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

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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.

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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.

 

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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.

 

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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.