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Inside op-amps

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RichW View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RichW Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2022 at 10:45am
Originally posted by BackinBlack BackinBlack wrote:

In my early yoof, I used to design and build in the latter days of valves and the new fangled germanium transistors. Then University and earning a living distracted me. Earned a living by applying my skills to digging holes in the ground, then developing and applying machines for digging large holes through the ground. Detailed electronics design became other peoples problems, I just developed the concepts. Nowadays I find that although I have retained the basics, a lot of the detail design whilst interesting is not something I can "do" anymore. Physically building electronic devices still interests me, but I leave the electronics design to those who can. Much of my enjoyment these days comes from designing, building and flying large model aeroplanes, the camaraderie at the flying field is also a great pleasure.
So that's my take on the current level of interest in designing and building Electronics!

Designing, building and flying model aeroplanes is a fantastic & fulfilling hobby Ian.
I must start it up again.Smile

There's an analogy here with the 'DIY' aspect mentioned earlier.
These days the majority of model flyers buy pre-built ('ARTF') models - for various reasons -
cost, time, skill etc. and there is a decline in those who build from scratch.

Go back a few decades & it was frowned on if you didn't carve your own propellors!






Edited by RichW - 10 Aug 2022 at 10:47am
Elevator, Accession M, Majestic/Enigma, Reflex M, CuSat & Lautus.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2022 at 11:59am
I don't know which way I should take these comments.

It's pretty safe offering an op-amp based phono stage design (the Genera), because there's little to go wrong. The op-amp can take some "abuse" and still retain its performance characteristics. It has quite a bit of built-in protection.

But a power amplifier carries a lot more risk. I know this from my "first time" when I switched-on and it didn't work, and I knew squat to be able to fix it. OK, that was a very long time ago, and it didn't put me off my designing career.

Now, except for one silly little accident, the 70's power amp has survived through hundreds of modifications. It's not because it's fool proof but because I knew what I was doing.

It can take quite a bit of abuse, but it cannot withstand changes to its fundamental design. By changes, I mean a misplaced component where it matters the most. And how would you know if you didn't understand the circuit?

To offer it as a parts kit, I realised I must write a manual to provide that understanding, and it's at 136 pages so far. Recent comments are a bit unnerving.

It isn't about carving your own propeller, but it's about stability, and safety of the amplifier as well as that of the constructor. It isn't a cheap parts kit either - the parts are expensive - and the labour in packing it is expensive because of the responsibility of getting it right. It's not something that can be automated, simply because it will never go mass market. We're talking about ones or twos.

So please don't take offence, but the things I've been asked for I am unable to do as painting by numbers. I can only do it like a constructional article, and constructional articles about discrete circuitry tend to assume some level of knowledge and competence.

I like to share knowledge and I'm a giving type. Will somebody tell me it isn't all in vain?
Not simple enough for Google-Bot to understand...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackinBlack Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2022 at 3:54pm
Graham, my comments were not meant to be disparaging, sorry if they seemed so. I have thoroughly enjoyed your dissection, re-evaluation and dissertation on making the 70s design work as intended.
Some of the analysis took me a little time to understand, but understand I did. I have generally made it a principle to know how things work and what can be done (or not done).
Whilst I may not have been actively involved in audio design and construction, I have completed many other electronic projects allied to my other interests. I understand your "painting by numbers" comments regarding the assembly of the amplifier. I consider myself more than capable of building the "kit" in a safe and competent manner, even though I haven't carved a propellor since my days at school!
I certainly don't think you're wasting your time.

Ian
Just listen, if it sounds good to you, enjoy it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 10 Aug 2022 at 5:29pm
FWIW I thought the 1970's amp and transformer design thread was brilliant work and take your point about the manual.

Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RichW Quote  Post ReplyReply Direct Link To This Post Posted: 11 Aug 2022 at 8:58am
Oops no, comments made about aeromodelling were just intended to illustrate the general decline in DIY.

Personally, having had previous experience of DIY audio electronics the kit is of great interest & it would hopefully also be to many others.
Your difficulties in writing a manual are understandable but your work isn't in vain.

(Incidentally carving a prop isn't easy & a badly made one can be dangerous.Wink)


Edited by RichW - 11 Aug 2022 at 8:59am
Elevator, Accession M, Majestic/Enigma, Reflex M, CuSat & Lautus.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote gwebster Quote  Post ReplyReply Direct Link To This Post Posted: 11 Aug 2022 at 11:09am
As an electronics DIYer, I'm happy to design op-amp based phono and pre-amps from scratch (not to Graham's standard by any means) using all the freely available software tools available on the web.
  • LTSpice simulation software is free and works well (so long as your models are valid). 
  • KICAD is free and well supported PCB circuit design software
  • FreeCAD is free and well supported 3-D CAD software for mechanical design, e.g. front and back panels
  • LibreCAD is free 2-D CAD software for those metal case suppliers (e.g. Modushop) that don't accept 3-D
Back in the day, I wouldn't have had anything like this available to me and had to use a slide rule or calculator while doing circuit design work, sticky tape and transparent film for circuit layout and play around with nasty chemicals to etch my own boards as there weren't any cheap Chinese PCB sources available .

I certainly wouldn't tackle a power amplifier. Last time I did that (trying to emulate the Quad 303), all I did was get magic smoke from several sets of power transistors.

Hats off to Graham!
Inspire Apollo tt, O/L modded RB250, Ortofon 2M Black, Slee Different Approach inspired Phono, Putzeys Pre, Cusat, Raspberry Pi/Volumio, Bitzie, Self Load Invariant Power, Acoustic Energy AE509s
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 11 Aug 2022 at 4:17pm
Originally posted by gwebster gwebster wrote:

(trying to emulate the Quad 303)

Back in the day before simulators, some designers worked "blind" and perhaps expected miracles...

They would, I assume, have had a better education than I, but in the 303 schematic, I can see some similar mistakes that always seemed to result in click-bang-smoke.

It was always a good idea to stick with the 2N3055"H", but eventually the instability penny dropped - it had to after they took the "H" away - either that or change career. There became a fear of second breakdown (the "H" didn't have one), and stability criteria had to be learned (both HF and thermal). After which it didn't seem so bad.

Still, and I must admit, I half grasped the HF stability part due to my lack of mathematical "tools", but after gaining them things looked so easy (slight sarcasm warning).

When the 405 came out, I swear I could here the distant shouts of "Jonah!"

Not simple enough for Google-Bot to understand...
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