David Hafler
Encyclopedia
David Hafler was an American audio engineer. He was best known for his work on an improved version of the Williamson amplifier
using the ultra-linear
circuit of Alan Blumlein
.
In 1950, Hafler founded Acrosound with his colleague Herbert Keroes. This company was primarily in the business of designing and manufacturing transformers for tube amplifiers. Around this time Hafler and Keroes popularized the ultra-linear
output-stage for audio amplifiers. However, the partnership did not last.
In 1954 Hafler founded Dynaco
with Ed Laurent. Hafler was instrumental in bringing affordable, high-quality audio kits to hobbyists, making his name a household word in the US audio community for many years.
In the 1970s Hafler promoted "passive pseudo-quadraphonic
s", an inexpensive method of recreating ambient sounds at the rear from ordinary stereophonic recordings. Known as the "Hafler hookup", this consisted of two similar additional rear speakers, connected in series (typically 8 + 8 or 16 ohm
s total) between the live feeds to the front speakers. The crosstalk or loss of stereo separation in the front speakers was generally less than 2 dB
while the rear sound level in a typical recorded live performance was about 7 dB below the front, but clearly audible. The Dynaco QD-1 Quadapter based on this idea, added a variable resistor to control the volume of the rear speakers. This passive method worked fairly well compared to the matrix decoders of the period, which attempted to reconstruct a surround sound field from a two channel recording. It has been observed that ambient sounds in a concert, such as applause or coughs from the audience, are generally received in a non-correlated phase by the stereophonic microphone
s, while sounds from the musicians are generally in a more or less synchronous phase. Thus, if rear speakers are fed with the difference between the stereo channels, audience noises and echoes from the auditorium can be heard from behind the listener.
In 1977, Hafler founded the David Hafler company in Pennsauken, NJ (Philadelphia suburb). His first two products were the DH-200 power amplifer and a companion preamplifier, the DH-101. Also notable was the rugged DH-500 stereo amplifier which was rated a 255 per channel and saw great success home, studio, and live environments. Following the Dynaco business model, these units were available in both kit form and factory assembled. Both units were acclaimed for their breakthrough sound quality and exceptional value. Both are still highly prized today. Hafler made several different models of amplifiers and preamps over the years. Hafler products were also fertile ground for improvements through upgrades and modifications, that were done both by hobbyists and small audio companies.
Hafler sold his company to the Rockford Corporation in 1987. Today, the Hafler company primarily makes products for the professional sound market.
David Hafler died May 25, 2003 in Philadelphia, Pennsylvania
, USA.
Williamson amplifier
A Williamson amplifier refers to a type of vacuum tube amplifier whose circuit design is similar to that originally published by D.T.N. Williamson.- Explanation :...
using the ultra-linear
Ultra-Linear
Ultra-linear is a term used to describe a type of electronic circuit that is used to couple a tetrode or pentode vacuum-tube to a load ....
circuit of Alan Blumlein
Alan Blumlein
Alan Dower Blumlein was a British electronics engineer, notable for his many inventions in telecommunications, sound recording, stereo, television and radar...
.
In 1950, Hafler founded Acrosound with his colleague Herbert Keroes. This company was primarily in the business of designing and manufacturing transformers for tube amplifiers. Around this time Hafler and Keroes popularized the ultra-linear
Ultra-Linear
Ultra-linear is a term used to describe a type of electronic circuit that is used to couple a tetrode or pentode vacuum-tube to a load ....
output-stage for audio amplifiers. However, the partnership did not last.
In 1954 Hafler founded Dynaco
Dynaco
Founded by David Hafler and Ed Laurent in Philadelphia, Pennsylvania in 1955, Dynaco was an American hi-fi audio system manufacturer popular in the 1960s and 1970s for its wide range of affordable, yet high quality audio components..-Early company history:...
with Ed Laurent. Hafler was instrumental in bringing affordable, high-quality audio kits to hobbyists, making his name a household word in the US audio community for many years.
In the 1970s Hafler promoted "passive pseudo-quadraphonic
Quadraphonic
Quadraphonic sound – the most widely used early term for what is now called 4.0 surround sound – uses four channels in which speakers are positioned at the four corners of the listening space, reproducing signals that are independent of one another...
s", an inexpensive method of recreating ambient sounds at the rear from ordinary stereophonic recordings. Known as the "Hafler hookup", this consisted of two similar additional rear speakers, connected in series (typically 8 + 8 or 16 ohm
Ohm
The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...
s total) between the live feeds to the front speakers. The crosstalk or loss of stereo separation in the front speakers was generally less than 2 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
while the rear sound level in a typical recorded live performance was about 7 dB below the front, but clearly audible. The Dynaco QD-1 Quadapter based on this idea, added a variable resistor to control the volume of the rear speakers. This passive method worked fairly well compared to the matrix decoders of the period, which attempted to reconstruct a surround sound field from a two channel recording. It has been observed that ambient sounds in a concert, such as applause or coughs from the audience, are generally received in a non-correlated phase by the stereophonic microphone
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
s, while sounds from the musicians are generally in a more or less synchronous phase. Thus, if rear speakers are fed with the difference between the stereo channels, audience noises and echoes from the auditorium can be heard from behind the listener.
In 1977, Hafler founded the David Hafler company in Pennsauken, NJ (Philadelphia suburb). His first two products were the DH-200 power amplifer and a companion preamplifier, the DH-101. Also notable was the rugged DH-500 stereo amplifier which was rated a 255 per channel and saw great success home, studio, and live environments. Following the Dynaco business model, these units were available in both kit form and factory assembled. Both units were acclaimed for their breakthrough sound quality and exceptional value. Both are still highly prized today. Hafler made several different models of amplifiers and preamps over the years. Hafler products were also fertile ground for improvements through upgrades and modifications, that were done both by hobbyists and small audio companies.
Hafler sold his company to the Rockford Corporation in 1987. Today, the Hafler company primarily makes products for the professional sound market.
David Hafler died May 25, 2003 in Philadelphia, Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
, USA.