difference seemed to me to be around 3 to 6 dB for the harmonics. I noticed it immediately and rechecked my wiring since I assumed that I'd made an error. I hadn't, it was indeed due to an energy thief.
Now, for some less than clear reason, the Tele neck pickup (the thief in this case) is located real near the 24th fret (two octaves up from the open string frequency). This will alter the string vibration for certain harmonics.
For those that play most clean, this may/will be an issue. For those that love the "dirty" side, it may/will not matter.
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Post by sumgai on Aug 23, 2006 2:07:49 GMT -5
Chris, Oh? Somehow I thought I was describing an electromagnet..... wasn't I?
Rather than go through a bunch of yadda, yadda, let me cut to the chase here..... It seems to me that you wouldn't have made your statement without a good reason, so where'd I go wrong here?
sumgai
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Post by ChrisK on Aug 23, 2006 17:28:32 GMT -5
An electromagnet is a structure where the magnetic field occurs as a function of an external current flowing into/thru the field winding.
A passive pickup is an magnetic/electro generator that causes an internal current to flow out/thru the sensing winding as a function of external modulation of the magnetic field.
While the pickup's internally generated current will have some effect on the magnetic field (similar to the internally generated counter EMF that limits the top unloaded speed of a DC motor), I suspect that it is minimal.
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Post by sumgai on Aug 25, 2006 3:18:55 GMT -5
chris, Excuse me, please, but in these two instances, does the magnet change properties or capabilities just because of the job to which it was assigned? I'd answer "no", the magnet will function equally well in either capacity. The problem with your scenario above is that using an electromagnet requires a sizable amount of current through the coil to produce recognizible changes in the magnetic field. Whereas, in a pup, we introduce a physical change in the magnetic field (the vibrating string), and the resultant current is not very large at all (in fact, it's miniscule). Other than that, the two modes of operation are identical, and can be freely interchanged in any analysis. Pardon me, but isn't that what John's been saying all along? The current generated by the shunted coil will be so minimal as to have no practical effect on the string. IOW, the conversion of electrical current to magnetic field fluctuations will be too small to affect the string, harmonics or otherwise. You just said that. And John's saying that even in a shunted coil, that will still be too small to be noticible. John, are you still here? Am I quoting your message correctly, vis-a-vis what Chris has just said? And if that's the case, then do you have any other explanations for Chris's first observations (where something is causing a drop in tone)? I can't get my head around this anymore. I'm of the opinion that John's results are more likely to be the norm. They are repeatable, and they use figures that are mathematically likely to be close to the real world. Anecdotal reports from a few players (albeit they are smart as all-get-out) are just that, reports of results that can't be repeated by others. (Different equipment, etc. - see my earlier reply on variables.) When the jury comes back in, call me, I'll be over in the Coffee Shop. ;D sumgai
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Post by JohnH on Aug 25, 2006 7:26:20 GMT -5
Yup, I’m still here. Just had to attend to little real-world work for a couple of days. All those nasty ‘g’ forces acting on my structures…….
But back to the important subject of sucky-toned electro-thiefs. I’m now satisfied that that, for single coils, the effect on tone is small enough to ignore if necesaary, with a margin of safety of two, since I had four coils shunted which is twice as many as would ever be necessary. I accept that to a trained ear in controlled conditions, there may be a slight difference. I would be delighted to hear a sample that I could discern, but I haven’t heard one yet. Not that that means much, I couldn’t even explain how a ‘Woman Tone’ is different to a ‘Quack’
I still want to test an Hb shunted in controlled conditions. Yes it is a simple test, but it needs getting out a soldering iron again. The LPmax would be my vehicle of choice for such an exercise.
No need for Sumgai to worry about us wasting time. While engineers are busy analyzing, the townsfolk can be reassured that they can pluck safely at night.
John
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Post by ChrisK on Aug 25, 2006 15:32:10 GMT -5
sumgai,
I misread your statement in that I thought that you thought that "electrical energization" was somehow being applied to cause the pickup's magnetic field to increase.
I diverged without leaving a clear trail. What I was discussing was the possible change to the pickups magnetic field due solely to the back emf internally generated from the current induced by the moving string. In a DC motor (a motor is a generator and a motor), the back emf internally generated while the motor is running limits the top no load speed of the motor. I was speculating that a pickup (a generator is motor) while being modulated by a vibrating string is also generating an internal back emf in AC form.
I was not referring to tone damping, but to electrical motor theory.
In essence, while the magnetic field of the pickup is always present, the effect of the pickup under load must increase the magnetic damping on the string since more work is being done.
Again, a DC brush motor with fixed field magnets will generate a constant magnetic field. Spinning the rotor will generate an output voltage. Shorting the rotor winding will cause the rotor to slow down much faster. More work is being done, energy is being taken from the spinning rotor faster.
Ergo, a shorted coil will drain energy faster and dampen the waveform either thru harmonic distortion or increased nodal disturbance effects at the 24th fret.
It was most discernible to me in my setup. It caused me to completely recheck the wiring of the ToggleCaster, which was not at fault.
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Post by sumgai on Aug 25, 2006 20:57:00 GMT -5
Chris, Thanks for clearing that up, I think we're on the same page now. You and I, and John, are pretty much in agreement for the same analytical reasons, but we're not quite in agreement on the amount of the effect. But like John, I'll stipulate that it's possible to include the effect in one's wiring layout, therefore, it behooves one to design without shunted coils whenever possible. D@mn, do you realize what this means? The Side-Slap-Strat is now null and void...... scheiße! Back to the CAD machine I go. sumgai
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Post by ChrisK on Aug 26, 2006 19:45:50 GMT -5
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Post by sumgai on Aug 26, 2006 19:53:47 GMT -5
Chris, My chiro asked me send along a note, thanking your for the lovely schema and schematic diagrams that are posted sideways! ;D Seriously, my first impression is that I need to break this down and trace it all out, there's probably something to be learned here. (By me, anyways. ) Thanks for the tip. sumgai
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Post by JohnH on Aug 26, 2006 19:54:26 GMT -5
Chris is the only person I can think of who can combine the words 'easily' and '8P5T' in a single sentence.
John
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Post by ChrisK on Aug 26, 2006 20:01:53 GMT -5
If you'll notice, most of my designs are symmetrical.
Inherent in symmetry is beauty, and inherent in beauty is simplicity.
Thinking upside down, inside out, and sideways is a good start.
My framework is willful schizophrenia coupled with inherent incorrigibility.
It's NEVER been suggested that I was normal.
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Post by UnklMickey on Aug 28, 2006 9:17:52 GMT -5
...D@mn, do you realize what this means? The Side-Slap-Strat is now null and void...... scheiße!... nope, totally do-able with a 4PDT. you only need to decide whether to make it: A -- series dominant. B -- parallel dominant. C -- with an added 6PDT rotary to make it selectable between the 2 schemes. just examine the diagrams i previously posted. guitarnuts2.proboards45.com/index.cgi?action=gotopost&board=wiring&thread=1145483375&post=1145890975look carefullly at the "housekeeping" tasks. then make sure to re-configure the use of the lower right portion of each switch to accomodate the changes. unk
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Post by sumgai on Aug 28, 2006 17:13:11 GMT -5
unk, Remember, one of the stated goals in the Side-Slap Strat was to use as few switches as possible. It was determined (by you and others) that some combos were not possible, due to the shunting needed in the series selections. (I later did add a DPDT switch to overcome that deficiency, one can now obtain all possible combos with my layout.) But, even if we disregard the number of switches used by either you or me in our madness, there still remains the spectre of "tone-suck" due to shunting. Even in your message (linked above), you mention that shunting is present for the usual reason. All I was saying was that I have to go back and see if I can eliminate the shunting itself...... and I've not yet done that, things are a-hoppin' here at the ol' homestead. One of us should keep this on a back burner, for later this year when the madcap summer "home-owner's repair season" is over for the year. ;D sumgai
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Post by UnklMickey on Aug 28, 2006 17:21:59 GMT -5
...Even in your message (linked above), you mention that shunting is present for the usual reason.... if you are referring to this statement, ...the lower left pole is used to shunt it's place in the serial group when the selector is off, or in one of the parallel positions.... i didn't mean that the pickup itself was being shunted. i was referring to it's "place" in the series group. in other words, maintaining continuity for the series group. no pickup ever gets shunted in that design. HTH, unk
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