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.
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.
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.
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]
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.
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.
Pro-Tecc in Durban sell their own brand. Last pricing was R46.00. Mono only. Spade or terminal posts – easily modified.
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.
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.
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.
In our next article we will drill down to the changes showing stereo preamplifiers with tone controls and switching. This will include LFE out.
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.
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 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.
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.
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).
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.
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.
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.
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?
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….
Good artisans in South Africa – a sought after breed
Here we give a high five to those really in the trade.
A question often coming up over the last five years and more so now in the RSA and especially after all the turmoil at almost all the universities in South Africa is what has happened to the artisan?
Mathematics and Science – bring out the abacus
It’s no hidden secret that everyone wants to become an engineer in high school but our average 16 year old sadly does not have the level of understanding in maths and science that a pupil in the Netherlands or Germany has. Trying to gypo the system through lower pass rates and barrier to entry into engineering courses defeats the object. We allow no error latitude in aviation so why should we in civil, structural or mechanical engineering.
Here’s the thing though – when I matriculated in 1976 it was not frowned upon to become a boilermaker, plumber, electrician, mechanic or sheet-metal worker. Recently, I do believe it was the January edition of Popular Mechanics a youngster asked why we South African’s don’t design and build their own cars? It’s a simple but very good question. We had the Flamingo and Dart and the Ranger (by GM, believe it or not), a copy of the German Opel with a 2.5L 4 cylinder motor. All things considered, this is where we should be. Heavens above, we should have the talent. (take note younger readers – Google Basil Green Motors, Capri Perana V8 and Willie Meisner, Bob van Niekerk and Verster de Wit. Those were the days).
Good not Mediocre makes an artisan
What many people forget is that a “good” artisan, a diesel mechanic, electrician and millwright earn often more than university graduates. What makes their qualification and four years experience worse than that of a B.Sc grad in any event. We laugh about the adage that a tradesman fixes the engineer’s mistakes. .
Forcing out artisans as we compete in a space which is often thought barren, the engineering sector, we are creating another hole. I do not know whether the educational sector is looking into this and what their plans are – we do not read about this in the media. We do read about the carnage at the universities though. Oh yes, at trade school there is also no time for mischief, one used to get ousted for any misbehaviour. God forbid the electrician who burns down his or her trade school because it’s their constitutional right. What happens around the DB or repairs to the mission critical control circuity once they start getting their hands dirty? Maybe an unstable mind at work in a medical lab or hospital auxiliary supply.
Many of our top scientists are those that do not have the luxury of university education. They went through the “Street School” and understand the mechanics of life. And are better off educationally and financially.
Michael Faraday remains one of my firm favourites. Maybe not exactly an artisan but certainly an expert in his field without the degree.
Bring back the artisan! Stick your neck out and give us a good story.
The difference between JIMC and the Compact Linear Collider Test Facility
*Having ordered some decals and buttons for two Technics turntables from KAB in the USA (https://www.kabusa.com/) some near three months back I am disappointed to find out that to date I still don’t even have a conversion number for the USPS number to track the parcel.
After numerous calls to the Johannesburg International Mailing Center of which none were answered, numerous emails, of which two were replied to and now, subsequently directly to the postal service where a lady replied to 2 of the 3 emails, I am none the wiser. Yes folks, it takes three months to still not know where my parcel is except it left the USA on the 4th November. Is this really possible?
An owner of a large ecommerce company said that absolutely nothing had changed in this respect – the postal services remained just plain useless. This saddens me. We were all expecting a massive turnaround after Mark Barnes with a well proven track record took over. And South Africans world over rely on this service.
Government even complained to us through the news media that ecomm in South Africa was behind the times, we needed to re-invent, to change, make things better, make it South African, a first, breath-taking technology, hellfire and brimstone. But sadly it is not to be because the postal service which would be or at least should be the backbone to this industry just cannot play ball.
With a multi-billion Rand courier industry within our borders it’s crazy to think that the SA Postal is still not trying to get in on this act. But then again that’s why we have a billion Rand courier industry.
Near three months and still no sign of even a delivery date but we have space vessels already having landed on Mars. Wicked, absolutely wicked.
There are thousands of people living in the RSA whom import at the mercy of the postal services. We need to change this.
*Update: 2nd Feb 2017 – my LT-1200 has finally arrived from KABUSA. Received a final collection notice on the 1st. Don’t know about the other two but yes, all ready for fitting and playing.
The conundrum of audio, the one that all audiophiles abhor, Class D. There are many beliefs behind this one of course, one being chiefly that Class D is digital because the output devices are running in one of two states, on or off, 1 or 0.
The theory is not so simple however. 1s and 0s are binary which is not only fundamental to all computer languages but is set at a reference predefined voltage e.g. 5V and frequency (clock). The class D amplifier utilises sampling, modulation and switching as a basis of operation. The switched output before filtering will show pulses of varying mark space ratios – the 1:1 or equal ratio has no audible output.
One thing that always struck me as distinctly odd was how the marketing machine would advertise a specific brand of car audio as digital or switching amplifiers. This can be seen on the Hi-Fi scene as well as in Pro-audio. The car audio amplifiers used switched mode power supplies with class AB audio, the rest, well digital amplifiers known to us as class D. A throw-around of quick catching and nice sounding phrases which never described the equipment adequately. An amplifier with a DSP component could be called a digital amplifier I suppose but it doesn’t fully describe the amplification technique does it. DSP can be added to the input of an audio amplifier running class A and then be called digital. Class D however is not digital, sorry. It’s a switching amplifier. Period.
And more marketing
Along with rail shifting amplifiers with all their glorious classes, the fantastic class T switching amp, digital or switching class D the public must by now be thoroughly confused. I think even professional designers must be confused as hell – as soon as one class becomes relevant another one takes shape. Years back we had class AB1, 2 etc. Class C was for RF (yep, Morse code was one use) and the top end amplifiers were supposedly all class A. In fact, us, the general user should only know three things – does the output stage amplify the entire signal (class A), are the positive and negative excursions driven separately with minimum distortion (class AB) or does the output contain varying mark space pulses (class D). Over the last fifty years all three have been in use and still retain the same definition. Whether the amplifier uses +150V at high power or only +50V below 20W is really irrelevant. Whether it amplifies the entire signal or only part of it on purpose by design is relevant.
Can we hear the difference between the classes?
Many people can hear things I cannot. We have listening tests to prove or disprove which amplifiers are best. Theoretically the best audio amplifier should be the Class A beast. Heavy in power supply and cooling (as it is the least efficient), very expensive, it amplifies the entire input signal as it should – in absolute mirror but for amplitude. The pedantic will cry for no phase shift either.
Truth be told Class A amplifiers do have a good reputation but usually when built by reputed companies or if self built, there is no expense spared for power supply and cooling.
Class AB amplifiers – we call them AB because in pure B we would have switching distortion which sounds horrific so a little bias is applied to the output stage to push them into their linear region (ahhh, slowly going back to class A). Class AB can sound just as good as A if designed properly but there is always that niggling suspicion that we have that damned crossover distortion and the output stage is not linear. But over a few watts of drive into the speaker they do come into their own.
Class D. Try as I might I always think, believe, hear whatever that AB has better reproduction at the high frequencies. Having said then we need to be looking at class A, possibly bi-amped.
And what does my 40 years of experience tell me? Build your own. Play around a bit. Have fun. That’s how the best engineers started. Your home built amplifier will always sound best.
One of the best designs (although I never used the commercial PCB but regret it now – this will come next though) was Rod Elliott’s 60-100W project: http://sound.whsites.net/project03.htm. I used a NAD pre-amp (1020A) to drive these modules. OK, so I never used a PCB and yes, I only built these because I was interested to get back into electronics as a hobby – I was really very, very impressed. The noiseless monster. In the late 70s I built a kit which used an MJ802 and 4502 which knocked the socks off the competition – well this one was better. I really think where this project stood out was that it was better than the 3020A (remember that the 1020A is a 3020A without the power amplifier). I always thought that the 3020A sounded too flat.
Going to purchase the project PCBs at the end of the month. (31st January 2017). Let me know whether you need so we can consolidate costs. webmaster at analogian dot co dot za
Take your pick, tube or valve? All irrelevant – ones Americanism (tube) and the other English as in UK (valve). We have a plate (American) and anode (South African and English). Cathodes are directly or indirectly heated (indirect = heater to cathode) which emits electrons which is attracted to the positively charged plate. Place a controlling electrode (grid) between this flow of electrons biased negative and you will be able to control the flow of electrons. Place the electrode close enough to the cathode and you will be able to with very little change in grid voltage change the flow of current by a large magnitude.
I studied radio valves ad nauseam doing our radio telecommunications course. In the 70s this was still mainstream – transistors just did not have the high power capabilities of transmission tubes. Tubes were also easier to understand than semiconductors – to a degree. Don’t be fooled by their simpleness. Radio engineers of old were very clever people. As this is not a science or electronics lesson I would like to cover what I felt was interesting about tubes – the part essential to us still using these beasts, my practical hands on experience will assist of course. 🙂
Besides for the high voltage DC and low voltage heater voltages tubes were remarkably resilient except for the diodes – big, cumbersome and had a tendency for the bottle exploding when you were twelve years old and working on a tube amp without parent supervision. In the palm of your hand you could be holding a 2kW device. A great example of a modern day tube is one which is made from ceramic, the 4CX800A, a 800W device. It is 9cm long and 7cm wide. You could try the 3CX10000A7 which is only about 20cm high and 17cm in diameter but can dissipate up to 10kW. These ceramic tubes were blast air cooled. Oh yes, they can be used in audio amplifiers as well. The 10000A7 costs in the region of R40k per unit. With two of these you could be pushing a 30kW amplifier. The heaters would be drawing about 200A.
The interesting fact about the above is that with just 8 tubes you can make a 20 to 30kW audio amplifier which should be enough for some people’s ears. The driver for each tube would need to be in the region of 1kW. Hell, there are AM transmitters running at 500kW (even the SABC had them, the old short wave variety). For modulation you would be looking at 250kW audio amplifiers.
Whether triode, tetrode, pentode or power tetrode they all served a purpose. In radio receivers (and other devices) the tubes were designed to act as mixers as well which meant you would have part of the tube being an oscillator and part the mixing stage (i.e. your intermediate frequency would be difference between local oscillator and input frequency e.g. 15MHz input, 14.530MHz local oscillator with a 470kHz intermediate frequency or the more popular 455kHz. Ingenious to say the least. Much easier to amplify a 470kHz signal than 15MHz. Think now of radar working at 10GHz and how difficult it must been for engineers to amplify any signal at that frequency without an I.F. amplifier.
Moving back to the last ten years we have found an abundance of audio gear coming back into the market place with tubes or more probably hybrid systems which use the best of both worlds – tubes and transistors. Enthusiasts roll their tubes, changing or swapping out with other makes and types to get the result they find pleasing to their ears. This is an expensive exercise of course. Musicians specifically find the best mix and stick to that.
As an exercise, one without prior experience and wanting to get into vacuum tube audio should look at the most popular designs and what tubes are used. Almost all will have an ECC83 or 82 (12AX7, 12AU7), EL84 (6BQ5) EL34 (6CA7) – also 807, KT66, KT77, KT88. 6SN7. Besides having access to a huge selection of NOS (New Old Stock) we also have newcomers (not Russian NOS, they have been around for eons) from Russia and China.
The one problem with all tube audio amplifiers is the need for audio output transformers – this matches the high impedance load to a loudspeaker load. Besides being very quirky to manufacture one needs to understand that there are high voltages on these devices. They are also very expensive. Solid state just does not need them because they are already fit for low impedance drive.
A question often asked is whether to have a tube preamp and SS output stage or SS preamplifier with tube output stage. I get very convoluted answers to these questions – what is relevant though is that it is believed to be the audio output transformer adding to the magical tube sound. This puts paid to having the output stage being SS or purchasing a tube preamp. Huh – nah, each to his own. My own experience though is that listening to a tube amplifier with headphones (Sennheiser monitor) which is connected through the output transformer and then having a tube preamp through SS output stage into the same set of headphones (with headphones connected to SS power amp and not tube preamp :-), the sound was virtually the same.
Tube preamplifiers with SS or tube power amplifiers, often the single ended output stage EL84 or 34 are often used to drive the high range speakers in a bi-amped system. SS to the bass driver. For me, that’s the match in heaven.