Help needed: Using Mangler PCB for Tonebender Mk1.5

[morkmango]

I was wondering if anyone would be able to give me a hand. I am trying to use to the Mangler PCB to build a Mk1.5 Tone Bender. I understand they are, for the most part, the same aside from some values.

I have been using the following schematics to work through this. I have been able to identify most of the changes that need to take place, but a few things on the Mangler PCB confuse me. These are mainly:

R3 - 220R (on mangler schematic) - can't find this on the mk1.5 schematic and I am wondering its purpose/effect on tone

C4 - 10pf (also on mangler schematic) - also not on the mk1.5 schematic...

I think I have sorted the rest out, and obviously there is more going on with the built in road rage power system as well.

I have included the images. Thanks for any help.

Mk1.5
<a href="http://s17.photobucket.com/user/morkmango/media/TonebenderMk15FinalLayout.jpg.html" target="_blank"><img src="http://i17.photobucket.com/albums/b66/morkmango/TonebenderMk15FinalLayout.jpg" border="0" alt=" photo TonebenderMk15FinalLayout.jpg"/></a>

Mangler:
<a href="http://s17.photobucket.com/user/morkmango/media/manglerschem.jpg.html" target="_blank"><img src="http://i17.photobucket.com/albums/b66/morkmango/manglerschem.jpg" border="0" alt=" photo manglerschem.jpg"/></a>

[midwayfair]

R3 is simply a limit on the bias control. Together with the trim, the total resistance is 220-20,222 Ohms.

C4 used to be explained in the build document, but I guess it got taken out in one of the versions. It creates a low pass filter for very high frequencies. Some higher gain silicon transistors would create oscillation in the circuit, so the capacitor is there to prevent it. You can leave this off until you build the effect to see whether you need it.

[morkmango]

Thanks for that reply... It was a lot of help!

[morkmango]

C4 used to be explained in the build document, but I guess it got taken out in one of the versions. It creates a low pass filter for very high frequencies. Some higher gain silicon transistors would create oscillation in the circuit, so the capacitor is there to prevent it. You can leave this off until you build the effect to see whether you need it.

Sorry for being such a noob... but would I have to run a jumper lead between the solder pads of C4 if I were to leave it out?

Thanks.

[midwayfair]

C4 used to be explained in the build document, but I guess it got taken out in one of the versions. It creates a low pass filter for very high frequencies. Some higher gain silicon transistors would create oscillation in the circuit, so the capacitor is there to prevent it. You can leave this off until you build the effect to see whether you need it.

Sorry for being such a noob... but would I have to run a jumper lead between the solder pads of C4 if I were to leave it out?

Thanks.

EDIT: Actually, instead of just giving the answer for this, let's learn something. What happens if you put a jumper there?

[morkmango]

Haha. I won't have all the parts to fully complete this build for a bit, so I can't actually test it out yet.

I'm not the greatest at looking at schematics (this is my first non-BYOC pedal build) but I did check it out... I would guess that nothing would change... But I'm probably wrong!

[midwayfair]

Haha. I won't have all the parts to fully complete this build for a bit, so I can't actually test it out yet.

I'm not the greatest at looking at schematics (this is my first non-BYOC pedal build) but I did check it out... I would guess that nothing would change... But I'm probably wrong!

Fortunately, this is a very simple schematic: Your guitar signal enters the base of Q1, is amplified and clipped (distorts), comes out of the collector, and then enters the base of Q2, gets amplified and distorts further, and then comes out through of the collector -- where it goes to the volume pot -- and out of the emitter, where it loops back around to the input and creates negative feedback and the bias to make the first transistor work. Gain is increased by lowering the resistance between the emitter and a 22uF capacitor connected to ground in Q2. Q2 is biased with a trim pot. If you need a more thorough explanation, read through "The Technology of the Fuzz Face."

Okay, let's look at some nuts and bolts of circuitry in general and then apply it to this pedal.

First, do you know how a capacitor works? You should read the Wikipedia article. At least read the introduction. The whole introduction. Leave this window open and come back. Okay, now that you're back, do the same thing for resistor and transistor. It's okay if you didn't understand all of that, but you should have understood a couple things.

Okay, now that you've read that, some ... "philosophy". In pedals, we're mostly concerned with impedance (something "stops" a signal from going somewhere) and voltage dividers (something sends voltage in two places). Everything useful in a circuit does one of those two things. Resistors and capacitors create impedance, and MANY things are a voltage divider, but the one you'll find in nearly every pedal is a volume pot.

Let's look at some things that make up the Mangler. It's not a lot of types of parts if we ignore the charge pump and just focus on the classic fuzz face part of the schematic:

1. A resistor impedes ALL current and voltage, regardless of frequency or whether it's AC or DC. Your audio signal is AC -- it swings across a center point -- and it has a frequency (pitch). The power supply for your pedal is DC. We're not going to worry about the DC part of this circuit right now. It makes things go, that's all we really need to know right now!

2. A capacitor impedes AC at frequencies above a certain level (depending on the size of the capacitor and resistance) and impedes ALL DC ("infinite" frequency). A capacitor is Gandalf and DC is the Balrog, except the capacitor totally kicks DC's butt and lives every time.  A small amount of capacitance is only going to pass very high frequencies. A large amount of capacitance might allow some amount of nearly all frequencies to pass, even ones that are too low to hear. Capacitance is measured in Farads. A very small capacitor might be measured in pF (picofarads). A moderate sized capacitor for a pedal will most likely be measured in nanofarads (nF). A large capacitor is measured in uF (microfarads). We don't mess with stuff larger than that because we're not trying to build death rays and we want to live and make music and not get electrocuted a hundred years in the future when we forgot to drain one of the capacitors in our youth.

Capacitance and resistance together can form filters -- low pass (everything passes but higher frequencies), high pass (everything passes but lower frequencies), band pass (only middle frequencies pass), etc. Filters and how to calculate them are worth learning about at some point, but you don't need to know that for this lesson.

3. I don't want to start describing how transistors actually amplify or anything like that, but it would do you to go read some very basic stuff on it. The simplest explanation is: Your signal goes in at the base, and it will come out at the collector with voltage gain (an increase in amplitude -- it gets louder) and that signal from the collector is 180 degrees out of phase with the original signal; any signal at the emitter is in phase.

I bring up the phasing because it's important for something else in the circuit description and useful to know in general. Out of phase signals will cancel each other out and reduce the signal size. In other words, if you loop some signal that's out of phase (from the collector) back around to the transistor's input, you will get less gain. That's called "negative feedback." If you look at my description of the Mangler circuit in my first paragraph, I mentioned negative feedback. We can now add to that description that your signal is flipped out of phase by Q1, and then you can see (I hope) that the 100K connected between the emitter of Q2 and the base of Q1 is out of phase -- this is a way this circuit gets some negative feedback. There are other ways to get it.

4. Okay, we've also got another "component." A piece of wire, which could also a trace on a circuit board, a solder bridge, anything that creates a "short" -- a short is no impedance: EVERYTHING passes. No connection is infinite impedance -- NOTHING passes (electricity doesn't pass through air unless it's HUGE, big enough to murder puny humans).

Alright, now that I've explained all that --

1) If C4 is in the circuit, what sort of frequencies is it impeding (not allowing to pass)? What it is allowing to pass?
2) If you make C4 bigger, what sort of frequencies will it impede?
3) If C4 is taken out of the circuit completely, what type of component described above is now in it's place? Draw it out if you have to ... with a pencil ... so you can erase it. What would it be impeding in that case?
4) If C4 is replaced with a jumper, can you describe what it will be impeding?

And the main question. I PROMISE YOU WILL GET THIS RIGHT IF YOU THINK ABOUT YOUR ANSWERS ABOVE:
5) You know from looking at another schematic that C4 is not in the original fuzz face. You suggested replacing it with a jumper, and you now know what a jumper is in general. Look back at my description of how the circuit works and what a transistor does in this circuit. If you replace C4 with a jumper, what will NOT happen to your signal?

Bonus questions:
6) C4 has two connections, let's just call them left and right. What is the phase of the signal on the lefthand side of C4 compared with the righthand side? What happens w
7) Based on your answer to #6 and #1, and applying what I said far above about negative feedback, what happens when C4 is in the circuit?

[morkmango]

Wow. Thanks for all of your help. I will have a go at figuring all of this out today and get back to you.

Mark

[jalmonsalmon]

I recommend bread boarding from a tone bender Mk 1.5 schematic or fuzz face, that way you can tweak it to your taste and then commit to the mangler board.
And also if you read this thread... this will be your best friend! :-)
http://www.madbeanpedals.com/forum/index.php?topic=1140.0

[TGP39]

Hey Jon. I don't know about other folks, but I truly am thankful for the amount of work you just did so new pedal builders can learn something from this. Your above explanation just set off a ton of light bulbs over my head. I am really grateful when you  and other madbeaners are willing to share their knowledge so the newer builders like myself, can learn from it. Thanks again.

[lincolnic]

Hey Jon. I don't know about other folks, but I truly am thankful for the amount of work you just did so new pedal builders can learn something from this. Your above explanation just set off a ton of light bulbs over my head. I am really grateful when you  and other madbeaners are willing to share their knowledge so the newer builders like myself, can learn from it. Thanks again.

Chiming in here -- every time Jon responds to a tech help thread, I know I'm going to learn something.

[morkmango]

Just wanted to say that I truly appreciate all if your help and that I have been reading up on all of this stuff. Been a bit hard because I have been away from home, but I am definitely learning a lot.

I having a bit of a hard time with #4 ... But I will look into that more.

I am now fairly certain I am wrong about the jumper. I did not realise that a cap was in two halves, but it makes sense now when I look at schematics.

I'll get this figured out... Does my head in sometimes tho! Built a bumblebee during the week and also built the testing rig from the sticky at the top of the page but completely forgot about pnp wiring... So I am guessing that is why my bumblebee did not work on the testing rig.

Had to go away for a few days, so haven't been able to try and fix it!