That awful JRC4558 audio IC

That nasty 4558 beater the Texas Instruments INA217

The JRC4558 – tried and trusted workhorse

So there you have it, out of the horses mouth, the op amp we covered in the Dixon PM121USB is awful.  Reading about this chip on nearly all the forums I am surprised that we still use it. It’s cheap, nasty, has piss-poor bandwidth and lacks “quality” sound.

 

That nasty 4558 beater the Texas Instruments INA217
That nasty 4558 beater the Texas Instruments INA217 instrumentation amp.

 

The first time I came across this chip was when the Titanic was still afloat, perhaps in a preamplifier but more like a graphics equaliser.  The equaliser is about late 70s vintage early 80s. It was a repair job and once completed sounded damned good. Ahem, does that mean that the modern equalisers sound better? Does this chip do any circuit justice?

Let’s backtrack a bit and look at some of the older, so called mediocre ICs of our time. The 741 series was a masterpiece. We built all sorts of circuits with these chips and even for “mediocre” use, the disco mixers used them in droves in preamplification. Now in the 70s maybe this was like magic, this little chip which sounded pretty good. I recall the JRC (Japanese Radio Company) getting into the act – bringing out a dual op-amp, the JRC4558.  Now I did a lot of work on JRC equipment in the 70s and 80s, all marine receivers and transmitters and let me tell you, they were anything but junk. In fact when I hear anyone on the forums talking about junk gear, I, like many, would want to get into the persons head and discover for ourselves where they get their information from.

No, the 4558 is not junk, at the time it was a very able little dual op-amp and was well justified to be used in almost all audio (and other) gear. The TDA741 still enjoys use today and no, it is neither junk nor ill suited for any application.  The bigger issue is when it starts being put into high quality audio gear – the 4558 has a bandwidth of about 3MHz under optimum configuration, the 5534 10MHz, slew rate 1V/uS compared to 13V/uS and near immeasurable noise figures on the 5534. (real engineers don’t worry about all this especially when our hearing maybe caps at 16kHz and not 16MHz). So it’s no wonder that people complain about these units been used in a preamplifier. But when mass feeding the peoples we suddenly have a problem – the 5543 costs R15.00 each and the 4558 R1.00 to R5.00.

There is an advantage however, DIY.  Sticking expensive chips into breadboard is never a solution. The 4558 lends itself perfectly to the cause. Once all is good we can hopefully transpose with a better chip, like the 5532 or 5534.

The 4558 is still useful as a comparator, DC work or anything which doesn’t require very fast switching.  Sonically the more expensive chips do sound cleaner but then we need low noise resistors and high tolerance circuits.

For general purpose work I find nothing wrong with this old workhorse. If you really want good quality sound then I do suggest looking at the INA217 or the THAT1510P. Definitely NOT for HOT exchanges but then if you want to rip off the JRC4558 then you need to start afresh.

So no, sorry to retract – the 4558 is not crap. Different strokes for different folks. This article may be slightly tongue in cheek but be wary of why we don’t like something, it could be because we were told so.

 

Pulling apart the Dixon PM121USB mixer

Mixing board PM121USB - showing components

Teardown of a Dixon PM121USB mixer

A forum user, a musician and lead in a band has a broken active mixer and a small budget. He purchased the Dixon 8 channel mixer for his next evening’s performance and was surprised at the quality of this budget mixer. Of course we had to have the gunslingers ripping the gear off and in spite of all the negative commentary an audio engineer (a real audio engineer) qualified what the musician was saying by giving technical advice, positive criticism and wished him well with his new gear.  This is what forums should be about, not spiteful comments – a musician is very protective over whatever he or she may be using.  In this article we will look inside the Dixon PM121USB active mixer, the one sold by Crash Crusaders currently for about R 4 299.00

Dixon's PM121USB
The PM121USB Powered Mixer

Don’t judge a book by it’s cover, the PM121USB is a gem

Firstly, there are many parameters governing the quality of a mixer. Many die-hards look at the build quality first as they are sensitive to being thrown around, something roadies are prone to do. In a studio mixer the user may want ultra-quiet microphone preamplifiers which add no colour, some like to add equalisation whilst others don’t care as long as there is an output which is pleasing to their ears. And we have the USB, Firewire and Thunderbolt connectors and the digital mixer – all in good time. This is about a basic analogue mixer. In this case a powered mixer. A rebadged Chinese workhorse.

The Dixon active mixer has 12 real microphone and line inputs. There is a marketing ploy where advertisers list all the preamplifiers, even the tape or inserts.

Power Amplifer (the PM121USB is a powered audio mixer)

PM121USB Power Amplifier - showing cooling fan
PM121USB Power Amplifier – showing cooling fan
Power amplifier 200W x 2 into 8 Ohms
200W x 2 into 8 Ohms

The Dixon mixer power amplifier supply rails sit at about +60/-60V . I did not measure this. The transformer is rated at 42-0-42 and looks to be around 500VA.   Once rectified and filtered = 42*1.414.  This should be sufficient for about 200W into 8 Ohms. Into 4 Ohms, I doubt 450W at all – but I do think the retailers state about 300W RMS, which could well be within the ratings of the transformer and the transistors (the table below gives these Toshiba transistor spec at Absolute Maximum Ratings (Ta = 25°C).

Toshiba TTA5200 / 2SB1943 specifications
Toshiba TTA5200 / 2SB1943 specifications

Amplifier showing driver transistors, regulators (on heatsinks) and capacitors.

Close up of power amplifier PM121USB
Power amplifier – power transistors, regulators, drivers and smoothing capacitors.

The power amplifier uses 2 x 4700uFd electrolytics for smoothing which is something I would possibly be improving.

The preamplifiers – the Mixer with amplifier removed.

PM121USB Inside Mixer
PM121USB Inside Mixer – bottom removed.

Project Mixer – You can’t build for this price. You can modify easily as well.

The one thing I really like about this mixer cabinet is the space inside which lends itself to changes. The mixer has modules which are easily modified (pity about the soldered chips though which doesn’t encourage swapping).  The mixer only has a stereo bus which separates it from the big boys but using the back of the cabinet which has a lot of empty space one could add more inserts and possibly bus grouping using rotary controls.  I will be doing this in an upcoming project.  One thing the mixer does need are extra buffers to feed extra power amplifiers. The project may mean removal of the power amplifier and redesign of the power supply to feed other op amps. Re-bussing may mean groupings of 5 input, 4 input and 3 with one insert per group plus the main one, marked as return.  The price of these units lends itself to this because they aren’t meant to break the bank – if one is careful and caters for a specific need I would say that these mixers cannot be beaten for value.

Mixing board PM121USB - showing components
Mixing board PM121USB – showing components
Mixing board PM121USB - showing pots
Mixing board PM121USB – showing pots
Mixing board PM121USB - showing preamp chips - 4558
Mixing board PM121USB – showing preamp chips – 4558

The audio gurus don’t like the 4558 chip because of their age and poor sonic quality but it has it’s merits, pricing and low current draw. Because low current draw isn’t really a problem here the first thing worth upgrading would be these ICs.  The recommendation would be the 5532/5534/RC4560 or OPA2134 or 2604.  The one thing that must be mentioned is the current draw – again. This mixer uses more than 24 of these devices which in total is a mere 0.5A~0.8A, exchanging them you will be looking at possibly about 2A in total.  Voltage regulation needs to be beefed up and make sure you have enough time on your hands. But, it may well be worth it. From my side I didn’t think these ICs were of “poor” quality for an entry level function but it doesn’t compare with my 18i20.  For live performance these ICs are more than OK although they are now very long in the tooth.  The 4558 is ideal for tube screaming pedals (Ibanez with JRC4558D chips).

Mixing board PM121USB - potentiometers
Mixing board PM121USB – potentiometers – note line in (stereo 1/4″ or 6.3mm) bridge to XLR microphone inputs. The mono sockets are not of the highest quality but don’t budge.

 

The Effects Synthesiser

Effects synthesiser board
Effects synthesiser board
Effects and Master
Effects and Master Input

The weak side of this mixer/amplifier is the amplifier cooling / heatsinking and to be pedantic, the 4558 chip which is dated. For the casual user, a really great 12 channel mixer which cannot be beaten by price and of course, the mere fact that they are so easily modified.

Project:  Look out for an upcoming article showing mods made to this unit: bus grouping, additional inserts, line and USB 2 outs. Can this mixer be controlled externally? At a huge cost of course but it can be done.  Then there is the big problem of noise injection, something which we definitely do not want. Being of modular design and having ample space inside makes this mixer one of the best on the market for the avid tinkerer.

The PM121USB used in this article was purchased from Cash Crusaders as a used model, three years back for R 2 500.00.  Often seen on Gumtree sold way beyond their realistic value and in very shitty state. No knobs – don’t buy because it has been hammered. Electronic equipment should be looked after, no matter where it’s used. Because this was not an expensive product doesn’t make it crap. Hopefully as this article suggests it’s real value for money and for the DIYer, a gem.

Specifications (click to get bigger image. Apologies for poor quality)

Specifications - PM121USB
Specifications – PM121USB

SA Music – the beginning

SA Music – from the beginning of time (when I was born) – for our foreign friends

Kwaito – a little bit of African this and that, Johannesburg Style

South African music can be copycat, blend or township which strictly speaking should be South Africa’s own but is never.  Kwaito is referred to as house music with an African flavour, popularity booming in the 90s (yes, yes, especially since the Magic Madiba stepped into His Governor’s Shoes).

The Music

I am not a rap lover although admittedly I am fond of Eminem, Beyonce and Nicki Minaj. Possibly a bit of Kanye West, Dre and JayZee.  I have been to both the UK and USA and although as a teen I loved Brit pop culture it was only a visit to New Orleans that changed my habits.  And no, I am not biased, Aussie music, Dutch Golden Earing and the Germans ja! The Scorpions are all in my rack. I DJ’d early in the 80s as a hobby, hated the monotony of playing the same stuff every night except if it was my personal favourite. I doubt much of my personal favourites really hit the floor except Radar Love.

Music may be different from all over the world  but is never. Music, audio, sound and the equipment affiliated to the blends is of great interest, this includes the grand mastering of any good album. Dark Side of the Moon? One of my personal best.

Fogerty, Dylan, Young,  Crosby, Stills and Nash, Springsteen and one of the greatest, Grand Funk Railroad adorn my shelves with Deep Purple, Black Sabbath, The Who and Led Zeppelin. These groups forged my mind when I was young. As one gets older the passion still exists but the fire breathes colder, Sia, Lady Gaga and Rihanna have also made it there and of course a duplication, the video of Rodriguez, Searching for Sugarman – testament to the addiction of his music on South African fans.

I won’t forget Richard Branson’s book, “Losing my Virginity” either, where maybe I lost my own viriginity but it did throw some very interesting titbits on British music in the early 70s. Who can forget the Sex Pistols and Mike Oldfield?

In South Africa we had Hawk,  McCulley Workshop, Mango Groove, Miriam Makeba (deceased), Hugh Masekela, Yvonne Chaka Chaka and the highly controversial Brenda Fassie. Springbok Nude Girls and Arno Carstens, Just Jinjer and who can forget Four Jacks and  Jill?  There’s plenty others of course but as the all rounder who kicked arse we had the grand dad of them all, Johnny Clegg of Juluka and Savuka fame, the original Le Zoulou Blanc. Clegg remains one of my personal favourites and most probably many others.  Indeed I’d put him up with Hugh Masekela and Miriam Makeba as all time greats.  In the 80s we had Concert in the Park, 12th January 1985 at Ellis Park to be precise.

Concert in the Park, Ellis Park January 1985

Concert in the Park is actually an epic event for this country where 125 000 people of mixed races got together and partied to a huge genre of music.  Steve Kekana was my favourite act, “Raising my Family”.  And to the South African Pop Idol fans, don’t be too surprised to note that Mara Louw was there as well with “Motla le Pula”. Remember the girl on Idols who asked her what she knew about singing?  And there you have it and bloody marvellous as well.

The South African monopoly

Most money tied into big bands once they see popularity seems to do a disappearing act. Musicians in South Africa are as a whole badly paid I think but yet amongst some of the absolute crap that floats around I see fancy cars and houses. Music piracy is a big thing in these parts. Big names just don’t get mentioned as easily or as frequently as those of overseas artists. And our musicians are just as good or better.   Rabitt was our first international flirt with stardom overseas and no doubt they made a pretty penny but Trevor Rabin whom is amongst the world’s best only recently stepped into the Rock n Roll’s Hall of Fame (as a member of Yes, ‘nogal’).

Two huge South African Acts

To move on to 2017 two of my personal favourites are in the spotlight, The Parlotones and of course, Prime Circle. The question I ask myself is, am I being arrogant as a non-musician, non-professional to single out these two bands as being the two that occupy the most space on the news for South African acts when we have such a huge pool of talent? I certainly hope not.

The Parlotones are one very special act. I have seen them live a few times and offstage they are just the “guys in the band”. No airs and graces, just special people.  They make space for everybody, they joke and they don’t mind been photographed either.  And with your camera.

They have a distinctive albeit controversial style, Indie, or alternative rock or whatever, a distinctive and unique vocalist in Kahn Morbee – a very difficult act to follow which puts them in a class of their own and of course, up there with the best, no matter to which audience or where.

The Parlotones have long been criticised for being too commercial, horse and pony show, a marketing machine. Good for them then. Because if anybody knows just how tough it is out there should try it sometime. And please just have the talent.

Which reminds me, I need to get another T-shirt.  Saw them last at Paul Cluver, Elgin, 2015.

To finish off, we have “I’ll be there”.  Please support this great band!

 

Next up:  Prime Circle

From the mining town of Witbank,  this top South African band I’d rate as one of the world’s best.  They were a support act for Pennsylvanian  group “Live” then lead by Ed Kowalczyk a few years back (I saw them at the Bellville Velodrome) and were an instant smash hit with the audience.  Strangely enough some of the team I was with was actually there for them and not the main act.

Although very popular with local audience the power and charisma of this band has locked them solidly into the German and Euro musical culture where they are fast becoming the main act in very big events. Much of this can be read on the net so no use duplicating what is said and done suffice to say that this a group which well deserves the praise and recognition of being one of our top bands.  Again, please support this band!

“She always gets what she wants”, can we say more:

and one of my personal favourites, “Breathing”, just in case you think they sound like Nickleback:

Ummm, next up, the famous Keyboard Magazine interview with Manfred Mann, the Mighty Quin (the Eskimo)

Topic:  An American Touch – the group Live

The group Live has not come to our shores in a while and it’s indeed a great privilege to have them back again.  Grand West Arena 7th November 2017.

Live at the Chilli Cookoff 2010 - courtesy Gitman00 at en.wikipedia
Live at the Chilli Cookoff 2010 – courtesy Gitman00 at en.wikipedia

South African mains power – changes to receptacles

The South African SANS 164-1 and 164-2

RSA Plugs and Sockets – the SANS 164-2 requirement

Most people in South Africa may not be aware of the new 220~240V mains receptacles which came onto the market in 2015. With so many different standards used world-wide it’s interesting to note that this specific “style” or “form” is supposedly not only the safest in the world but is presumably the newest. “We don’t know because we don’t care” is a motto that seems to be that of most manufacturers opposed to the new IEC standard which means  (for them) more costs involved in shipping different plug types world wide.

The South African SANS 164-1 and 164-2
The South African SANS 164-1 and 164-2 (new) configurations

The new standard, known as the SANS 164-2 is nothing really unique. Indeed it’s not unique either that the IEC could never adapt every country in Europe to a common standard either, like a nationality’s flag.

As I see it, a common problem with our 240V mains plug system is that in the use of the “male” the top can come off exposing the live connection. The other is of course more common, the exposed trio of contacts, Live, Neutral and Earth just waiting for little fingers or in a tight fit connection, an uninsulated knife or screwdriver to pry the plug from the socket.

SANS protocol is that all electrical machinery is required by law to have our mains connector (plug) shipped with the device.  If not they do give the store or supplier a conformance notice which prohibits the sale of such goods until the devices are supplied with the correct mains plug, either three pin or two pin.

It’s disappointing that there are so many different standards because ironically this should be and is a government conformance measure – one would think that with either 110V or 220V there would be a) two different plug types to prevent incorrect voltage connection b) internally fused to be in line with wattage of the appliance c) correct pin offset to prevent Neutral and Live from being swapped c) waterproof and sealed d) loose plugs carry waterproof gasket e) the Live has a male/female part to it (meaning the live outer casing does not make contact) and of course f), the favourite – the socket having a safety cover.

Also, remember that if the socket is fused that is fine but it does not prevent a fire. A 15A fused socket powering a 100W device (say 0.5 A ~ 1A) which is not fused is inviting trouble. Homeowner’s should be aware of the risk here!

Dangerous appliances – does your toaster conform (or electrical blow heater)?

There are two very dangerous appliances in every home, one being the toaster which has mains live wiring accessible to any probing hand and the other, the washing machine. Yes, there are others but let’s stick to the toaster.  There are ways to make the domestic toaster much safer than what it is – starting with preventing the element wire from being immediately accessible by tiny hands. The Panasonic NB-G110P is a case in point. Nothing as glaringly sophisticated but still using infra-red.  Possibly a bit cheaper then, yes?

Cell phones and Downlighting

I believe the common and garden cell phone charger is a huge fire hazard, especially when plugged into bedroom sockets which are usually well hidden behind a fire waiting to happen curtain. I’d go the route of never putting a socket in a place where there could be a fire. Ditto downlighting, high wattage transformers, lamps and how is the cable? Down lighting should never be fitted by a carpenter, likewise don’t ask your electrician to build you a rocking chair. (actually I know of one that can).

I’m all for technology changes but let’s keep the safety standards consistent and the rules that govern this consistency be of an international standard. Every man for himself is sometimes just plain stupid.

Some reading:

SA to get new electrical sockets, plugs

https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets

 

Chinese electronic gear – hit or miss!

Chinese products hit ot miss

Steering clear of Chinese manufacturers – with or without merit

It’s a well known fact that most musos and audiophiles steer clear from the cheaper Asian imports like the plague. There is a huge amount of misconception about this, most probably stemming from the forums and ignorance.

Chinese electronic gear hit or miss
Spares Box

I am a huge believer of home brewed or “tuis gebakte” consumer goods and if it wasn’t for our rather feisty unions, inefficiency and poor education I do believe South Africa could be a manufacturing giant. We are in the motor industry but why not in the electronics sector? Many years back there was boastful talk about Stellenbosch being the second Silicon Valley. So what happened?  Price, efficiency, education.

Education is key for design – work ethic for manufacture

China has a mammoth manufacturing industry. They have a very high score rating in maths and science (here I should point out that Taiwan is or was the world leader). The people are bright, industrious and competitive. Anyone working in the electronics sector and specifically mixing with Asian engineers, marketers and the general sales force will understand the dynamics at play. Especially the enthusiasm. Mail a Chinese (or South Korean or Japanese) company today and you’ll have a reply within a few hours, not matter what time zone you are in. This kind of attitude makes China an attractive place to manufacture.

jack socket - stereo 6.3mm
Jack Socket – stereo (the nut is for illustration purposes only)

The argument is that as soon as a product goes to China for production the resulting products are always of poor construction.   To be clear, this was a problem with many brand names. We had the golden product which for some strange reason never shared the same quality of the resulting mass production. Shortcuts, poor quality materials and components and often rather unfinished goods were the order of the day. Quality workmanship did appear only once there was proper QC in place and there was rock solid supervision. I work in the sector so ethically I cannot mention the brand names (many) which succumbed to poor control and components. But at some stage the QC changed, control was tighter, things got more expensive and the complaints stopped. Ditto the professional audio market.

Our DIY sector 

Here is a standard dilemma for anyone building their own projects in South Africa:  Purchase a mono or stereo jack socket. They vary in price from about R10.00 to R75.00 ex VAT.  The cheaper variety is almost always of Asian build and the nut/threads are of exceptionally poor quality.  Why do we even bother? As soon as we start going up in price the quality improves until we get what we really want – a lifetime laster. At between R40.00 and R75.00 a pop. And they are also made in Asia i.e. China. (maybe I exaggerate a little but if a nut cannot be tightened beyond finger torque there may be a problem. How good are the contacts then?).

Doing the maths

The well known Dixon mixer PM121USB is a conundrum.  It features 12  audio channels and a stereo bus plus 200W per channel amplifier. This used to go for R 2 999.00 and now with ROE sits at R 4 299.00. This is very cheap for what you get. And the sockets are of very good quality (in my mind). So in mass production the manufacturers do get better quality products for less.  A rough estimation puts the total price on all the mono sockets at between R600.00 and R700.00 at current pricing.  No manufacturer would be buying in these products at that pricing (I give RRP not cost) even with 33% to 40% markup.  So in fact we are being ripped off – and not by the suppliers in Asia.

I mention the PM121USB mixer as an example purely because there has to be a break-even point – to self build a unit at RRP (recommended retail prices, if there is such a thing) it would cost double or more. The transformer alone sits at about R 1 200.00 to R 1 500.00 RRP in the RSA. But in mass production the pricing becomes attractive and I dare say, the quality is pretty damned good. Remember it gets used by DJs of all types and it does get bashed around, gauging by the images on Gumtree.

Focusing on the hardware

So where does this leave us?  Better quality mono and stereo jacks, fuseholders, switches and potentiometers?  This all falls within the spectrum of the DIYer.  We just cannot afford to pay 4 times the price to get a quality product, especially if we need this to last a lifetime.  (I purchased some sockets from a well known supplier where not one of the nuts could be tightened properly, the switches all had huge lateral movement, the fuse-holders had thin tin lugs, and the list goes on). Resellers should offer alternatives and not just online because often there is a stock shortage.

Margins are tight

Running an electronics store is not easy, especially those that survive on selling electronic components. Much of this is driven by a passion, margins can be tight as each store needs to be highly competitive.  But why the poor quality (of some components) in South Africa? I am not singling out any particular store, I do believe that in huge quantities components from companies like Farnell pricing to the consumer would be drastically cut and we’d end paying R20.00 for a good product as compared to R10.00 for a dud. And yes, most probably Farnell source from Asia as well. Just a point to note.

To close off, manufacturers in China have to be carefully selected, QC is vital throughout the manufacturing cycle, not just the Golden Product. This is a gap in our market – quality hardware at reasonable pricing.

The same applies to the chassis components (which includes rack mount)  and mains transformers. Compare the price of a computer rack mount chassis to that purchased through an electronics store.

Editor’s Note:  When it comes to to 200~240V a.c. plugs and sockets the mind boggles at the various qualities of build one has come to expect in South Africa.  Do they get checked by the SABS? Plugtops which can easily be pulled off the base leaving children access to the live terminal are frighteningly popular.  Multiplug sockets with a maximum of 5A wire rating.  And the ever popular mains two pin plug, with or without the earth strap. SABS/SANS is strict on this but we still see them.

The Wonderful Art of Mastering

home recording with Focusrite Scarlett 2i2

Everyone wants to become a world famous musician, conductor, cello player in a James Bond movie but what about a recording engineer?

A very good, rather excellent, website to get your talent juices flowing is that of David Mellor’s Audio Master Class,  where valuable time and money is spent in training dunces like me in the world of professional recording, giving free titbits of information and real world case studies.

home recording with Focusrite Scarlett 2i2
Focusrite Scarlett 2i2

I had just purchased a Focusrite Scarlett 18i20 and whilst doing some recording tests realised very quickly how important having a proper studio for this function is. And I mean, really is.  Spending millions on a home studio is obviously not within everyone’s reach but knowing what to do and how to do it on a budget is inevitably the best route to follow. Whilst we sing the old adage, “a bad workman blames his tools”, it’s no surprise to find that many started somewhere, mostly on a tight budget working their way up to being extremely knowledgeable in audio or sound engineering.

My first experiences in home recording is somewhat vague suffice to say it was with a four track tape recorder and ceramic microphone. Moving on a couple of decades and with a Live sound card and a great little mic I did some more tests and was amazed at my progress.  The thing is that when you do go the “professional” route, even with what the glassy eyed, snobbed out wannabes classify as an entry level mic preamp, the Focusrite delivers. It delivers so well that the Shure SM7 microphone and quiet little preamplifiers reproduced the stunning performance of the refrigerator next door. Ditto my Zoom H6 picking up the air-conditioner compressor outside switching on and off.

Yes, sound engineering isn’t for the faint-hearted.  I have heard some absolutely incredible recordings from solo artists and their Scarlett 2i2 rigs and to be honest, times have changed for the better.

This website is not affiliate to master Audio Class in any way. Before going out and spending upwards of R20 000 on a course in sound engineering maybe have a look and do some reading. Lots and lots of reading.  Exciting stuff!

You can get your 2i2 in South Africa at Sound Select the Shop (and no, we’re not affiliates here either).  Shop around if you wish 🙂

And in the beginning…. we had Ohm’s Law

Ohms Law - carbon resistors

Ohm’s Law – the Genesis of Electronics and Electrical Engineering

We all marvel at the intricacies of electronic circuits, electron current flow and Fleming’s Right Rule but to get right down to basics we need to know only one thing, really… Ohm’s Law, named after the German physicist Georg Simon Ohm.

Ohms Law - carbon resistors
Carbon Resistors

To know what current flows through a circuit we need to know the potential difference across any given known resistance, to get the voltage across a resistance we need to know the resistance value and current flow and of course, resistance value can be calculated by the known current flow and measured potential across the resistance.   In Figure 2 we have the Ohm’s Law triangle just to help learners get unstuck – remember V = IR or R = V/R or I = V/R. Get it?

If Ohm’s Law is just the beginning then where does it all end?

Most teenagers (or younger) start their hobby or later career in electronics by building circuits from magazines, the internet or many top class books available.  Electronics is just a term – from Wiki: “Electronics is the science of controlling electrical energy electrically, in which the electrons have a fundamental role”.  Yes, that is about it, Electronics is all about the flow of electrons. Electronics has many branches, industrial, audio, automation, light, RF, computers, etc. Ohm’s Law is used in every single circuit design or fault diagnosis.

Ohms Law Triangle
Ohms Law Triangle

We may learn about Kirchoff, Joule and Coulomb’s  Laws, Thévenin’s theorem but Georg Ohm’s Law always holds precedence.  Our analogue friends all talk about power to the loudspeaker measured in Watts but did you know that in simple terms one Watt is equal to one Volt times one Ampere. There again, back to Ohm.

AC has it’s own set of rules

Unfortunately nothing is ever as simple as ABC.  In the real world we have alternating current where suddenly we have terms like amplitude, frequency, period etc.  Now suddenly we have the effects of AC on an inductance and / or capacitance, current leading voltage or lagging. We hear about impedance, reactance, reluctance and resonance. We find pi or π now showing it’s face around every corner, most often in the format 2π times something or other…

The beauty about building circuits …

The reality is of course when building circuits you don’t need to know jack about π or reactance or impedance.   What you do need to know is always Ohm.

The truth is…

If you are like me, the article writer, you will be interested in RF, you will be interested in audio and then possibly sonar, radar and every other wee thing affiliate to this lovely hobby.  To me resonance is one of the most important aspects to understanding electronics in it’s analogue form – it covers so many different parameters used in circuit design that it is not surprising therefore that it’s one of the most written about subjects in radio technology. And just when you thought you knew everything, along came the NE555.

(author’s comment – this article is not meant to be simplistic but rather to give the young and interested an injection into the world of Ohm which I do believe is the stepping stone into the electronics industry).

 

 

Rebirth of a legend – the Nokia 3310

nokia 3310

Nokia 3310

Nokia has had it’s fair share of ups and downs but for most it remained the brand to have. Nokia became Microsoft and although I am suitably unbiased, in fact rather amazed at the quality of photo images and audio in some their entry level products, Nokia was said to be no more. But no sooner was this said when the 150 year old company boasted of their new batch of products, all running Android of course. What surprised most, but not to the die hards of course, is that Nokia claims to be re-releasing the 3310.

nokia 3310
Nokia 3310

Everyone that has had a cell phone would have had a 3310. Adorned with nothing except for a pendent to run ridiculously long on it’s small battery Nokia might well have a winner.

As said by their Chariman, Risto Siilasmaa: ” It’s almost as if the company has a soul. I really feel that the soul survived this operation.”

And, don’t forget what our website is all about of course…

Plus ça change, plus c’est la même chose – Jean-Baptiste Alphonse Karr (24 November 1808 – 29 September 1890

Samsung

I wonder what the head of contender number one, Samsung’s esteemed vice-chairman Lee Jae-yong has to say about this, pending his arrest for some dodgy government dealings which lead to the impeachment of president Park Geun-hye. Of course we can smirk that this is nothing new, we live in South Africa after all.

 

Autona AL125

Autona AL125 - VAS and current drive

As promised – the Autona AL125

The Autona AL125 was the workhorse of the 70s and possibly even early 80s in the DJ arena.  The amplifiers compared to what we see today were well made but I would not be surprised if the engineers pushed the SOA (Safe Operating Area) to the limits, the DJs even more so.  As promised in our previous article on the 2N3055 here are some pictures I have of three of these delightful little amplifiers.

Article as promised from the Silicon Bubble – the 2N3055

autona al125
The famous “little” Autona AL125

Note the one above on the RHS which has an interesting tale to tell. See below.

autona disco amp the AL125
Autona AL125

The amplifier on the RHS used to be used at a hotel for the PA system.  Using the amplifiers without an additional aluminium heatsink was just inviting trouble as can be seen by the very burnt fibreglass board where the 2N3055s are seated.

autona 125
A better looked after module
heatsink supplied with AL125
Autona AL125 with supplied heatsink

AL125 heatsinking

The alloy heatsink supplied with these modules were supposedly good for 50W into 8 Ohms. As a rush job this may well have sufficed but looking at the image above,  continuous playing into a load very much higher than 50W was a big no no.  The overheated one drove an entire floor of PA speakers, perhaps about 10 x 8″  8 Ohm drivers through a line transformer with no additional heatsinking – for more than 12 years.

Most teenagers during the 70s and 80s bought, built, modified or blew up replicas of these amplifiers. Not having a directly coupled output stage had its merits.

Autona AL125 - VAS and current drive
Autona AL125 – VAS and current drive

Further Reading:  The Quasi Complimentary Power Amplifier Autona AL125

The Sneaky world of Pre-amplification

Art pro digital mpa 2 - microphone preamplifier

Changing the Ambience with quality voltage control – the Preamplifier

One of the biggest advantages of having separate preamplifier and power amplifier stages is that the user can swap between the two either for upgrading or listening purposes.  The pro audio world may see this in  powered mixers versus the un-powered variety but it is a step invariably anyone interested in sound systems will eventually take.

Art pro digital mpa 2 - microphone preamplifier
ART Digital MPA II

Of course the so called best preamplifiers are supposedly just attenuators so here I need to tread carefully.

The path without a circuit is best

The shortest distance between two paths is invariably the straight wire so presumably we should ban the pre-amp entirely.  Not so quick though, the power amplifier usually needs about 1V at it’s input which does mean we need some sort of voltage amplifier of sorts. The attentuation is fine if one is feeding off a CD Player for instance which has a high enough voltage output sufficient to drive most consumer audio amplifiers.  Not if one is using a phono cartridge without preamplifier of course.  Attentuation is just that, usually a high quality potentiometer used in a passive setup which means less transistors, capacitors, noisy resistors and a hummin’ power supply.

Phono preamplifiers come in all shapes and sizes but is a necessity to amplify the very low mV values from the humble turntable cartridge, moving coil or moving magnet. The MC output, more popular amongst turntable junkies and audiophiles has an output often measured below 1 mV at full amplitude. This means in the wrong setup we are going to get a lot of noise, poor compensation and a very poor listening experience. Didn’t the supplier warn you that the cartridge was not MM?  Normally the cost alone is the “verboten’ element. Then we have the preamplifier or phono-preamplifier often advertised as MC ready but is not really, in fact it’s a bloody mess. High quality preamplifiers with MC input are simply put, rather expensive. But you can make your own then…

See DIY Audio Projects for MC

Rod Elliott for moving MM

The vintage era phono preamplifiers are making their mark as well and it’s absolutely no surprise.

See DIY Audio Projects “the Groove Watt”

Some consumer preamplifiers, especially high end have Hi-Lo MC and MM preamplifier input stages.  These come at a price, like the tube variety.

Mars 9 Phono Preamplifier Kit

Our article title, “sneaky world of preamplification” is really another way of looking at preamplification because in it’s simplest configuration would be a straight wire. We pay lots of money for high quality equipment and the one which we should be monitoring is this little voltage amplifier, with or without gain, levels and tone controls. Here we need to become aware of some interesting facts:

Build your own

  • Price doesn’t necessarily mean great quality. Read about the $5 preamp from Audio Master Class.
  • Building your own preamplifier will always sound better than any other – pseudo acoustic syndrome.  But hang on, there’s merit to this.  You can chop and change, make modular, run off batteries and even bypass for line use. And of course we have those that roll their tubes, why not the ICs.
  • Often the price you pay is for cosmetic appearance – what it looks like. Nothing better than having fancy looking gear in the sound room. I think the ART Digital MPA 2 is a typical example of very good looking gear – and the build and sonic quality is exceptional as well. ART are known for this.
  • Looking at the Dynaco ST-70 amplifier which was by no means the best looking amplifier (compared to MacIntosh methinks) in the world but having more than 300 000 avid owners bears testament to David Hafler’s technical know how and experience.
  • The low noise instrument preamplifier INA217  [pdf spec sheet](replacement for the SSM2017). This little chip in a ludicrously simple configuration outperformed many costly preamplifiers.

The essential recipe to the success of any circuit is simplicity, ease of design and cost.  Your cost will nearly always come down to what the end result should look like.

A vintage catch:  I had the option to purchase either the NAD 1020 or Hitachi HCA-6500 in the early 1980s.  Although I opted for the NAD which I used solely as a preamp in a DJ mixing console I was put off by how weak the pre-amp input board was – the RCA inputs felt weak and pressed in when exchanging input sources, which was quite often. The Hitachi was a more expensive piece of gear and to my ear was a better piece of equipment sonic wise.  You can pick the NADs up for over R2 000.00 on eBay, not a bad return on a preamp which I paid R200.00 for. Both, as you will know are very much in demand, the HCA-6500 is known as a sleeper (hidden away, not to be sold), the NAD a workhorse. Also, the NAD, if you do own one, has the same board as the 3020.

Article photo, the ART MPA II Digital

This is the digital version of the older PRO and it has a remarkably quiet front end and even with entry level microphones the sonic output quality is remarkably like, umm, well, tube like.  Remember that this is a tube microphone/instrument preamplifier but it reproduces phono (MM) with the proper RIAA compensation and preamplification front end (before the line in) in a remarkably civilised manner.  As this was never intended to be used for this purpose I can vouch that the quality is exceptional. (the RIAA circuit is the one sold by Yebo Electronics – due to be upgraded to the one linked above, the Rod Elliott link).