As well as here, I'd also suggest joining up at Ampage [="http://music-electronics-forum.com/home.php"]Music Electronics Forum - The AMPAGE Discussion Site[/]="http://music-electr…"]Music Electronics Forum - The AMPAGE Discussion Site[/], and asking there. A lot of knowledgeable folks there, like Aron Nelson, Mark Hammer, and R.G. Keen. Go to the "Effects" section.

Some other good research resources (some of which are sites by those guys):

[[url=http://="http://www.diystomp…"]DIYstompboxes.com - Index[/]="http://www.diystomp…"]DIYstompboxes.com - Index[/]

[="http://www.muzique.com/lab/main.htm"]AMZ Lab Notebook & Guitar Effects[/]="http://www.muzique…"]AMZ Lab Notebook & Guitar Effects[/]

[[url=http://="http://www.geofex.c…"]New Page 1[/]="http://www.geofex.c…"]New Page 1[/]

The answers are somewhere in the above.

Have fun,

Kapt.Krunch

I am reading through the AMZ site and for input impedance it is a bit confusing. For one, I need to review what exactly inductance and capacitance are, but that is something entirely different. In a certain example used to display impedance of a certain circuit it says this:

Let's compare what happens with a different type of booster circuit, such as the jfet amplifier shown here. Since the gate resistance of the jfet is a very large number, the input impedance (Z2) of the circuit is essentially the value of the R1 resistor, or 1M ohms

My question is, isn't that resistor wired in parallel and running to common instead of being in the circuit signal path? How that resistor would impede or resist the actual forthgoing signal escapes me exactly. What do you gain/lose by running the resistor in parallel as opposed to in series?

In parallel you are creating an equalizer. In series, an electrolytic capacitor will dictate the low-frequency pass through response and block any DC components or offset. I know folks that don't even want any electrolytic capacitor in series with the input section. I've heard some of these modifications and I don't think they are any kind of improvement. In fact, I've heard some of the weirdest stuff that way. But because we use DC operational amplifiers, their low-frequency response does go down to direct current. You don't necessarily want that. You want a cut off at or below 20 Hz but not down to DC since the amplifier can create a DC component at its output that will look like DC offset. Something to be avoided completely. You don't need to change any of the ceramic capacitors. Those are bypass and filter capacitors . Why the modifications? Why not just buy a piece of equipment you already like the sound of? I really don't believe in reinventing the wheel. Plenty of well educated electrical engineers have already designed circuits far beyond your comprehension. Sure, I could modify my Neve & API preamps to sound " better". But it's really not better it's only different. I want them to sound the way they sound already. Every amplifier design has its own character. You either like the character or you have purchased the wrong equipment. Better isn't always better it's just different.

My engineering dictates my sound.
Mx. Remy Ann David

I have no idea about the electronics side of it, but my understanding as to the purpose is that a lot of times - especially in a guitar pedal - you have the basic circuitry there but beancounterism has resulted in a few of the 'bottleneck' components not being top-notch, this results in a very well designed circuit (by a well-educated engineer) being compromised (by a decision made by the company's bottom-line thinking). While this thinking is less prevalent in pro audio, its also the case that in, say, Remy's API preamps, the cost is not the overwhelming factor, the quality is. In a pedal made by a well-known Japanese manufacturer, the cost often is the overwhelming factor and a corner is cut that for a relatively small investment, albeit one that would push the original pedal 20% higher and out of its cutthroat market, you can 'spec up' your pedal. Usually from my knowledge this is a much simpler mod than what you seem to be talking about, but modded pedals I own have things like capacitors, film resistors and the IC chip being replaced and are made true bypass or better-bypass.

A classic example is the Ibanez guitars, when they replaced the locking studs the trem mounted in with non-locking ones, as the decision was made by non-players on the basis that this didn't affect your playing experience. In fact, it lowers tuning accuracy on return by several percent - several critical percent. Its a $20 fix.

To blame, is the cheaply-made Chinese/Korean market that companies now feel they have to compete against - the same thing people rail about when complaining about prosumer gear reducing studio profitability.

So better can just be better sometimes.

Guitarfreak, post: 300377 wrote:

My question is, isn't that resistor wired in parallel and running to common instead of being in the circuit signal path? How that resistor would impede or resist the actual forthgoing signal escapes me exactly. What do you gain/lose by running the resistor in parallel as opposed to in series?

Yes, the 1M resistor is across the input, so has signal current running through it. Its function is to provide a d.c. operating point for the gate of the FET, since the input to the circuit is a.c. coupled. The input impedance is the parallel combination of that resistor and the input impedance of the FET. But the FET input impedance is very high (100's of M Ohm), so it can be ignored, and the input impedance is just the resistance of the 1M resistor.

In the circuit extract shown, all the three capacitors affect the low-frequency response. The C1-R1 combination produces a pole at about 1.6Hz, the C3-R3 combination at about 7.2Hz, and you can't say a lot about C2-R2 until you know what C2 is connected to next in the circuit.

Thanks for clearing that up. I am pacing back and forth in my head trying to understand how cap/res combinations result in only certain frequencies being gated. Like for the high pass the signal goes through a cap, where the bass/treble gets rolled off based on the capacitance value, and then encounters a parallel resistor and.... Or for a low pass the signal goes through a resistor, impeding all frequencies evenly, and then encounters a parallel cap and.... It's like I have most of it, but I fail to understand further.

Ignoring phase-shifts for the moment, just think of capacitors as resistors whose value decreases with increasing frequency. In a simple R-C or C-R circuit such as the C-R on the gate of the FET in the example you gave, the 3dB point is the frequency at which the ohmic impedance of the capacitor equals the resistance of the resistor. At 1.6Hz, the 100nF input capacitor has an impedance of -10^6j Ohm, which has a modulus value of 1 MOhm and a phase of -90 degrees.

I thought DC didn't have a phase component?

Attached files

Where does d.c. come into it? The example figures were given for 1.6Hz.

Boswell, post: 300440 wrote: Where does d.c. come into it? The example figures were given for 1.6Hz.

IDK, I thought an FX pedal was DC. Maybe the entire signal path isn't DC?

Huh? For it to be of any use, the signal path has to be audio: 20 Hz to 20KHz, or whatever numbers you care to choose. This is a.c. in circuit terminology. Pedals pass and modify a.c. signals while running off d.c. power. Condenser (capacitor) microphones receive 48V d.c. in order to operate, but transmit a.c. differential audio signals using the same wires. This is possible because of frequency division multiplexing: the d.c. flows one way at baseband and the audio flows the other way in the audio band. As another multiplex, the same cable can also receive UHF band from your interfering mobile (cell) phone and send pulses to both directions to the microphone and the pre-amp, causing the familiar noises.

oh ok. So inverting phase in a pedal is actually possible then yes? If so then that's ridiculously exciting :D

GF:
I think you need to read more about small signal amplifiers ("boosters" as certain countries call them) which is what this circuit is.

You're also forgetting to put you're guitar pickup (inductor) into the front end of that circuit schematic to fully gather the whole concept here.
Also you should review [[url=http://[/URL]="http://en.wikipedia…"]Thévenin's theorem - Wikipedia, the free encyclopedia[/]="http://en.wikipedia…"]Thévenin's theorem - Wikipedia, the free encyclopedia[/]

So you have a pickup coil connected from the input point to common (GND)
Start at your pickup. It generates a small amount of voltage and current (your "signal").
The .1uf cap in series blocks out any DC component that might be in the signal from appearing at the base of the JFET amplifier and "de-couples" the AC component to the input of your amplifier stage. There is always a cap in series between various stages of amplification to "de-couple" any DC and leave only the AC component (you're signal) from getting into the next stage.
The input impedance at the input base of the JFET with R1 (1megohm) is high (Hi-Z) which basically keeps the signal from being "padded".
If you were to put a resistor in series with that path you would "pad" the signal making it more difficult for the transistor to provide any gain in it's amplification of an already weak signal defeating the purpose of getting the most signal from the pickup to the base of the amp stage.
+V is a DC power supply and R2 and R3 act as a power supply voltage divider to "bias" the transistor (you can look that up). Basically bias is how you get gain out of a transistor....
The electrolytic is across the lower R3 to act as another DC bypass to keep the power supply (+ side is towards the positive DC supply) out of the signal path and the last .1uf cap on the output does the same thing as the input cap did (de-couple and isolate any further DC) in you're signal and you now have a nicely amplified AC signal with some value of gain from input to output ready to go into the next stage of amplification!
Viola! One stage of simple amplification.
Hope that helps

WOW. Thank you for taking the time to explain that, that was so much more comprehensive than my instructor's explanation today, who basically labeled the parts of a transistor and that's about it. Bahh, he's a lump. Well that also explains what the lectures said about capacitors being a short to AC and open to DC. That also clears up some questions that I had about resistance, namely why higher resistance sounds good in guitar volume pots and pedal input impedances. It's not the resistance you are hearing... it's the resistance TO GROUND... which results in more signal passed on to subsequent components. I've got some more questions though:

1. Is it possible to split a single AC signal into two equal halves?

2. Is it possible to invert the phase of an AC signal 180 degrees using components?

GF,

1. Is it possible to split a single AC signal into two equal halves?

2. Is it possible to invert the phase of an AC signal 180 degrees using components?

Yes and yes, you'll get to that in your electronics class. Op-amps routinely use the inverted signal, but I don't want to spoil the suspense and you've got much better qualified instructors here than I, in Boswell, Kapt. K, Remy, and DJ. (maybe Kev will chime in too) All geniuses in my book.

You also seem to keep coming back to this idea of changing the phase of DC. I'm not sure you're completely getting what the phase is. This is a gross over-simplification, (and there are other types of signals in the DC family you'll learn about when you study rectifiers,) but this is where I think the concept needs to start.

This would represent the kind of DC your effects pedal 9v battery might have. You can change the polarity of this kind of DC and make the electrons flow the other way, but it's still a flat line.

dvdhawk, post: 300508 wrote: You also seem to keep coming back to this idea of changing the phase of DC.

Oh no I completely get what phase is. At first when I wrongly asked if you could flip the phase of a DC signal I was actually asking if you could flip the phase of the AC signal within a DC powered unit such as an FX box. Case of wrong terminology. I keep asking because it really never gets answered, but if it is possible then I would love to know how because I could use it for some interesting sounds. I have a tone circuit in mind and I could use inverted phase to sculpt the output EQ according to my specs. I believe I mentioned it in another thread, the one about flipping the phase of a DC circuit.

The idea would be based on the ability to split a single AC signal into two equal halves. Could you use a transistor to do this? So long as you use it as a signal split and not as a signal combiner/booster?

EDIT: and here that link is
http://recording.org/cms-comments-chat/40141-electronics-class-i-am-taking-related-questions-3.html#post300102

If you chop AC in half you have what's called "ripple DC" or "half wave AC". Half the AC wave is above zero and the lower half is cut off or vice versa (below zero)....it sounds really noisy.....buzzzzzz.
It is the essence of a half wave bridge rectifier circuit which is the basis of making a DC power supply from an AC source.
DC is always considered any signal or voltage above zero (GND) or below zero but not both at the same.
AC is a continuous voltage that is moving across zero positive then negative (simple sine wave).

"Phase inversion" is just reversing the polarity of a circuit or signal...
[="http://en.wikipedia.org/wiki/Phase_inversion"]Phase inversion - Wikipedia, the free encyclopedia[/]="http://en.wikipedia…"]Phase inversion - Wikipedia, the free encyclopedia[/]

I'm pretty sure you wanted to mod your pedal?..Hehe....
and I completely understand you wanting to get a better understanding of the electronics...that's is what is cool about sound...but again I don't want your "head to explode"....and to be fair I'm sure your instructor understands most of what he's trying to explain to you....but basic electronics is a very difficult topic to comprehend if you don't already know and completely understand the basics of electricity...AC/DC theory, then simple resistance, capacitance and so on....it just gets harder and harder.....and it's not a guessing game, it's really just physics...it behaves in a specific fashion every time depending on how and what force you apply to it....electronics is just a means of controlling electricity....so the more you understand the basics the better off you will be....
I'm pretty sure you have an idea of what you want your pedal to do or sound like and maybe you could put that into words that make sense to you that might be able to be explained in terms of the electronics needed to do that.....

Oh and I keep forgetting to put my music up....which is what it's all about!
See...I can't even figure out how to put that in my profile....gheez

[[url=http://="http://www.myspace…"]Google[/]="http://www.myspace…"]Google[/]

Oh don't worry about my head exploding, I ask because I want to learn, if you've got it lay it on me. I also had the idea today for a boost/gain circuit which runs at 18v. Once you gate the input and set the impedance, you split the signal into two parallel signals (can you tell that I like this idea?) of 9v and run them through identical low-gain JFET gain stages and then recombine them later. From there you could run it through a tone circuit or straight to the output for a simple boost pedal. Or you could change one of the parallel stages slightly so that when they combine you don't get an even combination, but rather a lower output/smoother sound.

...I'd like to think that I've got some good ideas, who knows maybe they're not, but I need you guys to point me in the right direction so that I can learn the basics and get down to protoboard construction this summer. Basically I seem all over the place because well... I am.

I am...
1. Trying to get a better grasp on the basics in order to pass this class
2. Trying to understand my pedal enough to mod it according to my own specs rather than following a mod-by-numbers
3. Learning with the intent of designing and building my own circuit this summer
4. Just curious I guess :D

Thanks for all the help thus far guys. You really are a spectacular bunch :D haha

OK....I hear ya...it's actually great to hear someone like you who has the excitement and passion you do when it comes to your sound.
And now diving head on into the electronics....good for you....pathetic perhaps, geeky....ya pretty much.....naw just kidding.....doin things like that reminds of days gone by and I wish I still had you're ambition....so don't ever quit asking questions or stop trying to understand something....I'll bet your intelligent knowledgeable instructors get a big kick out of you! ....sound!....it will change your life!

BTW I was listening to your "clips" and I want to know how you stop your riffs so dead tight!
Are you using a gating thing or is that just you grabbing strings?

djmukilteo, post: 300513 wrote: I'll bet your intelligent knowledgeable instructors get a big kick out of you!

No, they hate me haha. I mean the intelligent ones love me because I keep them on their toes, but the ones who read straight from the book hate me because I'm reading the same book they are... hah

djmukilteo, post: 300513 wrote: BTW I was listening to your "clips" and I want to know how you stop your riffs so dead tight!

Haha, thanks bro. Which clips are you referring to? Part of it is practice, part of it is reamping, and part of it is volume automation. I hate using auto-gating, I never use it when I'm recording or mixing because it affects the tone too much. I get the amp talking the way I want it to and then capture it with the mic and that's it, once the tone is there I leave it.

Oh...I think if you go and look further in the online guitar circuit schematics, find a "splitter" circuit which is really the same as a "bus" circuit where you take the input line at the base of a stage amp and parallel it to another base and repeat the amp circuit. Then you have two outputs from the same input signal. Each circuit can then be separately routed to different effects stages....or you can invert one of the outputs using different types of transistors (NPN or PNP).
When you get into Opamps (as dvdhawk eluded to)....well then your gonna go crazy and realize they are so much more interesting to use instead of discrete transistor stages.....but.....really try and learn and understand the basic transistor circuit stage first and get a good grasp on how it works...because it will really help you when you do get to Opamps!....which are just elegant internal transistor stages all put together in one IC package with nice differential inputs and outputs and are much easier to apply and condition signal input and output using simple or even elegant R/C component combination's.....and then don't even get me started on digital electronics....stick with the linear world for now.....it too will pass....LOL

Guitarfreak, post: 300509 wrote: Oh no I completely get what phase is. .......

The idea would be based on the ability to split a single AC signal into two equal halves. Could you use a transistor to do this? So long as you use it as a signal split and not as a signal combiner/booster?]

Cool on the phase...

I'd build the simplest of op-amp circuits if I were trying to have two signals identical except for their phase. - if that's what you're saying....

Guitarfreak, post: 300514 wrote: No, they hate me haha. I mean the intelligent ones love me because I keep them on their toes, but the ones who read straight from the book hate me because I'm reading the same book they are... hah

That's why I said the "intelligent knowledgeable ones"....listen to them...take the others with a grain of salt....everyone has something to offer though!
Being a teacher is an honorable profession and the majority still try the best they can!
I can count on one hand the number of prof's that I truly learned from....

Haha, thanks bro. Which clips are you referring to? Part of it is practice, part of it is reamping, and part of it is volume automation. I hate using auto-gating, I never use it when I'm recording or mixing because it affects the tone too much. I get the amp talking the way I want it to and then capture it with the mic and that's it, once the tone is there I leave it.

So I don't play guitar (not well lefthanded but I have been known to plink like Jimi)....I'm a keyboard, organ, piano person...but I notice you really like the crunchy speed metal riffs in your songs....and what I'm talking about is when you speed chunk, chunk, chunk very fast and then pause "stop" it is very dead quiet and then you start again....which I know is a technique in that type of guitar playing....so not knowing how to play guitar I wondered how you're doing that...if you grabbed all your strings and hold them tight to stop them which seemed like a very hard thing to do and then jump back in, practice, practice practice....or I thought maybe there was a gate effect you used....and I hadn't thought about automation....do you mean going in and editing the wav or volume like a gate or what?

one more thing maybe just to clarify....
In linear audio circuits there will always be a DC power supply to bias transistors which you should understand is really "separated" from the signal path.
The "signal path" is usually a waveform of AC being modified or amplified or treated in some way as it passes from one stage to the next. (the signal path)
The DC power supply even if its just a 9V battery is merely the power supply for the circuit to operate and not to be confused with the signal path itself...
That is the task of the trusty capacitor in it's basic application.....DC doesn't like caps because it gets stuck at a cap, but AC doesn't really care at all and goes right on through and that's how you keep them apart. Now AC doesn't really like diodes much and they get stuck half way through (so to speak)...so they both have their quirks but it all gets balanced out in the end...you always need em both in a circuit but they act in different ways and they each have their own properties and purpose!
In linear audio circuits DC (even though it is required as a power supply rail and shares a common ground) is the enemy and must be blocked from the signal path at all costs!....and it sounds really bad when it sneaks in there....it leaks in everywhere it can!

djmukilteo, post: 300518 wrote: So I don't play guitar (not well lefthanded but I have been known to plink like Jimi)....I'm a keyboard, organ, piano person...but I notice you really like the crunchy speed metal riffs in your songs....and what I'm talking about is when you speed chunk, chunk, chunk very fast and then pause "stop" it is very dead quiet and then you start again....which I know is a technique in that type of guitar playing....so not knowing how to play guitar I wondered how you're doing that...if you grabbed all your strings and hold them tight to stop them which seemed like a very hard thing to do and then jump back in, practice, practice practice....or I thought maybe there was a gate effect you used....and I hadn't thought about automation....do you mean going in and editing the wav or volume like a gate or what?

Well there is nothing wrong with playing a different style, it's just a different feel and one is not better than the other. I learned from those old Hendrix riffs, let me see if I can find a clip to prove it... yepp, here it is.

[[url=http://[/URL]="http://soundclick.c…"]SoundClick artist: Bleeding Arrows - page with MP3 music downloads[/]="http://soundclick.c…"]SoundClick artist: Bleeding Arrows - page with MP3 music downloads[/]

As for the cutoffs, I do them first with my hand, it's a joint venture between my left and right hands, they are both involved in the cuttoff. Afterwards I edit the recorded tone using the automation line, which basically automates volume changes. I never touch the active signal though, I wait until the signal has deadened from my own muting (because natural cutoffs always sound better) and then automate the silence between the parts using the line. A friend at work said that the silence makes your ass cheeks smack together, haha. Now with such a high gain sound you'd think that there would be feedback. Nope, I record the dry pickup signal to my computer prior to amping so that I can edit the signal before it hits the amp. Amps love when you put a parametric EQ on a guitar prior to sending it through.

djmukilteo - Always when playing guitar, especially under high gain, you are consciously muting strings, for extra percussive effect, to stop disharmonic ringing, and to keep control.

Its a combination of the meat of the hand coming down from your right little finger, just turning at an angle to brush the strings, and the meat of your first finger on the left hand. No hard and fast rules, it doesn't matter how you do it - Jennifer Batten used to tie a sock around the nut of her guitar - after the event, gating and volume riding help, but this is very simple, not as complex as grabbing each string - just exactly what Guitarfreak said - the higher the gain, the more control you have over the strings; eventually its second nature only to let the ones in use ring out.

Jeemy, post: 300762 wrote: djmukilteo - Always when playing guitar, especially under high gain, you are consciously muting strings, for extra percussive effect, to stop disharmonic ringing, and to keep control.

Its a combination of the meat of the hand coming down from your right little finger, just turning at an angle to brush the strings, and the meat of your first finger on the left hand. No hard and fast rules, it doesn't matter how you do it - Jennifer Batten used to tie a sock around the nut of her guitar - after the event, gating and volume riding help, but this is very simple, not as complex as grabbing each string - just exactly what Guitarfreak said - the higher the gain, the more control you have over the strings; eventually its second nature only to let the ones in use ring out.

Thanks Jeemy for that explanation...I can't play guitar worth a shT, but I do tune them sometimes using the computer and keyboard and it's always a right-handed guitar and being left-handed I instinctively pick it up and play it upside down so I'm pretty bad!....but sometimes when I get in a groove (I have no idea what I'm doing) and some heavy distortion and effects, my buddies start calling me Jimi (mostly because of the left handed thing and playing it upside down)....but then my fingers start hurting after playing a couple chords....so I hand it back to the real guitar player and go back to my nice soft keys or my nice smooth faders....LOL
If you've listened to Guitarfreaks clips it probably makes more sense to you than it did me.
I was impressed with Guitarfreaks speed and sound and was curious on what he did....
Oh....and being Scottish and Canuk and having some relatives born in Edinburgh....someday I'm gonna get over there and see your city!!!
You have castles there don't ya....we don't have anything really old over here like that!...Hehe!
Cheers mate!
Still have Cubase 4 here too!....not sure about 5 yet...maybe it will be 6 before I upgrade!

haha yeah we have a few left, hurry up before we sell em to the japanese!

cubae 4 already scares me, too many colours. i'd buy cubase 5 monochrome edition.