John Curl's Blowtorch preamplifier part III

[billshurv]

For a larf, a recent outpouring from one of the stereophile writers The Problem With Tubes | AudioStream
This section caused me to smile

To my ears, amplifiers with low or no doses of feedback saturate the male and female vocal rage with rich tone and high levels of tactility. Amplifiers employing low or no-dose feedback deliver supple, bendy high-plasticity forms. Slightly larger doses tighten things up and raise the damping factor. Adding more than 30dB sounds like dragging a tin bar along a brick wall.

Sigh.

 

[scottjoplin]

It's a grate pity that Linkwitz retired, I thought that diyers never retire, he even stopped to add new things in his web site.

I hope I will do my DIY even after eighty.

Have you read it all? I keep thinking I have and then find the missing link (of course, I mean a link I've missed)

 

[gpauk]

Quote:
To my ears, amplifiers with low or no doses of feedback saturate the male and female vocal rage with rich tone and high levels of tactility. Amplifiers employing low or no-dose feedback deliver supple, bendy high-plasticity forms. Slightly larger doses tighten things up and raise the damping factor. Adding more than 30dB sounds like dragging a tin bar along a brick wall.

That's one for pseuds corner for sure! good grief....

 

[john curl]

Thanks for putting that 'outpouring' up Bill. It gives us a place to start a discussion in how to make exceptionally sounding audio equipment, and secondly, what is wrong with most conventional designs: Too much negative feedback! This is the cause of added FM distortion, and that separates the winners from the 'also rans', like what so many here use and think adequate.

 

[scottjoplin]

Funny, sounds to me the reviewer likes large doses of 2nd harmonic, haven't a clue what the rest was all about

 

[billshurv]

Recommended Components: Fall 2017 Edition Power Amps | Stereophile.com yes all of these are low feedback...NOT


You didn't comment on the fact that your amplifiers are 20dB worse than a vanilla LM-3886 on 18/19kHz IMD. I would be interested in your thoughts on that 🙂

 

[DF96]

Too much negative feedback! This is the cause of added FM distortion

Please explain to us how linear feedback "causes" "FM distortion" in a circuit which has no other source of "FM distortion".

 

[john curl]

No, he doesn't necessarily like added 2'nd harmonic to excess, but he doesn't find some measured 2'nd harmonic OK, listeningwise.

 

[DPH]

That's quite a stretch, John. Where's the frequency modulation showing up in the ultrahigh feedback ppm distortion monsters?


(To take it to the logical end, mind you I don't think ppm distortion is all that needed, albeit an intellectual exercise, much like a well performing z-gfb design might be)

 

[john curl]

Bill, you confuse AM distortion with FM distortion generation.

 

[Mark Whitney]

You do know that what they write is pure fiction. It never took place.

 

[dadod]

Considering he is now in hospice care for an aggressive cancer, we can hardly blame him. That is an even greater pity.

I am so sorry, I didn't know.
I followed his work on loudspeakers for very long time and learned the most things I know about loudspeakers from his work.

 

[billshurv]

John: we keep asking what you mean by FM distortion in this context and nothing.



DPH: Agree. Biggest problem is that most do their PPM measurements into resistive loads. Until everyone accepts a more realistic scenario we seem to be stuck.

 

[BV]

Bill, you confuse AM distortion with FM distortion generation.

Both types of "modulation" must produce new spectra components.

 

[john curl]

And how do you separate AM from FM distortions, and what sort of test conditions will give the most FM distortion?

 

[DPH]

Bill, of course. I mean most every distortion spec is into a resistive load, which obviously isn't what a speaker + wire is. More that these near-unobtanium levels of distortion are intellectual exercises more than anything else.

But I still haven't seen anything hinting at emergent frequency modulation or even phase modulation. Those have consequences that show up in stationary signals.

 

[billshurv]

John: you are speaking in riddles.

 

[scottjoplin]

It could be he's asking you a question 🙂

 

[Nelson Pass]

It did intrigue me that SL revisited his analog crossovers as his last big update on his website. I assume Nelson was helping out from some comments on there. It clearly wrankled him that he couldn't get the same performance from analog crossovers as digital.

Siegfried asked me to develop an analog crossover, as described at last
year's BAF, and which will be a kit in the diyAudio store next month. The
documents to be published shortly show his comparative acoustic results.

 

[anatech]

Hi Nelson,
That's really good news! Two or three way?

-Chris