On the Edge – amplifier design
Isn’t it frustrating to shop for the ultimate sound system on a limited budget. You see one, you hear one and that one on the next rung up always sounds that little bit better. Fortunately we have good news. It’s all in the mind.
Anyone being an avid reader of any electronics and audio magazine that does comparison tests will often get overwhelmed by the amount of products on sale, let alone by the costs of these high end pieces of equipment. It’s almost like playing chess against a grand master – no matter the move, there is always one better. So it is with audio gear. The problem is, we often fall foul of the marketing machine and sales personnel pressure. Don’t. Whatever you do, never buy a sound system based on whatever someone else tells you. What we do know is that power output is no longer directly linked to pricing, semiconductors are cheap. Even Chinese manufactured toroidals are no longer the price it was ten years back. But what should one know?
Inputs and more inputs, all with the same output
Most audio amplifiers brought out over the last few years have surprisingly good build and sonic quality. For movies one loves the idea of being able to set up the sound stage through a microphone and an automatic process. However, audio installers complain about most users not setting up their systems properly even with electronic assistance Read up on this in the manual. If you are only buying the integrated amplifier like most of us do then ensure you have sufficient inputs. This seems to be the most important thing in the designs found currently on the market – millions of inputs. On a practical level these inputs should be HDMI and one or two for legacy use.
Marketing trends push for big power and in our experience this is true, go rather for overkill. Pick up the amplifier, weigh it if necessary. Most of the weight is transformer and cooling based. A Class D amplifier is light – that’s a design advantage. Class AB will be heavy – that is also a design advantage. If it’s Class AB, delivers upwards of 60W x 5 or 7 channels it will be heavy. How heavy is heavy? We have our own estimations but do look at manufacturers such as Marantz and NAD. These guys don’t skimp on components least of all quality of the mains transformer. The importance of this is multi-fold. Read up on how tests are done and in this case, specifically output power measurement. Transformer secondary (output) voltages sag when under load. Power supply regulation is critical and to compete with the best there should be no compromise. This is where most budget systems cut costs.
Purchasing an amplifier which lacks oomph will cost more in the long run – you will be disappointed. If it’s a headphone amplifier you want then one needn’t be looking at killing your ears in one sitting. And no, you cannot put audio amplifiers in series to get more power. What you can do is purchase separate pre-amplifiers/processors and power amplifiers. It will work out cheaper in the long run if you need to upgrade for higher power. This a more expensive solution but possibly a better long term plan. A well looked after, carefully selected preamplifier/processor may even prove to be a lifetime “investment”.
Six channels or more, two is best
Two, three, four, five, six, seven or ten channels? Here the choice is yours. There are many audiophiles passionate about their movies but only use two channels or stereo. The home movie expert may prefer the most amount of channels he can afford. 5.1 is still rated about the most common. Quantity over quality? A good quality stereo setup beats a multi-channel movie theater setup for music anytime. (of course this is bias).
Tubes versus semiconductor? Dollar for dollar there is absolutely no equaling the transistor or semiconductor. (I will add this though – my own opinion is that early transistorised amplifiers lacked the musicality of tube amplifiers. If transistor amplifiers were first on the market maybe I would have rewritten this and in all likelihood battled to justify the rationale. The fact remains though, musicians on a whole tend to prefer tube sound. So there!).
Why on the edge? The objective of any audio amplifier is to faithfully reproduce the input signal as an exact image except for amplitude at its output. Through the years scientists and engineers have near perfected this art. A bench tested audio amplifier which reproduces with clinical precision the input program material to its output will sound good through a quality loudspeaker system. Most amplifiers today, except for cost cutting in the power supply will do exactly that. So where to now?
Digital is Doomed
Although we are living in the digital age man and machine will never be the same. Our logic is often irrational and therefore biased. We cannot live in peace with each other because of this exact reason. With audio equipment we take a very sophisticated (in scientific terms) analogue signal, convert to binary, we then read the binary and convert to analogue. We them chop the analogue at a high frequency, modulate with a sawtooth wave, switch at a high voltage and finally filter out the high frequency component. We then feed the analogous high amplitude signal to a transducer which is an analogous device. Then the marketers come along and tell us vinyl is back!
We have fine tuned the Class D amplifier for home use but yet it’s true advantage is when used in cellular technology. We have lowered the cost of high powered audio amplifiers through this technology but yet loudspeakers have always been the obvious weakness, both in cost and efficiency.
It is time for manufacturers to look at cheaper and more efficient methods to reproduce this amplified signal. The fixed magnet, moving coil paper or synthetic cone speaker *aka dynamic driver) should be cast to the ash heap, audio amplifiers have been re-looked at so many times that it’s run out of steam.
How it works… further reading: Loudspeaker types