Linear power amplifier
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TheseĪre not covered here because they are extremely uncommon in modern equipment, although a superficially similar arrangement is often used in regulated switchmode power supplies.įor anyone who would like to run transformer power supply simulations, I suggest you read the article Power Supply Simulation (Not As Easy As It Looks), which covers the tricks you can use to make a simulator emulate the 'real world' performance of transformers and rectifiers. There is one application where fast diodes are definitely recommended, and that's for 'choke input' filters, where the diodes feed rectified AC to the filter cap(s) via an inductor. In some cases you may get a small reduction in conducted emissions (high-frequency interference sent back into the mains wiring). There is no evidence that there is the slightest difference to sound quality if fast diodes are used, despite countless unsubstantiated claims. The idea that one rectifier type supposedly sounds 'better' than another is quite silly. Remember that the idea of a rectifier and filter is to produce DC which is then used by the electronics. They don't 'sound better' than ordinary diodes, and again, only double-blind tests will reveal if anyone can really hear the difference. Fast diodes essential in switchmode supplies because they operate at anything from 25kHz up to 100kHz or more. However, as noted in section 9, they don't do any harm and if that's what you prefer then use them by all means. You also won't find anything here that suggests or recommends ultra-fast or fast recovery diodes, because there's simply no point for 50Hz or 60Hz mains. It must be possible to obtain a statistically significant result - getting the right answer 50% of the time is no better than guesswork. All sighted tests (where the listener knows what s/he is listening to) are invalid, and this has been proven many times in many different disciplines. As always, any test must be double-blind or the 'results' obtained aren't worth the time spent obtaining them. Valve rectifiers have one (and only one) redeeming feature - they provide a 'soft start' as the filaments or heaters warm up.Īnyone who claims to be able to hear the difference between a valve and silicon diode rectifier is either suffering from wishful thinking or self-delusion. All valve rectifiers also impose an upper limit on the capacitance following the rectifier, and that usually means that the filter cap is far too small to provide acceptable filtering.
LINEAR POWER AMPLIFIER SERIES
For example, a 5AR4 has a typical plate resistance of around 50 ohms at 25mA plate current, and a silicon diode in series with a 50 ohm resistor will give virtually identical results. This is replicated easily by using resistors in series with silicon diodes, of a value similar to that found in the valve data sheet. Contrary to the firmly held beliefs of some, they have exactly zero sonic benefit in any design, but there are people who (for reasons that I can't determine) prefer the power supply to sag under heavy load. One omission that will be apparent to many readers is any reference to valve (vacuum tube) rectifiers.
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This depends on the type of rectifier used, and is described in more detail further below. If the voltage is increased, you simply need to ensure the diodes are rated for the worst case PIV (peak inverse voltage) to which they will be subjected. Most of the general principles described can be translated to higher or lower voltage or current with no change to the basic parameters. The purpose of this article is to explain the terminology used, traps and pitfalls, and give some insight by way of a few practical examples. These linear supplies should not create any problems for anyone, because they are so simple, right? Wrong! They appear simple, but there are many inter-related factors that should be considered before just embarking on your next masterpiece. This specifically excludes switchmode supplies, which are a great deal more complex. I do not intend to deal with 'esoteric' designs with interesting names, but the simple, unregulated linear power supply that is still the mainstay of audio power amplifiers. Power supplies are needed for every type of amplifier (or any other electronic equipment for that matter) we will ever use. Having searched the Web for reference material (and found very little!), this would appear to be the definitive article on the design of a 'simple' linear power supply for a power amplifier. 5.2 Increasing Capacitance / Transformer Size.