Seriously Nikko, there's some glaring errors in an otherwise well meaning post.
Hardly, see below.
[quote="restorer-john]Solid state class A amplifiers, from the respected manufacturers, on the whole, have way less inherent distortion than AB amplifiers. (notwithstanding silly audiophool ones- I don't count them)[/quote]Open ended statement. Which class A amplifiers, and what demographic do they make? Particularly, how many are capable of under 0.005%? In practice, Class A amplifiers have been the most distorted and noisy amps I've seen on the bench or have been tested by many elsewhere. Look at the Bedinis, for instance. Class A's superiority is marketing once AB amplifiers' devices are biased into their linear region. The entire audiophile debacle of class A having intrinsically lower distortion has been based on the misapprehension that all AB amplifiers should produce gross crossover distortion, which is quite false.
The lowest distortion amplifiers from 0.001 Watts upwards, that I've tested, and others, have exclusively been of the push-pull or AB variety, never single ended. I've yet to see a single ended amplifier with .005% THD, for example. Look at opamps, which are push pull with diminished distortion levels from .0005% even down to uV signal levels or full swing. Consider Yamaha's MX-2000 and MX-10000 HCA complimentary pair amps. The MX-2000's distortion was .00015% at 10W, .005% at rated power. For the MX-10000, distortion was .0003% at half power, somewhere around 0.003% at rated power. That distortion reduces as power is lowered, indicates the absence of crossover distortion. All wideband THD20-20k measurements, not just 1kHz. No single ended class A amp has ever achieved that. The only production amps to come close to those specs were Halcros, push pull.
[quote="restorer-john]Crossover distortion is NOT harmonic distortion, it never was and never will be.[/quote]That is incorrect. Always has been classified as odd harmonic distortion with amplitude distortion characteristics. It's in the educational text books and even Yamaha's manuals. All confirm that it is harmonic distortion that does not change in magnitude:
Yamaha P-2100 Manual, Page 13:
"Another form of harmonic distortion that occurs in some power amplifiers is called crossover distortion. Crossover distortion is caused by improper bias in the output transistors of an amplifier. The amount of crossover distortion stays the same whether the signal is large or small, so the percentage of the distortion goes down as the signal level goes up."
Keith Howard, Royal Academy of Engineering, AES UK:
"Other types of harmonic distortion, such as Class B amplifier crossover distortion, are undoubtedly dysphonic: even tiny amounts of crossover distortion are audible, and very unpleasant." http://www.aes-uk.org/forthcoming-m...the-missing-factor-in-distortion-measurement/
Daniel M. Thompson, Understanding Audio: Getting the Most Out of Your Project or Professional Recording Studio:
"This will happen regardless of the input level, and tends to be worse at lower rather than higher levels. The easy way to differentiate between crossover and harmonic distortion is that harmonic distortion can be eliminated by reducing the input signal level; crossover distortion cannot."
Lindos Electronics, Distortion Measurement Article:
"crossover distortion’ [is] caused by a kink in the transfer characteristic as the sine-wave crosses zero. This is a form of ‘high order’ distortion, and produces odd harmonics (3rd, 5th, 7th, 9th etc) which extend right up the frequency range, with little reduction in amplitude"
Below:
"This second image (corresponding to the FFT of the -45V bias point signal) shows a smaller fundamental, which indicates a lower output level of 12.5V as a result of increasing the negative bias voltage (the bias voltage affects the overall gain). However, the 3kHz distortion product is now 2V instead of 0.75V, which is only down -16dB relative to the 12.5V fundamental, and the 5kHz distortion product is now around 0.3V, corresponding to a 5th harmonic distortion level of -32dB. This indicates that crossover distortion produces mainly third harmonic distortion, which increases rapidly as the negative bias voltage is increased, or as the bias current is decreased."
[quote="restorer-john]Regulated front ends and separate power supplies for the driver stage is where PSU ripple is tamed. Most decent amplifiers for the last 30 years have been running independent supplies for the driver/voltage stage.[/quote]No one has stated otherwise.
[quote="restorer-john]Large value capacitors in the PSU make a phenomenal difference to the transient, continuous and low impedance capabilities of amplifiers.[/quote]That is a misconception. It does dictate the peak current available, but nobody produces 1 or 2 ohm speakers anymore for home hifi. Those that were around, such as the Wilson Audio Tiny Watt with its .5 ohm impedance at 200Hz, and the infinity Kappa 9s with their resonant bass enhancement would be considered quite flawed today. The impedance in the Mini Watts was in fact an error by the designer, according to Richard Schram.
The rest regarding transient response is patently false information. It can be disproved through measuring the transient response of the amplifier. A larger power supply reserve, measured in joules, does not increase the bandwidth or slew rate of the amplifier - they are dependent upon the design of the VAS stage and I stage while current slewing into low impedance is affected by the supply impedance path, not the capacitance. The amplifier will never produce a transient faster/higher than the recording, and treble is lower in voltage magnitude than midrange by several orders. Adding to that, a slew rate over 20V/uS in a 100W amplifier is double what's needed, as cleared up years ago by Walt Jung and Bob Cordell. Let's investigate it for a moment: 360 Degrees of a 20kHz waveform is equal to 50uS; each 1/4 of that wavelength is the peak rate of change. This is 12.5uS length. Recorded audio on CD contains no information above 22kHz. On high resolution digital sources, the medium is capable of greater extension but it is not used for audio. The bandwidth is allocated to moving the post filtering upwards in frequency so that a flat response with better square-wave response is achievable at audio frequencies, ie below 20kHz. For the pre stage, a full swing at audio frequencies is only 1V/uS. Vinyl can carry higher frequencies, but the level of those frequencies and its upper rate of change is low - 0.55uS at 20V RMS from the output of a 100W amplifier below clipping (28.3V = clip). According to Douglas Self's publications and others, 20V would only require 5V/us to accurately reproduce all frequencies beyond the audio range without slew limiting distortion. This is also collaborated by Walt Jung. A safety margin of 10V/uS is preferable for driving capacitive loads. All credible doctrines cite similar numbers. I'll add that doubling the amplifiers power does not constitute the requirement for twice the slew rate, as the relationship is not linear.
Douglas Self, Audio Power Amplifier Design Handbook, Page 256, direct references to the results of Peter Baxandall and Nelson Pass.
https://books.google.ca/books?id=TL...a=X&ei=_Bm9VK6jGISZgwSd8YGgBg&ved=0CAsQ6AEwAA
[quote="restorer-john]There is no specified capacitance value for a 90w/ch amplifier, there are rules of thumb that err on the side of being cheap and inadequate. 6000uF per rail on a 90w/ch amplifier in inadequate and ripple would be a problem at high power- no doubt about it.[/quote]Quite incorrect. There is a calculation we use to determine the required capacitance, along with CAD modeling. I have in my possession two amplifiers, one 90W/ch with only two 6800uF supply capacitors. There is absolutely no hum and no ripple on the output even driving it to square clipping across a dummy load. Spectrum analysis provides evidence. There is another member on this board that can verify that. Bryston, Carver and Phase Linear amplifiers also used small power supplies. Phase Linear 200 was 200W/channel, and I believe the supply capacitors were 2x 10,000uF, one on each polarity rail.
[quote="restorer-john]A S/N of 95dBA is pretty crap for an integrated amplifier. Consider it is always referenced these days to full power and a short input. I would expect 110dB from a 100w/ch integrated as a place to start.[/quote] That is the standard for noise measurement. I would be inclined to agree if this statement were inclusive or directed toward preamps, but it omits an important fact. The extant claim is somewhat contrived, because the integrated amp also includes a preamp stage coupled to its power amp. For power amps, the McIntosh MC-501 is 97dB, and the Pass Labs' X350.5 is 87dB, for instance. McIntosh's C-220 pre is quite poor at 90dB. Then, of course there are other preamp with much better SNR. The noise of the preamp is static since the volume control is virtually always located prior to the first gain stage, thus not attenuating the idle noise. This noise can be considered critical and mathematically described by Friis's formula, since the noise is amplified by the power amp...which is usually about 26-34dB additional gain for home audio amps. This is unfortunately how home audio systems are gain structured. A final signal to noise ratio of 95dB at the speaker terminals is quite excellent. Most home audio systems can't manage that due to the fact 3 lines previous.
