Is anyone interested with the Z80?

Did you know that the Z80 has different memory access timings for instruction fetches and standard memory accesses?

I worked at Mostek maintaining the Fairchild Sentry testers used to test the Z80s when they first began to manufacturer them. The second computer I every

built (parts, pcb, solder) was the SDB-80 which was the Mostek Software Development Board for the Z80 with 16K bytes (8 - MK4116 16K bit) dynamic RAMs

which Mostek also made. The first wire wrap board I ever made was a 48K byte dynamic RAM board also using MK4116s that worked with the SDB-80. I can

tell you there were a bunch of happy technicians when we were told that Mostek would be second sourcing the Z-80 and even happier when we were told we

could buy SDB-80 kits and build them ourselves! Those were really fun days. I still have a Zilog Z80 in a ceramic package that says it was manufactured in

Dallas even though Mostek was actually in Carrollton a suburb in Dallas County just north of north-west Dallas.

Thank you, COMPACT and Andrew Johnson !

Think I'm just privileged, having lived (better still: mostly had my youth in) the era of:

- the birth of the micropocessor

- the development from calculators into hand-held computers

- the 'transistorizing' of electronics

- the chip revolution leading to "zero cost electronics" (Scientific American, 1975), and ultimately to hand-held communication devices

- the development of LCD and similar display technology

and so on ...

It all began when awed by a self-built X-tal receiver, while visiting a cousin - almost mystically fascinating !

Not only did I blend together one myself shortly after, but also began reading books on radio history from the school library (which didn't have

anything DIY). And I got pretty jealous of inquisitive people like myself, who had been lucky enough to live during the age of say Heinrich Hertz,

Marconi, and the like (unfortunately I discovered Tesla much later). So obviously, some people just cannot be pleased enough ... !

Cheers

Ray

P.S.: the excitement of listening to your self-built X-tal receiver is similar to watching your first program do what you envisioned;

        in both cases, "you'll always remember your first time" ...

Come to think of it: I've also been privileged to live in the era of:

- the dawn of music registration on vinyl

- the transition (soon after) from mono to stereo

- transistors displacing vacuum tubes (while becoming a swiftly expanding family)

- the invasion of digital technology in the art of music registration and reproduction, culminating in the CD, but :

x NO, don't feel privileged, having to witness music quality being slaughtered by ease-of-use driven technology,

   like MP3, streaming, and what have you ? (Microsoft 'eliminated' prof. Johnsons's HDCD, the best digital format ever).

So, I feel privileged, being able to enjoy in the same lifetime:

- the unsurpassed vibrancy of shellac disc mechanical replay with horn reproduction (thank you Canned Heat for pointing that out, back stage !)

- the reappreciation of mono recordings and revival of mono music reproduction (even newly developed vinyl cartridges)

- the vacuum tube revival (thanks mainly to Russia, China, and Eastern Europe - with NOS running out)

- the reappreciation of pure Red Book, but moreover of analog audio in all its forms.

How come ?

Organizers gradually took over the pocket computer market, but mid nineties my son helped me realize, there was an end to this.

His expertise (my former hobby) was (still is) high quality audio. So we decided to start our own import company - later developping

proprietary products.

What's the point in all of this ?

In one word: digital ! While digital control of equipment functions is only remotely (pun intended) interesting, we focussed on DSP,

digital signal processing. At first I was somewhat puzzled by the notion of losses in file conversion and transition - never encountered

such problems while processing data files on a computer !  Admittedly, it took me some time to figure out the cause.

Anyway, let me end this 'chapter' with a cliff-hanging anecdote:

After we were asked frequently by the public, why we did not demonstrate with digital equipment at an audio show, we got tired of lengthy

answers, followed by ditto discussions. So we devised a 'cunning plan': a large poster of the Mona Lisa was fed through a shredder, which

we stopped just before the end was reached (if this seems familiar to you, having followed the news lately: we were fisrt !). Next we 'repaired'

the poster with transparent 'magic tape'; then with a felt pen we wrote under the picture: "NICE, ISN'T IT: DIGITAL ?". Problem solved ...

Cheers

Ray

Reading this reminds me of how old I am. Even dirt seems young these days.

Clem

Hi Clem (if that's alright with you ?),

Don't despair, I've become a 'grumpy old man' myself lately sometimes -:).

(My wife was born in the middle of WW II, glad I missed that period - if only just).

But writing about my experiences gives me the idea that it isn't all over, and of no use to anybody any more.

If I can fill in some white spots in other members' memories and/or knowledge, like they have done in mine,

that would make it worth my while (like they said in the old days). Just keeping readers amused is OK too, btw.

I had to stop my electronics experiments a few years ago because of deteriorating eyesight. SPICE for me is no alternative, as I believe it can not

reliably simulate a real novelty circuit. After all it stands to reason that you can't get out what has not been put in, can you ?

So the only thing left for me to do is devising new circuits ... mentally, and hoping I can get someone interested enough to put my ideas to the test.

Also rewarding is acting as a kind of sparring partner for my son, when he is figuring out, how to improve on existing vinyl cartridge cantilever

design e.g..

Hope I haven't annoyed you.

Cheers

Ray

As for degrading eyesight I'm reliant upon my bench binocular microscope just to solder 1960's tech like DIP ICs and through hole.

My spare parts are so old that I have to remove the unwanted oxide layer from them (just like my brain).

I don't like too much SPICE in my food.

Analog turntables - Don't get me started!  The analog signal is distorted prior to recording so it can be reverse distorted for playback to support the RIAA equalisation.

And also seem to also ignore other distortion influences such as wow and flutter, stylus/cartridge momentum and contact friction variations

Like oscilloscopes, sound should be sampled at about 5x or more than the desired maximum bandwidth.

And how does one get a speaker to playback perfect square waves?

All of this gives me the "jitters!"

Hi Andrew,

Reading your profile, several thoughts spring to mind:

- seems like a wonderfulfilling (language economy) job/passtime - educating people, in order to enrich nowdays' ict with an intriguing past

- visiting my wife's family in Canada years ago, we went to the Toronto Science Museum - I had the time of my life !

- your level denominator goes, well ... lovely with your 'job' -:)  Women's role in technology is grossly underrated, and almost neglected

  (ENIAC, NASA, etc).

Cheers

Ray

To the list of analog turntables (and vinyl records) problems vs CD you can add  poor channel separation, lower signal to noise, far less dynamic range, low frequency limits,

groove wear, warping, inherent vulnerability to acoustic feedback, tracking problems, and less resistant to injury and corruption.

As for reproducing square waves, as far as I know, no instrument other than electronic synthesizers produce anything that approaches the fast rise/fall times of a square wave.

That said, there are several groups that I like that use(d) synthesizers.

Hi COMPACT,

My son has a binocular microscope for his cartridge repairs/mods - tried it, didn't work for me alas (btw: there's a not-so-steady-anymore hand

to take into account as well). Thanks anyway for the uplifting tip.

I've read enough disturbing reports by pro circuit designers to stay away from SPICE and the like. My WYSIWYG-like statement lacked nuance,

that's true, but transitional phenomena e.g. are difficult to be measured correctly, and consequently just as difficult to predict/calculate/simulate.

And my experiments were on so called linear PSUs; btw: there's practically nothing 'linear' really in the operation of these classic power supplies.

As a result they are noisy, and hard to tame. Your average designer, however thinks, an overkill of microFarads + 'tripods' will easily cure this ...

Audiots frequently spend big bucks on external power supply 'upgrades' - on top of the just mentioned cure, these contain big transformers

with rediculous VA specs. While this might make sense for a power amp with underrated internal PSU, such upgrade PSUs for phono-amps are

outrageous ! We have performed in-depth listening tests here, and concluded that the advertised pros - improved bass response and dynamics -

didn't make up for the apparent loss of overall-quality: the music seemed robbed of its liveliness. Some team members stated: "As if an elephant

is sitting on the sound".

If you would want to consider RCA's Dynagroove technology* as a kind of early dithering, I would be with you, but calling RIAA equalisation

distorting the signal ... Changing the tonal balance in no way fits the definition of distortion. It is in fact a perfectly rational adaptation to the medium.

Its primary objective was optimizing playing time - so maybe one could call it a form of (physical) compression. The second aim, however is to

diminish and limit distortion - i.e. tracking distortion ! The famous ADC XLM cartridge from the sixties arguably was one of the most agile ever,

but it was not free from tracking distortion, of course. Here the question arises, how one is to discern between distortion caused by the vinyl

registration process, and distortion from the cartridge tracking the groove with its needle.

My son has done quite a bit of research in improving suspension in phono cartridges; he was surprised to find, how much there still is to be

gained in terms of tracking distortion this way - the experiments were done with state-of-the-art commercial carts.

(to be continued)

Ray

* dynamics at the end of the Pink Panther theme by Mancini e.g. really are impressive, but ... sure, it's just an effect - no HiFi.

Rather than perfect technical reproduction, modern audiophiles try to recreate a sense of being there at the original recording. To achieve this serious audiophiles place their speakers about 6-12 feet from walls and bevel or curve all orthogonal corners of the listening room and use sound absorbent materials as necessary. Even the stylus adds its own colour and audiohphiles usually have a collection of different ones to use for different recordings.

My Uncle is a really serious audiophile. He sends his used stylii cartidges to Switzerland to have them refurbished at $1,000 each, his pair of speakers cost about $500,000 and I'd hate to think how much he paid for is exotic Tube/Valve amp.

For those who aren't so as rich,  a pair of ELAC Navis ARB-51 Active Speakers designed by Andrew Jones is getting great reviews.  These $1,000 speakers are devoid of any Digital Signal Processing.

For me, I'm just happy to listen to my 1984 Sony D-50 Discman with headphones which still works today.

Hi COMPACT,

"Like oscilloscopes, sound should be sampled at about 5x or more than the desired maximum bandwidth", COMPACT wrote.

This ex-Tektronix test & calibration engineer couldn't agree more, but ... at the time of development, this was technically way out of reach for the

people working on e.g. the quadrophonic sound registration on vinyl, as well as those working on the Red Book standard.

Nowdays, cartridges with a frequency range of up to 50 kHz are available, serving people who have been convinced that they need super-tweeters

at the other end of their music reproduction chains ...

"And how does one get a speaker to playback perfect square waves?", COMPACT asked.

Peter Walker of QUAD Mfg fame came pretty close; in fact it was his ultimate way of testing (300 Hz) his almost single-handedly developped ESL

(Electrostatic LoudSpeaker; (fifties). Ever auditioned one ? You will never forget the listening experience ! We've also enjoyed Martin Logan's CLS

very much; of the electrodynamic units, Manger and Dynaudio probably have the best pulse responses. With ED speakers one tries to avoid square

waves because reproducing the top part would mean sending DC trough the poor unit(s), which very few would survive eventually. Furthermore,

audio is about reproducing natural sounds, not technical noises*; and music is the most complicated of sounds. Faithfully reproducing it means

getting the rise and fall right - these coïncide with the attaque of the musical instrument played, and the decay of the resulting sound. The most

demanding instrument attaque-wise, in terms of amplifier slew rate, turned out to be the harpsichord (& family), which is easy to understand once

you look at its playing mechanism. The same cousin who introduced me to electronics via his self-built Xtal receiver, made replicas of famous old

European harpsichords, together with his father (my godfather). I quickly grew to like the sound, that many audiophiles loathe. A possible cure might

be listening to the first chords of Bach's Italian Concerto in a harpsichord rendition (as it was meant to be) - it sings so much more that way than on

the piano ! (Try Glenn Gould's fifties recording vs. his almost anemiatic eighties registration by Sony).

(to be continued)

Ray

* I know, that same Peter Walker in an interview made a statement in relation to his ESLs that seems to argue otherwise ...

Hi COMPACT,

"Like oscilloscopes, sound should be sampled at about 5x or more than the desired maximum bandwidth", COMPACT wrote.

This ex-Tektronix test & calibration engineer couldn't agree more, but ... at the time of development, this was technically way out of reach for the

people working on e.g. the quadrophonic sound registration on vinyl, as well as those working on the Red Book standard.

Nowdays, cartridges with a frequency range of up to 50 kHz are available, serving people who have been convinced that they need super-tweeters

at the other end of their music reproduction chains ...

"And how does one get a speaker to playback perfect square waves?", COMPACT asked.

Peter Walker of QUAD Mfg fame came pretty close; in fact it was his ultimate way of testing (300 Hz) his almost single-handedly developped ESL

(Electrostatic LoudSpeaker; (fifties). Ever auditioned one ? You will never forget the listening experience ! We've also enjoyed Martin Logan's CLS

very much; of the electrodynamic units, Manger and Dynaudio probably have the best pulse responses. With ED speakers one tries to avoid square

waves because reproducing the top part would mean sending DC trough the poor unit(s), which very few would survive eventually. Furthermore,

audio is about reproducing natural sounds, not technical noises*; and music is the most complicated of sounds. Faithfully reproducing it means

getting the rise and fall right - these coïncide with the attaque of the musical instrument played, and the decay of the resulting sound. The most

demanding instrument attaque-wise, in terms of amplifier slew rate, turned out to be the harpsichord (& family), which is easy to understand once

you look at its playing mechanism. The same cousin who introduced me to electronics via his self-built Xtal receiver, made replicas of famous old

European harpsichords, together with his father (my godfather). I quickly grew to like the sound, that many audiophiles loathe. A possible cure might

be listening to the first chords of Bach's Italian Concerto in a harpsichord rendition (as it was meant to be) - it sings so much more that way than on

the piano ! (Try Glenn Gould's fifties recording vs. his almost anemiatic eighties registration by Sony).

(to be continued)

Ray

* I know, that same Peter Walker in an interview made a statement in relation to his ESLs that seems to argue otherwise ...

Hi COMPACT and Garry,

(Better late than never:) I'm sorry, if I have provoked replies that to me read like a kind of vinyl bashing ... won't go into that, because the

arguments are mostly too well-known to make a discussion in this day and age still worthwhile. I've been used to these arguments in audio

circles, but didn't expect them here, to be honest. And the worn-out objective vs. subjective discussion - culminating in head vs. heart ratings -

better be left alone, too, wouldn't you agree ?

Never mind; I was in fact just closing off some musings with an anecdote, but perhaps it would have been wise to present it with a bit more

context. Here that is yet.

The show was during the vinyl revival in the nineties, and we only had a speaker brand plus hi-grade vinyl at the time - all the rest was borrowed

from friendly colleague-importers. A high-grade CD-player was part of the demo set, but only used on request from our visitors. Btw, we didn't

do analog vs. digital comparisons.

The purpose of the shredded Mona Lisa poster was to show in a (simplified) pictorial manner, what digitizing is in essence. Apart from a good deal

of laughter, we als got recognition by colleagues referring visitors to our demo room. Only Philips was 'not amused' (and that was long before we

demoed the CD Clarifier the next year, thereby proving their slogan - "Perfect for Ever" - wrong; but that's an other story).

I also like to make an other point: as an importer of high-grade audio, I had to audition/listen to numerous gear/sets. With a few exceptions

the equipment was not 'my cup of tea', and I was pretty sure that I wouldn't be able to enjoy my music through it. Most of the time I tried to

imagine however, what enthralled the owner/seller. And by doing so, I often succeeded in 'hearing his point' ...

To prevent allegations that I'm living in the past, and that vinyl is obsolete, let me turn my eyes to the future* for a change: after virgin, HQ, and

Quiet Vinyl, vinyl lovers recently were treated to (the promise of) the Holy Vinyl Grail: HD-Vinyl. Multi millions have been invested in this project

that stems from the country where mr. Adolf H. was born, and that is frequently mixed up with your beloved 'Down Under', COMPACT. At the

risk of being judged too critical this time (and even because the concept is basically on digital), I think it's a mad men's scheme, and am certainly

not alone in that: https://www.analogplanet.com/content/hd-vinyl-exciting-concept-its-last-years-news .

Cheers

Ray

* the commercial product has been announced several times - yet have seen nothing so far ...

Take a look at this - I think it is impressive!

http://www.fagginfoundation.org/biography/

Sorry but those are easily provable deficiencies in vinyl recordings/turntables.

COMPACTS claim that audiophiles want the sense of being there at the original recording is a classic example of subjective.

How do they have the slightest idea of what the acoustics were at the original recording without actually being there? How

do you objectively reproduce something you've never heard?

The whole audiophile experience is subjective.

Our universe conspires to prevent perfect recording and playback and audiophiles are passionate of what constitutes a great sound.

I wish that some Astronauts would set up some speakers and microphones outside the International Space Station to see how well they work.

Here is one audiophile's take on things. Have a listen for 90 seconds.

The Australian company RODE is successful making microphones and associated paraphernalia. The recorded sound may not be technically perfect but it sure does sound crisp and clear.

Their latest offering is a wireless Lavalier microphone transmitter receiver combination for digital cameras. ("Go") which is very convenient.

"The whole audiophile experience is subjective."

That was exactly my point, aimed directly at Ray.  The problem with subjective interpretation of audio reproduction is

that it is always "in the ear of the beholder".

"and audiophiles are passionate of what constitutes a great sound"

They just can't explain in objective terms what constitutes that great sound. And there is clearly such a thing as being

too passionate. That is one reason why the ear of the beholder is not a good thing.

"The recorded sound may not be technically perfect but it sure does sound crisp and clear."

There are a few acoustic instruments that produce sound that is not crisp and clear, a muted horn is a good

example. Various kinds of distortion are widely used with electronic instruments and some of these also produce

sound that is not crisp and clear. Does a crisp and clear reproduction of these instruments constitute great sound?

It does not represent a faithful reproduction of the instrument's sound in the acoustic environment where it was

made (being there as you previously put it). And to me that faithful reproduction is what constitutes a "great sound".

It's just not possible to do, at least for now, no matter how much technology, subjective audiophile BS, or money

thrown at it.

The questions you've raised are certainly worthwhile, albeit far from new ...

First of all, there is broad consensus, that audio is the art of reproducing sounds, recorded in one acoustic environment, in an other - usually totally

different. As a (recent) result, room acoustics have become a hot item; with DSP prices coming down, ever more components in the reproduction

chain - both amps and active speakers e.g. - are equipped with some form of electronic adaptation. While this may seem progress, oldtimer audio

buffs (like us ?) probably wonder, what has become of good (?) old tone controls, or - a bit more sophisticated - equalizers ? The 'tilt control' on the

QUAD 34 pre-amp, beloved in the eighties (and not much unlike RIAA equalization, COMPACT), springs to mind. DSP-based room-correction

circuitry is said to spare you fysical adjustments, like COMPACT described; I don't think I'm convinced.

As to equalizers, in the nineties we were allowed one afternoon to 'play' with the famous Cello Audio Palette, originally intended for studio-use, and

the wet dream of many an audiophile. Although we really had a great time at the circular controls of that gem, we had second thoughts afterwards:

had we not in fact been indulging ourselves in 'bettering' recordings of top-notch mastering engineers ? Who did we think we were ?! Our host had

'encoded' the favourite tracks on his discs with the letters of the controls and the corresponding numbers of the scale settings ... (audiot).

Live vs. recorded comparisons were popular in both the UK and USA during the fifties, aiming at answering the question: how close have we come

with HiFi ? It was reported frequently that even highly experienced audiences (regular concert visitors) sometimes had trouble discerning one from

the other. But this only works in the same room, with the speakers exactly positioned, where the instruments/vocalists were before (and everything

else also kept constant, preferably). So there's not much hope of ever bridging the gap from concert hall/studio to listening room ... And "Bringing

the concert hall to your living room" a bluddy (marketing) lie !

The 'being there (present)' experience /illusion is in fact the last frontier in high-end audio. When auditioning a Cello set with Martin Logan CLS,

a much more experienced audiophile commented: "Ah, this is precisely the sort of set that enables you to hear a fly fart on the rear wall of the

recording studio !". That made us think: are we chasing ultra resolution in sound reproduction, or is our real aim musical satisfaction ? It took some

time to cure ourselves of 'audiophilia nervosa', but we have since been enjoying our music via much more down-to-earth equipment.

Stereo is btw. as much an illusion (and this goes as well for 'glued-together-again' digital signal samples, in an attempt to mimic analog sound).

I believe, though, ultimately most people do not care that they are listening to illusions, nor how far off they are from reality - they've simply come

to like them !

I hope you see my point: this kind of discussions is in fact a thing of the past, and when repeated all the same, bound to be ... pointless.

COMPACT  wrote:

 

Take a look at this - I think it is impressive!

 

http://www.fagginfoundation.org/biography/

Sorry for this late response, COMPACT (seen too many doctors lately) !

Thanks for sharing this fascinating, illustrated time-line through the life and works of one of the key figures in (micro)computer history.

I knew most of the facts and figures, but getting everything presented from the horse's mouth really is something else.

From the many things that caught my eye, let me comment on a few:

- (1965) "The Olivetti Programma 101 ... contained a small computer made of discrete components ... ". However much my admiration for the

   development of the IC, I've never been able to commit myself to applying them in my designs, still (since the sixties) preferring hand-picked

   discrete components over 'black boxes'. That way I feel full freedom and more in control of things, although I'm aware of the drawbacks; so

   call me oldfashioned ...

- (1970) "The layout of the Z80-CPU. Handdrawn by Federico (by two thirds) ... ". "Those were the days !" - no CAD-CAM. Has anybody ever

  assessed the error rate in both cases ?

Having written this, I wonder: wouldn't we have been better off here, sticking to your original question and everything directly related, than

wandering off(-topic) to audio nirvana ... ?

Cheers

Ray

(addendum to audio discussion)

It would seem that I was not right after all in stating that various audio debates have become a thing of the past.

(while visiting him, my son pointed this out to me:)

- (as to the objectivists vs. subjectivists debate) a class-D* power amp has been presented at recent Munich High-End Show**,

   which is said to be "100% mathematically correct". The following statement, however, is the relevant one in our issue:

  "We build what we simulate and simulate what we build. ... We believe that all matters for the sound quality can be measured

   although we often have to develop new measurement methods that are indicative of the subjective sound quality. We direct

   all R&D efforts on such measurable metrics. If this does not agree with the listening results we improve our objective metrics."

   For all interested:  https://www.audioxpress.com/news/purifi-audio-promises-to-reduce-distortion-in-speakers-and-amplifiers  .

   For all not versed in audio who-is-who:  the people behind Purifi are leading developpers in their field.

- (as to the being there - at recording - experience) Dr. Edgar Choueiri, professor of applied physics at Princeton University,

   has developped a 3D audio processor, enabling the listener to enjoy his records in 3D via a normal stereo set: BACCH SP.

   All we can do is hope and pray that MS will leave this alone, to prevent it from suffering the same fate as HDCD ...

Ray

*for all not versed in audio: the D does not stand for digital; class D means switching amps.

**once again: HD Vinyl nowhere to be seen (heard), no news, no nothing - a hoax ... ?