John Curl's Blowtorch preamplifier part II

[PMA]

Listening test. DOT.

[syn08]

Originally posted by PMA
Listening test. DOT.

Ah, ok, for a moment I thought it's more than your own, private, subjective, biased, non-controlled, listening tests.

[syn08]

Originally posted by PMA
Anyway, yesterday there was a request for PIM measurements. Images were displayed, so I would expect a comment.

Here's a comment: those results were obtained 40 years ago on the mighty uA741. They only proof that PIM may exist, something that nobody ever denied. Though, for all practical purposes, PIM is a non issue in almost any modern, wideband, high speed opamp. Stories about the audibility of PIM at -120dB and below levels are good for bedtime. The same applies for any decently designed audio amp.

If you really want to make a difference, you must look elsewhere.

[BV]

Listening test. DOT.

You are to sure with Yourself...
Sorry, but i must:
Why have You it not heard about half year ago, opamps in signal path and global NFB, and You said: "It is excellent"?
I can take transistors like AC127, make an discrete amp and present results.. It is the same with uA741 measuremets. Coment today´ measurements....

[Trevor White]

Originally posted by syn08


Here's a comment: those results were obtained 40 years ago on the mighty uA741. They only proof that PIM may exist, something that nobody ever denied. Though, for all practical purposes, PIM is a non issue in almost any modern, wideband, high speed opamp. Stories about the audibility of PIM at -120dB and below levels are good for bedtime. The same applies for any decently designed audio amp.

If you really want to make a difference, you must look elsewhere.

I remember reading this article in the AES years ago. It was possible to use a low grade opamp to match the dynamic performance of an emitter follower with all the advantages of feedback such as, low DC offset and drift, low output impedance and low distortion by using a feedforward floating power supply. It was possible to increase the slewrate performance of the 741 opamp from 0.5 v/us to over 300 V/us

regards
trev

http://www.aes.org/e-lib/browse.cfm?elib=3664

Feed Forward Floating Power Supply (High Response-Speed Equalizer Circuit)

This paper describes a method of drastically reducing nonlinear distortion and transient intermodulation distortion (TIM) from non-inverting unity gain amplifiers. The method utilized to accomplish this is from a floating power supply by which Feed Forward and Bootstrap techniques have been applied to it. Several applications of the method are also discussed.

Authors: Funasaka, Eiichi; Kondou, Hikaru
Affiliation: Victor Company of Japan, Ltd., Tokyo, Japan
AES Convention:67 (October 1980) Paper Number:1712

[dimitri]

Feed Forward Floating Power Supply

Trevor, this idea was published by Sandman, "Reducing Amplifier Distortion", Wireless World, 1974, Oct., pp. 367-371

[Trevor White]

Originally posted by dimitri


Trevor, this idea was published by Sandman, "Reducing Amplifier Distortion", Wireless World, 1974, Oct., pp. 367-371

You need to see the AES paper to see if it is the same thing

regards
trev

[brianco]

Despite the fact that modern cars often have more features or test 'better' than older cars, they are often found by experienced drivers to lack the feel, or even character of the older cars. The point is that to experience the improvement of an all new car, one has to adapt to the demands of the new technology incorporated. That is a personal choice. Take it or leave it.

But do we therefore need to retrain our ears and accept a bigger experiential difference between - say - an orchestra playing live and a recording of that same performance. I have found that the most up to date sound systems are imposing such demands, whereas a good DHT based system with miles of transformer wire on board, 50+ year old tubes can far more often give a real musical experience than the latest kit.

I was fortunate enough to hear the results of many amps built by Be Yamamura at the time he was testing opamps. (His VT4 SETs were for many streets ahead of even the most revered names in that field in the production of musical experience).

Although in Be's testing there were many 'newer' opamps which 'performed' on paper or testing instrumentation in a 'better' fashion than did many of the older simpler devices and j-fets, seldom did these newer devices offer any improvement in the quality of sound perceived by a variety of experienced listeners. Sure enough there were different but distinct improvements in noise performance etc but in terms of creating a musical experience from CDs, records and 1/4" final mix studio tapes they failed to deliver in overall subjective terms as well as some of the older stuff, and without exception BOTH groups - compared to j-fets - sounded more artificial. That is where I still stand but accept that the day will come when that may change.

Therefore it IS necessary to look very closely at new design and ALSO at old component design. It is necessary to find what is the essence in one compared to the other and then to improve - probably both. What is essential is that this work is executed by the same people. But as companies are in business to sell for profit, and 20 years of repeat orders are not going to be as profitable as a new product line every so often. Therefore it is unlikely that any real improvement will come other than by accidental means, monkeys typing footballer's memoirs etc.

Regarding sound reproduction there has been little acceleration in the upping of quality of recorded sound. The newer storage methods mean to often that they add even more compression and therefore any old equipment will do. [There was a BIG drop off in the number of new recordings made in the early 1990s as most record companies were putting back-catalogue into digital format; new recordings tended to be in the pop-dance sector and at that time (and still) most of it had little musical merit...."if you could, aided to the eyeballs, dance to it it would do - no matter how bad the recording"

Lets not forget what all of this is about. Rather than have these blood and guts falling outs lets think more about the reason for all of this....to recreate as real as possible a musical experience from a piece of plastic!

[dimitri]

Trevor, I read it twenty years ago...

[syn08]

Originally posted by Trevor White


I remember reading this article in the AES years ago. It was possible to use a low grade opamp to match the dynamic performance of an emitter follower with all the advantages of feedback such as, low DC offset and drift, low output impedance and low distortion by using a feedforward floating power supply. It was possible to increase the slewrate performance of the 741 opamp from 0.5 v/us to over 300 V/us

That's an interesting 1980 article that essentially describes a composite opamp, with a slow 741 and a fast discrete amp in a PF/bootstraping loop. That configuration has though quite some issues, starting with latchup and ending up with flexibility in configuring the desired (gain, etc...) parameters.

A similar configuration (intended only to greatly extend the dynamic range of an already fast opamp) that I experimented with very good results (SR is over 600V/us) is here: http://www.diyaudio.com/forums/showt...22#post1536373

Another very interesting composite configuration was described by by Schanen in US Pat. 5,045,805

And look at this composite sucker http://www.diyaudio.com/forums/showt...04#post1528904 You can combine a fast and a slow opamp with very interesting results. It's all about matching poles and zeroes