Akai M8 Schematic – just a simple tube amp

Akai M8 Schematic - head and motor switching.

The Akai M8 Schematic

Note that we have also details on this marvellous amplifier and deck on our sister website’s pages:  Analog Ian

So just what makes this tape recorder so iconic? To be honest, I don’t know. Sentimentality definitely. The fact that it has a tube amplifier in it – just possibly. The fact that it is a single stage class A EL84 is another reason. Audio gurus will rave about the EL34 though and let’s not go into the American tubes with low down grunt. The bottom line is that tube amplifiers are in demand only dampened by the exorbitant costs.  The mystery deepens when one finds that there are engineers modifying these amplifiers for the preamplifier only – i.e. the microphone amplifier and making good money out of it.  It’s no hidden secret that the output transformer is what costs the DIYer, the preamplifier here is just a voltage amplifying device, no snake oil and gecko juice. With a little bit of modification and a payback of U$1 000 one understands the demand. Throw in a VU meter and then we have a discussion piece.  I do believe the ART Pro MPA2 is also made pretty well and without modifications looks better.  Does it sound better though? Well the Akai M8 schematic beckons.

 

Akai M8 Schematic - left channel
Akai M8 Left channel with bias oscillator

[For all our readers please note that American manufacturing company Roberts also manufactured these machines under licence which was known as the 770X. There were some tiny differences, possibly improvements on the original design].

The left channel schematic is the same as the right except for the bias oscillator, V4 6AR5 pentode Hartley oscillator which feeds the erase and crossfield heads. There is nothing out of the ordinary here. We have a microphone, line and pickup (turntable) input. We have a 6X4 tube for rectification which the audio geeks either remove and replace with fast switching UF series diodes or leave as is for vintage reasons. Tubes used in rectifiers suffer from droop, silicon diodes conduct when the anode is about 0.7V positive to the cathode. Maybe there is merit here but the diehards prefer to not make the sacrifice and keep the tube in place. Different strokes for different folks.

As a standard rule all electrolytic capacitors should be changed starting with the high voltage cans across the anode (plate) supplies. With the 2 M8s I have to tinker with the anode rails are all over the place. Bear in mind emission of these tubes may not be all that great and these rails will be highly dependent on the tube quality – seen at the low end of R22 and R15 or across the cathode bias resistors.

If you are keeping the transport mechanism check the bias oscillator which runs at +/- 60kHz.  This is usually scoped at the erase head to get the waveform and using a DFM for frequency. With modern equipment the DIYer can fault trace far quicker than in the 60s but if in doubt get someone who knows his way around a scope and DFM.  The quality of your recorded signal depends on this.

If the tape transport mechanism is going to the junk yard (pity) and you are only using the preamplifier bear in mind that there is a massive slider switch which must be pushed into record mode to reproduce signal from the preamplifier.

Do not test these (or any tube) amplifier without a load. Flashover between tube electrodes or output transformer windings may occur is there is an input source, likewise spurious oscillation. I used to do this when I was a youngster to hear the tubes and output transformer “sing”. Very clever.

Clean all switch contacts and sockets – anything of this vintage will have cracks and pops when changing mode or jack plugs.

Akai M8 Schematic - head and motor switching.
Head and Motor switching

The head and motor switching is straightforward, the bigger issue being mechanical alignment of the heads when changing tracks. The motor start capacitor can be dud and needs to be replaced if the motor torque is low. C306 22uFd.  Clean all switches but do not touch head alignment – this can be very tricky to set up without a test tape.

Below we have 002a Erase Head, 002b Rec/PB Head and 002c the famous Crossfield Bias Head. Rotating 003 moves the PB and erase heads up or down. Readers have tried to adjust what they thought were misaligned heads with disastrous consequences. Always check tape path first.

M8 Head Block and switching
M8 Head Block and switching

If these recorders came out in 1963 one must marvel at the construction quality. The aluminium faceplates are top class, the print is still 100% and the control knobs solid and well, the whole darn thing is just so well put together.

Our next page on the Akai M8 schematic will cover all the images we could muster, what to do, what not to do and if all things go well, the voltages at those important points.Please be careful when testing these decks and amplifiers because of the high voltages and charged capacitors.

Note that the Akai M8 Schematic is available for download at numerous forums & associated websites. There is a whole service manual out there as well.

Akai M8 Restoration

M8 Left Channel

As promised we move on to the inner workings of this single motor transport deck and tube amplifiers.

Note that we have also details on this marvellous amplifier and deck on our sister website’s pages:  Analog Ian

Restoring an Akai M8

This tape recorder came onto market about 1965 sometime (HiFi Engine lists this as 1963). It was preceded by the M7 and then afterwards, the transistorised M9.  Both these models also proved to be very popular. Enthusiasts veer towards the tube amplified version, discarding the deck.  If the deck is still in good condition I would not advise this as much of the parts can still be purchased through eBay albeit at astronomical prices or if you are fortunate enough, repair machined locally.

I purchased two of these units over the last two months. The first unit was not in bad condition, the amplifiers still worked but the head switching mechanism (mechanical) was missing. The pinch roller shows capstan burn. Capstan/flywheel belt is loose. Counter belt also loose but has enough tension. A catch was missing from the lid as well as not having the metal rear cover.

The second unit was the conundrum. The photos on Gumtree did not do it justice. When received I found it to be in many ways better than the first deck although I was going to use this for spares to get deck number one running.  Both M8s cost about 200 U$ which I felt was pretty much realistic for what I was getting.  Paying more for these recorders may leave one frustrated if there is an issue with a tube, mechanical cam etc. Although everyone sells these as being in excellent working order guaranteed there’s going to be a hiccup – if not hidden in a sea of lies maybe through shipping damage. Tubes do not travel well. This deck also had a dodgy pinch roller (dried and cracked). The heads still looked very good though.

For those buying these recorders for the tube preamp and class A single Pentodes must note that these amplifiers run off 110V and not 220 or 240V. There is an auto transformer mounted in the case which supplies the correct voltage to these amplifiers – so you will need another 2:1 step down transformer for mono block usage. These amplifiers have their own 110V (primary) isolation transformers.

Both recorders had major pinch roller slippage (as received). Back tension also felt very high. The metal cams used in the FF/REW which everyone complains about was still intact and in great condition. Cleaning and de-greasing required. Start capacitors for motors seemed to still be good, both decks had very strong motors and FF/REW pull was like new. I don’t have test tapes – this is next on the agenda but right now we are aiming to restore only one M8 and do the other one later.

At this stage I must mention that although both these machines are over 50 years old the transport mechanisms were still in very good condition (bar the rubber).  There’s a few words of caution which must be heeded when working on any vintage circuits (actually all goods running from mains power):

  • The supply rails to tube amplifiers are lethal. We are not talking about starved anode supplies but the real M’Coy.
  • Discharge all capacitors after powering up and switching off.
  • Always remove the mains plug from the outlet.
  • When working live make sure you follow the one hand rule. (keep one hand behind your back if need be).

Electrolytic Capacitors

Electrolyte dries out of older cans and these caps need to be replaced. Enthusiasts call applying a low current source at the working voltage of the capacitor reforming. In many cases electrolytics should be replaced with new units. Sometimes we can get our hands on NOS (New Old Stock) cans and because we want to keep the equipment vintage we stick to these. It’s not always the best solution. Electrolytics can blow up entirely or blow smoke and flame through the vent, not a pleasant sight, neither smell. Electrolyte is conductive and will damage other circuitry – it’s just not worth it. (a certain Chinese brand of computer power supply was notorious for catching fire so be careful of the quality of these electrolytics – and this is not to say that all manufacturers in China make shoddy products, some are excellent).

If you can, power up through a variac or have a current limiting solution like a light bulb, possibly a 60W for high voltage and a regulated supply for low voltage reforming.

Mains Transformer

The mains transformer in the Akai M8 is not an isolation transformer but an auto variety. This is a multi-tapped transformer. A while back a reader asked how to connect this to his amplifiers because the wire colouring did not match that of the diagram. The rule of thumb here would be to have an accurate resistance meter do the work for you. The highest reading between the windings on resistance check should be the 220V leg. Midpoint would be 110V. A variac or lightbulb in series is the best way to check after you have done the resistance checks to prevent the transformer from burning out. If the voltage is too high the transformer will start sizzling – they can be resilient beasts but always be very quick on the switch. Never apply power to a transformer if you aren’t sure of the winding configuration with a load applied.

Before powering up

Always clean the insides. A spider or roach resting across the terminals of a high voltage source may catch fire putting an end to your project. Smell, look and feel.  Something that doesn’t smell right is not alright. The previous owner may have cooked the mains transformer, a capacitor may have leaked, a resistor may be burnt.

Make sure the voltage setting is correct. Especially if you live in a 220V country.

Next up, some circuitry to look at:

M8 Left Channel
Akai M8 Left channel with bias oscillator

Next Page:  The circuits

Tape Bias – Why and How

Otari MX80 Professional - sophisticated bias control

Before attempting to repair any tape deck or RTR one needs to understand one of the most critical aspects to magnetic recording – actually two:

Tape Bias and the Tape Path

Although a tape recorder is a relatively simple device there are a few criteria which has to be met to reproduce good quality recordings. The decks or reel mechanism needs to pull the tape across the recording or playback path at very high tolerance levels, with near zero speed fluctuation, the heads need to be totally demagnetised and lastly, there needs to be a bias signal applied to the recording head when recording. Oh yes, we also have pre-emphasis and de-emphasis – largely used in FM broadcasting but very important in the recording industry.

Otari MX80 Professional - sophisticated bias control
By Salvador Calyso – Own work, CC BY-SA 3.0

The electronics in an open reel tape recorder (we refer to RTR here) may look simple on paper but there’s an awful lot going on under the hood. By taking the output of an amplifier directly to the recording head and modulating the magnetic particles of a tape we notice two things on playback – it sounds bloody awful: no bass and lots of distortion. Unfortunately the transfer characteristics from head to tape is not linear. Engineers worked out a way to combat this problem – by applying DC bias to the recording head. By careful control of this direct current the working point was pushed to the center of the upper or lower parts of the transfer characteristic.  Due to the symmetry of the transfer area the recorded signal contained 2nd order distortion, poor signal to noise and strong tape noise generated by the magnetised head. Early and cheap mass produced cassette decks all used some or other form of fixed magnet erase heads seated close to the recording head. Cheap dictaphones used this format.

HF bias which is in the range of 50kHz to 150kHz is superimposed on the input signal to the recording head. The amplitude is usually in the magnitude of 5 times that of the input audio signal. This method of biasing was found to be vastly superior to DC biasing, resulting in good signal to noise ratios, superior frequency response and lower distortion. The negative aspect to this is that HF bias, if not set correctly to each tape type and capstan speed  would result in poor frequency response, low output and distortion.

Further Reading:

Hysteresis – http://hyperphysics.phy-astr.gsu.edu/hbase/solids/hyst.html

Pre-emphasis – boosting high frequency during recording

De-emphasis – boosting low frequency during playback

One further note: The cross-field or X-field – Wiki

Return:  Restoration of an Akai M8

The Revival of the Akai M8

Akai M8

The Akai M8 Crossfield Head Recorder

Dedication

Those who were around in the 1960s will remember the furor caused when this machine came to market. I dedicate this article to my late father Chris whom had one.

Akai M8
Akai M-8 – Vintage pre-1970

The Akai M8 was not the best machine out there, neither was it supposed to be at the price point it was released. It certainly wasn’t cheap but more to the point, those that had the test tape will remember that it’s fame was not around the tape quality at 15 i.p.s. but rather 1 7/8 i.p.s. and the Cross Field Head, licenced by Tandberg. Many audio enthusiasts unfairly compare this machine to professional machines at the time which came out with three motors.  The point here is that a machine with one motor is often more difficult to design compared to one with three motors. These motors can be very expensive and in order to mass produce at an affordable price point there was usually quite a bit of sophisticated engineering involved. (a case in point is that many enthusiasts in the 50s and 60s used to design and build their own mechanisms – often with three motors. Solenoid and switch control is easier to design (and build) than manufacturing cams, linkages and gears).

Revival

The M8 has made its appearance again over the last 5 years, not for it’s marvellous deck but for it’s audio amplifiers. I recently purchased one and will be restoring the deck and the audio section. A good price is usually around 100 dollars for a working unit. I paid about 65 dollars for mine. I do not know whether the amplifiers work because I should run them up through a variac first (which I don’t have) but the deck does need some maintenance. Strangely enough the pinch roller is not in bad nick although the belts will need replacing. This unit must have been kept in storage for some time gauging by a look at the casing.

Wow and flutter, hum and noise and cross talk may not have been perfect but I do recall on the new machine recordings of piano playing were usually exceptional – I recall this because I was ten at the time. When my hearing was still intact. A ten year old doesn’t know what wow and flutter may mean but will certainly complain if it was audible.  The other thing, at 15 ips these machines were very capable. Most RTR of the time were only 3 3/4 ips and looked their age. The M8 in comparison looked like a space ship. No, it’s not a Zoom H6 but in capable hands and with good quality tape some pretty damn near professional recordings could be had.

Restoration

This deck will be restored because I do believe the transport mechanism is not in bad shape (which we will come to later). Quite often on the forums we have the vintage collectors pleading for owners not to cannibalise or modify these decks for the amplifiers but personally speaking if the deck is in bad shape it may just not have any value to the owner in any event. Many of the students of tube technology have absolutely no interest in the deck – only the sound of the amplifier.  My recollection is that the amplifier quality was not bad,  a fairly flat response and the reproduction of vinyl was crisp. This was also in the 70s when transistorised amplifiers were making their mark. Not knowing much about audio quality I do recall the solid state amplifiers as being powerful and crystal clear, the tube amplifiers were just lost in all that power and “perfect” imaging of the program source.

I do not believe that tube amplifiers are better than SS. I do believe that they sound different and depending on their use tubes can be superior. I do not believe that tubes should be used for home theater and in my own experience if one needs a tube microphone preamplifier it should be all tube. Power amplifiers are cheaper in SS format and we shouldn’t be clipping them in any event unless that’s the desired sound required. Tubes are remarkably resilient and for those that now claim they have a lifespan of two years then I wonder how CRT manufacturers got away with for so many years. My personal favourite is Mullard. Tube biasing is a personal cringe I have. We have so many different types of biasing now available today one must wonder if the engineers of yesteryear were just plain stupid. No, it’s all marketing hype. I have worked on transmitters delivering thousands of Watts to the load and the only advantage we have in modern times is that the critical safety circuits have all gone the SS route. Because it’s cheaper and more compact.

The EL84 output stage of the M8 is nothing unique. The design was very popular and of course the EL84 was definitely one of our more popular tubes. In the USA we have other permutations and audio engineers had their own preferences, often very valid. Compare USA and Brit guitar amplifiers for instance. The more popular “Hi-Fi amp” was the push pull version of the EL84 amplifier. In the 70s I rarely came across any tube amplifier reproducing more than 15W and the El34 was seen as an extravagance – quasi-complimentary and complementary transistorised amplifiers were becoming popular, didn’t smell as much and were way more efficient. I mention “smell” here because anyone not familiar with tube equipment will think there’s something wrong when first powering up their vintage piece of equipment.

Something to remember:

Tube amplifiers use in most cases dangerous voltages on their anodes (or plates) and screen grids. The supply rails can be anything above 250V DC and in high powers 750V or more. This will cause serious burns and God forbid, your early demise if you are not careful. Ensure the equipment is switched off and unplugged. Discharge all smoothing capacitors either across their terminals (better) or across ground and + rail.  Do not use your multimeter probe to short out the capacitors if you value the probe. Tube circuits use high impedance and it’s not advisable to “probe” around on the control grid circuits unless your meter has a very high input impedance.

This Akai deck is often compared to decks costing very much more.  Indeed the M8 does not have a boastful spec compared to modern equipment but then again neither does Tandberg, Teac and Revox/Studer. The Akai GX series were funky looking and the quality on spec often superior to the older tube amplifiers and single motor decks. They can be obtained off eBay for fairly realistic prices. Magnetic material (composites) used on tape for recording and the biasing also plays a remarkable role in the end product.

Interesting article here:  The Roberts Akai relationship at the museum of magnetic sound recording. (we include this because there has been a large amount of nonsense written about these two brands in the forums).

Part Two – the restoration process

Tape Recorder bias

Tubes and Semiconductors

Tubes and Semiconductors – the great controversy.

So you finally decided to take the plunge and build or get yourself a tube (radio valve: UK) and discovered to your amazement all the joy that you had been missing over the last 1000 years.  You may be kidding yourself of course.

70W SE 300 Tubes
70W SE-300 Tubes – Courtesy: By Scscalal / Wiki

Radio valves have their place. As a designer and kit builder of many RF and audio amplifiers over the years thermionic emission devices were never as mysterious as semiconductors. Their inner workings were almost tangible. They were easily modified and to get brute strength of 50W or more took a different anode voltage and a more powerful output transformer. And this, oh boy, came at a price. Solid state amplifiers hold more of a mystery because they are prone to thermal issues, biasing can be critical for optimum performance and of course, they burn loudspeakers if directly coupled.

A well engineered solid state amplifier will however last much longer than a tube amplifier. Radio valves lose emission, become hissy and because of the high voltage, capacitors do some strange things like blowing up when switching on. Don’t get me wrong, thermionic tubes have their place – we all love them.  Right now however the marketers love them more than audio enthusiasts.

When I started out in electronics in the 1970s the two transistors which were cutting edge, the 2N3055 and 2N2955 could dissipate 100W into a 4 Ohm load. At one eighth the price of a 35W EL34 audio amplifier. They sounded different and although Elektor magazine took great pains to explain the differences to us learners we weren’t really interested. Youngsters like power, not quality.

Tubes used in audio amplifiers are actually remarkable in that they require very few components to get working but they do have one drawback – the high voltage anode and screen supply rails. This can be a problem if you are over enthusiastic and impatient.  The thermionic devices may be resilient but not once the anode starts glowing a bright rosy red, normally an imminent sign of ominous things to come. A 3kW transmitter I worked on many years ago would go into standby 15 seconds after switching to HT because the forced air cooling system had failed. This just shows how quickly these radio valves could overheat. Radio valves do like cooling so don’t think about enclosing them. Of course modern times enthusiasts like to display their wares out in the open so this should not be a problem. I think the mere fact that those glowing heaters look sexy gives us an added dimension to sound quality. And just possibly herein lies the problem.

Power, power and more power

MOSFET audio amplifiers also use very few components, they are after all voltage devices like tubes. A FET amplifier I built many years back  knocked the socks off any radio valve device I had either heard or built.  Although the amplifier was designed as a 100W into 8 Ohm module the device actually was way under-rated and could deliver in excess of 150W.  Another amplifier which I was very impressed with and I believe still very popular was the Maplin 150W version.  You can get these from Yebo Electronics in Cape Town – at under 50U$ this is pretty cheap.

On an international level many highly rated design engineers of audio equipment are antsy Mosfet amplifiers and from a design standpoint some of their arguments are valid and hold water. BJT topologies have also seen some changes through the years and although from an engineering standpoint much of this is now well established with most audio circuits nowadays using NPN and PNP output stages. The very simple circuits as in the NAD3020 have proven to be extremely reliable and whilst we can argue that simplicity is best this is only really true for the under 50W audio circuits, the beasts of power often having more sophisticated safety circuits than the actual voltage and current amplifiers in the audio chain. Safety circuitry used in the biasing of  tubes are often less sophisticated and of course, this bears testament to the resilience of these devices. Directly coupled transistorised amplifiers more often than not suffer catastrophic failure, sometimes even just when switching on.

BJTs and Mosfets

In the author’s opinion BJTs and Mosfet audio amplifiers do make the best audio amplifiers and with the ultra efficient class D stages driving high powers into very low impedance loads it is doubted that the versatile tube will be able to play catch up except through snake oil marketing ploys.  They cost less, are way more efficient and even in cheaper entry level equipment they sound better than a poorly designed valve amplifier.  Good valve amplifiers cost upwards of $2000.00 which puts the semiconductor version into upmarket for the same price. What is upmarket anyway?  Much of this may just be snob value. It’s a known fact that mass produced audio circuits always carry a cheap-arsed supply. Anyone with a modicum of interest in electronics will be able to change this for a few dollars. This will never be the case for tube amplifiers.

In the 60s the top bands used equipment which possibly only topped 500W at full power combined whereas with class D amplifiers it’s not unheard of to have a band with over 100kW of audio amplification equipment. But loudness does not equal quality and this is where a line needs to be drawn. Most tube enthusiasts are happy with their 10W per channel setup and possibly this is where the distinction comes in. One could not go to a head stomping party with a 6W per channel audio setup but in fact 6W per channel is more than adequate for most home systems if quality listening is the desired result. Move over for home theater systems.

Hellfire and Brimstone – move over Motorhead

Although the older venues for live music was often the local church or village hall and were the pre driver to our modern death and destruction sound systems many retired or now deceased musicians blamed headphones for causing deafness.  What about the multi kW sound systems used in motor vehicles these days?

Not too long from now we will see the result of this, just as headphones definitely cause deafness when used irresponsibly (or when drunk or smoked up). A well designed tube amplifier may not cause listening fatigue but often the critic is not reflecting the entire truth. Program source material is very important. Sound engineers have complained about CD labels applying too much compression in their recordings and this is often the case, especially in modern pop and rap culture.

Home theater systems may very well be applying all the very worst habits into the audio whilst the best into the video effects.  In many cases a simple stereo (or 2.1) setup has much better quality but in order to keep with the Jones’s we crank the power through our 7.2 DSP setup. Whilst it’s nice to have all the bells and whistles possibly this is just the problem – the musos and philes of this world have had enough and want to go back to what music is all about. Hearing the fingers on the fretboard, the cymbals and the true tenor of the voice.  Your vinyl collection may have just that and this may be just where tube amplifiers perform their magic.

 

 

 

 

DIYElectronics

admin 2014-01-10 07:04:00

 

Company/Business DIYElectronics
Website http://www.diyelectronics.co.za/
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Core Business Electronics parts, 3D and embedded systems
Address 1 Unit 6, Northmead Industrial Park
Address 2 10 Moreland Drive
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Town/City Durban
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Country South Africa
Zip/Postal Code 4051
Telephone +27 (031) 313 4701
Details/Additional Our Story

DIYElectronics, a specialist electronics business armed with three generations of unrivaled knowledge and expertise in the electronics industry, was born in 2013. We were born with the aim of providing quality hardware, electronics and support at the best possible prices to the public. Our vision is to drive innovation and change in our communities by making hardware and electronics easily accessible to hobbyists, semi-professionals and industry professionals alike.

We hope you share our vision and look forward to assisting you every step of the way!


The True advantage of Arduino

The Arduino – changing the perspective of electronic thinking!

For any fifty something whom studied electronics sometime in the 70s there’s going to be a big gray area in their knowledge of digital circuits unless they studied further in the 80s and 90s.  The analogue mindset still remains and as many technical gurus have lamented, their time came when the micro took front seat. I am just such a guy.

Arduino By <a rel="nofollow" class="external text" href="http://www.flickr.com/people/55909675@N06">Jeremy Blum</a> - <a href="//commons.wikimedia.org/wiki/Flickr" class="mw-redirect" title="Flickr">Flickr</a>: <a rel="nofollow" class="external text" href="http://flickr.com/photos/55909675@N06/6163087402">Arduino Leonardo!</a>, <a href="http://creativecommons.org/licenses/by-sa/2.0" title="Creative Commons Attribution-Share Alike 2.0">CC BY-SA 2.0</a>, <a href="https://commons.wikimedia.org/w/index.php?curid=16762163">Link</a>

The problem is that in the 70s we knew all about microcontrollers and processors but we really just did not understand it.  This was not something you just bought off the shelf like nowadays – they were expensive and what did you do with it anyway. The switch-over was very hard for the diehards brought into the world surrounded by the cheery glow of heater filaments and tagboard soldering.

 

 

For those who live for their daily electronics fix it was not that long ago where one could pop down to their local electronics store and buy a myriad and one items to build audio and R.F. amplifiers,  superhet receivers, test equipment and multivibrator cicuits. Almost overnight circuits started using surface mount components, switched mode power supplies and digital components to control every voltage, current and resistance known to man. No longer were schematics that readable – what pin did what was a mystery.

Television receivers started giving strange fault symptoms caused by irrelevant circuitry. No longer did we have a horizontal line going across the screen when the vertical amplifier failed but the screen went blank. Technical types resorted to a new set of rules to determine the problem. Many technical staff were laid off as components became more reliable. Efficiency and cooling became a big factor. Most electronics became throwaway and then there was the mass migration to computer hardware. Most electronic buffs hated computer hardware because of their inability to change. Those that embraced it made good money in the 90s and early 2000s.  As computers started becoming more reliable we see electronics graduates that program, use CAD and copycat circuits from TI. Electronics by and large remains a mystery to many and the layman is forgiven for showing no interest in this either as a hobby or professionally.  In many cases it’s no longer productive to build something which can be purchased ready built for half the price. But in came the Messiah.

As electronics has evolved from discrete components to analogue and digital ICs home prototyping became difficult.   Although this took place more than thirty years back it was only a decade ago that Massimo Banzi, David Cuartielles, Tom Igoe, Gianluca Martino, and David Mellis started work on this project – named after a bar in Ivrea, that after Arduin of Ivrea. Wikipedia. The target user was the non-engineer whom wanted to experiment with digital circuits. Through the last 10 years or so hundreds of thousands of Arduinos  (and other flavours) have been manufactured.  The design is strictly open source. Although open source the original design engineers insisted that trademark protection existed on the name and there have been numerous disputes over this.

 

 

An interesting aspect to the rise in popularity of this open source project is that of the many old school electronics hobbyists and retired professionals whom have taken up the hobby again, this time marrying analog to digital and creating circuits which just a few years was unthinkable without either breaking the bank or having a doctorate in electronic engineering.

Many of the current Arduino circuits have been designed and engineered by people in their 70s and 80s. There is again a community spirit associated to clubs and societies like the ARRL.  We now have the Raspberry Pi, the Edison, the NUC, the Compute Stick and the Beaglebone. All slightly different, some completely different but all throwing a new light on the electronics industry.

Electronics Stores – getting Durban on the map

Electronics Stores – Durban

Recently having moved from Cape Town to Durban I have been rather surprised at the lack of electronic stores.  This especially in a region where we have predominantly Indian youngsters whom gravitate towards electronics and IT in general.

electronics stores - heathkit

Heathkit HW8 Amateur Transmitter TX QRP RX CW

We have listed three new but well established stores in the Durban area, Candi and Protec (also known as DIY Electronics) and Audio Mart, suppliers of professional audio equipment.  We include AV Supply in the Cape Town, Canal Walk area. I recently purchased from all of these stores except Candi and can thoroughly recommend their good quality of service.

  • AV Supply – for all your converter and networking solutions. Great pricing on 4 – 1 HDMI switches with digital / analogue out.
  • Protec / DIY Electronics – Arduino and 3D printing, electronic components. Also affiliate to PQSound.
  • Audio Mart – professional audio gear at great prices.

Johannesburg and Cape Town

Johannesburg and Cape Town are two of the larger cities in South Africa and although it’s not a surprise to find Johannesburg having the bulk of the DIY electronic stores, Cape Town has been no slouch. Always check as to physical address – I do not like to shop from an IP address alone. There needs to be a walk in facility or at least a land line telephone number. Cell phone numbers associated with satellite companies leave me rather anxious.

Some previously listed stores, Communica, Yebo and Mantech are all very well established and found in both Johannesburg and Cape Town.  I would not be surprised to find a business model similar to Yebo doing very well in Durban.

Many electronics stores and smaller hobbyist shops are founded out of passion and although the intent is to make a profit they often provide a service which the public doesn’t fully understand. Going online does give a larger footprint and in a country like South Africa where mathematics and science takes a backseat we should embrace these stores. Because after all, electronics is all around mathematics and science.

Readers are encouraged to comment and give us a list of their favourite electronics stores in South Africa. As they provide a service so should we drive business to your favourites of the bunch. As South Africa needs more entrepreneurs in the electronics field, these stores may hold the answer.

Read:  Consumer Reports for best electronics stores.

 

The Danger of Autonomous Cars

Autonomous Cars – embracing the inevitable

Let’s face it, we all dream about it but know it can’t happen – a self driving car! Yet, this is on the cards. Mercedes, Kia, Toyota, Ford, Audio, BMW, Volvo, you name it, they all have a car which can drive autonomously. “Not on our roads though” say the authorities.

It wasn’t that long ago that our great-grandfather was told never to drive faster than 100 m.p.h. because the blood would leave his body. In those days 40 m.p.h. was classified as breathtaking. Now we have Andy Green in his ThrustSSC breaking the sound barrier. He might have been white as a sheet when he cruised to a halt but his blood flow was normal and his body parts were still intact. Of course we digress but isn’t this what science is about – proving it wrong!

Autonomous or rather automated vehicles which require external and environmental assistance through usually magnetic strips and road navigation transponders is not something new, in fact was on the drawing board in the early 1980s. However, with smaller, faster and more reliable computers, highly sophisticated sensor systems and state of the art electro-mechanical output devices we have come to a cross-roads – cars which are driven near autonomously and when to mass manufacture? Only time can tell although major manufacturers already talk about the latter part of this decade, some as near as 2017. Unfortunately all of this will come to a nought, we believe, because of the road traffic authorities. Actually more so, the fraternity of global electronic engineers all shake their heads in disapproval. The thing is, we can fly an aircraft totally unmanned only because there are critical backup and redundant systems in place, not many obstacles to bump into and even less corners to negotiate. Motor cars are on land, they rely on absolutely accurate input data at all times and last but not least, the critical thinking aspect to this entire exercise, no errors or hardware failure. And this is where we have a problem. Imagine driving merrily along at 70 m.p.h when a sensor fails, the radar decides to stop working or the computer decides to reboot (unlikely but who knows).  The global think tank may be right.

Control freaks will never let go of the steering wheel. They are also some of the world’s worst drivers. Every year hundreds of thousands of people, pedestrians, drivers, occupants, (animals too) are killed on our roads. Traffic authorities have all but given up. What percentage is caused by driver failure?

Partially automated vehicles already protect the occupants of a vehicle when crossing lanes inadvertently, applying brakes when needed, stabilising a vehicle which may be on the verge of rollover and preventing unnecessary skidding.  So why can’t they be made to drive the occupants to a destination without driver intervention?  Because it cannot. It’s called the unknowns. What happens if?

Interesting to note that driverless cars use the cloud but flight MH370 didn’t. Losing communication to the driverless car may make it pull over to the side of the road and stop. What happens if the side of the road happens to be a cliff, dropping 300m to the sea or a rocky outcrop? No thanks. Although the same electronic engineers designing the workings of your trusty four wheeled carriage will swear to the reliability, they are the first to banish the notion of driverless cars. Quite rightly.

Autonomous Cars – if the roads allow it

Just as one was told that you may drive safely but not necessarily the “other” driver so it just so happens to be the reason why driverless cars may be on the drawing board and even successfully tested, it’s the “other” car that remains the problem. Just because the roads in Sweden and Germany are better than most third world countries makes the very idea of driving the Yungas without a steering wheel a frightening thought.

But no, as a matter of fact we do believe that driverless cars are here to stay. We do believe that if the road is not safe the driverless car will stop and tell you that you are on your own. If a machine which has proven to have more powerful thought processes than the driver’s brain pulls over because it is not safe then believe me, you are not safe.

Many years ago most drivers took to the roads because of the pleasure of it. Nowadays it’s a case of whether you will make it back alive. We cannot blame the authorities neither can we blame the electronic, automotive and mechanical engineers. Unfortunately scientists and engineers alike know that we can no longer rely on the human element, there has to come a stage where there is forced intervention. We can only blame ourselves. The authorities and engineers shouldn’t put a ban on it but embrace it.

 

Audio Amplifiers – Passed the Edge

On the Edge – amplifier design

Isn’t it frustrating to shop for the ultimate sound system on a limited budget. You see one, you hear one and that one on the next rung up always sounds that little bit better.  Fortunately we have good news. It’s all in the mind.

Anyone being an avid reader of any electronics and audio magazine that does comparison tests will often get overwhelmed by the amount of products on sale, let alone by the costs of these high end pieces of equipment. It’s almost like playing chess against a grand master – no matter the move, there is always one better. So it is with audio gear. The problem is, we often fall foul of the marketing machine and sales personnel pressure. Don’t. Whatever you do, never buy a sound system based on whatever someone else tells you.  What we do know is that power output is no longer directly linked to pricing, semiconductors are cheap.  Even Chinese manufactured toroidals are no longer the price it was ten years back. But what should one know?

Inputs and more inputs, all with the same output

Most audio amplifiers brought out over the last few years have surprisingly good build and sonic quality. For movies one loves the idea of being able to set up the sound stage through a microphone and an automatic process. However, audio installers complain about most users not setting up their systems properly even with electronic assistance Read up on this in the manual. If you are only buying the integrated amplifier like most of us do then ensure you have sufficient inputs. This seems to be the most important thing in the designs found currently on the market – millions of inputs. On a practical level these inputs should be HDMI and one or two for legacy use.

Marketing trends push for big power and in our experience this is true, go rather for overkill.  Pick up the amplifier, weigh it if necessary. Most of the weight is transformer and cooling based. A Class D amplifier is light – that’s a design advantage. Class AB will be heavy – that is also a design advantage. If it’s Class AB, delivers upwards of 60W x 5 or 7 channels it will be heavy. How heavy is heavy? We have our own estimations but do look at manufacturers such as Marantz and NAD. These guys don’t skimp on components least of all quality of the mains transformer. The importance of this is multi-fold. Read up on how tests are done and in this case, specifically output power measurement. Transformer secondary (output) voltages sag when under load. Power supply regulation is critical and to compete with the best there should be no compromise. This is where most budget systems cut costs.

Purchasing an amplifier which lacks oomph will cost more in the long run – you will be disappointed. If it’s a headphone amplifier you want then one needn’t be looking at killing your ears in one sitting. And no, you cannot put audio amplifiers in series to get more power. What you can do is purchase separate pre-amplifiers/processors and power amplifiers. It will work out cheaper in the long run if you need to upgrade for higher power.  This a more expensive solution but possibly a better long term plan. A well looked after, carefully selected preamplifier/processor may even prove to be a lifetime “investment”.

Six channels or more, two is best

Two, three, four, five, six, seven or ten channels? Here the choice is yours. There are many audiophiles passionate about their movies but only use two channels or stereo. The home movie expert may prefer the most amount of channels he can afford. 5.1 is still rated about the most common.  Quantity over quality? A good quality stereo setup beats a multi-channel movie theater setup for music anytime. (of course this is bias).

Tubes versus semiconductor?  Dollar for dollar there is absolutely no equaling the transistor or semiconductor. (I will add this though – my own opinion is that early transistorised amplifiers lacked the musicality of tube amplifiers. If transistor amplifiers were first on the market maybe I would have rewritten this and in all likelihood battled to justify the rationale. The fact remains though, musicians on a whole tend to prefer tube sound. So there!).

Why on the edge?  The objective of any audio amplifier is to faithfully reproduce the input signal as an exact image except for amplitude at its output. Through the years scientists and engineers have near perfected this art. A bench tested audio amplifier which reproduces with clinical precision the input program material to its output will sound good through a quality loudspeaker system. Most amplifiers today, except for cost cutting in the power supply will do exactly that. So where to now?

Digital is Doomed

Although we are living in the digital age man and machine will never be the same. Our logic is often irrational and therefore biased. We cannot live in peace with each other because of this exact reason.  With audio equipment we take a very sophisticated (in scientific terms) analogue signal, convert to binary, we then read the binary and convert to analogue. We them chop the analogue at a high frequency, modulate with a sawtooth wave, switch at a high voltage and finally filter out the high frequency component. We then feed the analogous high amplitude signal to a transducer which is an analogous device. Then the marketers come along and tell us vinyl is back!

We have fine tuned the Class D amplifier for home use but yet it’s true advantage is when used in cellular technology. We have lowered the cost of high powered audio amplifiers through this technology but yet loudspeakers have always been the obvious weakness, both in cost and efficiency.

It is time for manufacturers to look at cheaper and more efficient methods to reproduce this amplified signal.  The fixed magnet, moving coil paper or synthetic cone speaker *aka dynamic driver) should be cast to the ash heap, audio amplifiers have been re-looked at so many times that it’s run out of steam.

How it works… further reading:  Loudspeaker types