Confusion regarding reading schematic

Ok, you got your soldering iron and nothing is going to hold you back, but you have no clue where to start or what to build. There were others before you with the same questions... read them first.
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fireflyva
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Post by fireflyva »

Hey guys - I'm brand new to this forum and an "absolute beginner" when it comes to building stomp boxes. My question: looking at a schematic that was listed on this forum under the jangle box

https://www.freestompboxes.org/viewtopic ... c&#p181001

and when I opened the schematic, there is a little section of the schematic at the top of the page that is not connected to the rest of the diagram. How do I read it? In other words, when it is not connected to the rest of the diagram/schematic, how do you know where it connects to the rest of the diagram?

Thanks in advance.

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Intripped
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Post by Intripped »

it's easy:
all the points named "+9V" must be connected together
the same for the ones named "VB"
idem for "GND"

this connections are usually represented in this way on the schematics, because it makes the schematic easier to read (once you know how it works)

also: in that schematic the connections of the sleeve (ground) of the two jacks are not represented: remember to connect them together with all the other "GND" points

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Post by fireflyva »

Thanks for your reply:

So what does VB stand for? Voltage Bus? and when you say all the ones labeled VB need to be connected together, do you mean they just all have a common connection?

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Intripped
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Post by Intripped »

not 100% sure but i think VB stands for "voltage B" - you can find also VA or VC or Vref
this voltage usually is lower than the primary one, that is indicated with V+ or directly with +9V (or 12V etc...) - in amplifiers schematics B+

in some other schematics you can find two capital letters - for example two "A" : this means that in the real circuit these 2 points are connected each other
as a general rule: all the points with the same acronym/initial are electrically connected in the circuit

so yes, all the VB points are connected each other

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Post by fireflyva »

Thanks for the information. If you don't mind, I have one more question.

When looking at the schematic, I can find the capacitors listed and their values. However, some of the capacitors are polarized and some of them are not. When I Iooked at the list of items needed to build the pedal provided by the person who came up with the schematic, none of the capacitors on the build list showed whether they were polarized or not. When I look at the schematic, some of capacitors were obviously polarized while others were unpolarized. Are certain capacitors just understood to be polarized while others are not? Or is the only way to know whether to use a polarized capacitor is to actually look at the schematic? Also, can polarized and nonpolarized capacitors be used interchangeably?

Again, thanks for your information and feedback.

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Intripped
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Post by Intripped »

typically capacitors bigger than or equal to 1uF (1 micro-farad) are electrolytic, and electrolytic capacitors are polarized
there are also NP (non-polarized) electrolytic capacitors, but you would find a note on the schematic and/or in the part list (also called BOM - bill of materials)
also tantalum capacitors are polarized

all capacitors in the nF (nano-farad) and pF (pico-farad) range are usually non-polarizad ones; also, nF-range caps are usually film capacitors, and pF are ceramic.
of course there are exceptions, but you would find a note in schematic or BOM.

why all these differences? most importantly: dimensions of the caps - 1uF film caps are already quite big, and maybe too big for the available space on your PCB

in general, you can sub a polarized cap with a non-polarized one

some suggestions:

it's very important that you spend some of your time studying schematics and learning how to create a real circuit starting from a schem
i mean: the target is to understand and actually SEE HOW the real circuit and the schematic are basically the same thing (conceptually at least)

...and finally (please don't get this the wrong way): the first thing to learn is searching in the internet (and in the forums) - your doubts are exactly the same that everyone has when approaching the diy electronics, so it's VERY probable that your questions have already been answered

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Post by fireflyva »

No problems - I don't take it the wrong way. I appreciate you taking time to explain this to me, but I don't want to waste you time answering questions that might have already been asked and answered. Again, thanks for your time and I will spend more time digging through the forum looking for this information.

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Post by Seiche »

feel free to always use the thanks button (the little 'thumbs up' symbol next to the "quote" button) if a post was helpful to you.

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Post by OMFUG »

This is great info - I had the same question. Thanks! Also, to the OP - in case you haven't seen it I find this IMMENSELY helpful in terms of some of the conventions I never dealt with in basic electronics (such as sassumign switchign knowledge and leaving it out of a schematic). From IvIark and Scruffie in the top absolute beginner's thread:
http://www.beavisaudio.com/techpages/Sc ... ToReality/

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Post by fireflyva »

Thanks for all the information. I have another question and I've been searching the forum but I've not found the information.

Again, as mentioned in an earlier email, I am attempting to build the "janglebox" as my first build and have been using it as a huge learning experience. I've assembled it 2x and have not been able to get it to work yet. After the first build I spent a lot of time troubleshooting and found a variety of problems, so many in fact, that I took it apart and started over. The second build was better but still plagued by mistakes but not as many. I've been building it on a breadboard and so I could pull the parts out and start over as needed. I'm learning a lot, and since I don't do this for a living and only learning to do this "late in life" as a hobby, I'm not starving.

Now, my question: it is regarding wiring the switch: on the schematic, the switch has been shown wired simply but I wonder if some of the problems I'm having is because I've not wired it like in this example:

http://www.beavisaudio.com/techpages/StompboxWiring/

is it understood that I should be wiring the switch this way even though the schematic doesn't reflect it? or is it "assumed" that builders should know this and when they see a schematic with the switch symbol that they need to wire it this way?

Thanks for your help.

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square wave
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Post by square wave »

If you're using a 3PDT switch for true bypass/stompbox operation, then it needs to be wired the same way regardless of what circuit you're connecting to. The only optional parts of that diagram switch wiring are the LED and ground connections, but most people want that.

Please note that even though that diagram shows two different grounds, they are all one ground and should be connected together.

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Post by fireflyva »

Thanks squarewave - I'll try and wire up the 3PDT switch like it shows in the Beavis article and see if it helps. Right now I just get a lot of "buzz and hum" with no guitar signal...we'll see how this modification works!

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Post by fireflyva »

OK - I've been searching this forum a lot and the internet and attempting to educate myself so as to save those who read this my stupid questions. I have spent several weeks time attempting to troubleshoot an effect I've built. However, I have a question that I hope someone can answer for me regarding how to wire the toggle switch in the schematic.

I'm using a DPDT toggle switch (on-off-on) as recommended in the build list. It appears as if the 2nd pole is wired to ground leaving the 1st and 3rd poles open to be wired as the schematic demonstrates. However, if I wire like I think it wants me to do, the toggle switch simply seems to take one path or the other and grounding it out, or in the middle position, seems to have no effect. Is this correct? Does the switch not have a power source other than one of the two pathways? And if this is correct, are the other 3 poles just left unconnected?

Again this is the same schematic for the jangle box whose schematic is included earlier in this thread. I hope I've used the correct terminology in referring to the switch. If not, I've apologize and will try to co better.

Thank you.

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Post by Lucifer »

Hi fireflyva,

Your assumptions about the switch wiring are just about correct. With the switch in the middle position, it is not grounding anything, but that doesn't mean it is not having an effect.

The terminology you're using for the switch is slightly awry. The 'poles' as you describe them are actually 'contacts' or 'pins'. You are using three contacts on one side of the switch, and together they are referred to as a pole. The two poles are the two rows of three contacts.
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Post by fireflyva »

Thanks for the reply, Lucifer.

To follow up with the next question, then, when the toggle switch is flipped over to one side or the other, but not in the middle, that side or line is being "grounded out, " right? Does that path become "non effective" meaning it is being taken out of the circuit, or am I trying to incorrectly view it as a "all or nothing" situation? I would assume that if that path is taking itself to ground, that perhaps that path is acting as the actual switch in the IC to make something happen? Am I oversimplying this whole process or just walking down a dark alley with my eyes closed?

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Post by Nocentelli »

We're still on the Janglebox, yeah? Grounding part of a circuit can do many different things depending on what is being grounded. If you ground a signal-carrying wire directly, you mute the circuit; If you ground a signal-carrying wire via a small (i.e. few hundred picofarads) capacitor, you form a low pass filter and high frequencies are bled off to ground, rolling off some treble from the signal that passes this point. Grounding a large value capacitor connected to a transistor emitter (or JFET source) can massively BOOST the signal.

In the janglebox, grounding the 22n cap effectively bypasses the 10k resistor connected to the large 2u2 cap hanging off the inverting input to the opamp: This gives a gain boost, but only to higher frequencies - it's just how opamps work. I presume this is a "bright" setting. The other throw grounds the 8k2 resistor, which is hanging off a small value cap, which is connected to signal: This will roll off some high end, and I presume this is a 'mellow'/'smooth' setting', and is like the example I gave at the start. The larger value resistors that are bypassed are there to prevent switch pop that might occur.
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Post by fireflyva »

Thanks, Noncentelli. That explains a lot.

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