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
V-Relay – the relay coil is grounded in “Mono” mode.
Tube Bias
Tube Bias

Mains transformer 110V or 220V primary

Secondaries

  • 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.

The JVC RX5042 – Some say it’s Good

RX-5042 - some say they are good

First up on the operating table – the JVC RX-5042

If ever I had to give an entry level home theatre amplifier 6 stars it would be the JVC RX5042.  Purchased in 2004 at the Hypermarket in Brackenfell for a mere R 1 600.00 I was expecting an amplifier from hell.  In fact, I did a little bit of research and on a forum and in German an owner said “Buy it!”. This was the only information I had so like a stupid boy blowing his pocket money I did just that. And was I surprised.

RX-5042 - some say they are good
JVC RX-5042 Great performance at low cost.

The RX5042 did not come with all the bells and whistles but it did have five shift rail power amplifiers rated at 100W into 8 Ohms. An entry level Yamaha at that stage cost R 5 000.00.  Home theatre is home theatre isn’t it, I thought. In fact the JVC was better than the Yamaha – in power that is.

Pink Floyd thundered into the night at full volume and after two six packs of Amstels. It ran hot, mightily hot into 6 Ohms.  It did not fall over, cry or blow off steam. This year I replaced it with another entry level amplifier, a Harmon Kardon. It has nowhere near the power nor the fidelity but it does have HDMI and Bluetooth.

Paying more for HDMI

This poses the question. Should one replace their amplifier because it doesn’t have HDMI capability?  Hell, no! Should you buy the 2017 Mercedes now that you have the 2015 Mercedes. Hell, no.

The big problem as I see it is for the corporate machine to continue rolling out new products to keep their sales up. We need to add more technology to make it more attractive. Ditto Mercedes. Ditto clothing, food, hygiene and cosmetics. The JVC was plonked into an entry level market at a sub entry level price. Think cheap. Think nasty. It’s none of those. It seriously whacked the competition in many ways except for the damned inputs.

RX-5042 Shift Rail Technology

The shift rail power supply technology is nothing new. It’s designed to be very efficient. Even NAD uses it.  Hey, NAD! But that’s expensive gear. The RX5042 uses the STK412-300 IC which is rated I believe at something like 150W per channel (two channels per IC).  Supply rails are +27, +55 and -27, -55V. Into 8 Ohms this equates to about 180W into 8 Ohms continuous or 350W into 4 Ohms.    ((Vcc^2)/(8RL)). These chips are even available at Communica for about R240.00 per pop. Actually, most of the power amp parts can still be easily obtained.

The amplifier is heavier than a lot of the modern entry level stuff which puts even the power transformer into a different league.  But no, be careful here – this is not a 500W machine.  On the safe side I would say the transformer is at most 200VA.

Digital Signal Processing – how to mess up the analog signal

The problem I find with home theatre is that the preamplifier and DSP circuits should not be designed by a kid with braces. I don’t like the DSP on most of these amplifiers, even some of the more expensive models. The JVC is no different. Actually, why would anyone want to reproduce a movie to sound like that coming from a tin can. We do need Dolby Digital though. Of course.

The JVC doesn’t come without problems of course. The gurus will shout out that the loudspeaker terminals are disgraceful, which they are.  Sometimes the optical loses sync. Sometimes there is no output at all. Sometimes it’s all user intervention and troublesome fingers. Mostly the JVC is mediocre input wise but all the analogs work.  So what to do, what to do?

Let’s Arduinofy it!

We won’t touch the DSP, we won’t even touch the audio circuits. We will add circuits though. We will add an RIAA preamplifier for vinyl, MC and MM. We will add a Baxandall tone circuit for the front left and right channels.  We will even bypass the preamplification and digital stages. We want analog. We will mute the other channels. We will equalise and have drive for a sub, just in case you want it. And of course this will all be driven off a remote control. I like my amplifiers simple and easy.

Next phase:  Getting to grips with the technology of 2004

 

(Editor’s note:-  these receivers get very good reviews based on price and in comparison to similar models of other brands. A common problem was the setup through remote and switching between analog and digital although there is an auto switch.  JVC was never known for building high quality audio equipment, their niche supposedly being in TV and of course the ever famous JVC VHS video recorder. The reality is that they largely make very good audio amplifiers. JVC is in many ways compared to Sony.  In our own tests the JVC outperformed power wise any models in a similar price range. Without blowing or tripping/fusing the thermal link to the mains transformer. In stereo mode, well over 130W RMS per channel. These amplifiers plus big brothers, the 6042 and 7042 can be picked up for under R 1 000.00 in the RSA. If you don’t have the wallet for the more expensive gear, try these models. You may be pleased at the results 🙂   )

Sound quality, tips and tricks

Tips and Tricks for Sound

Home user audio setup without the hassle.

Sound in this case refers to the non-noise variety.

In many instances headphones are man’s ultimate friend. Unfortunately in the real world we also like to feel the sound, have the luxury of depth, colour, bass and all the magic that goes with it. Whilst a good set of headphones does the trick often just two tools in your briefcase make a huge difference:

i) A scientifically calibrated microphone and (ii) REW, the free but powerful software program, Room Equalisation Wizard. REW helps you analyse your living or sound room acoustic performance for optimal placement of speakers.

Tips and Tricks for Sound
Using REW – Room Equaliser Wizard

The part we won’t like is always in the final analysis – too many times your room is just crappy. I am in such a position, the listening or home theatre room is in the shape of a polygon. (concave, where one wall angle is more than 180 deg).  For home theatre use it is extremely difficult to set up and really needs acoustic treatment. Ditto for home studio use as well, just too many reflections and of course, there’s a road at the back.

There are many articles written about the treatment of a room to get the best in acoustics and reproduction which mostly applies to studio use – here we will apply some common sense to prevent things from going wrong from the outset.

Notes for those techno gurus:

The USB microphone UMIK-1 from miniDSP is not available in South Africa as far as I know. You will pick them up on Gumtree from time to time otherwise look at the resellers overseas. 2nd hand they go for about R1 000.00. This piece of kit plus REW on your notebook make for easy setup. I used a Behringer ECM8000, Focusrite Scarlett 18i20 (overkill but I had one on hand) and REW on a notebook. Note that condenser microphones need phantom power.

Noise, buzz and hum

Buzzing is a serious irritation. Often swapping the live and neutral leads on the amplifier can make a difference. Is it advisable though from a safety perspective? No.  Your live is always switched. Check your screened cables. Don’t you just hate those cables which have about a millimeter of insulation thickness with a micron of copper inside. Sold to look expensive. Make up your own cables using proper microphone cable – best to get the balanced type which can be used for RCA, XLR and 6.3mm stereo jack plugs or sockets. (RTS), this is twin core with a good quality screen.

Balanced over non-balanced

Big advantage of professional audio is balancing the signal but for shorter 2m lengths this should not pose aproblem. Most users complain of turntable hum or buzzing. Hum is often caused by noise from the mains transformer – this can be 50Hz or 100Hz, the 100Hz coming from the output of the rectifier (South African mains frequancy x 2).  More often than not the hum/noise comes from either too many ground points (use a central grounding point), broken ground point (screen) and never forget the obvious, the HOT part of the signal is missing due to a broken wire. This one is so obvious that we overlook it – cheap and nasty cables are always the problem here.

Hum and noise is a big problem and even seasoned audio engineers battle to get the ultimate signal hence the ground lift on injection boxes. For your home system try switching off the amplifier and listen for immediate changes.  It could even be a leaky reservoir capacitor but this will be heard with no signal input.

Turntables

My own nightmare – hum from one cartridge (Audio Technik) and nothing from a Stanton.  Grounding wire inside the turntable tone arm making no contact.  Using a jumper with croc clips from tone arm to signal shield clears the noise. Both cartridges brand new. Same problem with both turntables, SL-1200 Technics. Ah-ha, different amplifier and the hum disappears.

Here’s the problem.  The Stanton did indeed ground to shield. Reversing the L-N mains connectors of the first amplifier made a difference.  The on off switch also switches both N and L.  Make sure the metal casing (if it has one) is earthed.

Turntables generate only a few mV p-p and noise is often a problem caused by poor grounding, broken cables etc.  For a moderately expensive turntable the LT-1200s failed to impress in the cable area. Whether you are a DJ or not always pay attention to the condition and quality of this cable.

Likewise microphones also run at only a few mV and setting up a mixer to have little or no noise at it’s output can be a tedious exercise. For live shows and studio recording this is a strictly no-go area.

Most complaints come from users noting that touching the casing of the turntable or amplifier reduces the noise.  To troubleshoot you will need to think methodically – was this problem there before,  are you using the same mains outlet, are you using a multi-plug, etc? Even pulling an input signal RCA plug out half way to break the earthing can make a difference. Sometimes in very bad cases the amplifier has poor grounding inside the chassis.  This can heard in the form of clicks and pops, speaker protection kicking in and worse case scenario, burning of the speaker voice coil.  (Akai amplifier, multiple grounding points, chassis corrosion causing output voltages to swing to +40 or -40V without input signal. Believe it or not).

KISS

Keep It Straight and Simple.  In every case where I have had a myriad input connections it becomes difficult for family to switch the inputs and/or we have a noise problem with low level signals. Home theatre amplifiers don’t have a MC or MM input. When playing around with signal matching always have a low impedance plugged into a higher impedance and not the other way round.

A turntable cannot be played through a microphone input because the signal needs to be RIAA (Recording Industry Association of America) equalised known as de-emphasising.  During the recording process it is emphasised, emphasising the higher frequency notes over the lower.  The reverse is applied on playback.  Your vinyl will sound absolutely horrible playing back without the de-emphasis and if I recall, very tinny.

Speaker setup

Ummm. Not very evident but placement can be a nightmare.  As a rule of thumb, main speakers 6 foot from amplifier or 12 foot apart, sub to the side. Latency to rear speakers setup according to amplifier manual. Volume control on each channel set up according to manual. If all else fails use stereo.  No jest here.  Many purists don’t watch their movies in 5.1 or 7.2 or whatever.  Magical speaker wire?  A test in the 70s states that telephone cable (you know the solid wire type) had the best results). Move speakers away from the wall.  There’s a lot of trickery in placement and a lot comes down to the speaker design. Fiddle. Don’t forget spikes, metal or rubber.

Noisy speakers?  Damaged voice coil or loose wire. The worst one is shorting cables because the amplifier is not going to like this one bit.

Amplifier showing protection mode

Use a hair dryer before switching on.  Sony amplifiers just love to be over sensitive. They are not the only ones.

As an aside…

Whilst some of the tips mentioned above won’t necessarily eradicate the hum, buzzes, clicks and grunts on your system it may prove to be helpful – a noisy background no matter how small is irritating. Shorted speaker cables are a very common occurrence which usually happens when the phantom does house cleaning.  Although amplifiers have current protection don’t hedge your bets that it’s totally fail-safe or foolproof.

As a DJ in the 80s it was seriously stressful to start any show which was perfect the previous evening with a background hum of sorts, even clicks from a fridge thermostat. In most cases it was caused by broken cables – retailers should be banned from selling poor quality cables with so called gold plating and crystal coated silver wire. Time and time again making up ones own cable sets were the best solution. In those days professional audio was only for the deep pocketed.  It’s really time that a standard be reached where your audio pre and power amplifiers start using XLR above a certain price bracket.

Next edition:  Setting up REW

The New Vinyl – magnetic tape

And the final outcome: Magnetic tape beats vinyl.

Well we don’t really know about this one but based on our research this seems to be the case.  But let us be realistic.

A good turntable is going to put us back about R7 000 to R8 000 and then we are only just starting up our engines.  A good professional series tape recorder, which you don’t really need is going to be upwards of R20 000.  But here’s the crunch: the tests get done on a master tape copy or at least as damned near to a master reproduction. These cost upwards of R4 500 per tape.

Magnetic Tape beats Vinyl
The cat “eMotion” enjoying some analog Part I Act II

If we take the vinyl and record to a professional series reel to reel deck the reproduction can never be better. Likewise tape recorder to vinyl unless you have the master copy vinyl already. We won’t bicker here – most people will understand this but here’s the crunch.  Just what amount, what value do we put on this reproduction which is so outstanding, so good, that the hairs stand up on your arms? What came first, the chicken or the egg?

Value wise digital lies top of the list.  I will argue the point that the Zoom H6 hand held recorder from record to reproduction at under R7 000.00 cannot be beaten by any analog system.  The audiophile community understand the rationale about having an excellent DAC and of course, ADC. Your digital CD player output frequency range varies between 20 Hertz and 20 kHz.  Those engineers behind CD format weren’t on Opium when they devised that 44.1kHz was the optimum sampling frequency. It’s twice the maximum frequency we can hear after all.  What then makes vinyl then second best and tape, the ultimate in audio luxury? Well these are analog pages after all, right?

Magnetic Tape beats Vinyl
The cat “eMotion” enjoying some analog Part II Act II

To put things in perspective one needs to be the right age, that age which brought us through analog into our digital world.  The first listenings to digital after twenty years of vinyl, R2R and cassette tapes. Crystal clear, frighteningly clear in fact. Great dynamic range and when played loud, no feedback. No skipping, jumping, popping and cracking. Just beautiful sound. Picture this in your mind for thirty seconds and now jump to 2010.  Invited into a friend’s home to undergo a blind listening test. No reason given – just blindfolded, ears open and listen.  Dark Side of the Moon.  Different, very, very different.  Ambience, colour, warmth.  No new amplifier, no new speakers just a Linn Sondeck and a brand new vinyl reproduction. This was the same freaky feeling I had when listening to my brother’s vinyl reproduction of The Wall after years of listening to the digital format.

What do you think?

Next:  Part II – start your engines folks and open your wallets – here comes the 1950s and 1960s Reel to Reel….