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.
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?
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.
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.
"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 ...
