Impedence

[panterica]

I need some help understanding impedence. I understand the concept somewhat, but I'm in over my head when I try to apply what I know when designing projects. I know different components and circuits have different input and output impedences, but doesn't this impedence change depending on how you use the components (single-ended/push-pull output, etc.)? How can I calculate what impedences I have in a circuit (for example: in front of and after a pair of 6V6 tubes in push/pull configuration)?

I'm also especially concerned because my bass tube amp is supposedly not very "effect-friendly," which is something I want to consider when building effects. It seems to prefer passive basses, unlike my Spector USA which has ungodly amounts of output. Also, some effects tend to cause nasty distortion and/or oscillations in the effects loop. 

If anyone could explain impedence in layman's terms and/or point me to some good reading, I would really appreciate it.

[alanlan]

google "small signal analysis"
this should give you a head start.  You really have to understand how various configurations work to understand input and out impedances/resistance thereof.

Impedance is the generic term including complex impedances i.e. capacitive and inductive.  It's too much to attempt to explain in a post like this.

[panterica]

google "small signal analysis"
this should give you a head start.  You really have to understand how various configurations work to understand input and out impedances/resistance thereof.

Impedance is the generic term including complex impedances i.e. capacitive and inductive.  It's too much to attempt to explain in a post like this.

You're right. I re-read my post and realized I would be lucky to get anybody to really answer all of that. I found an article on "impedence matching" on wikipedia that was somewhat helpful.

Thanks for the suggestion.

[jrod]

Yo, check it out! Go here: http://www.geofex.com/ In the menu to left click on "electronics". The first item on the next screen is about impedence. This should help.

[ashcat_lt]

I'd be willing to bet, since you've mentioned distortion, that your main issue is not one of impedance but one of operating level.  Generally impedance mismatches cause tone losses and occassionally volume losses.  If you're getting distortion, it's because you're asking some stage to provide an output voltage greater than those of which it is capable.  This is usually because the input voltage is too high.

[MannequinRaces]

Here is another good article on pedal impedance from Jack Orman.

http://www.muzique.com/lab/imp.htm

[petemoore]

  AC= ''waves wash on to the shore''.
  You can see the shape form as it gets toward a beach.
  Some shores have holes.
  If the wave is big and the holes are small...you don't notice the shape of any part of the wave details changed enough to tell.
  If the waves are small and holes are big, there might not be much wave left to look at, and you can't tell much about what it used to look like.
  Signal impedance matching / mismatching is a little like that....open for criticism but sometimes the water level[ for DC ] and waves [for AC] make decent analogies to try to help visualize the concepts...what do some of the sages think? blasphemy ?

[panterica]

  AC= ''waves wash on to the shore''.
  You can see the shape form as it gets toward a beach.
  Some shores have holes.
  If the wave is big and the holes are small...you don't notice the shape of any part of the wave details changed enough to tell.
  If the waves are small and holes are big, there might not be much wave left to look at, and you can't tell much about what it used to look like.
  Signal impedance matching / mismatching is a little like that....open for criticism but sometimes the water level[ for DC ] and waves [for AC] make decent analogies to try to help visualize the concepts...what do some of the sages think? blasphemy ?

I see what you're saying. I like that.

[rogeryu_ph]

Hey Ashcat_it nice to see you buddy
BTW petemoore, great analogy there.
Guys, are there more great analogy you could share..... I know Mhammer as lot on this
Anyway i got question and i think it's also related to Impedance, Why do some guitar amp has Hi and Lo INPUT i mean..what's the uses or different between High Input and Low Input on those guitar amp? Do i use HI input for Humbucker and LO input for single coil? Also if i have an active pick up should i use the LO input?

[petemoore]

   High and Low inputs generally refers to the gain.
 
    There are amps which have high and low impedance inputs, usually to accomodate a microphone or other..
  Magnetic pickup guitars have ~similar input impedances.

[MoltenVoltage]

I'm no expert, but this is how I understand it

Impedance, generally, is the opposition to the flow of an AC current.  It is measured in ohms.

What makes it so initially confusing is that resistance, the opposition to flow of a DC current, is also measured in ohms and is one factor in impedance.

Impedance is made up of three different components:

1) Resistance.  In the hydraulic analogy, resistance is equivalent to reducing the size of the pipe that water can pass through, so more pressure (voltage) is required to pass the same amount of water.

2) Capacitance.  In the hydraulic analogy, a capacitor is though of as a small rubber tank with one hole at each end and a rubber sheet sealing the tank into two separate halves.  The pulsing pressure (AC) on one side causes pulsing current (AC) to flow on the other side, but a constant pressure (DC) creates no change except when it is turned on or off (i.e. when it changes).  The thicker rubber means more opposition to current change.

3) Inductance.  In the hydraulic analogy, an inductor (coil) is a heavy paddle wheel placed in the current that restricts the water's ability to change speed either way.  What makes more sense to me is that an inductor builds up a magnetic field when it is charged, but it takes time and energy to build up that field, which limits the rate of change of the current flow.  When the power source is removed, all this energy stored in the magnetic field is released, which keeps the current flowing.  With DC, a charge can be stored in a coil and, if released quickly, can create a tremendous voltage (this is how the ignition coil in your car can operate the spark plugs with only 12 volts).  With an AC signal, the higher the inductance (the ability to generate a magnetic field), the lower the rate of change.  A transformer is simply two inductors that are right next to each other, so that when one changes, it induces a current in the other.  Depending on the ratio of windings in each inductor (coil), you can make current go up and voltage go down proportionally, or the other way around.

Impedance is a mathematical combination of these three factors, which combine to limit the flow of AC current.

See also:
http://en.wikipedia.org/wiki/Hydraulic_analogy

The most common problem is impedance matching, which I think of as matching the right sized pipes together to maximize the current flow.

See also:
http://en.wikipedia.org/wiki/Impedance_matching

[aron]

Did you check out the DIY FAQ?

http://www.diystompboxes.com/wiki/index.php?title=DIY_FAQ

Search for impedance.

[ashcat_lt]

Hey Ashcat_it nice to see you buddy
BTW petemoore, great analogy there.
Guys, are there more great analogy you could share..... I know Mhammer as lot on this
Anyway i got question and i think it's also related to Impedance, Why do some guitar amp has Hi and Lo INPUT i mean..what's the uses or different between High Input and Low Input on those guitar amp? Do i use HI input for Humbucker and LO input for single coil? Also if i have an active pick up should i use the LO input?

Yeah, I'm around.  I think part of this was answered, but...

The Hi and Lo are usually meant to refer to total gain.  Interestingly, though, they usually share the actual gain stage.  The difference is affected by way of a pad on the Lo Gain prior to the gain stage.  That is, the Lo Gain input is turned down a bit (usually something like 18db) before it is amplified.  This is usually done by way of resistive voltage divider, which can change the overall impedance of the circuit.  Anyway, the Hi input is usually for passive instruments.  Lo is for actives.  If you were getting objectionable distortion out of a very hot humbucker, you might try the Lo input, but that might knock it down too much, and/or cause some tone loss.

[rogeryu_ph]

Hey Ashcat_it nice to see you buddy
BTW petemoore, great analogy there.
Guys, are there more great analogy you could share..... I know Mhammer as lot on this
Anyway i got question and i think it's also related to Impedance, Why do some guitar amp has Hi and Lo INPUT i mean..what's the uses or different between High Input and Low Input on those guitar amp? Do i use HI input for Humbucker and LO input for single coil? Also if i have an active pick up should i use the LO input?

Yeah, I'm around.  I think part of this was answered, but...

The Hi and Lo are usually meant to refer to total gain.  Interestingly, though, they usually share the actual gain stage.  The difference is affected by way of a pad on the Lo Gain prior to the gain stage.  That is, the Lo Gain input is turned down a bit (usually something like 18db) before it is amplified.  This is usually done by way of resistive voltage divider, which can change the overall impedance of the circuit.  Anyway, the Hi input is usually for passive instruments.  Lo is for actives.  If you were getting objectionable distortion out of a very hot humbucker, you might try the Lo input, but that might knock it down too much, and/or cause some tone loss.

Thanks Ashcat_it buddy.

[panterica]

I'm no expert, but this is how I understand it

Impedance, generally, is the opposition to the flow of an AC current.  It is measured in ohms.

What makes it so initially confusing is that resistance, the opposition to flow of a DC current, is also measured in ohms and is one factor in impedance.

Impedance is made up of three different components:

1) Resistance.  In the hydraulic analogy, resistance is equivalent to reducing the size of the pipe that water can pass through, so more pressure (voltage) is required to pass the same amount of water.

2) Capacitance.  In the hydraulic analogy, a capacitor is though of as a small rubber tank with one hole at each end and a rubber sheet sealing the tank into two separate halves.  The pulsing pressure (AC) on one side causes pulsing current (AC) to flow on the other side, but a constant pressure (DC) creates no change except when it is turned on or off (i.e. when it changes).  The thicker rubber means more opposition to current change.

3) Inductance.  In the hydraulic analogy, an inductor (coil) is a heavy paddle wheel placed in the current that restricts the water's ability to change speed either way.  What makes more sense to me is that an inductor builds up a magnetic field when it is charged, but it takes time and energy to build up that field, which limits the rate of change of the current flow.  When the power source is removed, all this energy stored in the magnetic field is released, which keeps the current flowing.  With DC, a charge can be stored in a coil and, if released quickly, can create a tremendous voltage (this is how the ignition coil in your car can operate the spark plugs with only 12 volts).  With an AC signal, the higher the inductance (the ability to generate a magnetic field), the lower the rate of change.  A transformer is simply two inductors that are right next to each other, so that when one changes, it induces a current in the other.  Depending on the ratio of windings in each inductor (coil), you can make current go up and voltage go down proportionally, or the other way around.

Impedance is a mathematical combination of these three factors, which combine to limit the flow of AC current.

See also:
http://en.wikipedia.org/wiki/Hydraulic_analogy

The most common problem is impedance matching, which I think of as matching the right sized pipes together to maximize the current flow.

See also:
http://en.wikipedia.org/wiki/Impedance_matching

Thanks, man! I'm a very visual thinker, so it helps a lot to have it explained like this. I've taken electricity and electronics classes in college, but I learned just enough to pass and then forgot most of it. When I can visualize what I'm thinking, I can remember it forever. Thanks again.

[terminalgs]

I thought:

HI and LO was for impedance matching to your instrument.  it was much more common in the 50s and 60s to have HI and LO inputs for amps,  because there was a wider range of pickup impedance among all the various pickups at the time..  think Tele bridge pickup vs.  a Les Paul Recording pickup.

even older  amps, from the 30s and 40s, had "Instrument" and "Microphone" inputs,  plugging into one or the other changed the values of the one or both of the grid stopper resistor and the grid load resistor.