Schematic reading help, please

Hey guys =) Just when I thought I was getting a decent handle on reading schematics, I have hit a wall. Below are schematics for two types of Varitone circuits. Both include dotted lines with a directional arrow at one end.

I'd never encountered a dotted line of this type in a schematic before, so I did the Google thing. I found the dotted line part (shielding) but nothing with a dotted line with an arrow at one end. I added red arrow pointers in the drawing to show where the lines in question are. So...

1) What do the dotted lines mean in this particular circuit?

2) In the top drawing, lower section, I don't understand the numbers 1 through 7. I've seen pictures of a few different Varitone switches and in each one, all of the negative posts from the capacitors are wired together and sent to ground. However, in this particular application, there is an inductor in between the caps and ground. The numbers 1-7 are shown before the inductor (choke), so I'm a bit lost. Additionally, there's that dreaded dotted line again, coming from #2. Would someone please explain this part to me?

3) Again, top drawing. Reading from right to left, the 10 Meg resistors (I think those are resistors), just past those, there's a split by the number 3, with one wire heading toward the pickup selector switch and another wire running parallel, with a 100k resistor in line. Am I reading that correctly? Two wires, split parallel at that point, one having a 100k resistor in line, then reconnecting on the pickup switch side?

Sorry this is so long and wordy. If needed, we can address these things one at a time. Thanks in advance for any help!

1. The dotted line just indicates that the switch wiper (which the line extends from) moves to make connection with the other contacts. When looking at a schematic that has this many dots connected to wires, it may not always be obvious that you're looking at a switch. The dashed line helps make this more obvious. Since the top schematic has a two pole switch, the line also establishes a common direction of rotation for the two poles.

2. As alluded to above, a second pole has been added to the switch. The first pole is the same as the 1961 mono circuit, and selects a filter cap. The second pole appears to have been added to completely disconnect the filter caps from the inductor and ground when the switch is in position 1. I'm guessing the implication is that there would otherwise still be a small amount of tone suckage through those 10M resistors.

3. Think "path of least resistance". What's throwing you is the way they've arranged the components. When the switch is in position 1 then the output jack tip is connected directly to the pickup selector switch, and that 100K resistor is shunted - you can effectively ignore those other components. In any other switch position, there's a 100K resistor in series with that wire, and a capacitor and inductor in parallel to ground.

My guess is the 10M resistors are there to bleed off the capacitors when they're disconnected in order to avoid any popping.

Ugh. Feeling a bit overwhelmed right now. I'm going to copy this page so I can try to do a drawing with actual components to see if that helps and then come back with more questions, I'm sure.

The 10M resistors, I did get that part. I didn't remember the correct terminology to use (capacitor bleed-off), so thank you for adding that in, too. That's the part I mentioned earlier about using a make-before-break/shorting rotary switch instead, so there's no need for bleed-off resistors.

I really appreciate the help!

(edit): are you saying that the top diagram represents use of a 2p6t rotary switch? I'll have to look up how those are wired to get a better understanding. The 1p6t ones I can deal with.

There are so many different conventions people apply when drawing schematics it's not always possible to make a definitive statement. Sometimes you just have to look at what they've drawn in context with the rest of the circuit.

Strictly speaking, the schematic is drawn as if there were two different 1P6T switches. When the poles are part of the same physical switch they usually indicate this, either by drawing a dotted line between the poles to imply the mechanical connection between them, or using a suffix on the reference designator (e.g., "SW1A" and "SW1B", etc.). In this case they did neither, which might imply that they were two different switches. However, that wouldn't make any sense in context with the rest of the circuit. Breaking the connection between the inductor/ground and the capacitors only makes sense when the upper switch pole is in the first position, which is what the second pole would do if it was part of the same switch.

I don't think there's any doubt they meant to use a 2P6T switch.

Welllll... I tried to draw the darned thing out with depictions of actual parts in place of the schematics and I reached an impasse. That's fancy talk for my head began to hurt.

So, I went back to the basics and just drew up how the typical Varitone is done these days. This part, I can easily understand. Apparently I'm not ready to tackle the big kid stuff in the other schematics I posted earlier.

Unless I boned this one too, this is basically how it's done these days:

The question mark where the #1 position is there because originally, I thought it was straight to ground, but that didn't make sense, so I put a mystery cap in its place. The cap normally used with a typical LP tone pot (500k) is a .047

I second this. Five 10Meg resistors in parallel is 2Meg, which is beginning to get significant.

Your simplified version is probably good enough. You might get some popping without the 10Meg resistors but you won't know till you build it (and this is dependent on whether the first stompbox in your chain leaks a bit of DC back into the guitar). Without the 10Meg resistors there's no need to disengage the inductor with that second pole.

The original circuit probably would have been clearer if the second pole of the switch and the inductor were swapped positions. Then it's clearer that it's disengaging the entire tone circuit.

As mentioned previously, I'll be using a MBB/shorting rotary switch so I won't have to use the 10M resistors to avoid noise when switching. I probably won't be switching during songs anyway, but I don't know yet. This is more of an experiment for me, along with a few other mods, including utilising a bit more than the standard three pickup switching options (going all out - split coils, parallel, series, etc). I've never done any of that before so this is an adventure for me. Hell, I've been playing strictly acoustic for the past 10 years. My last electric was an '84 Washburn.

Anyway...

So do I need a cap in the #1 position? Without one, is that a complete bypass, other than the inductor, or can it go straight to ground?

Thanks again, guys!

Your simplified wiring diagram missed the 100K resistor that used to be in series with the signal from the pickup selector switch. Position 1 doesn't need a cap, but it was SUPPOSED to bypass that 100K resistor, and route the pickup selector switch directly to the output jack.

I also don't see the pickup selector switch in the diagram. In your second post you mentioned using a make-before-break switch, and alluded to a previous mention of this point, but I don't see anything about it in the first post. Was that in another thread that I missed? Did you also intend to remove the pickup selector switch? Are you now using one tone pot for both pickups?

In addition, the original circuit didn't have the additional capacitors controlled by the tone pot, but still had 0.02uF caps on the tone pots.

What you've done is replaced the tone pot cap with the varitone circuit, rather than adding the varitone circuit to the output signal line. I don't think this is going to produce the same results as the original circuit.

That's where I'm getting lost. I decided to build my own Varitone. That's the simple part. Rotary switch, some decent caps of different ratings and an inductor. Some of the setups I've seen just substitute the Varitone in the place of where there usually would be a .022

I don't think most engineers have a magical ability to picture things in their head. In fact, I have the opposite problem you have. Pictorial wiring diagrams confuse the hell out of me. They just look like spaghetti. Until I can see the circuit in a proper schematic it doesn't make any sense. I think it's because we approach the circuit from different viewpoints. You want to see how it will be constructed. I want to see how it works. A schematic unravels the spaghetti and shows me where the signal goes.

Ok, I get the idea of doing this with one volume and one tone pot. The "few toggles for pickup switching" is throwing me off track a bit. Exactly how many toggles will there be, and exactly what will they do? If you can tell me these things then I think I can put together a schematic AND a layout that will work. Since you're visually oriented, please also tell me what type of pups and switches you'll be using.

In upper diagram of post #1 a 2P6T switch (2 poles/wipers, six positions) selects between connecting the signal path to open end of one of the various capacitors that together with the choke (inductor) form a series resonant band-stop filter (a notch filter). Different capacitance in this circuit equals different notch frequency. The initial position of the switch (as depicted in the schematic) breaks the ground path of the resonant circuit (hence the LC circuit becomes disabled) and also bypasses the 100K resistor that isolates the resonant circuit from the pickup. Schematic wise, you can imagine that arrow (pole) sliding horizontally and touching the various

Hey, i was thinking of making something like this reciently. Here is my question: where does one get the 2P6T rotary switches?

Pups are passive EMG humbuckers. Here's the drawing I'll be going by for the toggle switching:

Mine will be just slightly different than that. SW1 and SW2 will be DP3T (on/on/on) toggles, and SW3 and the pickup selector will be DPDT (on/on) toggles. The Varitone will go in place of the capacitor used on the tone pot. At least that's the plan so far.

teemuk: I think this is the switch you may be looking for (spec sheet for that one in PDF format is here). If that's not the right one, try the list on this page. Hopefully that second one will come through correctly.

That was a great example. I look at that diagram and I see circuit pathways going everywhere. The only way I can figure out how that works is to meticulously follow each wire and imagine what route it will take with the switches in each position. I had to stare at that diagram for ten minutes before I understood what they doing with those on/on/on switches. One of the problems I had was they didn't make it clear which two pairs of lugs will be shorted when the toggle is in the center position. I know that it will usually be opposite corner pairs, but they didn't indicate whether it's the upper left/lower right pairs, or the lower left/upper right pairs. I finally figured out it was probably the lower left/upper right pairs, since (in the case of the neck pickup) this would connect the north coil to the pickup selector switch, and short out the south coil.

This type of switch isn't difficult to find, and will take up less space than a DP3T on/on/on switch. Is there a reason you want to use a DP3T instead?

Which switch are you saying isn't difficult to find? I have DP3Ts already. They're mini-toggles. I have larger "standard" toggles around, but I rarely use them because I mainly deal with DC stuff that's 12v or less.

I have to test the DP3Ts that I have to see if they are laid out the exact same way as the ones used in the drawing from guitarelectronics.com (they have some great info there and decent prices on parts). I understand how the switching works; I've been reading up a bit in the past few weeks about various guitar switching configurations, so I have a pretty good line on things and if the switches are controlled differently, I'll know which poles to use.

Oops. I missed another one. Back in post #5 above, I left the #1 position capacitor designation in the drawing with a question mark because I'm unsure whether it should have a cap or can be left open (with nothing between the rotary and the inductor, or bypass the inductor too and go straight to ground). Opinions, anyone?

Again, I'm open to other ideas as well. I'm just having fun with this and want to experiment with both pickup selection and tone control at the same time. I want to find what I like best.

The switches in the diagram aren't DP3T's. They're DPDT's configured as "on/on/on". It's the latter part that makes them somewhat unusual.

A true DP3T switch would have two poles. Each pole would have one lug for the moveable contact, and three lugs for each of the fixed contacts (i.e., three "throws"). That's four lugs per pole, or a total of eight lugs. Some DP3T switches have even more lugs, and use external jumpers to configure them.

A DPDT switch has one moveable contact per pole and two fixed contacts, which is what the switches in the diagram have. There is no third fixed contact which would make them "triple throw" switches. However, they aren't like conventional DPDT switches either. The bat can stop in the center position.

Most DPDT switches that have a center stop for the bat are "on/off/on". This means that in the center position the moveable contact isn't connected to either of the fixed contacts; i.e., it's "off".

In this particular switch, since the moveable contact is still "on" when the bat is in the center position, the question becomes which of the two fixed contacts it's connected to. In this case, the moveable contacts for each pole are connected to OPPOSITE fixed contacts. The pole on the left is connected to the lower lug, and the pole on the right is connected to the upper lug.

What I was saying is that this switching arrangement is unusual, but the switches themselves are not difficult to find because they are used often enough for switching pickups.

I've seen the ones you mention, with eight posts on them, but the ones I bought are listed as DP3T, with two contacts per throw (three positions = on/on/on = 3 throw, correct?), both on the web site I obtained the drawing from, as well as the source I purchased my switches from.

I did goof earlier in saying that the pickup selector switch is being replaced with a DPDT. It'll be another DP3T, where top is on for neck pickup, middle for neck and bridge, and bottom for bridge only. The DPDT (SW3) is solely for parallel/series switching. I considered including a phase reverse switch, but so far everything I've read points to it really being a tone killer in most instances.

Would someone please answer the question in post #16, referring to my drawing in post #5? (pretty please)

I'm not sure what you

I know what is a potentiometer and what is a switch. Read my post more carefully, please. In post #5 diagram you have the resistance of the

I think I confused others when I switched to discussing the original diagrams in my first post and went directly to the diagram in post #5. I thought maybe you were confused by what I wrote concerning substituting the entire circuit in the other diagram (from post #5) for where the existing capacitor is.

Please try to understand that I think differently than some people when it comes to stuff like this, and I'm an amateur.

Okay, back to the circuit. Is this what you (teemuk) mean?

Please ignore the values of the capacitors in position numbers 2-6. They're basically there just to have something on there. {edit} I also left out the pickups and volume/tone controls for now. I want to be sure I understand this part first.

IF I have the diagram done correctly, what is the purpose of the 100k resistor at the beginning of everything? As for the 10M resistors, I covered that a few times before: I am told those are not needed if a shorting rotary switch is used. The original used a non-shorting switch and the resistors were used to keep it from popping when switching from one position to another. Sorry, but I forget the term used for that.

Thanks for hanging in there with me, guys.

teemuk, you still around?

Yep, that looks correct.

I think the purpose of the 100K resistor is to decrease the quality factor Q of the notch filter, which in turn makes the notch bandwidth greater. With greater bandwidth the effect of the filter is much more prominent than in a case of higher Q that would make the notch appear at a very narrow band of frequencies. See:

When the LC filter is removed from the signal path (in the 1st throw of the switch) the 100K resistor would just become an unnecessary series resistor and therefore it is bypassed.

The make-before-break switch (or whatever that is called) likely stops the popping.