How was clipping done in the good old days?

[FranceBB]

Alright, it may seem an odd question, like "why would a youngster be interested in analog systems?", but it's something I have been wondering for quite some time.

You see, nowadays when I got into this wonderful world of encoding, everything was digital already.
Even when I arrived at the very beginning, I always had to make sure that luma and chroma were in limited TV range 8bit so I not only made sure that each and every camera was the same by checking it with my beloved waveform monitor (Tektronix WVR 7020), but in order to be "safe" I also applied clipping so that no matter how bad and unpredictable a shot of a certain sport event would have been, it wouldn't have exceeded the limited TV Range threshold 16-235.
Now, for me it was (and has always been) just a thickmark on a video server for live events encoding or a command in Avisynth for offline video encoding [Limiter(min_luma=16, max_luma=235, min_chroma=16, max_chroma=240)], but how was this done back in the good old days when I wasn't here and StainlessS, Groucho and tebasuna were young? (no offence xD). The reason why I'm asking it is pure curiosity as analog systems are very much dead, but, out of curiosity, how do you get your signal to stay between 0.0 and 0.7V in an analog system? From my understanding of electronics (what I studied at university), I believe that you would need some sort of high-pass and low-pass filters, which basically means that an RLC circuit was employed which - as far as I know - is made of a resistor (which is a simply anti-isotropic material most of the time in which the current flowing causes dissipation in terms of heat due to Joule effect), an inductor (which "stores" energy in terms of a magnetic field made out by the flow of current due to Lenz's law) and a Capacitor (which acts as a resistor 'till it's fully charged). Am I right? But then, I fail to understand how this could literally clip the signal, like, let's say that I'm overshooting and it goes above 0.7V (which is actually 770mV) to let's say 0.8V (800mV), how does an RLC circuit behave? How can it bring it down to 700mV? Shouldn't I have something like a "reverse amplifier" which reacts to changes in the frequency? And beside, this would be time-dependent as the signal changes with time, so it means a differential equation but I fail to see what would give me the "adjusting" of that.

In other words: I do have a very vague understanding of how it may have worked in the past, but I don't really know and I might be terribly wrong about it. Sure enough, nowadays it's literally just a thickmark, but how was it done before?

[Cary Knoop]

I would assume that quality-conscious folks in those days attenuated the signal towards the limit before doing a hard cut.

[lvqcl]

out of curiosity, how do you get your signal to stay between 0.0 and 0.7V in an analog system? From my understanding of electronics (what I studied at university), I believe that you would need some sort of high-pass and low-pass filters
...
wat

[StainlessS]

Zener diodes are sometimes used for things like dat, either voltage too high, or too low as in low battery indicator.
https://en.wikipedia.org/wiki/Zener_diode
https://www.digikey.co.uk/en/maker/blogs/zener-diode-basic-operation-and-applications
https://www.elprocus.com/zener-diode-circuit-working-applications/
https://www.google.com/search?source=hp&ei=wwgNXvmcG_GNlwTE9q2wBw&q=zener+diode&oq=zener+diode&gs_l=psy-ab.3..0l10.1064.3612..3825...0.0..1.458.1519.5j5j4-1......0....1..gws-wiz.......0i131j0i10._fg7Gb7zkVE&ved=0ahUKEwi5iuGXpuPmAhXxxoUKHUR7C3YQ4dUDCAc&uact=5
EDIT: Multiple zener diodes could be used in a circuit to provide knees at several amplitudes, enabling parts of the circuit only at certain amplitudes.

Op-Amps, were used for all manner of analog application, & were (I think) first developed (maybe by the R.A.F, Royal Air force, or more specifically for the RAF)
to calculate wind speed, air speed, ground speed, height, and when to drop your bomb. They work kinda like a network of water pipes, you open a tap, and the water flows,
nobody anywhere is calculating how much water will come out, it just happens based on pressure and how much the tap is open (and a few more things).
so op-amps are used as a sort of analog computer. The most used (at least 30 years ago, most used) was the ubiquitous 741.
Op-Amps were originally made from valves (Brit) or vaccum tubes. https://en.wikipedia.org/wiki/Vacuum_tube
[The Colossus at Bletchley Park, made famous for cracking the Enigma Code was also made from Valves, often attributed to Alan Turing, but it was Tommy Flowers
(a GPO engineer) who designed it initially on the back of a cigarette packet, in a pub].

https://www.computerhistory.org/revolution/analog-computers/3/156
https://en.wikipedia.org/wiki/Operational_amplifier
https://electronicsforu.com/resources/learn-electronics/operational-amplifier-basics
https://www.electronics-tutorials.ws/opamp/opamp_1.html
https://www.google.com/search?source=hp&ei=wwgNXvmcG_GNlwTE9q2wBw&q=op+amp&oq=op+amp&gs_l=psy-ab.3..0l10.3455.4853..5160...0.0..0.284.1047.3j2j2......0....1..gws-wiz.....0..0i131.fBCb75uaJE8&ved=0ahUKEwi5iuGXpuPmAhXxxoUKHUR7C3YQ4dUDCAc&uact=5
741 op amp:- http://www.technologystudent.com/elec1/opamp1.htm
https://www.google.com/search?ei=mhMNXsPTMp2BhbIPy-GbeA&q=741+%22op+amp%22&oq=741+%22op+amp%22&gs_l=psy-ab.3..0l10.1930.2179..2444...0.2..0.115.219.0j2......0....1..gws-wiz.......0i71j0i7i30.lYyNXfBm9mY&ved=0ahUKEwjDiJXDsOPmAhWdQEEAHcvwBg8Q4dUDCAo&uact=5

EDIT: Tommy Flowers:- https://en.wikipedia.org/wiki/Tommy_Flowers

[Groucho2004]

how do you get your signal to stay between 0.0 and 0.7V in an analog system?I just rustled something up in my Simulator.

The simplest method would be this:
https://i.postimg.cc/FRY7cmdS/schematic.png

The output signal at the point with the little square would be this (yellow, generator output is the green trace):
https://i.postimg.cc/ydppQh85/700.png

This is however not very accurate and the clipping voltage depends on current and temperature. For accurate limiting you'll need a more complicated circuit with a reference voltage source and at least one Opamp/comparator.

Edit: There's probably a chip out there that does all that with very few external components.

[Sharc]

Some examples
https://www.261.gr/limiters.html
https://en.wikipedia.org/wiki/Clipper_(electronics)

[Groucho2004]

Some examples
https://www.261.gr/limiters.html
From what I can see, none of these prevent the voltage to go below 0 V. They are all symmetrical.

[Groucho2004]

...
watI agree. :confused:

[FranceBB]

I just rustled something up in my Simulator.

The simplest method would be this:
https://i.postimg.cc/FRY7cmdS/schematic.png

This is however not very accurate and the clipping voltage depends on current and temperature. For accurate limiting you'll need a more complicated circuit with a reference voltage source and at least one Opamp/comparator.

There's probably a chip out there that does all that with very few external components.

Thank you for the example and the graph as well. Sure, there were definitely more complicated circuits with OP-Amp/Comparator, but I got the idea behind it.

Zener diodes are sometimes used for things like dat, either voltage too high, or too low as in low battery indicator.


Oh I see, so Zener diodes are essentially like normal diodes who let the current flow only in a certain direction and block the one flowing in the opposite direction according to how they are polarized. When the current trying to flow in the opposite direction of where they are polarized goes over a certain threshold (the breakdown current), it lets it go through it but unlike normal diodes, Zener diodes can fully recover while normal diodes would just be permanently damaged.


Multiple zener diodes could be used in a circuit to provide knees at several amplitudes, enabling parts of the circuit only at certain amplitudes.


Oh well, yes, it makes sense, so they can be widespread in the circuit according to the needs and if in series they can overcomes individual limitations, right?



Op-Amps, were used for all manner of analog application, & were (I think) first developed (maybe by the R.A.F, Royal Air force, or more specifically for the RAF)
to calculate wind speed, air speed, ground speed, height, and when to drop your bomb. They work kinda like a network of water pipes, you open a tap, and the water flows,
nobody anywhere is calculating how much water will come out, it just happens based on pressure and how much the tap is open (and a few more things).
so op-amps are used as a sort of analog computer. The most used (at least 30 years ago, most used) was the ubiquitous 741.
Op-Amps were originally made from valves (Brit) or vaccum tubes.

Oh I see, so they were invented for bellic purposes but have then be used for any kind of applications thanks to their usefulness.



...
wat

Well, I actually thought that an RC circuit could have been employed. My idea was to basically have a voltage source a capacitor and a resistance. As far as I know, the reactance of the capacitor is very high at low frequencies, so the capacitor acts like an open circuit and blocks any input signals at V-input 'till the cut-off frequency point is reached. Above this cut-off frequency point, the reactance of the capacitor has reduced sufficiently as to now act more like a short circuit allowing all of the input signal to pass directly to the output so that the signal is attenuated or damped at low frequencies with the output increasing 'till the frequency reaches the cut-off point. At least, I thought this was what they were doing for the loudness correction in order for it to be constantly within a certain threshold (I don't know whether it has always been -24LUFS or not), so I thought that something similar was going to be used for video signals as well, but I might have got it terribly wrong. In other words: why can't I have that sort of constant output from an inconstant input with - let's say - an RLC circuit? Shouldn't an RLC circuit be able to do the trick as well as it can act as a band-pass filter, band-stop filter, low-pass filter or high-pass filter? I mean, I feel like I'm comparing oranges with apples as I know that these kind of filters - when applied to video - were used for things like denoise (if I'm not wrong), but is the frequency domain a completely different thing compared to the whole signal in terms of peak luma and chroma? Shouldn't removing certain types of frequencies still attenuate the signal? Sorry if those questions make no sense, but as someone who has always been working with digital systems I feel really odd and difficult to wrap my head around analog systems.

[StainlessS]

I must not have read your post properley, or came back later without reading it again, but what I posted on zener diodes was not really appropriate,
zeners are really for higher voltage stuff, signals in say 0.0-1.0 volt ranges really would be using ordinary signal diodes as per Grouchy post (signal diodes tend to be little glass devices).
An arrangement of (I think) a Resistor, Capaciitor, Inductor, where values calculated to be at resonance, can be used as an Acceptor or Rejector circuit (think thats the terms),
where you can pass only a specific frequency [with a bit of tolerence, as in a radio station tuner], or reject only a single frequency. Resonance also used in eg CRT monitor,
for the huge scan coils for deflecting the electron beam. Where the current oscillates, and is given is little 'push' at exactly the right time, somehow, to keep it going with small amount of power,
somewhat similar to giving a little push to someone sitting on a swing.

I once knocked up (about 30+ years ago) a little crystal radio tuner circuit [https://en.wikipedia.org/wiki/Crystal_radio],
but I dont think I had a proper 'cats whisker' diode and think I may have used a germanium diode instead, anyway, with an antenna about 50 foot long, I picked
up some asian station, sounded like maybe Hindi, or Urdu [but only on the edge of hearing], was well impressed that we could pick up such a distant radio station.
As it turned out, put signal through an amp, and it was a London Asian Radio station. [EDIT: maybe a couple of streets away] :(

EDIT: Cats Whisker:- https://en.wikipedia.org/wiki/Crystal_detector

[FranceBB]

I must not have read your post properley, or came back later without reading it again, but what I posted on zener diodes was not really appropriate,
zeners are really for higher voltage stuff, signals in say 0.0-1.0 volt ranges really would be using ordinary signal diodes as per Grouchy post (signal diodes tend to be little glass devices).


Oh, I see, so normal diodes are used for this voltage range.



An arrangement of (I think) a Resistor, Capaciitor, Inductor, where values calculated to be at resonance, can be used as an Acceptor or Rejector circuit (think thats the terms),
where you can pass only a specific frequency [with a bit of tolerence, as in a radio station tuner], or reject only a single frequency. Resonance also used in eg CRT monitor,
for the huge scan coils for deflecting the electron beam. Where the current oscillates, and is given is little 'push' at exactly the right time, somehow, to keep it going with small amount of power,
somewhat similar to giving a little push to someone sitting on a swing.


Oh, an arrangement of a Resistor an Inductor and a Capacitor is an RLC circuit, so my vague idea was somewhat not too terribly far away from the truth.




I once knocked up (about 30+ years ago) a little crystal radio tuner circuit [https://en.wikipedia.org/wiki/Crystal_radio],
but I dont think I had a proper 'cats whisker' diode and think I may have used a germanium diode instead, anyway, with an antenna about 50 foot long, I picked
up some asian station, sounded like maybe Hindi, or Urdu [but only on the edge of hearing], was well impressed that we could pick up such a distant radio station.
As it turned out, put signal through an amp, and it was a London Asian Radio station. :(

Ahaha I can imagine the disappointment when you found out xD
Anyway thank you for the clarification and for the funny anecdote as well. :)

[StainlessS]

Oh, I see, so normal diodes are used for this voltage range.
Well, cant say that I've ever seen a zener with operating [zener] voltage in the 0.7v range [they may exist, dont know].

EDIT: Another interesting arrangement is a voltage doubler, [or a voltage multiplier ladder circuit, might not be correct terms],
where capacitors and diodes (possibly resistors cant remember) used to bump up the DC voltage.

EDIT: Voltage multiplier:- https://en.wikipedia.org/wiki/Voltage_multiplier
EDIT: Seems that above circuits require AC input, I thought that there was a DC version, maybe not.
EDIT: Still not sure, think maybe can use DC if input DC converted somehow to square wave [via maybe a 555 Timer chip], and then voltage multiplied.

EDIT: Yep, DC voltage doubler using 555 timer:- https://www.nutsvolts.com/magazine/article/dc-voltage-converter-circuits

[Groucho2004]

I once knocked up (about 30+ years ago) a little crystal radio tuner circuit [https://en.wikipedia.org/wiki/Crystal_radio],
but I dont think I had a proper 'cats whisker' diode and think I may have used a germanium diode instead, anyway, with an antenna about 50 foot long, I picked
up some asian station, sounded like maybe Hindi, or Urdu [but only on the edge of hearing], was well impressed that we could pick up such a distant radio station.
As it turned out, put signal through an amp, and it was a London Asian Radio station. :(
Still a cool project.
I built my first "radio" when I was 12 (so, 50 years ago :eek:). It consisted of a coil, a variable cap and a germanium diode and was connected to headphones.
I was blown away back then that something so simple could let me listen to the AM band (although just one station was listenable).

[Groucho2004]

Seems that above circuits require AC input, I thought that there was a DC version, maybe not.Greinacher and Villard doubler/multiplier circuits only work with AC input.

Still not sure, think maybe can use DC if input DC converted somehow to square wave [via maybe a 555 Timer chip], and then voltage multiplied.Yes, that's very roughly how modern DC-DC switch mode converters work.

[StainlessS]

When I was about 14/15, my bother bout 18 month younger, he knocked up an AM transmitter,
I stayed home with AM reciever, and he set off on long trek giving running commentary of where he was, came back about two hours later,
(having walked some good distance), and asked, well, how 'far did we get', 'top of the street' came the reply :)

EDIT: He (my lil brother) also made a Dalek voice translator, was well cool [again 555 timer, dead easy, it just inserts gaps/silence in the audio every so often].

[filler56789]

EDIT: Voltage multiplier:- https://en.wikipedia.org/wiki/Voltage_multiplier
EDIT: Seems that above circuits require AC input, I thought that there was a DC version, maybe not.
EDIT: Still not sure, think maybe can use DC if input DC converted somehow to square wave [via maybe a 555 Timer chip], and then voltage multiplied.

Certainly reinventing the wheel :o but many years ago and just for learning purposes I built a VERY-rudimentary DC voltage-multiplier, and it just worked. Its goal was not "noble" :) at all, its function was to feed a blue LED with just one 1,5-volt AA battery :D

[StainlessS]

Wonkey_Monkey voice emulator:-
https://www.nutsvolts.com/magazine/article/build_a_voice_changer
http://www.seekic.com/circuit_diagram/Basic_Circuit/VOICE_EFFECTS_SIMULATOR_CIRCUIT.html
EDIT: When using the voice emulator, you still have to inject a bit of a 'manic urgency' into your voice to get an authentic wonkey sound.

EDIT:
Like the 741 Op Amp, the 555 timer is ubiquitous, used all over the place (one billion units are manufactured every year):- https://en.wikipedia.org/wiki/555_timer_IC
http://www.555-timer-circuits.com/
https://circuitdigest.com/555-timer-circuits
https://electronicsforu.com/electronics-projects/555-timer-circuits
https://www.electronicshub.org/555-timer-circuits/

741 Op Amp:
https://www.electroschematics.com/tag/741-circuits/
https://www.electroschematics.com/tag/741-circuits/page/2/
https://www.eleccircuit.com/simple-lm741-circuit/
http://www.circuitstoday.com/op-amp-circuits
http://www.theorycircuit.com/category/electronics/ic-555-ic-741/
https://www.homemade-circuits.com/make-these-simple-ic-741-opamp-circuit/
https://bestengineeringprojects.com/operation-amplifier-741-based-projects/

EDIT:
feed a blue LED with just one 1,5-volt AA battery
They generally run quite well using the standard CMOS battery type button cell (3v I think), with/without a series resistor [but the should really have one].

EDIT: A few years back I had a keyring style mini LED torch [not much bigger than a CMOS button cell], inside was a rechargable Lithium button cell,
and it had a flip out handle which you could wind up to recharge it (from Maplins).
By the way, for you Brits out there that are missing the defunct Maplin stores, is back up and alive on-line since Jan 2019:- https://www.maplin.co.uk/

In 2000, I had a calculator with CMOS style 3v lithium battery, the battery was the same one as when purchased, and so was 13 years old [lifespan supposed to be max 10 Year].
I had used calculator about 1/2 hour earlier and it had auto shut down after 60 seconds of non use. Switched it back on and BANG!, blew off the battery compartment cover,
with real thick cloud of jet black smoke. Put in a new battery, and works still like new, still using it now, Casio fx-3800P but non of the batteries since then have lasted anywhere near 13 years.
EDIT: Battery had blown itself apart exposing an orrible black gunc inside, and gaping mouth where the two parts had blown apart.
EDIT: Web says Casio fx-3800P was released in 1989, so maybe memory in error, and was only 11 years old.

EDIT: Wind up keyring torch, was a bit like this. but single LED and metallic case.
https://www.amazon.co.uk/Lights-Wind-Up-Micro-Keyring-Keychain/dp/B005CNSHUK

[Emulgator]

While just looking up some consumer camcorder's schematics (Video8/Hi8 Sony TRV-64E) I haven't found any dedicated limiter after CCD/CMOS imager output.
These sensors limit by design anyway (charge max, so electrons per gate), so a simple maxGain while AGC seems to ensure that Y ends up in valid range.
Can not talk about earlier tubes like Vidicons.
A enlightening article here, some drawings.
http://www.vikdhillon.staff.shef.ac.uk/teaching/phy217/detectors/phy217_det_output.html