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Post Options Post Options   Thanks (0) Thanks(0)   Quote DogBox Quote  Post ReplyReply Direct Link To This Post Posted: 11 Mar 2019 at 11:11am
Wot? Emitter degeneration.. ? Is that a happening thang going on inside the LME's and the OPA's or something inherent in BJT's I wonder..? Interesting concept! I finally got to read the http://www.douglas-self.com/ampins/discrete/2Q-RIAA/2Q-RIAA.htm page right through + the other sites/articles he referred to. Wonderfully interesting [headache forming] stuff that, I started to see what he was on about! The article he referred to - the link didn't work -  http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1965/Transistor%20High%20Quality%20Audio%20Amplifier.pdf is a brilliant read I didn't have enough time for, for it to add its bit to the story. Talk about looking at the contents to see what you need... follow the links keeps you in reading material for ages!... Also, another article from the Bibleography (?)  https://www.stereophile.com/features/cut_and_thrust_riaa_lp_equalization/index.html Pages 1,2,3,and The Neumann 4th pole (sic) - after pages 1&2 I ran out of time and my duties of looking after my mum take precedence... ah well, I needed a break! 
There's another guy I was waiting for on your list of 'Who got it right..' was Mr Pass.. or didn't he? 
Nelson seems so switched on it would be a real buzz to watch one of his seminars... shame I don't have the intelligence to grasp a lot of what he says - even if he does keep it pretty simple! 
 I am determined to read all of the 45 or so pages of the forum/phono-preamp-project_topic745.html and see if THAT won't teach me a thing or two! I figure, something like that has got to be worth a heck of a lot where you get the results along the way down the yellow brick road and the best explanation of why the bricks are arranged the way they are! Extremely valuable in my book! Something you just don't normally get - unless your Dad was an electronics technician, starting in the PMG (Australian Post Master General that looked after the phones in those days where you could also learn about electronics and he also got his Amateur Ham Radio Licence - built his own tube transceiver, learnt Black & White TV which he ended up selling and servicing,...) I just wasn't clever enough as a young fellow to know how wonderful it all was! Until I became interested in radio comms... my real start into electronics! Then dad died so I couldn't ask the questions I needed answers to for my learning to make sense. Thank goodness for Google! 
Now, a question that occurred the other day when you were talking about NFB... Can it be amplified along the way so that you can have the level you need to really be beneficial? I mean, once you create it in circuit,.. can't you then amplify it or increase its gain level to a point where it will then be beneficial? to the circuit? See, i'm showing my ignorance again and asking questions like this would drive my dad nuts! 
 Oh well, one day... Looking forward to my Genera Kit arriving so I can let IT burn in...slowly...!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: 11 Mar 2019 at 8:10pm
Know how to read bode plots?

LF356: 75 degrees phase margin and better than 30dB gain margin.

OPA602: 22 degrees phase margin and they don't (daren't?) extend the graph below zero crossing so we have to guess gain margin (it won't be much).

My own thoughts are that people like the brightness of instability. I'd prefer a treble control to boost treble if I wanted brightness. The trouble is semantics: hi-fi isn't high fidelity anymore, but a majority will search "hi-fi" when looking for high fidelity (so we call ourselves HiFi System Components Ltd...)

The LF356 is not without problems though. It has an asymmetrical slew rate which isn't good for driving RIAA or tape head preamps using NFB EQ. And is why I never ventured further with it in the Genera.

The LF351 is better in that respect, and can beat the pants off these newbies. But they've made it difficult for the DIY'er to use by making it surface mount.

The LME49710 is "so superior" it doesn't need to show a bode plot. In my book that's arrogance, and close to subterfuge.

The LM4562 bode plot shows manipulation of phase at its unity crossing. Thanks to that it has 60dB phase margin, and I guess 20dB gain margin. It is the better of the two. But it rolls off from less than 10Hz (probably 2 or 3 Hz). The gain bandwidth and slew rate using The Art of Electronics formula says it hasn't much in the way of emitter degeneration, and the noise spec says it probably hasn't any at all. The slew rate calculates as 16.5V/uS but it shows 20V/uS suggesting "forced slew rate".

We tried both devices some years ago and found them to be highly signatured, which looking at the data looks about right for "hi-fi" (as in not high fidelity). But I'm sure my life would be much easier just to go along with the crowd.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DogBox Quote  Post ReplyReply Direct Link To This Post Posted: 11 Mar 2019 at 9:46pm
...how to read bode plots? Well, er, no.. [Me thinks I need to get this The Art of Electronics quick!] 

 ...easier just to go along with the crowd. Easier?!! You? Nope. Can't figure why you'd want to when you've figured out the circle the rest keep going around in! And it won't suit you. 

ThankYou! so much for putting up just the necessary comparisons for when looking for likely devices for RIAA duties. The world is fond of ones like its own. And that conform to its doings. I appreciate that you are not like that. You also have a wonderful patience to put up with numb-skulls like me who can only try and keep up but miss out on having the intelligence to do so. 
 You also touched upon something I have just come to realize: How the designers/committee board relegate what case they will release a device in... PDIP or SMD only + now their mobile phone miniatures! I would gladly have 50-odd BC184's to solder in than one of those things! 
  The semantics have dug their own grave. But they forget that people exist who will tell the king he's naked and an idiot and won't want to listen to something that isn't High Fidelity. Alas, they have the kind of money that these pieces of equipment require for ownership. So, getting back to DIY,... Have you thought of doing another Kit like the Genera? Still a RIAA amp but maybe a level up? Has 'nothing new' come about in the world of renewed interest in "playing records" again but this time, like we've never heard before? An easy tell that CD just can't replace the vinyl we love?!  I don't particularly like it when some say that vinyl just can't produce the frequency response that digital can as I'm not ready to get one of those DAC thingy's... Don't see a need... 
Meanwhile, I need to get myself another book: The Art of [getting things right this time!] 
     
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar 2019 at 1:54am
Can I answer one of your questions by asking if your Genera kit has arrived yet? When built and "run-in" I think it might approach the suggested nirvana. Not saying it will be like you've never heard before, but maybe an improvement on what you have heard?

Although the circuitry I like looks simple, and is simple most of the time, doesn't mean folk can build any close-enough values round an op-amp and rely on the op-amp to give them staggering results. And I'm glad you're seeing past the smoke and mirrors. Just need a few thousand more like you (it won't happen).

Both DIY and industry are full of opinions aimed at pulling in the crowds. It's how money is made. We all need to make a living, but some are "more equal" than others. Mostly I see people being pulled in by things I'd find very difficult to give a technical explanation of. This doesn't mean I'm right and they're wrong, but it might do.

Thank you for pointing me at Nelson Pass. I read http://www.firstwatt.com/pdf/art_dist_fdbk.pdf. Quite eloquently put, and I would have difficulty writing such a convincing piece. He is of course right with some of it.

He concludes saying: "By contrast, it appears that if you can make a single stage operate at .01% 2nd harmonic with a single tone without feedback, you could also achieve the 0.1% peak in the complex IM test. I like to think the latter would sound better."

"If you can" being the operative words. If I could make a single stage without NFB do 0.01% it would be a miracle. Obviously most of this  is written with a view of selling his class-A amplifiers (a guy has to make a living after all).

So let's take a quick look at the figures I last measured from my class-AB 1970s Design Indulgence, a simple amplifier with negative feedback...

Overall THD. Not just 2nd harmonic, but all its others summed by the 1 kHz THD test: 0.015%. IM: 0.05%.

Listening however exposed other problems and the test measurements at 10 kHz and 20 kHz were not out of the ordinary. At high frequencies there are more non-linearities, and can be around 0.1% THD which is higher than the 1 kHz most quote, and that's because open loop gain is falling as frequency increases.

Sacrificing some phase and gain margin to obtain 6dB more negative feedback (yes more NFB) made it sound much better. But then again will it still be better once the brand new dominant pole ceramic capacitors "bed in" after a few days constantly on? And how many lectures discuss constantly on?

I guess I'm an objectivist subjectivist.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote DogBox Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar 2019 at 11:04pm
"I guess I'm an objectivist subjectivist." Perfect!! ClapWink 

Just quickly, no it hasn't arrived yet but there IS a suggested delivery of this Friday.. (yet they [UPS] say it's arrived for customs in Koeln, Germany) I have been told by the post here to disregard a lot of their tracking messages... Confused it'll arrive when it gets here! I'll let you know as soon as it does! Thanks! 
After getting used to Frequency Response graphs - I would never buy a speaker unless I could check out its response first! so I am thinking, once I get the hang of the Bode Plots and what to look for, the rest will come easy. 
I'll get back to the rest of this later... Really appreciate your Help and Guidance! 
DogBox [Steve 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DogBox Quote  Post ReplyReply Direct Link To This Post Posted: 15 Mar 2019 at 12:50am
Well, today is the day when I should receive my Genera! I am so very tempted to update my amplifier system to separate Pre and Power units. I also was fortunate enough to get myself a Class A amplifier [also in kit form - going to be busy! yes!] that has rated distortion levels with lots of zero's after the decimal point until the first numeral! Although integrated, I think it has only one set of RCA inputs. 
 If the Genera is as good as it can get, I notice that the use of Carbon resistors are among the Metal Film.. I would have thought to try and "select" all components as close to the schematic as possible?  Are there places on the circuit board where Metal Film resistors are not a good idea because of their makeup?  
 I was also wondering if you could transfer a single op-amp to circuit board to be then able to alter it to your specific needs IN a project build?? too much trouble? Can't alter any further what makes up a Packaged Op-Amp design to specialize it to do what You want it to do? 
 I would have thought the Designers of op-amps would have to cater to a 'large market' to have their product viable to do many things... Why can't you have a Op-Amp only good for One application and One design parameter? The Best Chip you could possibly make for a RIAA pre-amp that wouldn't be any good for any other purpose because of its makeup? 
No, I don't know enough about electronics to answer my question, so maybe the clever, illustrius, objectivist's may. If they can design a chip to do a multitude of things - why can't they design one to DO only One thing, really good! 
Probably because life wasn't meant to be easy...I know... but.. I had nearly forgotten about an article that really made me laugh, because of the fun involved and the building of speakers of which is my main passion. Nelson Pass, with some help, made these speakers called "El Pipe-o" from 2002 that I first read in Audio Express magazine [also found here at the 2002 date  http://www.firstwatt.com/articles.html ] I'm all over things like this! Absurd? yeah, so? 
C'mon mr delivery man...  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 15 Mar 2019 at 8:15am
All metal film here: https://www.hifisystemcomponents.com/forum/phono-preamp-project_topic745_post6492.html#6492

Should be all metal film in the parts kit too, unless a substitution. I have a CF assortment I bought years ago and used some (when I couldn't find an MF) when developing the Genera as can be seen in earlier photos.

The people who pack the kits (to order by the way) are the same people who build everything I do: John and Leo, so will have hopefully got it right. Wink I don't because my eyesight is worse than theirs...WinkWink

Interesting you have a "zero distortion" class-A one-input integrated amp kit. I'd try the Genera with what you already have. The music will keep you focussed as you ponder all those transistors.

Single op-amps often have offset-null pins, which are "inputs", and using the right pin you can tailor the response to taste. For example you can put a 10 pF cap between pin 6 and 5 on a TLO-71 and half its open loop bandwidth.

If you know how to bias it, both inputs can be tied together and AC grounded, and the offset-nulls then become (low impedance) inputs. AC ground one of them and you have a single sided op-amp. If you use pin 5 as input you can make a virtual earth (inverting amp).

Why you'd do that for audio calls sanity into question, but such techniques get used with video op-amps (for video use of course).
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