John Curl's Blowtorch preamplifier part III

Status
Not open for further replies.
Jump to Latest
#20,081
jneutron said:
Actually it was quite consistent. The slew rate of a signal is it's derivative. As the signal gets larger, so does it's derivative.
Click to expand...


You know, we pitchfork wielding EEs call this (in those particular cases when it makes sense) “rise time”. And it’s not a constant, that’s why we use a particular way to define it (time from 10% to 90% of the rising signal amplitude).

“Slew rate” is reserved for something else which does not depend on the signal amplitude.
 
#20,084
billshurv said:
Aw come on Ed, 30+ years ago in school they were teaching this correctly where the leader heads down from the cloud (whilst at the same time going up in the cloud) and then when it reaches the ground the discharge goes back the other way.

And lightning doesn't always hit the ground!
Click to expand...

Yeah, sometimes it hits my TV antenna which, despite being stoutly grounded and gas-tube protected, came into my house through an FM split to my office and bit me in the foot, exiting my hand. Knocked my body off line from my brain for 30 seconds (conscious but no sight or hearing) and did 10s of thousands of dollars damage to infrastructure. I feel lucky to still be here. Not an experience I wish to repeat, so everything directly attached to antennas here is optically coupled to anything else.

Ironically the reason my TV antenna was hit likely has a lot to due to its lower impedance to ground than the surrounding objects...of course had it not been well grounded the effects in the house would have been MUCH worse...

We hate lightning...
Howie
 
#20,085
scott wurcer said:
I'm pretty sure if you flip the phase on one channel it will sound wrong. 😕
Click to expand...
For the testing duration speakers inverted wrt each other is useful and allows real time comparison of speaker polarity and real time comparison of interconnect direction.
At end of testing session optimal speaker polarity and optimal interconnect direction is decided and implemented both channels,
Was that hard to understand ?.

Dan.
 
#20,086
simon7000 said:
When Benjamin Franklin first decide on positive and negative he thought of electricity as a fluid going from a supply to a deficit. When the current actually radiates from the negative source the current begins to really flow when it reaches the positive end. This starts the arc for some cases which grows back to the actual source. So he decided it flows from positive to negative based on observation. It was much latter that folks realized it moved the other way.

So convention calls current flow from positive to negative. Others sort of correct this by say electron flows from negative to positive.

You got it right at school.
Click to expand...
Does anyone still teach "electron current?"

I recall seeing an electronics textbook with the label on the cover "Electron Current Edition." Clearly there was also a "Conventional Current Edition."

When I started college I somehow managed to learn that in engineering school everything was conventional current (current flows from positive to negative), whereas in technician's school (vocational or vo-tech school) electronics was taught as electron current (current flows from negative to positive). There's few if any "electronics technicians" anymore, so I presume electron current is no longer taught.

And then there's current in semiconductors ...
 
#20,089
scottjoplin said:
Would I have to listen to them individually?
Click to expand...
I prefer to run both speakers at medium level and stand in front of each speaker individually to decide which polarity sounds better in real time (no pauses or 'dead air' time).
This is audio 101, lesson 01, first day before lunch time, after lunch we can continue with speaker cable direction and then interconnect direction.

Dan.
 
Last edited:
#20,093
scottjoplin said:
There is something to be gained by standing in front of one speaker whilst the other is polarity reversed and then standing in front of the other? This is so screwed up I'm not sure I'm understanding you correctly although I fear I am.
Click to expand...
When standing in front of one speaker the other speaker is also audible allowing real time comparison, moving listening locations including centre position reinforces preferences.
This is about comparing the sounds of two speakers according to speaker connection polarity, this really is elementary stuff to be mastered before progressing to auditioning other system changes.
 
#20,095
Chris Hornbeck said:
"Slew rate" in amplifiers is the limiting condition measured at the output with a zero rise time input. It's kind of a misappropriation from mechanical widgets, where it has a quite different meaning.
Click to expand...

However that definition can be misleading. More useful comes from the frequency where the distortion (or departure from feedback linearity) exceeds a threshold. I remember 3% as a useful number which may yield a much lower slew rate than the "all transistors inside saturated" slew rate number for the marketing materials. It also means below that slew rate the output can be meaningful.

For any modern opamp in audio applications this is a non-issue. It may be for HDTV if there are any analog stages left. . .
 
#20,096
Best slewing I ever saw was a French Crotale (sp?) rocket launcher at White Sands where I was grunting. Two vehicles linked by a giant umbilical - radar dish on one, bunch of rockets on the other. The dish and rockets moved together so fast it was hard to see the motion; they were pointed one way, next instant another. 1971.


All good fortune,
Chris
 
#20,097
Max Headroom said:
When standing in front of one speaker the other speaker is also audible allowing real time comparison, moving listening locations including centre position reinforces preferences.
This is about comparing the sounds of two speakers according to speaker connection polarity, this really is elementary stuff to be mastered before progressing to auditioning other system changes.
Click to expand...

Tell me, do you manage to keep a straight face whilst typing this stuff?
 
#20,098
Chris Hornbeck said:
Best slewing I ever saw was a French Crotale (sp?) rocket launcher at White Sands where I was grunting. Two vehicles linked by a giant umbilical - radar dish on one, bunch of rockets on the other. The dish and rockets moved together so fast it was hard to see the motion; they were pointed one way, next instant another. 1971.


All good fortune,
Chris
Click to expand...
That conjures up quite a terrifying image
 
#20,099
jneutron said:
You have missed the point entirely. I apologize for the brevity of my post, as I tire of repeating the same thing over and over so kept it short. (Too short I guess..sorry)

The analysis has absolutely nothing to do with amplifiers driving 1nSec signals. I could have said femptosecond, or simply an ideal step...same thing. The only requirement is that the step signal have a slew rate sufficiently faster that twice the transit time for clarity.

This is a step response analysis of a system, commonly used in other engineering disciplines.

What it shows is that given a line to load mismatch, the system does not settle to final value as one would think. It will settle based on the cable z, mismatch, and length (or classically, a lumped element LC line).

So I do not care about 1nSec response... I care that a typical zip cord 20 feet long driving an 8 ohm load will have a load impedance dependent phase shift. I care that the load impedance is dependent on the time history and instantaneous state of the load.
I care about soundstage quality, and soundstage quality requires time/phase accuracy and stability in the regime below 10 uSec.
Click to expand...

John, I do care as well, but only about the phenomena that may happen, not about the hypothetical ones.

Below is a step response just now measured on an audio amplifier with 20 feet of zip cord speaker cable and loaded with a speaker. Measured at speaker. Where is the problem that you are describing?????
 

Attachments

  • step_cable_spk.png
    step_cable_spk.png
    50.2 KB · Views: 219
Status
Not open for further replies.
Top Bottom