Both configurations in basic form, since there are many variations are shown in Figure 7. For the most part these typical lightweight amps satisfy the light users, but not the pros who have used these amps and hear the lacking bottom-end at high power levels. The original harmonic distortion standards for audio were laid down by D. This creates both the low order harmonics of the valve amp, plus high order harmonics which may be very fatiguing. The results are degraded distortion figures, especially at high frequency, and poor thermal stability. This small biasing arrangement ensures that both transistors conduct simultaneously during a very small part of the input waveform by more than 50 per cent of the input cycle, but less than 100 per cent. Although this will introduce local feedback and reduce the available gain , it is non-linear, resulting in distortion as the current varies during normal operation.
The power amplifier will clip asymmetrically, and is no longer operating in the linear range - it is distorting. The use of the compound pair requires no more components - the same components are simply arranged in a different manner. Capacitor Ripple Current - It is well known that bigger transformers have better efficiency that small ones, so it is a common practice to use a transformer that is over-rated for the application. Again, the subjectivists would have it that these fail to take into account some mysterious area of our brain that will compensate for a restricted response, and allow us to just enjoy the experience of the sound system. I don't know the reason s they may have had for not using the complementary pair in every design they published this magazine is a lot younger than I. This can lead to a phenomenon called 'cross-conduction', which occurs because the transistors cannot switch off quickly enough, so there is a period where both power transistors are conducting simultaneously. As mentioned above, additional local feedback 0.
It's not essential, provided that the setup instructions are followed carefully. For a 40 Volt supply, if Tr2 were to have a gain of 50 at 1A, then. What I truly enjoy about this book in comparison with other books on the same subject, is the fact that Douglas self discusses many exiting topologies used in commercial amplifiers as opposed to just giving you idealized models, you can see actual circuits of many amplifiers spanning decades ago and Douglas Self will point out its advantages as well as deficiencies. Input Stage Summary Based on the tests, there are pros and cons to all approaches single transistor, long-tailed pair and symmetrical - and I'll bet that came as a surprise. It is common to bias the Class-A driver stage so that it can provide between 1. Had a current source or similar been used as the load, I would not have been able to measure the gain accurately, since the input levels would have been too small.
If you want to get full power at 100kHz or more why? With the right layout and components, you can build a Hi-Fi amplifier that sounds better than some retail amps selling for thousands of dollars. A 6µH inductor as shown in Figure 10 will introduce a low frequency loss assuming 0. The final value depends to some extent on the current in the Class-A driver stage and the gain of the driver transistor, but the final arbiter of quiescent is the Vbe multiplier stage. Show more Douglas Self offers a tried and tested method for designing audio amplifiers in a way that improves performance at every point in the circuit where distortion can creep in — without significantly increasing cost. It is greatly enhanced from the 5th edition and the 4th Edition for that matter which I also own. Having said that, there are some very well respected amplifiers using Darlington emitter-follower output stages.
The author Rod Elliott grants the reader the right to use this information for personal use only, and further allows that one 1 copy may be made for reference. With opamps, the equivalent solution is to connect the stopper resistor in series with the +ve input, and the capacitor between the +ve and -ve inputs, with no connection to earth. This is nearly always when the amp is driven, and is more likely when current is being drawn from the circuit. The vast majority of all the off-the-wall claims you will come across can safely be ignored. At the opposite extreme, the driver will have to cope with 16mA when it is turned on fully. With the values indicated in Fig. Depending on how the voltage amplifier stages are configured, the distortion can be less, greater, or about the same.
Except where noted the values of components do not appear to be particularly critical, and 10% tolerance resistors can certainly be used without ill effect. In reality this is rarely the case - if it measures as disgusting, then it will almost invariably sound disgusting. There is some evidence to show that an apparently symmetrical input stage may be better than a more conventional asymmetrical stage, but there are countless very good amps that don't use the extra circuitry. As a secondary safeguard, using a suitable diode string in parallel with the servo may be useful. Sighted tests where you know exactly which piece of gear you are listening to are fatally flawed and will almost always provide the expected outcome.
If resistor R1 in Fig 9 is instead a trimpot i. If one were to combine all the 'best' configurations into a single amp, this is no guarantee that it will perform or sound any better than one using 'lesser' building blocks. So by placing two or more resistors in series across a supply voltage we can create a voltage divider network that produces a set of fixed voltages at the values of our choosing. This is shown in Figure 11. With the values of the reservoir capacitor shown in table 3, the ripple level will be less than 10mV at the rated output current, provided that the current gain of the series transistor is greater than 40.
In some cases, you'll see a comparatively high value used. It is not realised by everyone, but a single unity gain transistor stage can oscillate. One way to overcome this temperature related problem is to replace the resistors with diodes to use diode biasing. This book is the essential reference for audio power amplifier designers and engineers. I have heard some amps that fall into that category that sound 'interesting' - not necessarily bad, but definitely not hi-fi by any stretch of the imagination.