John Curl's Blowtorch preamplifier part II

[Bob Cordell]

Originally Posted by jneutron

No problem w/rt to words in mouth..

It is more an understanding of physics.

It is not physically possible to get a 500 foot line to settle down down in 2 or even 10 microseconds if the load is not matched to the line.

No way, no how.

When the load is 8 and the line is 100 and you step 80 volts at the source, the load will not have 10 amperes within it for a very long time.

You are confusing a matched termination with the abysmal thing we do with speaker wires.

jn

jn,

This is crazy. I think you missed my simple point. Once again, please understand that I was only making a comparison of time delays - nothing having to do with settling times. I do not disagree with you that settling time might be an issue with 500 feet of mis-terminated cable.

My simple point was that effective differential time delay introduced by crossover component tolerances can be orders of magnitude larger than the differential time delay that might be created by speaker cables. This was all in the context of imaging.

BTW, every couple of years some nut-case comes along and argues that speaker cables should have a characteristic impedance of 8 ohms so that they are properly terminated by an 8-ohm loudspeaker, even if the run is only 10 feet. This is completely silly.

At the same time, we are wise to be mindful of the impedance presented to the amplifier by the combination of the speaker cable and the loudspeaker out to perhaps 10 MHz - impedance that in some cases can get nasty as a result of reflections at high frequencies that might de-stabilize some amplifiers. Please go to Figure 18.4 on page 376 of my book to see what I am talking about. A 120-ohm Zobel at the loudspeaker end assures at least some kind of termination at high frequencies, since many loudspeakers begin to look inductive and Hi-Z as the frequency approaches the MHz region.

Cheers,
Bob

[Esperado]

Originally Posted by Bob Cordell

My simple point was that effective differential time delay introduced by crossover component tolerances can be orders of magnitude larger than the differential time delay that might be created by speaker cables.

You both agree on that from the early beginning, it seems. In fact it seems you agree on near everything, just you forgot to tune your violins the same key. Reason why i both punished-you, naughty boys.

Funny you mention the behavior of coils up to MHz, i was talking about that for zobels.

[jneutron]

Originally Posted by Bob Cordell

jn,

This is crazy. I think you missed my simple point. Once again, please understand that I was only making a comparison of time delays - nothing having to do with settling times. I do not disagree with you that settling time might be an issue with 500 feet of mis-terminated cable.

Ah, good, that helps.
.
Now calculate the settling time, say to 80% of final value, for a step from a source to load, 3 meters, dielectric coefficient of 4, line Z 100, load Z of 4.

Use either the ideal eq, or include R and G. Or, simply go to the belden site, they actually graph some of this. Hint, the results are worse.

You attempted to use simple prop delay into a matched non reflective load as a response to a calculation of mismatched termination settling time.

I'm not that easy. And, I expect better.

Originally Posted by Bob Cordell

My simple point was that effective differential time delay introduced by crossover component tolerances can be orders of magnitude larger than the differential time delay that might be created by speaker cables. This was all in the context of imaging.

I know precisely what you were saying, what you were doing.

Originally Posted by Bob Cordell

BTW, every couple of years some nut-case comes along and argues that speaker cables should have a characteristic impedance of 8 ohms so that they are properly terminated by an 8-ohm loudspeaker, even if the run is only 10 feet. This is completely silly.

I cannot argue the nut-case aspect. I certainly meet that description.

However, diss me at your own risk. If you haven't figured it out by now, hopefully you soon will..I kinda know what I speak of. I tend not to speak when I am not sure.

I am very happy being quiet and allowing the experts speak their stuff on the forum.. When I am not quiet, you have to figure out why..

cheers, jn

[Pano]

Originally Posted by jneutron

Or, simply go to the belden site, they actually graph some of this.

I'm searching, but not finding. Any clues?

[scott wurcer]

Originally Posted by jneutron

Only if all ground loop issues are designed out as well.

jn

OK optical source to amp, if you have bits anywhere in the path no need for any new complaints.

[kgrlee]

Originally Posted by jneutron

If you haven't figured it out by now, hopefully you soon will..I kinda know what I speak of. I tend not to speak when I am not sure.

Neutron, I think you have said you have conducted extensive research on aural perception.

Can you tell us when & where?

I'm interested cos I have some small experience of this but am a bit rusty cos a beach bum for more than a decade.
______________________

Originally Posted by Bob Cordell

At the same time, we are wise to be mindful of the impedance presented to the amplifier by the combination of the speaker cable and the loudspeaker out to perhaps 10 MHz - impedance that in some cases can get nasty as a result of reflections at high frequencies that might de-stabilize some amplifiers. Please go to Figure 18.4 on page 376 of my book to see what I am talking about. A 120-ohm Zobel at the loudspeaker end assures at least some kind of termination at high frequencies, since many loudspeakers begin to look inductive and Hi-Z as the frequency approaches the MHz region.

Bob, I think its unlikely any of your designs need such elaborations.

However, it is highly likely (certain??) that certain $zillion Golden Pinnae designs would be embarrassed if such exotic precautions are not taken.

[PMA]

Originally Posted by vacuphile

But since a Zobel needs a resistance anyways, it may just as well be taken care of (partly) by the ESR of the cap. It's more about tolerances and degradation in this particular example why Elco's may not be preferred.

Both ESR and ESL and inductance of wires limit the Zobel effectivity.

[Esperado]

Originally Posted by PMA

Both ESR and ESL and inductance of wires limit the Zobel effectivity.

Oh, please, not you, PMA. It is a LCR serial circuit.

You can use a very high resistance value for the coil (little wire diameter), you just have to subtract this value from the resistance value. As you just have to substract the inductance of the cap from the inductance value (low under the tolerance of the coil).

[PMA]

My comment was to Zobel as R-C terminator for VHF at cable end. I did not mean bass or midrange driver impedance compensation.

[Esperado]

Originally Posted by PMA

My comment was to Zobel as R-C terminator for VHF at cable end. I did not mean bass or midrange driver impedance compensation.

Not a question of bass or medium, it applied to any tweeters too. It was about impedance compensation of the resonance peak of drivers. Not inductance compensation.