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


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).

The silicon audio bubble – the 2N3055

2N3055 Amplifier schematic

This slow old dinosaur, the 2N3055, outlives many new devices

Imagine building an amplifier in the late 60s which didn’t break the bank but could outperform most tube amplifiers in terms of raw power.  Rand per Watt silicon has no equal in the audio industry.  Audio meaning reproduction of a  music source of course,  pressurised air or steam is in a different league.

2N3055 Amplifier schematic
50W 8 Ohm Amplifier (let us know if this is copyright – webmaster)

There were many ‘transistorised’ amplifiers in the 60s, mostly low power and Germanium. Germanium was the runaway king, a little bit too temperamental for DIYers and of course they could be very expensive.  The common configurations used the AC128/AC127 and AD161/AD162 transistors. Philips made some pretty good audio equipment with these devices but it wasn’t until the birth of the Silicon wonder, the 2N3055 that things started to take shape both in terms of reliability and power.

Gramps’s Gramaphone

In the 60s most homes would at maximum have a sound system of a few watts, perhaps 5 to 6, powered from a single tube output stage in what was known as a Gramophone, the radio-record player combo. You know the type granny and grandpa had that you were not allowed to touch.  Ball and Claw, magnificent finish. If the reader here is under 25 I doubt you know this or possibly have ever seen one.  Even reel tape recorders were not that common unless you were a real geek and here we would be looking at 300Hz to 7kHz for an entry level model.

RCA – the 2N3055

The 2N3055 was an RCA invent, introduced in the 60s but really only seeing a wide usage in the early and middle 70s. The ratings, as I recall, which I won’t state from the book spec was 115W, 15A, 60V, Hfe 20 at 4A and a cut off Ft of about 800kHz. These were well suited to linear regulators and inverters. They had to run cool, 100W quickly became 60W at about 70 degrees C or even lower.  Catastrophic failure was usually caused by inadequate cooling,  short circuits and my personal favourite – bad seating of the transistors on the aluminium and a common problem in these earlier devices, “secondary breakdown”. (just watch your +Vcc friend).

The all time best seller in South Africa was the legendary Autona 125W 4 Ohm (with 4 transistors in the output stage) running on a single rail 80V supply. Coupling to loudspeaker was through a 2200 uFd electrolytic which alone was enough to either blow the transistors on switch-on or take the tweeters out. These “disco’ amplifiers were sold at the legendary Hamrads in 1976/77 for about R36.00 each.  The DJ fraternity stuck to Fane and then Novik 12” speakers, mostly 8 Ohm.  (audio out 80W into 8 Ohms).  Compare this to the bullies of today.

In time these amplifiers made way for split rail power supplies and the complimentary 2N3055/2N2955. Were any of these actually any good? Almost definitely – bear in mind that we listened to loud and not quality. Quality wise, well one shouldn’t forget that NAD 3020 used these transistors as well. In time these transistors were made more reliable, for instance the 2N3055H had a higher operating voltage and of course manufacturers were looking at higher cut off frequencies due to changes in design technology.  (hometaxial to epitaxial). The 2N3055 is also a highly counterfeited commodity which nearly always renders them useless in any circuit – I always looked for the Toshiba range. They were also more reliable, along with RCA (if they were not the counterfeit ones).

See picture here of a 2 x 50W into 8 Ohms amplifier.

So where does one find ourselves modern days?  The 2N3773 became my favourite for reliability and then of course as we moved to the insane amps of the era, we had the Carver 400 and 700 Watters.   Here most technicians are using MJ15003s/complimentary pairs. They aren’t cheap but when one is building an amplifier to power a 300W sub these speakers are not cheap either. 4 transistors per leg is not uncommon and at rails sitting at about +/-50V to +/- 80V things start becoming complicated if care is not taken.

The 2N3055 may be old, but it certainly hasn’t been forgotten.

I’ll remember to post a picture of the 125W Autona modules this weekend coming 18/19 Feb 2017.  These units could run 50W with the aluminium heatsink supplied into 8 Ohms at 50V DC.

[Editor’s note: in the forums many newbies are put off building a 2N3055 audio power amplifier by the “experts” because of the age of the device. I find this rather disappointing, there were thousands of amplifiers around then and now too, using these transistors. Yes, there are many replacements which may or will sound better at a price but for anyone wanting to learn, let them do so at their own pace, their own pocket and at proper instruction – not just “don’t do it!”]

Changing the argument in modern audio – the digital sound

Asus Xonar U7

The DAC and digital sound – big quality at half the expense

Coming from an analog website it may sound as if we are doing a 180 here but the truth remains, we still have the analog versus digital argument.  Something which will never quite be put to bed, the digital war continues.

My first CD player was the Sony CDP1, a small, heavyweight, state of the art digital ‘icon’ to the audio world. In fact at the time I was not even aware that it was first commercial release, rather just wanting to get my hands on a CD player, a Sony, to impress my friends.

The vinyl years

Two things stood out at the time, one without doubt the easy way to play the media – damn but vinyl was finicky, and then you had the problem of friends playing disks which were so bad that it would damage the stylus (was I the only guy that had a freakin’ sound system) and the big one,  no crackles, pops, buzzing, clicks, jumping, feedback and of course,  the big one – lifting the arm to change tracks.

As time went by CD players dropped in price, had more functions and became quite a part of our lives. Everyone had one by the 1990s. Turntables were packed away or trashed, vinyl was dead. Or was it?

The CD years

I stopped listening to vinyl for about fifteen years, it was always cassette tape or CD and then DVD.  I gave away both my Sony turntables which I DJ’d with in the early 80s. The marketing machine was fine tuning us for the silver disk and they did a remarkable job except for one thing – multimedia computers came on the scene in the mid-90s.  (PCs and Windows, Apple was always the front-runner).  We suddenly could compress our 40MB file to 4MB in the form of MP3s. We became used to this,  piracy was no longer something we found on the high seas, it was in everyone’s home.  iTunes suddenly kicked in and we could buy individual tracks not the whole CD where the artist possibly had only one good track. CD prices started falling and before we knew it the audiophiles started reminded us of a couple of things that we had forgotten about.  CD quality is 20 to 20, vinyl is so much more.  In the last decade suddenly we found vinyl on the shelves again.

The shortest route between two points is the straight wire

The digital versus analogue argument is all about the shortest path, sampling frequency and DAC quality. Vinyl has two paths, de-emphasis at the RIAA amplifier (where disk cutting excursions on the lower registers uses a lot of space the engineers de-emphasise these excursions and boost the treble). On playback the reverse is applied. The second path is the amplifier itself.  Simply put, cut out the unnecessary and only amplify the necessary.  Add tone controls if you wish but make sure the amplification is flat, as close to dammit from 0Hz to 100kHz. Wishful thinking but yes, technology can allow this.  Makes one think how the NAD 3020 became so popular with an output stage using transistors from the Ark.   But let it be said that these amplifiers were very popular and indeed, more because of vinyl than anything else.

Vinyl supposedly reduces fatigue, is non-sterile, not compressed to hell and back and also, importantly, does not have the 20 to 20 limitation.  A guru even went so far as to say that music is something we also sense outside the audio spectrum.  He is a very good musician, who am I to argue. So what has made that incredible CD player now near redundant?  The DAC and the internet of course.  Breaking up an analog signal into parts and then re-assembling  these parts or as in a CD, taking 1s and 0s and then re-assembling to get a ‘resemblance’ of analog is just not on.

Technology has allowed us to push the clocking of a digital circuit into the hundreds of Megahertz, the Digital to audio converter now even runs at 384kHz or higher.  CD players, or rather the media is sampled at 44.1 kHz. Using the Nyquist–Shannon thereom, sampling frequency must be a minimum double the sample rate – 44.1kHz also encompasses anti-aliasing filters which reduce the bandwidth.  Lots more of that on wiki.  Bottom line is that all CD players run at 44.1kHz – man decided that our uppermost frequnecy limit is 20kHz so let it be. But DACs have improved in leaps and bounds over the years, high end DACs costing upwards of R30 000.00.  Ouch. But here’s the thing.

We take an analog signal, slice and dice so it can fit nicely onto your computer and then rebuild this signal through the DAC to reproduce a nice sliced and diced analog signal. Why not just copy your vinyl onto a high end tape recorder, preferably an R2R where the media can sit for 10 to 20 years and hopefully not be subject to degrading.  Oh, yes this happens.  The Audio Technica AT-LP120-USB Turntable sells for about R 7 500.00, throw in a RTR for about R 10 000.00 and Bob’s your uncle, or aunt.

Asus Xonar U7
Asus Xonar U7 – 192kHz A-weighted 114dB front at 24bit/96kHz freq response 10Hz to 46kHz

But no, not to be, not to be.  Just have a look at how long it takes to set up your reel to reel – your computer boots up in 20 seconds and then you have the Xonar U7 as I have. Exceptional quality and in only 60 seconds you have YouTube, access to free downloads, very good quality audio. And that’s the thing – if you want a no frills, high quality audio setup go the digital route. If you are looking at the pseudo-acoustic route go analog. Real analogue. In the real world a high quality setup of either can be expensive. For Sunday afternoon listening pleasure I opt for the analogue.  Day to day listening, digital. It’s all in the head any way.

The Internet of Everything

We have all heard this phrase and it’s not one which will go away quickly – the IoT or Internet of Things is going to change the way we react with the net and the universe.  At home you will have a menu listing trillions of songs and movies. You won’t need to keep a library – you will need to pay royalties but as the companies supplying this service become more popular these royalties will be measured in terms of cents.  It’s happening now already.  We live in a quick fix world – digital streaming media is the way things are happening.


Technics SL-1200 MKII Refurb

Changing the buttons on an SL1200

New buttons for the Technics SL-1200

The Technics SL-1200 MK2 turntable is still very much in demand. So much so that when manufacture stopped in 2010 an army of DJs got together and requested Matsushita – Panasonic to continue with the model. Yes, it was relaunched tail end of last year for a staggering amount – have seen them here going for between R 28 000 and R 45 000 per turntable. For a turntable that many audiophiles claim to be mediocre this is surprising. But is it that?

Technics SL-1200 MK2
Technics SL-1200 MK2 – about to have a refit of knobs and decals

The first 1200s were made for the Hi-Fi market in the 1970s and not DJs as what is suggested.  They were also by no means mediocre, if that were the case DJs the world over would not be seeing these as the be all and all of turntables. But it’s not in the sound quality alone, moreover in the build quality. Built like a tank, quartz locked, heavy – no frills, no fancy controls and definitely nothing exuberant.

The 1200 MK2 especially was the DJs favourite.  “Pitch perfect” as the saying goes. Although the weight should be a giveaway as to where Technics were heading it must never be forgotten that what made these TTs so popular was the high torque motors, near instantaneous start up to controlled frequency. How many DJs dropped these heavy machines only to find that after a bit of panel beating here and there they would still work flawlessly.

Although most of us in the audio world get on our high horse when the gurus come out to play and make comparisons of these decks to others, usually the more expensive units we need to also be careful. The Technics was and still is a very capable machine.  It is also a direct drive – this is what makes them attractive in the world of beat.  The gurus scoff this off, real turntables are belt driven. To be sure I have had cheapy belt driven even idler turntables which performed marvellously well – none of them are still in my cupboard though.  A turntable which has been running for the last 4 decades is nothing to be sneezed at – and there are plenty of them. First and foremost we need to look at the mechanics of these turntables. This may also have gotten Technics into trouble in the first place because as far as high end turntables go these were actually quite cheap.

Not to repeat what a thousand other forums and blogs have to report, we will only go so far as to say show us the longevity of hard working turn tables and then how much money they have made for the owner? Unfortunately DJ controllers have killed the turntable market, audio modeling software is frighteningly accurate, MP3s and other media are highly portable – in other words there is NO way out for the turntable except into the hi-fidelity space of your home. The Technics may have it’s haters but one thing is for sure, to make a comeback after 6 years is going to breathe new life into your home audio.

Against all promises to myself I purchased two of these turntables off a DJ recently (yes, I know, I know – try to buy them off anyone else?). They had not been well looked after but in hindsight what are we supposed to expect – these are workhorses, not showpieces. The plastic buttons really looked horrific, the heads and cartridges were Stanton,  setup definitely for slip.  Changed these two first off for Audio Technica 95s, head shells were generic, changed mat, ordered in from KAB USA buttons, oils, greases and a overhang tool.

SL-1200 Pitch control 1
SL-1200 Pitch control – looks pretty shot (after 25 years).
SL-1200 Pitch control 2
SL-1200 Pitch control – nice and new from KAB USA
Technics SL-1200 button replacement
Some more buttons to go – all from KAB USA

Note that both turntables were sprayed black – this reflects the plinth of the 1210 and not the 1200 which was silver. Tell a DJ not to change the colours of his deck. I am pedantic about this but forget that these were not show pieces.

Anyway, I was impressed with the service of KAB USA and will use them again. It’s not just the service though, their pricing is better than most on eBay. From picked, invoiced to shipment outside USA waters took 4 days. They sell all spares for the 1200 and 1210.

In order to refurb completely is going to be a month long exercise. Although the previous owner said that these turntables had been recently serviced it must have been done by someone who used a feather duster.  Servicing a turntable such as this properly is going to take more than an hour or two. This includes changing the stereo output leads, fine tuning weight and tracking and lubricating the moving parts.

Peavey Classic 50/50 – EL84 screamer

ART Pro MPA2 Digital with Peavey Classic 50/50

The classic Classic Peavey 50/50

Thanks to Paul in Kenilworth, CT,  I picked up this real Classic at a great price. They realistically go for even up to R5 000 in good nick and then one still has the overseas shipping charges to contend with and possible re-tubing. I do believe there are many of these power amplifiers floating about in South Africa so keep your eyes open.

What is so marvellous about this amplifier is that it can be easily modded, can be set up for home use and best of all these are stereo units or more in pro circles, two channel 50W RMS. And yes, of course – 50W per channel for tube amplifiers at a near giveaway price is the main attraction. Bear in mind that a 35W per channel EL34 aplifier is going to empty your wallet of some R20 000.00.  But keep this a secret please!

Power output of the Peavey Classic 50/50

Sceptics are often quoted as being surprised at the output performance of these amplifiers as they use the baby brother of the EL34, the EL84.  Well not really. The EL84 is a high gain pentode which requires very little drive to bring it into saturation. Aha!  This explains the popularity amongst the overdrivers. The 6BQ5 is the USA equivalent. The 6V6 is less sensitive. The EL84 used in guitar amplifiers brings out a distinctive and prominent treble tone. Do not confuse this with lacking bass – EL84s when in the right configuration make exceptional quality amplifiers.

The manufacturers of guitar amplifiers regularly configured the output stages of these EL84s to run at a plate (anode) voltage of between 400V and 425V – over 100V that of the manufacturer spec. Before jumping to conclusions remember that tube specs are given for max plate current and voltage. Reducing the plate current and supplying high voltages is not uncommon. One just cannot do both – the EL84 can dissipate up to 14W in a controlled environment – controlled meaning reducing screen grid voltage as well. These amplifiers are known to run sometimes for up to 15 years+ without a tube change. Coming from a radio telecommunications background it was not uncommon for SSB transmitters to never have their output tubes replaced. In class AB1 an SSB transmitter is also running at about 50% efficient, 3kW in for 1.5kW out in marine use.  The bigger issue was power supplies – often over 100kg to power these beasts. Tubes are survivors and are many times more resilient than the older RF transistors (even in audio use).  So tube amplifiers designed around the manufacturer spec is often downplayed for many years of reliability. Even at 400V applied to the plates of an EL84 does not mean it will fall over in 3 months to a year as many doom and gloom harbingers decided.

The one thing to be careful of though is driving any tube amplifier without a load.  Especially when pushing a tube plate voltage to the max such as the Classic series. This will cause breakdown in the primary windings of the output transformers. Note the two diodes across the EL84s. Wonder what they are for?

One channel Classic 4040 Power Amplifier
One channel Classic 5050 Power Amplifier

Looking at the schematic it’s no wonder that these were so popular. Besides the design being super simple tube rollers had fun because the tubes are very easy to change.

Classic 5050 EL84 Output Octet
Classic 5050 EL84 Output Octet

These amplifiers rely heavily on the added fan cooling often not seen in low power tube audio. As the tubes are pushing their maximum ratings within a very compressed space however it’s not just a good idea, it’s essential.  These Peavey amplifiers are also known for their compact size and weight, a 2U chassis makes it easily transportable, in rack or out.

Troubleshooting these Peaveys

Trawling through the net one often is surprised not to see skilled technical folk not warning wannabe repairmen to ensure that whatever voltmeter, DMM etc they will be using is indeed high impedance. Years back one would have a VTVM (Vacuum Tube Voltmeter) which was designed for this and measurement of ultra low voltages.  The cheap low Ohmic meters of the day, chiefly analog of course, would play havoc on tube bias.  Unsuspecting DIYers were often surprised at the rosy glow coming from the anode when measuring control grid to ground.  So, please be careful.

There are four main checks when it comes to tube performance: Plate or anode voltage, screen grid,  control grid bias and heater voltage.   If you are not sure, have not worked on tube gear before then now’s the time to call in skilled help.  Tube voltages kill!

All voltages and currents should be in the service manual, but not always.  The general rule of thumb is to remove the tubes with power off and capacitors discharged. Clean the socket properly – tube heaters draw a fair whack and if not seating properly there will be a very large degrade in performance. I mention this as well because an amplifier I repaired years back lost bias through poor socket connections with the tubes going into saturation and showing a healthy red glow from the anode. So just be extra cautious, socket pins can cause problems, especially in road gear.

Heater filaments very seldom burn out. I have found that because of the current draw on bigger amplifiers (and some smaller) if there is a fuse-holder make sure that the fuse is seating/connecting properly.  This was a big problem with portable TV sets where the last thing the tech looks at is the voltage drop across the fuse. Even older fuses cause a drop but don’t now make this a fetish – just make sure the heaters sit at spec value.

Control grid voltages: always in audio negatively biased to Cathode. Below is a brief description and also gives transformer secondary voltages.

Bias supply
Bias Supply – control grid bias and 12V relay coil for stereo / mono use.
V-Relay – the relay coil is grounded in “Mono” mode.
Tube Bias
Tube Bias

Mains transformer 110V or 220V primary


  • sec 1       300VAC @ .318 amps  =  425V feed to anode/plate  /  100 Ohm 5W dropper to screen grids
  • sec 2      41.5VAC CT @ .318 amps =  – 58V to control grids
  • sec 3      6.19VAC @ 5.16 amps = heater supplies
ART Pro MPA2 Digital with Peavey Classic 50/50
ART Pro MPA2 Digital with Peavey Classic 50/50

Next up will be the test, tube pre-amp to tube power amplifier.

The Harman/Kardon AVR161S

Harmon/kardon AVR161 review

Home Theatre AVR161S 5.1 harman/kardon

Being pretty frugal when it comes to buying audio equipment I felt it time to replace my tattered old 2004 JVC with a receiver which would not break the bank. Having four options at hand,  Yamaha RXV379, Harman/Kardon AVR161S and the new Yamaha RXV381 or HTR4068 I was stumped for choice. Knowing someone years back with a harman/kardon repair job who was a first class arsehole left me dodging the 161 like a Bryan Habana. But and this is a very big BUT, many folk have raved about the reliability of this brand and of course the quality. As the retailer was selling this unit for at least R500.00 cheaper than competitors I felt it was money well spent for a known good brand with a switched mode power supply. Not that I have anything against either Yamaha or linear supplies.

Harmon/kardon AVR161 review
Harmon/kardon AVR161

The audio output is nothing to write home about, 85W RMS x 2 channels driven.  I needed the HDMI more than anything which was 5 inputs, more than I needed in any event. Optical and coaxial inputs, 2 x analog RCA inputs and composite video output make this HT receiver as barren as the Sahara but this is what appealed to me.  And the setup is ridiculously easy. Neat and tidy. An omni-directional microphone is part of the package and we were up and running within ten minutes.

AVR161S - rear connectors
AVR161S – rear connectors

Not going into what it can and cannot do, it’s all in the manual, it must be emphasised that this little receiver has excellent reproduction quality, it is quick to set up and the power is more than ample.  The on screen display is simple to understand and all inputs are easily allocated – in fact I would say it’s the easiest installation I have ever done. But then again this is what HK is all about.

This is not a multi zone receiver like the 171 – I really don’t know of many people using this function either properly or on a practical level.

I did not like the volume control illumination but I did like the fact that the dimmer on the remote reduces this to a pleasing level.

For a little home theatre amplifier albeit big brand coming in at just under R 8 000 on the South African market is a rare steal.  Thumbs up to Govan Mani in Durban.

harmon/kardon AVR161S
The AVR161S all set up and in action

I’d like to say this was an elementary review but when one purchases something for their own entertainment and nobody else it may come across as being biased justifying the purchase. In essence – just Iove it.

[Editor’s Note:  Harman International Industries is headed up by Dinesh C. Paliwal as CEO. In November 2016 the company revealed it was to be acquired by Samsung. I wonder what Mr. Trump thinks of this?

Brands include: Harman Kardon, Becker, JBL, Crown Audio, dbx, Martin Professional, AKG Acoustics, Lexicon, Infinity, Mark Levinson, Revel, Soundcraft and Studer]

The Famous L20 – sold on eBay

L20 - 350W audio amplifier

There is one amplifier that seems to get more attention than most and that’s the L20. I have no have experience of the L28 which has a built in speaker protection circuit.

L20 - 350W audio amplifier
L20 200W 8 Ohms – 350W 4 Ohms at +/- 60V – advertised on eBay

Straight talk, these are mono amplifiers, there is no bias preset neither speaker protection so make sure you get one for each amplifier or the Vellemann K4700 dual channel protector.

Communica sell the K4700. I purchased mine from Velleman USA. In 2014 R300 incl. import. These are for two channels.

K4700 - dual channel speaker protector
K4700 Velleman dual channel speaker protector

Pro-Tecc in Durban sell their own brand. Last pricing was R46.00. Mono only. Spade or terminal posts – easily modified.

Mono speaker protector
Speaker protector – mono – from Protec Durban

The Kit

Easy to assemble, no schematic, painting by numbers. One can build one amplifier in an hour easily. Be careful of polarity. You must have a DMM to actually measure the resistances before populating – sometimes the colour coding can be a bit daunting especially in low light or when you are no longer a spring chicken. Board quality from most of these Eastern suppliers is very good although some of the manufacturers do complain of counterfeiting, poor quality boards and dodgy transistors.  Make sure you have PayPal protection and the supplier is authentic.

The power supply

Power supplies are obtainable from most of the exporters or kit suppliers but be warned, exporting of Toroidals or even EI transformers are very expensive due to the weight. Support local.  Swiftheat is one. See below.

Transformers for these amplifiers was supplied courtesy of a Sony audio guru in Cape Town. The STR500 series (plus others) carries a 220 : 42-0-42 transformer which seems to be adequate for one channel. I very happily became the proud owner of 4 of these.  Why? They are prone to overheating when these amplifiers are slammed hard, the heat protection sensor in these transformers goes open.  With a bit of digging one can remove the sensor and bypass.  Once full wave rectified and smoothed out you should be looking at about 60V DC per leg or +/-60V.

Smoothing caps were 2 x 10 000uFd per leg, obtained from Yebo in Bellville. Code ELC108, currently priced at just under R100.00 each.

Note:  The original power supply which I still have was made up of 6 x 400~500VA 7-0-7 (14V) UPS transformers.  I loaded the power supply so that there was a constant draw of about 25A per leg at 52V (3 in series * 1.414) without any sign of a dodgy heating pattern amongst these transformers over about 8 hours.  The problem is that the power supply weighed in at 24kg.

A really great alternative is to try Swiftheat in Johannesburg – their pricing for a 1000VA toroidal used to be about R 2 200.00 exclusive VAT.  This is a very fair price based on what it would cost for an import or through the DIY channel. This included washers and dipping for audio use.  Note that this pricing was April 2015.  Include 7 days after payment for manufacture.

Heatsinking was obtained from Mantech, code A0M0097. Purchased two 8 3m lengths. Each amplifier used a 40cm run.

L20 Sound quality

Exceptionally good. I was worried about bias, this is factory and designed and obviously we would have concerns about transistor mismatches etc. Not to be, all four amplifiers I purchased were rock steady and from what I can recall about 20-30mA.  The amplifiers were tested into 2 * Dixon 600W 4 Ohm (you know the one – 18″ bass driver and millions of piezo high frequency drivers) plus 2 x Dixon 15″ (which sound pretty shitty but for clubbing, who cares).

The quality of reproduction is amongst the best I have ever heard.  To be frank I did not trust the Sony transformers but they held out.  The original PSU bank of UPS transformers laughed off the current draw, bearing in mind that when using a program source such as music, proper music, Floyd, Deep Purple, Black Sabbath and Metallica 🙂 the current drain is really minimal compared to potential. And that potential one could nearly weld with.

Some little things to remember:

The heatsinking at full power is not really adequate once boxed. Use a fan blowing onto the output transistors ensuring each transistor gets the same treatment. You do not want to have thermal issues causing the output transistors to start current grabbing.

The original PSU using UPS transformers had sensing on each secondary rail. Because each transformer was separately fused primary and secondary this would shut off power if only one fuse blew preventing one rail of the PSU output to remain hot.

The speaker protection circuits, whilst great for peace of mind will not prevent voice coils burning in the event of a relay contact being burnt shut.  These relay contacts are not designed for professional and high powered use. Bear this in mind.

In conclusion

I still have the L20 x 4 channel amplifier which was going to be used for home theatre. I subsequently purchased the Behringer NU6000 4 channel amplifier. The L20 is in Cape Town, I am in Durban otherwise I would have posted photos. I am looking for McIntosh style VU meters though. Like most, these really add a professional finish to any home built equipment.

McIntosh Amplifier
McIntosh Amplifier – damned gorgeous

The JVC RX-5042 mods

RX-5042 Amplifier blocks

Why the RX-5042 for modification?

In our previous article we rant about the cheap RX-5042 which can be picked up for next to nothing.  The problem is that it is a home theatre amplifier, along with the poor tone controls and lack of MM or MC cartridge inputs.  To keep the audio circuitry strictly short path analog and of course ensure that power amplifier speaker protectors remain operative we add minor changes – a separate stereo preamplifier plus RIAA turntable input.

Relays configure the routing of the left and right channels, the center and surround inputs are muted (grounded) and an LED shows when analog with Baxandall tone controls have been selected.

RX-5042 Power amplifier
RX-5042 Power amplifier – click to get bigger image.
RX-5042 Amplifier blocks
RX-5042 amplifier showing modules – click for larger image

In our next article we will drill down to the changes showing stereo preamplifiers with tone controls and switching. This will include LFE out.