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Amplification Components 6 Phono Stage Preamplifiers Auricle Publishing 2 Introduction to Amplification Components 6 Phono Stage Preamplifiers Auricle Publishing 8 Number 10 2003 $25.00 US Line Stage Preamplifiers 10 Surround Sound Processors Amplification Components PART 1 13 Charles Hansen udio Perfectionist Journal #9 explained the stored on the recording and some of that information of Ayre Aimportance of source components. We demon- is lost or altered during amplification, even flawless 18 strated that source component quality is critical speakers will reproduce a diminished or colored repli- Luke Manley because the component that retrieves the signal from ca of the original event. The small signal from the of VTL the recording sets the limit of resolution for the entire source component must be processed, buffered and 24 system. Remember this fact as presented in Journal amplified with minimal loss of signal information and Processor vs. #9: Any musical signal that emerges from the speak- a minimal addition of noise and distortion. This is a Preamplifiers ers must have been retrieved from the recording by far more difficult task than you might think. 26 the source component. PREAMP Preamble If the source components fail to retrieve the musi- 27 cal signal from the recording, that signal certain- Aesthetix Calypso & Rhea ly won’t be reproduced by the speakers, no mat- ter how expensive or exotic they may be. But 31 the source component can’t drive the ARC Ref 2MKII speakers directly; the signal must 33 first be processed and ARC SP16L amplified. Here’s a fact 35 that will be demonstrat- Ayre K-5x ed in Journals #10 and 36 #11: Any musical signal Ayre K-1x that emerges from the speakers has 39 BAT VK-51SE passed through the amplification com- 42 ponents and you’ll hear any Linn Linto alterations that occur in the process. 43 Rogue Audio Magnum Ninety- Nine The signal that the source component retrieves from Audio Perfectionist Journals #10 and #11 will the recording must be processed and amplified to a explain how amplification components work and how 45 Emmeline level sufficient to drive the loudspeakers. The amplifi- they can potentially degrade the signal. Journals #10 CA-2 & XR-2 cation components, which include a preamplifier and and #11 will suggest the best ways to choose and a power amplifier, provide this processing and ampli- assemble these components to minimize this signal 47 VTL 7.5 fication. The quality of the amplification components degradation in order to get the highest quality sound is critical for obvious and not so obvious reasons. from the speakers. 49 VTL TL5.5 If the source component retrieves all the information 51 What Did We Learn Today? www.audioperfectionist.com Introduction to Amplification Components Common Myths You have probably been presented with a lot of false or mis- leading information about amplification components and we’ll have to start by exposing some widespread myths. Regardless Let’s start by defining the component names we’ll use and of misinformation that would have you believe otherwise, ampli- explaining some technical terms that you may encounter here fication components are critical to the sound you hear from the and in magazine reviews and manufacturer advertising. This speakers because they create an amplified replica of the signal will help you to fully understand the information that will be pre- from the source component. This will be explained. sented in Journals #10 and #11 and to wade through the rhet- oric you may encounter elsewhere. You may have been told that amplifiers make little difference in sound quality. False. You may have been told that you can get high-end sound without the use a of a high-end preamplifier Head Amp and a high-end amplifier. You can’t. You may have been told A head amp is a device that is used to raise the output voltage that an expensive surround sound processor can replace a level from a moving coil cartridge to match the input sensitivity high-end preamplifier with no sacrifice in sound quality. Not of a phono stage that is designed for moving magnet or moving true. You may have heard that modern receivers are nearly as iron cartridges. Head amps are essentially obsolete because good as high quality separate components. Sorry, not even virtually all of today’s phono stage preamps can directly accept close to true. the signal from a low output moving coil cartridge. Here is some basic information about head amps for those with vintage preamps. Using a (low output) moving coil cartridge with a phono preamp designed for moving magnet/moving iron cartridges will require the use of a head amp or step-up transformer. Here’s why. Amoving magnet or moving iron phono cartridge will typically produce 2mv to 5mv (.002-.005 volts) output at a groove veloci- ty of 5cm per second. A moving coil cartridge may deliver one tenth of this output voltage, or about 200-400µv (.0002-.0004 volts) at the same groove velocity. If you have an older phono stage with input sensitivity suitable for moving iron cartridges, you’ll need a head amp or transformer to raise the output volt- age from a moving coil cartridge to a level that will drive your phono stage. Impedance matching is also a factor. In a digital age, preamplifiers may seem to be superfluous. Most phono stage preamplifiers designed for moving They are not and we’re going to tell you why. Some manufac- magnet/moving iron cartridges have an input impedance of turers would like you to believe that surround sound processors about 47k ohms. Most moving coil cartridges will perform best and receivers can offer equivalent performance to high-end into an input impedance of 100-500 ohms. A head amp, or separate components. They cannot and we’ll show you why. transformer, will provide the proper input impedance and elec- trical damping (loading) for a moving coil cartridge. Modern amplifiers, even those in receivers, have miniscule amounts of measurable distortion. This leads many people to assume that The output of a head amp is a phono level voltage (typically amplifiers are essentially perfect and that most can provide equivalent 5mv or so). A head amp feeds the phono input of a preamplifier performance for high-end music reproduction. This is certainly not the or phono stage. Head amps usually don’t provide phono equal- case and we’ll explain why in this Journal and the one that follows. APJ ization (see next page). 2 www.audioperfectionist.com Introduction to Amplification Components Phono Stage or Phono Preamp amplifiers work with line level source components like CD play- A phono stage is a preamplifier designed to provide the gain ers, and usually don’t provide the extra gain and equalization and equalization necessary for vinyl record reproduction. necessary for vinyl record reproduction. Phono cartridges produce output voltages that are very low Some preamplifiers incorporate a phono stage, providing the compared to line level sources like CD players. Lots of voltage functions of both phono stage and line stage preamplification in one unit. A preamplifier produces a line level output signal with limited current capability and is designed to drive a high impedance load (10-200k ohms) like a power amplifier. Power Amplifier A power amplifier receives a line level input signal and provides output with the voltage and current necessary to drive a loud- speaker. The output from a power amplifier is a speaker level signal with high current capability designed to drive low imped- ance loads (typically 4-8 ohms) like loudspeakers. gain is required to raise the cartridge output voltage to a level which is sufficient to drive a line stage preamplifier or an inte- Amplifiers must provide power (the product of voltage and cur- grated amplifier. rent) to perform work (drive a loudspeaker). See analogies that follow. Vinyl records are made with equalization that boosts high fre- quencies and reduces low frequencies as they are recorded on Power amplifiers, sometimes referred to as basic amplifiers, the disc. This equalization allows the reduction of groove spac- don’t have volume controls and input switching capability. ing to extend playing time when low frequencies are present in Amplifiers with volume controls and input switching are called the recording, and raises the level of high frequency informa- integrated amplifiers. tion relative to surface noise. A phono stage provides equaliza- tion that restores flat response during playback while reducing surface noise. Recording and playback equalization follow the Integrated Amplifier RIAA curve established by the recording industry. See illustra- An integrated amplifier is a combination of a preamplifier and a tion. power amplifier. An integrated amplifier will usually provide the features of a line stage preamplifier, including input switching The output from a phono stage is a line level voltage. This sig- and volume control, and will drive loudspeakers directly like a nal is usually fed to a line level input on a line stage preamplifi- power amplifier. Integrated amplifiers may also include a phono er that can provide additional gain and attenuation. A phono preamplifier. stage may have provisions for adjusting gain and cartridge loading to make it compatible with a wide range of cartridges but phono stage preamps usually don’t have input switching or Receiver Areceiver is a combination of a radio tuner, a preamplifier and volume controls which are found on line stage preamps. a power amplifier on a single chassis. Other components such as a phono preamplifier, a surround sound processor, a video Preamplifier or Line Stage switcher, and a digital-to-analog converter may also be includ- A line stage preamplifier is a control center for a home audio ed in the same unit.
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