John Curl's Blowtorch preamplifier part II

[Cobra2]

Get well soon!

Arne K

[SyncTronX]

Originally posted by scott wurcer
(snippage)in the beginning was way oversold like some of the early press on Kaman's two-wheeler.

Way oversold indeed. Back when I was going training development
and interactive stuff, Sharp started advertising a new display. They
showed this thing projecting a foundry pouring, sparks and all.

This was around 1985 and I was stunned at the quality, I called
Sharp and wanted to buy it along with a a lot of stock.

The advertising was fake, the thing wasn't projecting anything
in the ad at all...the ad agency was using a a pic of the foundry
in the ad copy along with a pic of the projector and did it during
their set up process.


John, sorry to read about your eye problems. I'll keep you and
them in my prayers.

[john curl]

All that I can and will say, is that: Quadrature is everything in audio electronics quality.

[Joshua_G]

Hello John,
Good to see you.
What exactly do you mean by Quadrature?

[SyncTronX]

Originally posted by Joshua_G
Hello John,
Good to see you.
What exactly do you mean by Quadrature?

Joshua,

I would imagine John is talking about the following:

Quadrature

and

QAM

Interestingly the latter has a pic of a Vector Scope screen, used
in TV production.

Wow, I never understood what the fundamentals were behind it
but the wiki does a damn good job of it for the choromanance information, I and Q.

and everybodies favoriate, Fourier, yeah.

The second article also talks about PSK in the intro and I think
that was used in the some of the early TADIL links. I think it
also plays a role in some of the G3, G4 stuff now too.

I kind of see the implications of it, but it is way over my head.

Here is one for the the following:


mouse

interesting...

[MikeBettinger]

Originally posted by SyncTronX
Joshua,
I would imagine John is talking about the following:
Quadrature
and
QAM
Interestingly the latter has a pic of a Vector Scope screen, used
in TV production.
Wow, I never understood what the fundamentals were behind it
but the wiki does a damn good job of it for the choromanance information, I and Q.
and everybodies favoriate, Fourier, yeah.
The second article also talks about PSK in the intro and I think
that was used in the some of the early TADIL links. I think it
also plays a role in some of the G3, G4 stuff now too.
I kind of see the implications of it, but it is way over my head.
Here is one for the the following:
mouse interesting...

I'm having trouble visualizing what these links might have to do with analog audio amplification. Is this really what John was cryptically hinting at? I guess we'll never really know.

Oh well, another night of troubled sleep while the brain tries to fit Quadrature into the big analog puzzle...

[1audio]

Perhaps he is referring to differential phase and differential gain measurements. That is what screws up good color rendition in an analog color video system. Its also not easy to measure or fix.Diff Gain and Diff Phase is a real good introduction to measuring the errors. And everyone has an HP8753D sitting around don't they? (I have access to a newer version and I may try to set up the test per their drawing.)

The concept will help understand aspects that feedback may not hide. The audibility of these remains to be studied.

[john curl]

Yes, thank you, 1Audio.

[1audio]

To fill in the blanks a little more this is a phenomena where the gain and phase of the amplifier changes as a function of the input DC level. It also changes per the signal level. It can be seen as a form of intermodulation but not easily measured that way. The normal measurement is done at the color subcarrier (3.58 MHz in the US). Not many audio products can pass that high a frequency.

Its also conceivable that the modulation can happen at much lower frequencies and interact with transient signals. I'm not sure how to measure that at all but it may be possible that a 100 Hz signal could get phase modulated by a DC shift. If the shift is at 1 Hz seeing the sidebands would be very difficult.

The core question that will be argued (not by John, he has other more pressing things to deal with) is the effect of the open loop rolloff of the opamp on this. Does the integration inside the loop affect the timing of the signals passing through it?

[PMA]

Audio is a quadrature of the circle