What matters - what doesn't

[Wales]

If you don't have a desoldering bulb or desolder braid, you can just strip some thick stranded wire (like speaker wire) twist it together and it will suck up solder.

[ninjaaron]

What matters? every part in a design.

Therefore Beginner's guide to tinkering with other people's designs:

1. If you swap around parts, and you don't notice a difference, it probably has to do with noise filtering or power supply regulation. Everything else, you must mess with, or you're not a real man. (disregard this statement for your first few builds)
2. Words are your friends. There is a lot of great info on sites like here, GeoFX, Beavis Audio, AMZ, (freestompboxes.org) etc. There are also some decent books out there by folks like Wampler, Orman, and Anderton. The more you understand what you are doing, the more smoothly things will go.
3. On a related note, the more schematics you look at, the more you will eventually understand. The do, eventually, become interesting.
4. Solderless Breadboards are great tools, but they are far from perfect tools.

[gigimarga]

Use a DMM to double check your resistor's value's just before you solder them in.

In a Triangle Big Muff the 120 ohms resistor and one of the 10K resitors are a source of big troubles!!!

[trendyironicname]

people - little pieces of metal that, when arranged in certain ways, vary something about a small alternating current.



oh, but get some double sided tape.  I put a little on the edge of my bench because that's where most of my caps, transistors and resistors wind up when I'm changing out components.  It's also where my forearms wind up.  Before this, the other stuff would,ultimately, wind up on the floor. Now, not as big of a problem.

[cathexis]

An oscilloscope is not strictly necessary for debugging, but it sure makes things a lot easier. Esp. when building complex stuff (read: flangers).

[FlyingZ]

Tubescreamer fans: A twenty year old JRC4558D chip sounds no better than a new JRC4558D chip. Save your money, forget the mojo and hype, and buy the new chip. Truth is, there are better IC's out there for the TS-9/808: RC4558, RC4559, NE5532, TLO72, to name a few.

Better is subjective. In my specific case testing proved the stock TA75558P best and the vintage RC4558P 2nd.

[eleanor296]

All grounds do not have to connect to the same point, but all grounds need to be connected together.

Except when you use something like a 555 in your project... then it's a whole different story.  Found that out the hard way 

[JDoyle]

Well, it took five years but I need to correct myself:

In a bipolar transistor (BJT) amplifier stage, the base voltage needs to be at least 0.6V above the emitter voltage; and the current through the collector is controlled by the current through the base.

The above is wrong.

The current through the collector/emitter is controlled by the base-emitter voltage.

The base current is an error current due to the construction/action of a bipolar transistor.

The reason that beta is so variable is because the base current/collector current ratio (i.e. beta)is based upon an error current and is also why transconductance is a better, and infinitely more stable/predictable, parameter to use in designing BJT circuits.

Regards,

Jay Doyle

[ClinchFX]

Quote from the textbook "Introductory Electronic Devices and Circuits" by Robert T Paynter, currently in its 7th edition:

Chapter 5  Bipolar Junction Transistors

The transistor is a current controlled device.  The base current (I_B) can be varied to control the amount of emitter current (I_E) and collector current (I_C).

FETs are voltage controlled.

[newfish]

Favourite tool when building? Swiss Army Knife. 

It's like your wire strippers, cutters and trace cutter all in the same place.

If you're stuck for bench space, it's a great piece of kit.  Still pretty good even if you have acres of room.

Also...

Print off a second copy of any diagram you're working from.  Use this copy to tick each component as you solder it in place - or even draw a trace for it if you're etching.  Finding you've missed a component off your super-neat PCB you were so pleased with can be a bit of a downer.  <speaks from experience>

[ClinchFX]

Print off a second copy of any diagram you're working from.  Use this copy to tick each component as you solder it in place - or even draw a trace for it if you're etching.  Finding you've missed a component off your super-neat PCB you were so pleased with can be a bit of a downer.  <speaks from experience>

Good point - I use a highlighter pen.

[Pedal love]

Try to keep a journal of everything you do that day at the workbench. It might pay off later.

[connie_c]

still newbie at pedals but lots of soldering experience, steel wool is great stuff, rub a little over your circuitboard or perfboard and the solder will stick to it much better. its also great on the back of pots when grounding them in guitar wiring or any jacks or whatever that look a little dull.

[JDoyle]

Quote from the textbook "Introductory Electronic Devices and Circuits" by Robert T Paynter, currently in its 7th edition:

Chapter 5  Bipolar Junction Transistors

The transistor is a current controlled device.  The base current (I_B) can be varied to control the amount of emitter current (I_E) and collector current (I_C).

FETs are voltage controlled.

Somehow, I knew this would happen. I can't even say that I am wrong without someone disagreeing! 

- First, just because something is repeated ad nauseam as 'the truth' doesn't make it so.

- Second, I am sure Mr. Paynter is a very capable engineer/educator/author, but your quote from his work just proves that you can't believe everything you read.

- Third, take a BJT, emitter tied to ground, collector to some V+ and then attach to the base a current source which originates from some V- (below ground, so that the voltage required for the CS to operate doesn't also effect the base-emitter voltage). No matter how stiff, perfect, or large that current source is, unless you are able to find some way to bring the voltage at the base up to the cut-in voltage of the base-emitter junction (around 0.5V for Si, 0.1V for Ge), you will not be able to get the transistor to conduct at all.

- Fourth, taking a gander at the Ebers-Moll model for emitter current:

I_E = I_ES (e^V_BE/V_T - 1)

Where:
I_E is the emitter current.
I_ES is the reverse saturation current of the base-emitter diode (i.e. the leakage current, NOT the injected base current); normally on the order of 10^-15 to 10^-12 amperes.
e is the exponential function or 'Euler's Number', an irrational number and mathematical constant with a value of 2.71828..., and the inverse of the natural logarithm.
V_BE is the base-emitter voltage.
V_T is the thermal voltage; approx. 26mV at room temp.
(There is also a 'correction' factor constant, n, which sometimes precedes the V_T term, ranges in value from 1 to 2, and is material and somewhat device dependant.)

Therefore, the only NON-constant in the equation is V_BE. (While the reverse saturation current and the thermal voltage 'vary', once determined for the device and situation, respectively, they are, for all intents and purposes, constants.)

Nowhere in the equation for emitter current is the term I_B, the base current.

It would be both ironic as well as funny to me if Mr. Paynter's book happened to include a discussion of the Ebers-Moll model, while stating that a BJT is current controlled, because in order to determine the current through the emitter - the only variable available is the voltage between the base and emitter.

In other words: a bipolar junction transistor is a voltage controlled device.

- Last, though by no means the least, I will supply my own quote:

"The BJT is a voltage operated device, and the base current that flows is merely an inconvenient side-effect of the collector current induced by said base voltage. This is why beta varies more than most BJT parameters; the base current is an unavoidable error rather than the basis of transistor operation." - Douglas Self, Audio Power Amplifier Design Handbook, 4th Edition, Newnes, 2006, page 337

(Note that this book is in it's fourth edition because of actual updates to the content, not just simply reformatting the old content to change the page numbering, and/or other trivial changes, which is common in textbook publishing to force students to buy the newest edition, rather than allowing them the choice of reusing/buying old editions - as the latter results in zero profit for the publisher.)

Regards,

Jay Doyle

[edited to correct typo]

[ayayay!]

You don't HAVE to etch your own PCBs.  Perfboard or Vero are perfectly acceptable.

Provide strain relief for parts, using the enclosure itself as that relief when possible.

Imagine seeing through every step of the build process.  Now mulitply that time times 10 and spread it over a few days or nights.  That's called patience. 

A cheap Dunlop inductor is perfectly acceptable in a wah.  *Wah questions or myth-busters here:  http://www.diystompboxes.com/smfforum/index.php?topic=74969.0  *

[ClinchFX]

take a BJT, emitter tied to ground, collector to some V+ and then attach to the base a current source which originates from some V- (below ground, so that the voltage required for the CS to operate doesn't also effect the base-emitter voltage). No matter how stiff, perfect, or large that current source is, unless you are able to find some way to bring the voltage at the base up to the cut-in voltage of the base-emitter junction (around 0.5V for Si, 0.1V for Ge), you will not be able to get the transistor to conduct at all.

And conversely, if you attach a pure voltage source - incapable of sourcing or sinking current - to the base of a BJT, you will not be able to get the transistor to conduct at all.  Accepting the quote from Douglas Self,

the base current that flows is merely an inconvenient side-effect of the collector current induced by said base voltage

the transistor will still not function unless that base current can flow.

- Fourth, taking a gander at the Ebers-Moll model for emitter current:

I_E = I_ES (e^V_BE/V_T - 1)

Where:
I_E is the emitter current.
I_ES is the reverse saturation current of the base-emitter diode (i.e. the leakage current, NOT the injected base current); normally on the order of 10^-15 to 10^-12 amperes.
e is the exponential function or 'Euler's Number', an irrational number and mathematical constant with a value of 2.71828..., and the inverse of the natural logarithm.
V_BE is the base-emitter voltage.
V_T is the thermal voltage; approx. 26mV at room temp.
(There is also a 'correction' factor constant, n, which sometimes precedes the V_T term, ranges in value from 1 to 2, and is material and somewhat device dependant.)

Therefore, the only NON-constant in the equation is V_BE. (While the reverse saturation current and the thermal voltage 'vary', once determined for the device and situation, respectively, they are, for all intents and purposes, constants.)

Nowhere in the equation for emitter current is the term I_B, the base current.

I've also seen the Ebers-Moll model used to prove that I_C=ßI_B

I'm not about to get into a quoting contest.  These are effectively two different theoretical ways of explaining how a BJT works, and the Ebers-Moll model can be used to explain both.

I apologise if I caused you any distress.  I'll turn away from this thread now.

Peter.

[JDoyle]

I've also seen the Ebers-Moll model used to prove that I_C=ßI_B

You don't need to use ANYTHING to prove that ß = I_C/I_B as that is the definition it was given when it was created - by humans NOT by Mother Nature. There are simply no laws of physics that relate to beta - which is why it is so variable.

Beta is entirely a human construction, whereas the V_BE to I_E relationship is related to actual device physics.

One varies widely from device to device even within the exact same type of transistor.

The other is a universal formula for all bipolar transistors.

Which sounds more accurate?

Why is it so hard to believe that the conventional wisdom is wrong? ESPECIALLY in the field of physics.

These are effectively two different theoretical ways of explaining how a BJT works, and the Ebers-Moll model can be used to explain both.

Except that the voltage controlled version is correct and universal, whereas the current controlled version is misleading, at best, because it relies upon a relationship CREATED OUT OF THIN AIR by man, and varies wildly from part to part, instead of one that had to be DISCOVERED yet is relatable to every situation. There is a reason Beta has no unit of measure, in no way does it relate to nature.

AND - what you said in the quote above, is NOT what you said in response to my previous post - you flat out called my post incorrect, or rather, used someone else to do so, in a condescending manner that implied ignorance on my part. Am I not allowed to defend myself?

None of this 'distressed' me in the least, I enjoy a good debate even though my writing style apparently comes across as acrimonious. I completely realize we are not curing cancer here, but that doesn't mean we shouldn't want to be correct in how we approach these things.

It seems to me that the one who is distressed is the one who is heading off into the sunset once the debate became not so clear cut as they thought. It's a lot easier to build them than it is to know what really makes them tick, isn't it?

Regards,

Jay Doyle

[Chris S]

I noticed that the posts have slowly slid from what matters to general advice so in that vain...

1. Don't leave the soldering iron on the floor and walk around in bear feet.
2. When you first plug in a new effect expect that it won't work
3. Before you shell out $$ for odd parts search for work arounds. The Reverse log pot work around (RGs secret life of pots) is an example
4. Test pedal and then drill holes for in your box. I made a nice univbe box and then didn't get the thing to work.
5. Just because you're feeling confident with 9v don't move up to 240v (mains electricity) I have no idea how many times I've received a 9v shock because I can't feel it. You don't want to risk that with 240v
6. Check to see if adjoining solders joins are touching each other - if you're soldering is as messy and bad as mine was in the beginning this will be likely.
7. Check everything. I almost threw out a pedal I had checked over and over again when I realised the output from the board was not connected to the jack - very dumb but it's so sobvious you forget.

For fear of making myself look silly I'll stop there

[studiostud]

1. Don't leave the soldering iron on the floor and walk around in bear feet.

Maybe you meant "bare" feet?  Although, how sweet would it be to have "bear" feet.  Gimme a lion's head too while you're at it.   

6. Check to see if adjoining solders joins are touching each other - if you're soldering is as messy and bad as mine was in the beginning this will be likely.
7. Check everything. I almost threw out a pedal I had checked over and over again when I realised the output from the board was not connected to the jack - very dumb but it's so sobvious you forget.

These are both so very true.  I've been doing this kinda stuff for several years now and feel like I've gotten pretty good with soldering and I still find mistakes on a regular basis.

[MoltenVoltage]

Always put the 0.1 uF cap as close as possible to BOTH the positive and negative pins on microcontrollers.