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Post by ChrisK on Nov 18, 2008 16:31:23 GMT -5
The Tillman model is flawed. As one moves the pickup on either side of the 12th fret, the response should be an identical/mirror image. This is not the case in his model.
Note that when the pickup location goes past the bridge to the right, the response IS mirrored about the bridge. They must be mighty powerful magnets.
I mentioned this to him some time ago, he agreed.
Also, while the model intends to show the frequencies detected for a given position and sensing window width (which is not changeable), one cannot easily discern the response as a function of the harmonic multiples of any given note, for more than a few harmonics.
The best way to do this is with a spreadsheet that calculates the sines of the fundamental and all interesting harmonics, and plots them as well as sums them for a given frequency and positional ratio of string length.
In essence, for any given reasonable position inside a string end, you can't get all the harmonics.
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Post by ChrisK on Nov 18, 2008 16:09:55 GMT -5
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Post by ChrisK on Nov 18, 2008 0:23:22 GMT -5
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Post by ChrisK on Nov 18, 2008 0:03:19 GMT -5
That's an excellent idea.
This infers another question; what is the string spacing on the harp?
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Post by ChrisK on Nov 17, 2008 23:59:00 GMT -5
Talk about a product name predicting future price......
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Post by ChrisK on Nov 17, 2008 23:57:08 GMT -5
Pickups are wound with #42 to #44 gauge wire. #42 has a resistance of about 1.5 Ohms per foot. A Fender single coil pickup has a resistance around 6K (for the sake of this argument). That's 4,000 feet of wire that is 0.003" in diameter....................................  |
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Post by ChrisK on Nov 17, 2008 23:24:25 GMT -5
Welcome a'board.
I have a few questions.
Why do you need two pickups per 6 strings?
Why do you need a switch?
Are the 12 pickups identical? What pickups did you buy?
Are the ones that you are pairing together RWRP (Reverse Wound Reverse Polarity) with respect to each other? For a combination of two pickups to be hum canceling, one has to be wound the opposite direction as compared to the other. The magnets also have to be of opposite polarity. The former is trivial to change (just reverse where you connect the leads into your circuit), the latter is not, especially in individual pole magnet pickups).
Testing for opposite magnetic polarity is easy; magnets of opposite polarity attract.
If the pickups are not RWRP in pairs, they will not be hum canceling.
If the pickups are not identical, you will need to have level adjustments. This means a volume pot for each set. Now, you could use trimming potentiometers to do this and still have a master volume.
What is the lowest frequency/note that will be produced by this instrument? If it is lower that 80Hz, you might want to consider using bass pickups for those notes. A standard 34" scale bass guitar has its lowest string tuned to about 40 Hz. For a 40" string length, you could go no higher than four steps lower and maintain the same string tension.
Speaking of tension, you should do a total string tension calculation for all 36 strings. You will be surprised by how much it is.
Since the step ratio in the equally tempered scale is 2^1/12 or 1.059463, one can determine the optimum tone for a given gauge of string by converting the length ratio difference against that of a standard string length (34" for bass, 25" for guitar).
For instance, if the length is about 19" for a guitar string, you would get a note 5 steps higher.
You mention using 6 tone controls and a master volume.
Why do you want 6 tone controls? Presuming that this instrument will have a tuning interval of a string for every half-step, you will have three octaves of notes possible. A 24 fret electric guitar has a range of four octaves and does quite well with one tone control.
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Post by ChrisK on Nov 17, 2008 20:08:18 GMT -5
You could get one at Radio Shack but it may not be of low enough quality for use in a guitar amp.  |
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Post by ChrisK on Nov 17, 2008 19:57:17 GMT -5
I would recommend that you first measure the resistance of each coil. You can assume that within each 5 conductor cable, both coils of the same humbucker will be found. Tag one of these cables for future identification purposes. Once you have measured the resistance, please post the results.
Once I see these, I can give some further advice about how you might want to wire this, For instance, if both pickups in the MB have the same resistance, one could presume that they are nearly identical. If so, one might question the need to have both available independently.
I have a DiMarzio Multi-Bucker (somewhere) that I modified for 8 wire like the MB. It made sense to do so since all four coils were quite dissimilar.
I'd ask WD but my experience with their acuity on technical issues finds them to be perennially stuck between a burro and a burrow (ie, what's the switching on the Kent Armstrong "special" 4P3T toggle switch - huh, we don't know?). (They are the only U.S. source for this.)
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Post by ChrisK on Nov 15, 2008 21:20:38 GMT -5
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Post by ChrisK on Nov 15, 2008 21:12:01 GMT -5
That's what the drawing showed to begin with.  You haven't answered my question. "Does this mean that you interchanged the wiring from each pickup to the push pull switches on the pots without changing the pot wiring itself?" I need an exact answer to ensure that something didn't get mixed up when you moved things around. This determines how I think anymore about your circuit problem. No. The tone capacitor will be exposed to a maximum of perhaps 5 VAC under any possible conditions, including an attack with a particle beam weapon. For tone controls, in a passive guitar circuit, 25 VDC is more than enough. |
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Post by ChrisK on Nov 15, 2008 15:48:34 GMT -5
Does this mean that you interchanged the wiring from each pickup to the push pull switches on the pots without changing the pot wiring itself, or does it mean something else?
This seems like either a shorted capacitor (or a value waaaaay too large), or a short in the wiring to the capacitor. If the wiper of the tone pot was shorted to its case (and the case was grounded), it would function as an output shunt.
Can you post a dpic of your pot wiring?
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Post by ChrisK on Nov 14, 2008 22:17:01 GMT -5
What impedance speaker do you have anyway?
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Post by ChrisK on Nov 14, 2008 21:50:45 GMT -5
Because it's a "pickup system designed and built in the USA exclusively for VOX by DiMarzio." Because this isn't a ........  I suspect that the P-Rail will cover much if not more than what the DiMarzio does. In my P-Rails (or not) post I discuss and link to Pawar guitars. They use a custom multi-coil pickup designed specifically for them by Seymour Duncan. What you need is one of these;  They can be found for $400'ish when on clearance. Then you can get real cute and coil'y in a P-90 kind of way. The top one is the one that I'll do by routing for and moving the bridge P-90 to the middle. The new bridge pickup will be either a DiMarzio DLX-Plus or Virtual P-90 (I have both). If you think that these are neat, you should see the rest of my furniture! ;D     |
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Post by ChrisK on Nov 14, 2008 20:56:24 GMT -5
While the specifications tell the story from the maximum perspective, the graphs are helpful in seeing the continuous function. At the bottom of page 8, on the left side is a graph titled "Maximum Output Voltages BTL." We are using BTL since this is bridge connected. It indicates for 4 Ohms only up to a 4.5 VDC supply. It goes up to 6 VDC for 8 Ohms, up to 9 VDC for 16, and up to 12 VDC for 32. An observation of the 16 Ohm line indicates that at a 9 VDC supply, there is 14 VDC of output voltage. This is peak to peak since this is bridged. In reality, each output can generate a 7 VDC peak drive signal. Since this is at 1 Khz, this is a sine wave. The R.M.S. of a sine wave is the peak divided by 2 ^0.5. This gives a 5 R.M.S. output voltage. This correlates to 1.5625 Watts at 16 Ohms. Moving on the the "Power Dissipation vs Output Power" graphs on page 9, we see that at a 4.5 VDC supply (the maximum recommended for a 4 Ohm load) and 10% THD, a 4 Ohm load can have an output of 0.8 Watt at a power dissipation of 1 Watt. an 8 Ohm load can have an output of 0.6 Watt at a power dissipation of 0.55 Watt, and a 16 Ohm load can have an output of 0.6 Watt at a power dissipation of 0.25 Watt. If we look at this curve for 1% THD (that sine wave thing), we see that for a power dissipation of 1 Watt, we get a power output of around 1.55 Watt (which correlates with what I derived above). So, for a given supply voltage, providing that the maximum output current limitation is not exceeded, a lower impedance results in higher output power. It also results in significantly higher power dissipation (a bad thing). There are three limitations afoot; the absolute maximum rated supply voltage (15 VDC), the absolute maximum rated peak output current (1 A), and the absolute maximum rated power dissipation (0.7 Watt for the DIP package). Let's start with the absolute maximum rated power dissipation (0.7 Watt for the DIP package). The "Power Dissipation" curve on page 8 indicates that the 0.7 Watt rating starts to reduce as the ambient temperature goes up above 25C. While most humans are not comfortable at 50C, it's likely that the local ambient temperature around the chip and on the PCB WILL go that high. That means that for long-term reliability, we should operate this at about 0.5 Watt of power dissipation. For minimum power dissipation, the supply voltage should be as low as possible for proper operation as a given load. This would be about 1 Watt maximum at 16 Ohms from a 9 VDC supply. For the long-term survival of the IC, limit the supply voltage to 4.5 VDC for 4 Ohms, 6 VDC for 8 Ohms, and 9 VDC for 16 Ohms. Limit the power dissipation to 0.5 Watt. That can be derived only from the datasheets of the affected components. |
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Post by ChrisK on Nov 13, 2008 20:49:55 GMT -5
Do your homework - read the data sheet. |
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Post by ChrisK on Nov 13, 2008 20:24:58 GMT -5
We quietly wish that we too could "just say no."
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Post by ChrisK on Nov 13, 2008 20:23:08 GMT -5
You certainly can do this (connect the "ground lug" on the volume pot to the case) EXCEPT on this neck volume since the case is usually grounded and the "ground terminal" on the neck volume pot isn't grounded in two of the 5 5-way positions (that's how series works).
I don't generally connect the "ground" lugs to each case since I follow good engineering practice in grounding (versus generally tolerated guitar practice). I practice star grounding.
I also rarely discuss grounding since most don't understand it and it's just a lot easier not to. What's been done in guitars for 50 years is good enough for most ears.
In this design, only the bridge volume pot's "ground" lug is always actually connected to "ground" (and only if one isn't practicing the "faith of the isolation capacitor").
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Post by ChrisK on Nov 13, 2008 20:04:12 GMT -5
Click on the part number to the right of "Datasheets" half way down the page on the left side. search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=NJM2073D%23-NDIt's an NJR (a division of JRC) NJM2073D It's used in a bridged configuration to get 2 Watts of output at 16 Ohms. 2.5 Watts may be optimistic. ;D ;D Now the bad news; ya ain't gonna get even 2 Watts of DC power out of a 9 VDC smoke alarm-sized batt'ry. You need a real power supply or a beefy wall wart. I'd wanna use at least a 500 mA @ 9VDC supply. Maybe using a 9 VDC batt'ry causes that there "tube sound".  And, at 2.5'ish'ish'ish'ish Watts of output power, the power amp might just get somewhat toasty.  |
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Post by ChrisK on Nov 13, 2008 18:15:56 GMT -5
Yes, hook it up to a 25 Watt 10 Ohm rheostat, run it at full power, turn the rheostat down toward 0 Ohms, and when it's too much, you'll be the first to know.  Or, you could look at the ICs on it and post their part numbers (or a photo of the module). We could then search a'web and get the data sheets. |
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Post by ChrisK on Nov 12, 2008 21:06:27 GMT -5
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Post by ChrisK on Nov 12, 2008 18:40:58 GMT -5
If you have the pickups at hand, measure the resistance from both the red and white wires to each other and to the shield. Use the 20K ohm scale. Post the results. The important thing is that neither the red nor white wires are internally connected to the shield. This is a 4 Pole 5 Throw rotary switch. It will have 6 terminals for each of the four sections (poles). This is for 5 position selections and one for the the pole common. It has 24 terminals in all. The 4P5T lever super switch is a 4 Pole 5 Throw rotary switch turned sideways with a lever attached to the shaft. It will have 6 terminals for each of the four sections (poles). This is for 5 position selections and one for the pole common. It has 24 terminals in all. "Seems" can be deceiving. It's the same in functionality. |
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Post by ChrisK on Nov 12, 2008 16:02:12 GMT -5
No. What I was saying, from the perspective of teaching on the use of RH pots for blending in a parallel pickup, is that the pot must be rotated to "0" for full blend-in (0 Ohms) and to "10" for full blend-out (250K Ohms). Otherwise the taper response will act more like an on-off switch than a blender (as your experience with mirrored wiring has shown). In other words, the RH pot must be turned counter-clockwise (anti-clockwise to the rest of the world) for full blend-in. This is backwards compared to the volume control, and similar to the tone control for full high frequency cut, but we tend to view the tone control as an anti-tone control and are more comfortable with "normal" being "10" (it's a perspective thing). It's just counter-intuitive to the RH operator. The way that the wiring diagrams that you posted show it is correct (these already turn the RH wrong way). Wire as shown. You betcha'. As ashcatlt stated, things will be a bit brighter. But that's why we invented analog (as in continuously adjustable) tone controls anyway. |
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Post by ChrisK on Nov 12, 2008 14:08:22 GMT -5
Actually, there aren't that many new combinations in series. My post on Possible Coil Combinations shows what one can do for two, three, and four coils. You need to make a list of precisely the ones that you want as I do have designs that realize all 18 combinations for three coils (The HSS All Mode 'Caster) as well as we have many existing designs for subsets thereof. We also have the capability of generating fairly complex wiring designs for specifie combinations. |
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Post by ChrisK on Nov 12, 2008 11:57:15 GMT -5
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Post by ChrisK on Nov 12, 2008 11:33:41 GMT -5
Yes, a no-load pot is a single element audio taper RH pot with the resistive element disconnected near "10". Some do this by scraping the element. Fender actually have these available. I don't know the commercial part number for an over the counter unit, but if you look on the parts list for the American Standard Strats, it is called out there (the authorized repair center replacement part number). I apologize for not knowing the external numbers, but I tend to source many of my parts directly thru an authorized repair center (in business, as in life, it's who you know....). As I had mentioned, a RH pot will need to be wired backwards (0 Ohms at "0") to be an effective blend(ing)-in pot. Otherwise, the taper is all wrong and the pickup already has 100K of series blend resistance at "9" if you wire it for 0 Ohms at "10". We call this an on-off switch. That being said, a no-load pot or a home-modified pot can be used, but make the element disconnect at the "10" end and most certainly not at the "0" end. My experience with series blending (where one pickup is blended-in thru a varying series resistor to the pickup fully-on) is that 200K is the maximum resistance above which no appreciable effect is noticed (by me). JohnH seems to favor about 100K (but then, he has a certain fondness for Marshall stacks...). Using the no load pots does have a silver lining for the LoH. While the volume and tone will operate "backwards" at least the blender will operate correctly for the Left of Hand. I've again posted the link to guitarpartsresource. I have never ordered from them nor do I have any commercial interest or experience with them. They just happen to have the good sense to have good reference pics and descriptions on their site, so I use them in place of 1,000 words. www.guitarpartsresource.com/electrical_fenderpots.htm |
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Post by ChrisK on Nov 11, 2008 20:23:12 GMT -5
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Post by ChrisK on Nov 11, 2008 19:42:02 GMT -5
to run them over.....
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Post by ChrisK on Nov 11, 2008 19:39:50 GMT -5
Which in the U.S. is everything previously illegal (but rigorously practiced) and awesome becomes legal, and hence, boring....
Happy birthday, old man.
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Post by ChrisK on Nov 11, 2008 19:35:37 GMT -5
Welcome a'board.
As it stands now, you have one wire from each pickup (hot) going to the 3-way switch. There are probably two wires from each pickup that are connected together (for the coils in series), and one wire from each that is grounded.
After you implement the series/parallel push pull switch wiring, there will still be only one wire (hot) coming from this switch going to the 3-way switch and one wire coming from this switch going to ground.
Note the color of the current wires from each pickup going to the 3-way switch (hot) and to ground.
Note the colors of the two wires on each pickup that are connected together. Using a digital multimeter, measure the resistance of each of these wires to the ground wire, and to the wire (hot) going to the 3-way switch for each pickup. Use the 20K ohm scale. Note which one has measurable resistance (not "1" or open) to the ground wire and which one has measurable resistance to the hot wire (on the 3-way). This measurable resistance pairing indicates the wires for each coil.
In series, these two wires are connected as they currently are. In parallel, the wire paired with the ground wire goes to hot, and the wire paired with the hot lead goes to ground.
In essence, the series/parallel switching is just an intra-pickup affair (a submodule if you will). This switching is done between the existing pickup and the existing 3-way wiring.
I hope that this helps.
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