What are input and ouput impedances?

[PureBasic]

So, what are we talking about here?
Impedance balancing for single ended emitter and receptor? Balanced output impedance for differential line? Transmission line?

For me that power balancing with -3dB stuff is just some crap every teacher do in ELE101 to get you started... I mean, look at a opamp datasheet. Doesn't need any of that anymore.

 

[PureBasic]

Just drive your cables hard (47R) and don't be too greedy on the other end (10K).

 

[JohnRoberts]

It would be really interesting to see how to find the optimal load impedance for a power amplifier design that has a negative output impedance.

Just add some speaker wire in series....

Back last century while I was power amp product manager at Peavey, Jack Sondermeyer (RIP) developed a circuit that could deliver negative output impedance. His goal was to deliver silly high damping factor specs for the "more is better" data sheet reading crowd. He used a slight negative output impedance to cancel internal wiring losses.

In theory at least a negative output impedance could compensate for speaker wire losses between amp and loudspeaker. For the more adventurous one could play games with loudspeaker cabinet tuning and altering driver characteristics unnaturally. This technology was way too much for our Peavey customers to grasp and use in practice so we just stopped at specifying crazy good DF (2000:1 from production line testing IIRC) and left it at that.

I suspect a really smart loudspeaker designer could implement this inside a powered loudspeaker cabinet and do some slick tricks. AFAIK this hasn't been done commercially, or if they did they didn't publicize it.

JR

 

[PureBasic]

There are some servo speakers out there. Mainly subwoofers. Take a look at the stuff from Velodyne and Pirate Logic NL... Impressive time domain response.

 

[JohnRoberts]

There are some servo speakers out there. Mainly subwoofers. Take a look at the stuff from Velodyne and Pirate Logic NL... Impressive time domain response.

Servo loudspeakers is pretty mature technology... IIRC Phillips did one back in the 70s.

JR

 

[abbey road d enfer]

It would be really interesting to see how to find the optimal load impedance for a power amplifier design that has a negative output impedance.

U being the open voltage, R the source Z and X the load
P=X[U/(R+x)]²
and
dP/dX=U²[R-X/(R+X)²]
Max power is obtained when dP/dX=0
One of the solutions is R=X, so also a negative load. There maybe anothersolution, I don't know, I haven't practised math since kindergarten.

 

[moamps]

One of the solutions is R=X, so also a negative load.

A step before in that calculation is
R² = X²
so it is possible that both positive and negative equal resistance satisfies the equation. Nevermind.

One global example shows where Rsource=Rload is not used in LF power transmission, which is the distribution of electricity.

 

[Bo Deadly]

Power transfer usually refers to a situation where a source of impedance Zs is connected to a load of impedance Zl. Then the max available power to the load is when Zl=Zs.
However, the efficiency is low, at 50%, with as much energy wasted in the source than is available for the load.
This does not apply to power amps and speakers, because the very low impedance of the amp exists only as long as the amp operates in its linear operating region. If you load a power amp with a 0.1 ohm load, the amp either goes into protection, or the PSU collapses or it goes in flames (unless you run it with very low signal).
Maximum power transfer could be seen as maximum efficiency, which happens when the load tends to infinity, since the losses in the source tend to zero.
In the end it's a matter of semantics.

Ah, yes. So this is what RF was talking about. So yeah, this is still not applicable to audio because just about all audio I/O is bridged. Certainly power amps are where the source impedance is like 0.1 ohms but designed to drive a load 40x higher. And for signal transmission, you're more concerned with maximum information transfer and not maxium power transfer.

 

[JohnRoberts]

Shows how the Godwyn point is easily reached, even in a non-political discussion.

There must be a corollary to Godwin's law that suggests whenever someone is losing a political argument on merit they accuse the winner of racism.

JR

 

[CJ]

i just use the speaker jack that sounds the best.

16 ohm speaker load?

sometimes the 8 ohm tap on the transformer sounds better than the 16,
sometimes not.

8 ohm speaker load?

sometimes the 16 ohm tap sounds better than the 8.
sometimes not.

takes 59 seconds to find out.
reading a transformer book on complex impedance might take two hours.

so i save 1 hour and 59 minutes and 1 second which can be used to review NFL highlights on all those tight playoff games.

kiss it, Chiefs!

 

[Newmarket]

There must be a corollary to Godwin's law that suggests whenever someone is losing a political argument on merit they accuse the winner of racism.

JR

I had to 'google' that tbh but yeah.

 

[zmix]

-Guitars typically 5K ohms to 20K ohms, but with the output pots they can vary fro the pickup impedance to 250K ohms


I'm sure someone will correct somethings, but I'm trying to simplify 50 years of learning into one page.

That would be me, Paul..!

Way, way back in the 1890s (yes the decade of grunge) I did some impedance plots of some passive guitar pickups I was studying. I discovered that a typical dual coil "humbucker" had an impedance of over 160kΩ at resonance (which was around 3.2kHz). In terms of impedance matching this explains why low value pots can reduce the "brightness" of a guitar pickup - they act as a zobel of sorts and damp that resonant peak.

 

[JohnRoberts]

That would be me, Paul..!

Way, way back in the 1890s (yes the decade of grunge) I did some impedance plots of some passive guitar pickups I was studying. I discovered that a typical dual coil "humbucker" had an impedance of over 160kΩ at resonance (which was around 3.2kHz). In terms of impedance matching this explains why low value pots can reduce the "brightness" of a guitar pickup - they act as a zobel of sorts and damp that resonant peak.

1890s... I thought I was old....

JR

 

[FIX]

Here is what I used to calculate my impedances. I proves that it can be high and low at the same time.

 

[CJ]

no diff eq allowed.
and you will need more variables if talking about inductance.

note that guitar players like to get the tubes operating out of their linear zone, thus infuriating the engineers who strive to design tube circuits to do just the opposite.

 

[PureBasic]

no diff eq allowed.

*Laplace left the chat*

 

[CJ]

if it don't have j operators then it don't mean squat.

 

[matriachamplification]

no diff eq allowed.
and you will need more variables if talking about inductance.

note that guitar players like to get the tubes operating out of their linear zone, thus infuriating the engineers who strive to design tube circuits to do just the opposite.

Hello CJ,

is this why some guitar players use variacs to bleed or push tubes out of their comfort zone?

Thanks,

Wall and Family

 

[CJ]

i am sure many are familiar with Eddie Van Halen stating in his first Guitar Player Magazine interview something along the lines of "i like to boost the amp with a Variac and watch the tubes melt!" this leading to a public safety message from GPM to the note of "Please do not try this at home!"

i think people lower the voltage maybe, but raising it does pose questions about filter cap voltage ratings which can be quickly become exceeded due to the step up ratio of the HV secondary.

the best way is to just use a stomp box like a Xiotica BB Preamp ,MXR Brown Acid, Boss OD-2, Fulltone Fulldrive 2, Dunlop Fab, Pro Co You Dirty Rat, Route 66 Fuzz/Comp, Zen Drive, Fuzz Face, Tone Bender, but now we are talkin a lot of money to mimic impedance mis-match so you better go here>

https://aionfx.com/

 

[JohnRoberts]

The common practice was to variac guitar amps down to lower mains voltage to force premature clipping at lower power output.

JR