# Help me understand schematics



## Mark Brown (Jan 4, 2022)

Hey all. I have decided it is time. When I was a kid I tried to learn Latin, that didn't go so well and was not all that practical. Now I am on to this, much more useful.

So I have been having a hard time with this, as I am one section into this simple layout and cannot seem to sort out where the ground is labeled on the second input. Do you just assume grounding on a schematic, that seems crazy, or not. Anyhow, show me where the ground is denoted on input 2, please.










And not that anyone needs it....


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## Alan Small (Dec 30, 2019)

Docendo Discimus










the jacks are 'switching' style and connect a path with or without a plug inserted

Those little arrows say ' i have a spring loaded 3rd tab'


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## Thunderboy1975 (Sep 12, 2013)

Thats what i thought too. Good to know!👍🏼


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## Mark Brown (Jan 4, 2022)

No matter how hard I try and see it I cannot. 

I cannot for the life of me understand how that input 2 gets tied to the grounding bus, is it because the first input routes through the switch on the secondary and then that is the ground path for what is labelled R1 input?


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## Jerome (Dec 4, 2015)

If you are wondering how the "sleeve" of the input jack connects to ground , the nut that tightens the jack to the chassis causes the body of the jack to make a physical connection to the chassis , providing a path to ground .


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## 2N1305 (Nov 2, 2009)

Mark - Good question.

The ground is actually NOT schematically represented. And I looked a long time at that schematic too. IIRC, all early Fender drawings are like that. IT is true, like others have said, that your signal remains grounded until the body of the connector breaks ("opens the circuit") the connection between ground and the signal node. HOWEVER, the schematic does not show the actual "barrel" (labelled s "SLEEVE" in drawing of post # 2) of the socket.

My terminology is as follows :

"Socket" ---> Female connector (Socket to me baby, wontcha?)
"Jack" ---> Male connector (Jack is guy's name right?, there ya go)

if you refer to this schematic you will see the ground sleeves schematically represented, directly connected to ground.


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## Mark Brown (Jan 4, 2022)

So basically schematics state....

Hey dumb ass, just get it to ground!

Unless we go and tell you where to get it to ground.

So the reason that resistor shows ground is because it is not independently grounded in any way and needs to get tied to the lug for chassis ground through the jack. The reason the second input does not show a ground is because it is chassis grounded.

The reason the ground lug on input two, which in the diagram shows a ground wire traveling to the preamp bus, is not listed is because it is not part of that input/signal chain and its only function is a ground path LATER in the circuit to connect back to ground for other thing.

.... I think


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## Granny Gremlin (Jun 3, 2016)

Jerome said:


> If you are wondering how the "sleeve" of the input jack connects to ground , the nut that tightens the jack to the chassis causes the body of the jack to make a physical connection to the chassis , providing a path to ground .



Exactly, and sometimes, like in that Champ diagram, the sleeve connection (as per the jack diagram in post #2 at the very bottom) is not shown and implied/assumed. If it is shown you will see the ground arrow connected directly to it.

All you see in the Champ diagram is the signal to ground through the input resistor, which is not the guitar ground connection (which is one reason it is such a big resistor gate keeping the path to ground; an actual ground should have the lowest resistance possible, but here's it's like a dike to overflow runnoff; a capacitor to ground is basically allowing some frequencies easier (lower resistance) access to ground than others (e.g. treble bleed mods in guitars; crossovers in speakers, tone controls etc) because a cap is (among other things) a frequency-dependant resistor. An inductor (or choke) is the same, but works in the opposite direction as regards which end of the frequency spectrum the resistance is highest at. Using the example of basic 1st order speaker crossovers, you have a cap in front of the tweeter which makes the ground path for bass a lower resistance than going through the cap, and an inductor in front of the woofer, making a lower resistance path to ground for the treble. And it's not a brick wall but progressively more and more resistance as you go up/down in frequency. So that's how you get a rolloff slope. The cap/inductor value sets the point at which the filtering starts. This also demonstrates the difference between resistance and impedance (R vs Z) - Z is variable: resistance + reactance (capacitance and inductance are "reactive" to frequency). This is why an 8 ohm speaker measures not (eg) 8 Ohms but a bit less; the rest is the voice coil reactance (a coil is an inductor).

You may be thinking, but tone controls in guitars use a cap but reduce highs (vs the tweeter as above where it is filtering out the lows; why is that not an inductor?) - that's because it is used differently (and inductors cost more and can cause noise, thats why the chokes in a Lucille varitone circuit are humbucking and sheilded): instead of being in series with the signal path (blocking access to the next stage), it is gatekeeping the ground, so the treble can get through it to ground as a ralatively lower resistance, but the mids and down cannot so they continue down the signal path. The tone pot then allows you to control the relative R of signal as a whole to the cap vs the other way down the signal path - if you make the R higher to the signal path, the treble has a lower relative R to ground. Signal will take the path of least resistance.


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## Jerome (Dec 4, 2015)

As far as i know , the jack is the female connector that is mounted to the chassis , the plug at the end of your guitar cable is the male . 

S12B.210" ID Open Frame Jack, 3 conductor


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## Mark Brown (Jan 4, 2022)

Let me maybe make a little more sense in my question as there seems to be a lot of focus on what I do know and not particularly what I am asking which I will assume is always my fault for never knowing the right questions to ask.

On "Input 2" you can see in the diagram that there is a ground wire running from the ground lug on the input jack to the "preamp ground bus" yet this particular connection is not directly listed anywhere on the schematic. 

Following that ground, it runs from the cathode on V1a and passes through the resistor and cap to ground. I guess the thing messing up my brain is how does that particular connection get assumed?? What makes the ground bus connect to the lug on that jack? Simply because it is an available path to chassis ground?


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## 2N1305 (Nov 2, 2009)

The "Jack" (as I have been corrected) body thread is bolted to the METAL chassis. The terminal strips or other connections that are indicated on the schematic with the ground symbol also are soldered to the metal chassis. Everything that you see having the ground symbol on the schematic is linked electrically together by the metal chassis.

What makes the ground (not bus, that is the chassis) of the connector connected to ground is the metal to metal contact between the thread of the jack and the 18Guage steel chassis.

Does this, per chance, answer your questioni?


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## Mark Brown (Jan 4, 2022)

Move away from the schematic for a second and look at the wiring diagram like us plebs 

See how the ground lug on the input 2 jack is connected down to the ground bus for the preamp stage? Now when you look at the schematic, there is no notation to show that connection. The individual components are shown running to ground, but nothing connects them to that specific lug on that specific jack.

What I am trying to understand in the interpretation of schematics, or this particular schematic to be specific, is how is it determined that the lug of that jack becomes the grounding point for the "preamp bus" in the diagram. Is it simply that you pick a path and take it and in this instance the easiest/best/least populated path would be the grounding lug on Input Jack 2??

I understand the concept of "to ground/earth" but what I am trying to understand is where the path is not directly noted, which is just about everywhere, does one just assume the shortest/best path?

I should add, I appreciate the time and help. Gotta get there somehow.


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## 2N1305 (Nov 2, 2009)

I understand your question now. I will have it simmer in my brain for several thousand milliseconds...

I'm an electronics dude, it's my pleasure, although I should be working


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## Frenchy (Mar 23, 2011)

AC/DC - She's Got The Jack live at VH1 studios - YouTube


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## Paul Running (Apr 12, 2020)

The schematic that you are trying to understand is very busy with information that is not required for signal path flow. I would erase all the component identifiers and component values, until you understand the circuit's operation. Here's an example schematic of the simplest instrument amp that I know, the Gibson Mastertone.


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## 2N1305 (Nov 2, 2009)

Mark Brown said:


> I understand the concept of "to ground/earth" but what I am trying to understand is where the path is not directly noted, which is just about everywhere, does one just assume the shortest/best path?


In short, yes.

This is always what is preferred for electricity. Leo Fender probably just chose that lug arbitrarily as he was building his prototype, who knows.

I guess you should study RobRobinette's webpage, which is very well done by the way, in order to fully understand the signal flow, while reading about basic electricity/electronics.

The Chassis is the best ground, usually. But common points are usually chosen to tie several components to ground. Also you will see "eyelet lugs" on transformer bolts or similar mechanical items where ground connections are made.


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## Mark Brown (Jan 4, 2022)

2N1305 said:


> In short, yes.
> 
> This is always what is preferred for electricity. Leo Fender probably just chose that lug arbitrarily as he was building his prototype, who knows.


Thank you!

Schematics are not diagrams per se, I get that, and as such are open to interpretation. They are a signal/current/circuit/whatever you want to call it reference. The rest of "how to" is up to you. 

In the 5 hours since I made this my mission today, I can at least understand the bloody thing. That isn't as hard as I thought it would be. Following is easy.

I just kept looking and when you see grounds all over hell and creation and they don't "lead" anywhere i couldn't wrap my pea sized brain around how they "end up" anywhere. Well, they end up to ground..... but that should more or less be an arbitrary path given how grounding works.

A ground is a ground is a ground.... unless it is getting interference from something else, but that is another conversation.


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## Mark Brown (Jan 4, 2022)

Paul Running said:


> I would erase all the component identifiers and component values, until you understand the circuit's operation


While I appreciate this advice, I do not have a problem following the signal in the schematics. I am very familiar with wiring in diagram form and I understand the "concept" if not the functionality.

Electrical schematics are just not a language I have a grasp of fully. You can throw a circuit board or an amp, vcr, pc, automobile at me and I can follow the signal path. The problem is when I try and understand it/explain it my terminology is... let's just say bad.

Without the higher function of values and components on the schematic it truly is of no value to me as I do understand the pathing.


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## 2N1305 (Nov 2, 2009)

Mark,
how is you parts provision coming along? Have you found "iron" yet? (cool slang term for transformers) I suggest getting the chassis, power transformer rectifier and capacitor first, that way you can build the power supply and verify its operation with a simulated load. By this I mean loading it with something like a power resistor of a similar load to the circuit. You can do this by calculation, or if that sounds super boring (I would think so as well), connect something like a 68Kohm 5W resistor to the output cap.

Anyway, when you get there.


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## greco (Jul 15, 2007)

@Mark Brown 

What electronics test/measure equipment do you have access to? Just curious.


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## Mark Brown (Jan 4, 2022)

greco said:


> @Mark Brown
> 
> What electronics test/measure equipment do you have access to? Just curious.


Multi meter and a wet finger 


2N1305 said:


> Mark,
> how is you parts provision coming along? Have you found "iron" yet? (cool slang term for transformers) I suggest getting the chassis, power transformer rectifier and capacitor first, that way you can build the power supply and verify its operation with a simulated load


All the parts are presently headed to me in the mail from here, there, everywhere and some very generous members of the forum.

I'm headed to metal supermarket today or tomorrow to get a sheet of 1/16 plate aluminum so I can fashion the chassis. Haven't been in too much of a hurry because without the board and components all I can fashion is a box and I have much more interesting projects to undertake right now. Like Electronics 101


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## Mark Brown (Jan 4, 2022)

So here is another food for thought moment in the mind of me.

Schematics are useless for copying a circuit 

So, that might be a loaded statement but let me explain myself. Like I have previously said, I am a diagram guy, me and Ikea furniture instructions get along great. Schematics have always confused the living hell out of me because they look nothing like what they are explaining. 

Take that 5F1 schematic for instance. Where AC enters from the wall, it shows an amp and switch before the power transformer, that makes sense. Then you run off and look at the diagram which is a SPST switch on a 1Meg pot. Except the schematic has the switch way over in the circuit where it is, the pot is no where near the switch. Now with my slightly better understanding of how that circuit is drawn, knowing that it is drawn for only that purpose, that makes a lot of sense. Seeing as those two components are not even a little related to one another even though they share the same space. I always was lost trying to make the schematic into the circuit, or diagram that I just gave up trying to understand because the two things just didn't correlate. 

I find as I learn the "what" the "how" seems to make a whole lot more sense too!! Looking at the grid to plate interaction on the schematic is honestly probably the biggest "Ooooooh that is how that works" moment I have ever had lol. Other than when my first kid popped out of my wife, but this is a close second.


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## DBS_180 (Oct 2, 2018)

Mark Brown said:


> So here is another food for thought moment in the mind of me.
> 
> Schematics are useless for copying a circuit
> 
> ...


I think for anyone who's building an amp and referencing old schematics, it's more important to aim for similar voltages than using the same part values (e.g. a 22k dropping resistor in a 5E3 might not give you the desired preamp plate voltages).


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## tomee2 (Feb 27, 2017)

I've spent years trying to understand schematics. I can say I can confidently tell the difference now between a tube amp and a transistor amp. Haha... seriously, Am I allowed to say schematics aren't easy? No one is a dummy for not understanding them. It's a specialized form of documentation/ communication. Like trying to understand an architect's drawings, some stuff is obvious other stuff needs pointing out.


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## Mark Brown (Jan 4, 2022)

tomee2 said:


> I've spent years trying to understand schematics. I can say I can confidently tell the difference now between a tube amp and a transistor amp. Haha... seriously, Am I allowed to say schematics aren't easy? No one is a dummy for not understanding them. It's a specialized form of documentation/ communication. Like trying to understand an architect's drawings, some stuff is obvious other stuff needs pointing out.


I am finding myself in the opposite situation. The more I actually stop thinking it is complicated and just learn what it is trying to tell me the more I realize they are actually rather simplistic. Now, I will be the first to admit, my starting point is a very, VERY, simple schematic but it isn't like the first book I read was the Iliad.

Looking at the 12ax7 in the schematic shown in the first post here, this morning I took one look at that nonsense and then went and got more coffee. However, after a momentary lapse in learning, knowing that it is really just 2 tubes in one tube(yeah yeah, laugh at how I describe it  ), then the notation in the middle of it made all kinds of sense. Where else would you denote the circuit directly effecting the tube than in the tube?

I can fully understand how one might look at it all and think it nonsensical and hard, I did and still will, I am sure. Hell, if we are being honest still do would accurately describe it. However the path to understanding is not so fraught as one would assume. At least that has been my experience for the last 8 hours since I started actually trying to understand. If I can figure out what it means, I have to assume most anyone can 

@tomee2 if I could offer a strong suggestion, go look at that schematic/diagram interaction and depending on your level of understanding, pull a schematic legend or symbol key off the old interwebs if needed and I think you too will discover with an honest look, it truly is quite simple.

I have always found the greatest barrier to understanding is the assumption that things are outside of our understanding.


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## DBS_180 (Oct 2, 2018)

If you want to learn the basics, Uncle Doug has some great content on YT explaining them (e.g. plate resistors, phase inverters, input cct, transformers, etc.).


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## Mark Brown (Jan 4, 2022)

DBS_180 said:


> If you want to learn the basics, Uncle Doug has some great content on YT explaining them (e.g. plate resistors, phase inverters, input cct, transformers, etc.).


Rob Robinette has been my go to and thus far and has not left me wanting. However if I find myself lacking I shall head on over. Thank you for the suggestion. I do tend to hate having to watch videos to gain information however, I like text myself. 

See, the more I look at this, the more it really does start to make sense. I just sat down and thought I would draw a schematic for "normal folks" brains, which is to say mine. I started drawing to make the circuit linear as that is how most folk work in their brain. I thought, perhaps this might make some understanding easier to grasp. I just finished the rectifier circuit and initiated the path of the first B+ voltage, then it dawned on me. The schematic is already rather linear, it is just a matter of what path one is following. Being an "electrics" guy, naturally I wanted to follow the path of electricity, however when you flip that over to the signal side, well I'll be a monkeys uncle would you look at that. The schematic in this instance is rather linear if not exactly what a diagram would show. Suppose the input signal is electrical voltage too, but to me it is the "sound" side of things. 

I will finish the exercise, as it is helping me grasp the concepts better, but there is a good chance I will not be building a better mouse trap any time soon. I might be able to write one of those "For Dummies" books someday as it takes one to know one.


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## Mark Brown (Jan 4, 2022)

So for anyone bold enough to partake in my quagmire of insanity, here is another burning question,

Are all like tubes pinned the same? I would have to assume they are lest mayhem ensue. But are all 12ax7s pinned 4-5 for heaters 2, 1 respectively? I note in that particular champ schematic that the corresponding tube pin values are not listed as I have seen on other schematics so I have to assume they are all the same across tube type?

By comparison this looks to be miles ahead in terms of logical schematic design



https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-57-Twin-Schematic.pdf


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## gtrguy (Jul 6, 2006)

Signal grounds for the input jacks not shown in the original schematic you posted just the switching part of the jack that grounds the input when that jack is not in use. Regards to your pinout question- all 12A_7 tubes have the same pinout.


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## Hammerhands (Dec 19, 2016)

All tubes are not pinned the same, in fact, some tubes are pretty much identical to other tubes except for the way they are pinned. You need your datasheets.

The 12AX series follows the same pattern.


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## Hammerhands (Dec 19, 2016)

The layout of the parts in the schematic mostly stick to certain patterns. You can tell one section of the schematic is a gain stage, or another section is a certain type of inverter, by how the components are laid out on the schematic.

In fact, you can often tell a schematic is based on a Fender, or the RCA layout that Fender used, by the overall shape of it.

If someone was thinking of a different amp's tone controls when they were designing, they would draw [pretty much] the same circuit quite differently.

I recall reading that all amplifiers are oscillators, but you draw an oscillator differently.


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## Mark Brown (Jan 4, 2022)

I am noticing this, the more of them I go off and look at, you can see how they start to make a lot of sense in how they are laid out. Once I decoupled the idea of the schematic looking like the finished product, the ability to see it became a lot clearer.


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## DavidP (Mar 7, 2006)

@Mark Brown, as you have no doubt surmised at this point of your deep dive into amp circuits, the layout often bears little cognitive resemblance to the schematic for a specific amp. Fenders are a prime example. I call the layouts "Paint by numbers" as you readily see where components and lead dress belong, but the actual circuit can be challenging to follow. One way to get a grip on this is to go back to Rob Robinette's site -- he has signal flow plots for both the layout and schematic for various Fender amps.
Having fun yet???


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## Mark Brown (Jan 4, 2022)

DavidP said:


> @Mark Brown, as you have no doubt surmised at this point of your deep dive into amp circuits, the layout often bears little cognitive resemblance to the schematic for a specific amp. Fenders are a prime example. I call the layouts "Paint by numbers" as you readily see where components and lead dress belong, but the actual circuit can be challenging to follow. One way to get a grip on this is to go back to Rob Robinette's site -- he has signal flow plots for both the layout and schematic for various Fender amps.
> Having fun yet???


I am having more fun than I care to admit, ok that isn't true. I am enjoying this so much I bet there are members here who have blocked me lest they have to listen to me prattle on about it! 

However that being said, I am rather proud of myself for at the very least grasping the concept. My poor eyes don't just glaze over at the simple mention of a schematic. That is a plus. Now the arduous task of becoming familiar with them can begin. That I cannot do over night and no amount of study can really get you there in my experience. One has to put the knowledge to use to gain familiarity, so I look forward to getting deeper in. It is too late to turn back now. 

Rob's site is where 100% of my information is coming from as from what I can tell, the fundamentals are all there and concise. Next phase of understanding is going to be to learn how the components specifically interact with one another because I now know what they do, but not how they do it. Why use a 475V 16uF axial capacitor? Why? But that information luckily is all entirely scholastic and I have never had a problem in that category of learning. I mean come on, it wasn't that long ago I was referring to tone pot caps as resistors, for shame 

What I have never really had up until now is two things. Mostly the desire to learn any of it and secondly the people around me willing to help. 

I won't lie, becoming part of a community of people who in part dedicate a large portion of their lives to the study and understanding of this particular tech may have steered me in this particular direction but once I found a focus I am entirely fascinated. Just think, soon I will be selling hand wired amplifiers at a whopping 80% below the hard cost of their components like any good amateur amp builder because that is what the market will bare


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## 2N1305 (Nov 2, 2009)

Mark Brown said:


> So for anyone bold enough to partake in my quagmire of insanity, here is another burning question,


LOL I like someone who is humble

Plus, I like the way you write, you are rather eloquent.


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## Mark Brown (Jan 4, 2022)

2N1305 said:


> LOL I like someone who is humble
> 
> Plus, I like the way you write, you are rather eloquent.


I know how I come across when I get my mind on something man. I'm am personality adjacent to a meth addicted squirrel when I take an interest in things. My wife is ready to divorce me over how persistently I bother her with my jubilation.

I also know the things I find fascinating in the learning and the questions I pose are rater trite for anyone familiar with the subject. 

For those two reasons I am sincere when I say, I appreciate anyone willing to help 

Humble on the other hand, well my ignorance is obvious, I might as well just let loose and embrace it. We cannot overcome that which we can not acknowledge and this is as close to 12 step they have for amp junkies.


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## knight_yyz (Mar 14, 2015)

Watch some youtube videos on how to take a schematic and put it on a breadboard. It will teach you a ton.


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## 5150EVH0515 (10 mo ago)

great post. Im trying to get more into understanding tube amps as well. I posted something about books to read or information online that is worth reading and many of the fine people on here have made great suggestions. It has really helped me a lot to understand the inner workings of a tube amp. I also find that it translates to pedals as well mostly overdrives which i am more interested in. I really like Uncle Doug on youtube, he has a great way of explaining things as well. Here is a link to one of his tutorials/lessons... Worth a look. 





I also like Rob Rinette's website, find it very useful


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## Mark Brown (Jan 4, 2022)

Videos are my least favorite medium to learn from. Perhaps it stems from childhood when the VCR or heaven forbid the projector with its antiquated lo-fi magnetic tape deck would be wheeled out to display to our young blossoming minds the stylistic offerings of the National Film Board of Canada. That or I just don't retain the information because almost four decades of "television therapy" turns off whatever part of my brain is used for information retention.

It is a shame because there is a wealth of information contained in YouTube and more and more often I find myself forced into it as the scarcity of printed information grows.


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## knight_yyz (Mar 14, 2015)

Should have bought a Trinity. they give you a schematic and a drawing... For example...


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## Mark Brown (Jan 4, 2022)

knight_yyz said:


> Should have bought a Trinity. they give you a schematic and a drawing... For example...
> 
> View attachment 431530


But now you gave me the drawing and think of all the money I can save 

Seriously though, how could anyone possibly argue that a schematic is better than a diagram/drawing for the sole purpose of building the thing. You could be completely illiterate to the concepts and complexities and still build an amp with that much detail on a diagram.


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## Latole (Aug 11, 2020)

Mark Brown said:


> But now you gave me the drawing and think of all the money I can save
> 
> Seriously though, how could anyone possibly argue that a schematic is better than a diagram/drawing for the sole purpose of building the thing. You could be completely illiterate to the concepts and complexities and still build an amp with that much detail on a diagram.



You mean building a amp with a layout and ignore how to read a schematic ? 

On the other hand, building an amp that will work well is more complex than simply assembling parts by soldering. The arrangement and length of the wires and parts is very important.
And if in the end the amp doesn't work or doesn't work well, the troubleshooting should be done with the schematic.


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## Mark Brown (Jan 4, 2022)

Latole said:


> And if in the end the amp doesn't work or doesn't work well, the troubleshooting should be done with the schematic.


Couldn't agree more.

Nor would I say it is unimportant to understand a schematic, but there is a severe amount of information lacking from a schematic as well. While a schematic is solely focused on the circuit, the drawings give a much more concise depiction of the amplifier. One without the other is still lacking in complete information, but that is not to say one cannot exist without the other.



Latole said:


> You mean building a amp with a layout and ignore how to read a schematic ?


I would not say that I don't think. If that were how I felt, I wouldn't have taken the steps necessary to learn to read a schematic 

It would be entirely possible to build an amp without a schematic however as I am sure it is done all the time. In all honesty, if one learns to interpret both I could see not requiring a schematic if the drawing were detailed enough. It is clear that it contains all of the same information in the particular example from my first post, as long as a person is able to read it.

That last sentence may get me tarred and feathered, but I am ready!


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## Paul Running (Apr 12, 2020)




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## Mark Brown (Jan 4, 2022)

Paul Running said:


> View attachment 431545


Hey now, I never said they were useless. That isn't fair. I'll take the feathers though 

Schematic is the most clear and concise depiction of the circuit that makes an amplifier. Full stop. That is why I wanted to learn how to read them. There I said it, ya happy now


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## diyfabtone (Mar 9, 2016)

Too bad the F1 schematic and layout don't show the actual physical TRS jack connections - would have saved you some time


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## tomee2 (Feb 27, 2017)

Mark Brown said:


> Hey now, I never said they were useless. That isn't fair. I'll take the feathers though
> 
> Schematic is the most clear and concise depiction of the circuit that makes an amplifier. Full stop. That is why I wanted to learn how to read them. There I said it, ya happy now


The classic Fender amps all have circuits and layouts available (on the web, Robinette site etc.. ) which are nice to learn from. 
There’s also the Ceriatone documentation that shows a layout but I’ve not seen the circuit schematic for them.


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## Mark Brown (Jan 4, 2022)

diyfabtone said:


> Too bad the F1 schematic and layout don't show the actual physical TRS jack connections - would have saved you some time


The thing with that is that I was never in doubt about the jack grounds, I was lost on where the diagram clearly showed the ground bus connected to the jack acting as its ground point but how it was not specifically denoted on the schematic, mostly because the schematic doesn't care how it gets to ground


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## 5150EVH0515 (10 mo ago)

something else I am really fascinated by right now is coupling capacitors, cathode bypass caps and resistors and their affect on tone/gain etc... Also how certain makers (Marshall/Soldano/Fender etc..) have different layouts and values. So cool.


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## diyfabtone (Mar 9, 2016)

Maybe this will help explain how the F1 Input grounding works? I added the 'Sleeve' or Ground element of the TRS Jacks to show the chassis connections. Pardon the poor drawing quality.


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## 2N1305 (Nov 2, 2009)

to diyfabtone: But wait, if that's the case, when only INPUT 2 is plugged to a guitar, the grid only "sees" 68K to ground! How does that work? Wouldn't that just not make the tube work properly? I say this because usually triode grids have over 500K to ground to lower the input impedance of the tube.


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## Mark Brown (Jan 4, 2022)

I might be getting ahead of myself here.... but I'm gonna try. Plugged into the secondary, or low, how would the grid path back to ground? As the AC signal enters the grid, is is already grounded through the jacks. The grid "ground" would be through the cathode, but I don't think my terminology is correct. Either the grid sees current from the AC guitar signal, or it does not. No signal, no pull. Lots of signal lots of pull and more voltage across the plate?

What am I missing?

For rhe record, I am trying REALLY hard


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## Jerome (Dec 4, 2015)

If you are plugged into #2 input , the signal goes through the first 68k resistor , to the grid . The second 68k resistor is now the grid resistor.


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