Now why would they change i to j all of a sudden? That's what it is in math. Probably to add to the noobfusion. Gah.

ORIGINAL: Roflcopter

Now why would they change i to j all of a sudden? That's what it is in math. Probably to add to the noobfusion. Gah.

you're right i also = square root of -1 in MATH, in engineering we use j. that could have gotten confusing in school!

you're right i also = square root of -1 in MATH, in engineering we use j. that could have gotten confusing in school!

Talking about which, you'll be having to relearn some definitions come 2011 - they are proposing a redefenition of the kilogram, the ampere, the kelvin and the mole in terms of fundamental constants.

Quote:

Since a coulomb is approximately equal to 6.24150948×1018 elementary charges, one ampere is approximately equivalent to 6.24150948×1018 elementary charges, such as electrons, moving past a boundary in one second.

As with other SI base units, there have been proposals to redefine the kilogram in such a way as to define some presently measured physical constants to fixed values. One proposed definition of the kilogram is:

The kilogram is the mass which would be accelerated at precisely 2×10-7 m/s2 if subjected to the per metre force between two straight parallel conductors of infinite length, of negligible circular cross section, placed 1 metre apart in vacuum, through which flow a constant current of exactly 6 241 509 479 607 717 888 elementary charges per second.

This redefinition of the kilogram has the effect of fixing the elementary charge to be e = 1.60217653×10-19 C and would result in a functionally equivalent definition for the coulomb as being the sum of exactly 6 241 509 479 607 717 888 elementary charges and the ampere as being the electrical current of exactly 6 241 509 479 607 717 888 elementary charges per second. This is consistent with the current 2002 CODATA value for the elementary charge which is 1.60217653×10-19 ± 0.00000014×10-19 C.

You see? Muuuuuuuuuuuuuuuuch simpler.

http://en.wikipedia.org/wiki/Ampere#Proposed_future_definition

I think I'll pass! We use the new impedance meters by Agilent for our measurements at work. automated for testing production equipment to be used on fighter jets! Much simpler than your method!!! LOL!

ORIGINAL: Roflcopter

you're right i also = square root of -1 in MATH, in engineering we use j. that could have gotten confusing in school!

Talking about which, you'll be having to relearn some definitions come 2011 - they are proposing a redefenition of the kilogram, the ampere, the kelvin and the mole in terms of fundamental constants.

Quote:

Since a coulomb is approximately equal to 6.24150948×1018 elementary charges, one ampere is approximately equivalent to 6.24150948×1018 elementary charges, such as electrons, moving past a boundary in one second.

As with other SI base units, there have been proposals to redefine the kilogram in such a way as to define some presently measured physical constants to fixed values. One proposed definition of the kilogram is:

The kilogram is the mass which would be accelerated at precisely 2×10-7 m/s2 if subjected to the per metre force between two straight parallel conductors of infinite length, of negligible circular cross section, placed 1 metre apart in vacuum, through which flow a constant current of exactly 6 241 509 479 607 717 888 elementary charges per second.

This redefinition of the kilogram has the effect of fixing the elementary charge to be e = 1.60217653×10-19 C and would result in a functionally equivalent definition for the coulomb as being the sum of exactly 6 241 509 479 607 717 888 elementary charges and the ampere as being the electrical current of exactly 6 241 509 479 607 717 888 elementary charges per second. This is consistent with the current 2002 CODATA value for the elementary charge which is 1.60217653×10-19 ± 0.00000014×10-19 C.

You see? Muuuuuuuuuuuuuuuuch simpler.

http://en.wikipedia.org/wiki/Ampere#Proposed_future_definition

and all at once, the metric system evangelists stutter in mid-sentence... those of us who stood firm by the standard system point and laugh... of course the ampere, mole and kelvin thing sucks...

I only love shop talk when I can understand it.... Electrical Engineers...sheesh

quote:

ORIGINAL: wst3

quote:

ORIGINAL: Beagle

I think I'll pass! We use the new impedance meters by Agilent for our measurements at work. automated for testing production equipment to be used on fighter jets! Much simpler than your method!!! LOL!

My tax dollars at work!!!

That's right!!!!

Yes, but can you surf the web with it, download mp3's, and watch video?

Thank you all for your interest and kind replies!

A couple of things useful for all 'Direct Recorders' out there:

1) Build a preamp. http://www.till.com/articles/PreampCable/index.html
They explicitly say that 1mohm is the minimum acceptable. This (or similar things) are actually a BUFFER: an preamp with 0dB of gain, but adapt impedances: In -->1mohm. Out--> 10Kohm (like a line out level).
This leads to 2)

2) Passive pickups sound different than active. Not True. "Electronically", they are exactly the same. The difference is that the preamp or buffer is inside the guitar. So, why do they sound different? Because the amps and boxes 'expect' to see a hi impedance input, like a passive pickup. Note that active are 'cleaner', since you can have long cables without loosing too much signal, since that out is relatively low impedance (comparing to the passive pickup).

3) A band aid for everyone that works!!! : There are 2 types of pedals :True bypass and Not True bypass. As the names implies, true bypass means that when the FX is OFF, there is a JUST CABLE from input to output. You can recognize those for its switch, like a wha wha or a RAT (Pro co) distortion. Not tru bypass is like any BOSS pedal. When they are off they STILL GO thru circuit. That is why you can not use without a battery!!!! HOLLY SOLUTION: Take ANY pedal (BOSS preferable) and put a good power supply. Put it in off (Bypass). Connect your guitar to its input, and its output to any line level input. BINGO!!!!! you have a SUPER DECENT DI with propper 1 mohm input impedance!!! I guaranty you will see the difference. I record my guitar traxs like this thru my EMU1820 (it has a 'fake' hi z input).

4) I would personally avoid DI. While it adapts impedance, you may need further preamp, especially in case of passive DI. With method 3) you wont probably need pre amp. Believe or not, the guitar has output voltage comparable to any line level source. The problem is that the impedance is SOOO HIGH, that you just can not connect to any line in!!!! With 3) you input the guitar very clean!

Hope it helps!!!!

DANNY BULLO

PS: Not true that true guitar players wont record direct! C'mon!!!! Are we gonna discuss like "I need a rack like Yngwee Malsmteen to sound decent"????

;)

ORIGINAL: Roflcopter
Like I said earlier, I have to rely on paper specs and google.

http://www.bkprecision.com/appnotes/fg/9.htm

Did I win anything?

You win the admiration of your peers!!!

That's the trick, create a voltage divider, and when the voltage drops to 1/2 the initial measurement you have matched the input (or source) impedance.

the internet is your friend<G>!

Back when I was a teacher I used to make my students use this method to measure both source and input impedance of a black box. Then I let them use the fancier test equipment, which in this case was a bridge with both volt meter and current meter attached. Finally I let them loose on the college's automated test rig. Back then they still had to write the program to get the test set to measure impedance, but it was pretty simple.

These days most of the high end test sets run on either embedded Windoze or some flavor of *nix... makes programming them much easier, but since they come with programs to do pretty much anything one can imagine programming them is not always necessary.

I can say that YES - ALL electronic components have both resistance and capacative or inductive components to them.

now, what I can't tell you since I haven't worked with tubes, is what a typicaly impedance for a tube is, if that's what you're asking, but they would also vary with the type of tube you used (and will even vary somewhat depending on the manufacturer or even within the same manufacturer within different lots).

FWIW, for this purtpose a simple transistor preamp like those found of boss pedals is just perfect. The sound is goos thru the whole guitar spectrum.
the idea describen in this topic is enter the guitar signal into the computer as clena s posible.

Danny

I had always assumed that an Impedance Specification in audio terms was standardized at 1khz unless specified differently. But that may have been from way back in the time machine.

ORIGINAL: Beagle
yes, you're right, normally impedance specifications are listed at 1kHz. they *should* specify otherwise if that's not the case.

I beg to differ, but if no frequency is specified then any impedance specification is meaningless, and if it is specified at only one frequency it isn't entirely meaningless, but it is entirely useless! What if that 1000 ohms at 1 kHz spec is describing a pure capacitor? I'm betting that it would sound pretty darned bad on any real world audio!

This is a huge problem right now, because the dumbing down of specifications has invaded the professional audio world! Used to be that if one was purchasing a so-called professional piece one would get very complete specifications (and a service manual complete with schematics, but that's another rant!), not, we get the same garbage specifications that the consumer world has always been plagued with.

Specifying frequency response without amplitude measurements - please, all that "20 Hz to 20kHz" tells me is that someone was able to detect signal in that passband. At the very least you need to know how the level varied in that passband, e.g. "+/- 3dB from 20 Hz to 20 kHz" which tells me that within the passband the amplitude varies 6dB, which isn't all that impressive, and certainly is audible. Better: "+/- 1dB from 63 Hz to 16 kHz, -3dB at 20 Hz, -2 dB at 20 kHz" - we still don't know everything, but at least we know estimate the low pass and high pass behavior. Best: a chart!

Specifying distortion without levels and bandwidth, and fully specified test conditions is meaningless.

One of my favorite, though, is speaker specifications that provide directivity or Q without a graph. The real winner though is A/D and D/A converters that use the number of bits to define dynamic range. Please, there isn't a 24 bit converter chip on the market today that can deliver 24 bits of dynamic range, and even if they could, designing the analog stages to that level of performance is very difficult, maybe even impossible.

Other pet peeves include specifications made in laboratory settings. I can design a microphone preamplifier with fixed gain that can exceed a 100 dB S/N ratio if I shield it carefully and terminate the input with the proper pure resistance. Sadly, most microphones behave nothing like a pure resistor, and those pesky microphone cable cause all sorts of problems, and there aren't a lot of preamplifiers sold with fixed gain.

Specifying system or component behavior is not difficult, nor is it new. But many products would look bad on paper if their manufacturers published accurate and complete specifications. The irony here is that they might still sound good! Really... I've measured the behavior of guitar amplifiers at the phase inverter input and it's categorically bad. And some of the old standby dynamics processors... you don't want to know!!!

OK, clearly I get annoyed by this stuff, and I'm veering OT, so I'll shut up now!

I beg to differ, but if no frequency is specified then any impedance specification is meaningless, and if it is specified at only one frequency it isn't entirely meaningless, but it is entirely useless! What if that 1000 ohms at 1 kHz spec is describing a pure capacitor? I'm betting that it would sound pretty darned bad on any real world audio!

Yes, Bill, I agree with you. after I posted that I thought about what I said and realized it was incorrect. I posted in haste! most capacitance and inductor tests are at 1kHz standard, but impedance is not. my apologies!

most consumer and prosumer "impedance" specs rarely ever have the amplitude and phase angle listed, which is really why they're not actually giving you impedance specs. they're giving resistance measurements, but even that's not meaningful because if they're calling it impedance then how did they come up with the resistance measurement? at DC? then it's not impedance, it's resistance. at some frequency? what frequency? therefore if stated as resistance only then it's really not an impedance measurement or it's incomplete.

I guess I wasn't being clear there, I didn't mean specifying IMPEDANCE measurements for capacitors or inductors done at 1kHz, I meant that TESTING to determine VALUES of those components are typically done at 1kHz. at least most of the testers I've worked with default to 1kHz for testing inductors and capacitors and you have to change them for different frequencies.