John Curl's Blowtorch preamplifier part II

[janneman]

Originally Posted by Charles Hansen

[snip]Maybe "two different ways" wasn't the best way to describe it. But the amp will certainly sound "two different ways" at high frequencies and low frequencies. At low frequencies there will be a lot of feedback around the entire circuit, including the output stage. At high frequencies there will be a lot of feedback around one stupid little transistor, and the major source of distortion (the output stage) will have much less feedback.[snip]

This is incorrect. Wheter you use Cdom to increase the fb around the Vas transistor, or whether you use resistive Vas loading to extend the olbw, in both cases there's the same fb available to the output stage at the top of the freq range.

jan didden

[Curmudgeon]

Originally Posted by john curl
For the record, both Charles Hansen and I have degrees in Physics rather than Engineering, and I think this is the ONLY fact that we can be criticized for.

I'd heartily disagree that criticism might be merited; engineering courses at most schools tend to be products of their time. Often a tendency to teach the known, and the graduates seem a bit more rigid (encased in a wall of certitude as it were) than might be best. One reason why engineers often become obsolete so quickly.

Fif.. err, some years on, the Physics degree, a science degree, should still be useful, as it should have included the methods and philosophy of research, the tools for continued learning, scientific method, perhaps experiment design; (how do you know you know, and why does it matter?) and all that.

And the engineering degree from that long ago is apt to be long irrelevant.

[janneman]

Originally Posted by Curmudgeon

[snip]the Physics degree, a science degree, should still be useful, as it should have included the methods and philosophy of research, the tools for continued learning, scientific method, perhaps experiment design; (how do you know you know, and why does it matter?) and all that.

And the engineering degree from that long ago is apt to be long irrelevant.

I beg to differ. What you have learned about methods and philosophy of research, the tools for continued learning, scientific method, perhaps experiment design, will never become obsolete.

jan didden

[IngemarR]

"Sound better" is such a personal thing. But I think that the plot on the right has lots of feedback, and the one to the left less feedback (but still FB).


Regards,
Ingemar

Originally Posted by PMA

OK, if we go again, let's bring some examples. The only difference in these 2 measurements is feedback factor. Which would 'sound better'? Which is preferred by whom and why? I guess I know answers beforehand.

[PMA]

Yes, you are right.

[IngemarR]

John,
Charles,

When you design an amp, what OL BW goal do you set out for?

Thinking about THD vs Freq curve flatness and OL BW, this amp of mine, is a dream (yes, simulation "only"):



/Ingemar

[Joao@AltheaMusica]

@ Charles Hansen

When you're taking about amplifiers without NFB please clarify

1. wihtout overall/global NFB - from output to input
2. without local NFB - no feedback at the amplifier stage as well

Thanks

[Curmudgeon]

...

What you have learned about methods and philosophy of research, the tools for continued learning, scientific method, perhaps experiment design, will never become obsolete.

Some sort of misunderstanding Jan, that's what I thought I was saying. I believe that we're in complete agreement.

To try to clarify, those tools are usually not included in the engineering curriculum to the same degree (if at all) as in a science degree, at least in this country. (With exceptions, Terman being perhaps most notable.)

PS. Enjoyed Volume 0; I hope there will be more.

[AndrewT]

Originally Posted by godfrey

OK, I'll bite.
The one on the left looks better to me (due to less high-order muck). There's something fishy about those plots, though.... Hopefully you're going to give us an idea of the circuit used and the changes made?

Originally Posted by PMA

Yes, you are right.

the only downside to the left example plot are the highish levels of 5th and 7th.
I suspect that making these lower, even at the expense of raising 2nd to 4th would sound better.
Is there a way to achieve that without bringing back the >8th harmonics?

[janneman]

Originally Posted by Curmudgeon

...

Some sort of misunderstanding Jan, that's what I thought I was saying. I believe that we're in complete agreement.

[snip]PS. Enjoyed Volume 0; I hope there will be more.

Yes we are.

jan didden