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Dave Friday View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave Friday Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2019 at 11:08am
And it isn't strapped as a triode!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DogBox Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar 2019 at 10:59am
Graham said:"So I think we can agree it isn't a cathode follower?" and 
Dave said: "And it isn't strapped as a triode!" 
So, Steve thought... "Can the RCA Manual be wrong...?" What if you replaced the 6J7 with a BC184 transistor..? And fixed up a few other things (?) Could it [even remotely!] be some sort of a simple Ceramic Phono Preamp? 
I really should study this. Basic transistor amplifier. Aren't "transistor-type" Phono Preamp's the best sounding? So, why is it so popular to 'use' 'Op Amps' when, with a little extra doings, you could have a superior unit? Or, are they "just" so noisy...?! 
Might have to ask our illustrious Master Slee... Thumbs Up 

Kind Regards,
DogBox [Steve] 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar 2019 at 7:19pm
Illustrious?

If you're interested in making a transistorised phono preamp you can read about the pitfalls at the Doug Self Institute, and on Rod Elliott's website. Both consider op-amps to be superior, and they could be right.


I've made numerous transistor phono stages (amongst other transistor amplifier stages) and op-amps are much easier for the DIY'er to understand. I'd better not say that all the work's been done for you in an op-amp, because it hasn't, but most beginners can get some sort of performance out of an op-amp circuit with minimal understanding.

Getting them (op amps) to outperform the esoteric and often expensive stuff is a different matter. Then again, some of the expensive stuff is simply that: expensive, period.

My long-winded 70s Design Indulgence topic will eventually get back to the subject of a transistor phono stage, which is part of the transistor only concept of which I'm trying to achieve (a transistor integrated with offshoots).

The negative thing about op-amps is that you're stuck with the characteristics of the op-amp you choose. You don't have much control of the outcome. But often, to achieve the same measured spec using transistors, you end up with a discrete version of what's in an op-amp. Then why bother? Just use an op-amp to start with.

Op-amps have these characteristics (or signatures) because of how they were designed, and why they were designed as they were. For example the NE5534 and its offshoots. It was designed by Philips 40 years ago. It was a miracle of its time. It is signatured because of the way in which it was conceived: to follow audio thinking at that time. It was easy enough to make it have a complimentary output stage, but it's quazi-complimentary complete with Baxendall diode. I could go on about it but I'll save it for another topic.

I'll end up by saying that if a job's worth doing it's worth doing right. Watch the 1970s Design Indulgence topic to learn about the finer points using transistors.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DogBox Quote  Post ReplyReply Direct Link To This Post Posted: 07 Mar 2019 at 9:56pm
Originally posted by Graham Slee Graham Slee wrote:

Illustrious?

Getting them (op amps) to outperform the esoteric and often expensive stuff is a different matter. 

Ok, so what are we talking about "esoteric" and "expensive"? 
I went looking on the Texas site and found - only surface mounted, mind you! - a chip with 8 legs for $(US?)46.00...? an OPA??? of sorts..  

My long-winded 70s Design Indulgence topic will eventually get back to the subject of a transistor phono stage,.... 

I wait with baited breath! 

The negative thing about op-amps is that you're stuck with the characteristics of the op-amp.. You don't have much control of the outcome.... 

I thought that once you had found a Low Noise chip op-amp with a High Slew Rate, you could pretty-well pack everything around it to get the result you're after? Apparently no... Ouch

 Watch the 1970s Design Indulgence topic to learn about the finer points using transistors.
 
Since it's been a little while, I probably have catch-up to do...Embarrassed Forever grateful for all the patient teaching! StarClapClap
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 08 Mar 2019 at 9:05am
You can't blame TI cashing-in on the mania. The gravy train holds vast fortunes for those who kissed the blarney stone. Unfortunately my Irish great grandmother's contribution to my DNA didn't contain that skill Wink

Op amps can be designed by an individual, or they might be designed by committee (a bit like the saying "a donkey is a racehorse designed by committee"), and I very much doubt anybody takes a good year over its discrete development, listening to a pile of records/flacs at each turn, prior to its large scale integration...

Wireless World served as an outlet for a number of talented designers to show off their design prowess, but we can also see their mistakes as we try and progress. As a consequence the NE553X includes a few of these - sounds great until it's been on a few days, when unless the designer compensates for its idiosyncrasies, it takes on a very dry and boring musical presentation.

Dogma can be false sometimes, and we run the risk of our eyes trying to cheat our ears. We are given 5 senses which are of equal importance, so why do we try and tell our hearing something is right just because our eyes saw it?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote DogBox Quote  Post ReplyReply Direct Link To This Post Posted: 10 Mar 2019 at 11:59pm
Unfortunately my Irish great grandmother's contribution to my DNA didn't contain that.... 

But you 'have developed' a "skill" that hard work and a penchant for the truth as close as you can get it of understanding and designing "pleasure to your [and our!] ears!" 

Unfortunately, as you've said, sort-of, that when a "committee.." go about designing anything - money - is usually the main motive. Sad that money - more than ever, is still driving the world's rotation.. 
At least we get more pleasure and fun out of a belt to turn our's! 

I did see your encouragement to one member desiring of more knowledge, advising The Art Of Electronics... Upon my search to acquire that textbook; the price had me stopped in my tracks and to see if there was something else on the subject a little friendlier to the back pocket... I ummed and erred and decided on Electronics for Vinyl by Douglas Self. I'll get the other one next... Just hoping I have enough [never enough!] upstairs to make proper sense of it all! I'll probably need The Art of... to make sense of Elect for Vinyl! There is never a short cut to understanding... 
 I also went on the search for LF356 chips which don't seem as plentiful as I thought... Looking at the best offerings from TI: LME49710 & LM4562 are their top offerings..(?) I had it suggested to me that instead of the LF356 to opt for the OPA602AP with much faster slew rate?? 
 I'm sure those pieces have come before you prior to now and you can't wait to tell me how rubbish/committee designed they are! 
 I'm all ear's..! 

DogBox [Steve] 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 11 Mar 2019 at 10:05am
They say there is no correlation between wide-flat open-loop bandwidth and sound quality...

I liken it to Dorothy's black and white dream from the Wizard of Oz, and at the end of the film the charlatan pulling the levers (strings) is revealed (by a dog).

No correlation at all if you use 1920's test methods. We still rely on Harold Black. The baby-boomers generation onwards sit on their brains: stagnation.

Valve enthusiasts are hearing what wide-flat open-loop bandwidth does for sound quality, yet they'll buy the opposite for a preamp stage or headphone amp. Actually it's distortion most of them like.

Sorry Walt Jung, you, like me are wrong. Bob Pease, Doug Self, Bob Cordell (etc) are obviously right (based on 1920s discoveries). Otherwise I have much respect for Doug Self and perhaps a bit more for Bob Cordell, because he believes in emitter degeneration.

The Art of Electronics explains things from an independent position. It helps if you know how to make a basic transistor preamp to start with then everything else falls into place. You read textbooks via the index, to find what you need, and to find everything you need. It's not cover to cover (as I hope you know).

Seek and ye shall find... It's a sod for people like me who bought the books at such high prices, but most of them can be found as PDFs if you search long and hard (or even by accident).

The good sounding op-amps are being replaced by forced slew rate op-amps (or enhanced slew rate as the manufacturers prefer to call them). The bandwidth starts top-left at some ridiculous high gain, and rolls off to "light" on a constant -20dB per decade. Negative feedback is always 270 degrees at all frequencies, and not 180 degrees as it should be in our hearings range (just my opinion - and Walt Jung’s).

Input slew rate is natural slew rate, and JFET inputs or degenerated BJT inputs do that, but in doing so gain is the cost. That's no good in the op-amp market where gain is everything (high gain with NFB gives disappearingly low distortion). So it's forced at the output by feed forward techniques, cutting phase and gain margin to the minimum, often stating a minimum gain for stability. Such circuits can sound good at first, until they're burned-in. Always switch off as soon as you can...
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