I have and still use what i and many others consider to be the first "straight wire with gain" preamp ever made. It was built and designed by David Spiegel under the company name of Audio General, Inc. The original model was called the 511 and later became the 511A with several options available. The original product was designed in the mid 1970's and was literally light years ahead of the competition.
The 511 was the only preamp to make it into International Audio Review's Class 1A category for many years. It was the only product that AGI ever went to market with and was produced until appr 1986 or 1987 or so.
In terms of construction, it used mil-spec circuit boards, mil-spec potentiometers (Allen-Bradley) and mil-spec switch assemblies. Capacitors were hand selected using an impedance bridge and consisted of polystyrene, metal film and tantalum in all critical areas. For circuit stability, the preamp was always on BUT did have a power switch. This switch simply turned on the convenience outlets located in the back of the preamp. As such, the power switch was rated at 20 amps and used coined silver contacts so that it could handle any of the amps that were in current production. The chassis was relatively small but came with optional rack faceplate widths with a total of 6 available. You could get either width ( standard or rack ) in black, brushed aluminum or Gold. If you opted for the real Oak or Walnut cabinet, you could only use the standard width faces.
In terms of operation, it had very basic controls, hence the "straight wire with gain" comparison. The only adjustments available were volume and balance controls. Mode selection consisted of two seperated rows of spring loaded pushbuttons. The unit did have full tape monitoring facilities for two tape decks along with a special option. Since the unit did not have any tone controls from the factory, David saw fit to include a switchable "processor loop". This meant that you could install ANY type of processor ( equalizer, subsonic filter, and even novelties like Quadraphonic and reverb from the 70's) into the system. They could then be switched in and out at random and not tie up a tape loop. This comes in handy even today as you can use the preamp in a 2 channel based system and then simply insert a surround sound processor into the loop.
Electrically, it was extremely fast with wide bandwidth for its' day. It can still run with most of the gear today without breaking a sweat. With rise times of .01 uS for the phono and .25 uS for the line section, a slew rate of 250 v/uS and a frequency response that was linear out to beyond 300 Khz, THD and IMD measurements below .005%, etc... you knew that it had quite a bit of planning behind its' design. The output impedance of the preamp was 47 ohms, making it possible to drive ANY load or length of interconnect cable. All of the active components were installed using 24 karat gold plated beryllium copper contacts for ease of troubleshooting, replacement or individual component testing purposes. The phono stage was extremely good and fully adaptable to just about any input impedance or capacitance that you might want to achieve through factory available plug in parts. From the time that a signal went into the phono section till the time it came out of the preamp was less than .0035 uS. This resulted in no time delay. Square waves could be easily reproduced at 20 Hz or 20 Khz with preamp output levels in excess of 5 volts with no phase shifts noticeable.
Keep in mind that this was originally put together in 1974. There were literally NO amps that could come remotely close to the performance that this preamp provided. While David did design two power amplifiers (100 wpc & 200 wpc @ 8 ohms and slewed at over 1000 V / uS ), he never put them onto the market for some reason.
Even with the quality of parts used and the extreme amount of forethought that went into the design of the 511, it had a base price of $499. Keep in mind that there were several preamps retailing for appr $1000 or more in that era. Most of those were loaded with bells and whistles but couldn't get out of their own way sonically.
In stock form, the 511 sounds extremely clean, fast and detailed. Many fans of "musical" components find it to sound "lean" although it is not harsh by any means. Much of this can be corrected by simply replacing some of the original factory wiring with current offerings. I've also upgraded all of the RCA's and replaced the power supply caps and a few within the audio circuitry since the unit is now well over 15 years old. I have several of these units. Some with the factory optional Burr Brown circuitry ( who had heard of Burr Brown back then ??? ), various phono options and faceplates & cabinetry. My Brother uses one in his quad-amped system and my Father will be replacing his Counterpoint tube preamp with one of these once i'm done upgrading it. After comparing the AGI to my Fathers' Counterpoint in his system, my Mother called the Counterpoint "a piece of junk".
As such, many of you have probably never heard of this unit. It was not widely distributed and not pushed real hard by many of the "audio salons" that did sell it. Due to its' very reasonable price, there just wasn't a big profit margin involved. On top of that, there would be little need for "upgrading" into another preamp once the customer bought something like this. Even if it was sonically and mechanically excellent, it became kind of a "tainted item" in the eyes of many audio retailers. I know several "industry" people (manufacturers, reviewers and shop owners) that have these units. Even though they may not be using them, they simply won't sell them for some reason.
While David still services his units, he left audio to go into designing safety / security / monitoring systems for Nuclear power plants. He currently has contracts in several states and plays with audio as a sideline. Some of you might remember him as the "creative force" behind blind listening tests as he built the first ABX boxes that were ever available on the market.
Hope you folks found this "rambling" interesting and learned a little about this "blast from the past". Given that "super fast / ultra widebandwidth / low noise" circuitry has been around for over a quarter of a century in designs like this, how far have we REALLY come ??? Sean
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The 511 was the only preamp to make it into International Audio Review's Class 1A category for many years. It was the only product that AGI ever went to market with and was produced until appr 1986 or 1987 or so.
In terms of construction, it used mil-spec circuit boards, mil-spec potentiometers (Allen-Bradley) and mil-spec switch assemblies. Capacitors were hand selected using an impedance bridge and consisted of polystyrene, metal film and tantalum in all critical areas. For circuit stability, the preamp was always on BUT did have a power switch. This switch simply turned on the convenience outlets located in the back of the preamp. As such, the power switch was rated at 20 amps and used coined silver contacts so that it could handle any of the amps that were in current production. The chassis was relatively small but came with optional rack faceplate widths with a total of 6 available. You could get either width ( standard or rack ) in black, brushed aluminum or Gold. If you opted for the real Oak or Walnut cabinet, you could only use the standard width faces.
In terms of operation, it had very basic controls, hence the "straight wire with gain" comparison. The only adjustments available were volume and balance controls. Mode selection consisted of two seperated rows of spring loaded pushbuttons. The unit did have full tape monitoring facilities for two tape decks along with a special option. Since the unit did not have any tone controls from the factory, David saw fit to include a switchable "processor loop". This meant that you could install ANY type of processor ( equalizer, subsonic filter, and even novelties like Quadraphonic and reverb from the 70's) into the system. They could then be switched in and out at random and not tie up a tape loop. This comes in handy even today as you can use the preamp in a 2 channel based system and then simply insert a surround sound processor into the loop.
Electrically, it was extremely fast with wide bandwidth for its' day. It can still run with most of the gear today without breaking a sweat. With rise times of .01 uS for the phono and .25 uS for the line section, a slew rate of 250 v/uS and a frequency response that was linear out to beyond 300 Khz, THD and IMD measurements below .005%, etc... you knew that it had quite a bit of planning behind its' design. The output impedance of the preamp was 47 ohms, making it possible to drive ANY load or length of interconnect cable. All of the active components were installed using 24 karat gold plated beryllium copper contacts for ease of troubleshooting, replacement or individual component testing purposes. The phono stage was extremely good and fully adaptable to just about any input impedance or capacitance that you might want to achieve through factory available plug in parts. From the time that a signal went into the phono section till the time it came out of the preamp was less than .0035 uS. This resulted in no time delay. Square waves could be easily reproduced at 20 Hz or 20 Khz with preamp output levels in excess of 5 volts with no phase shifts noticeable.
Keep in mind that this was originally put together in 1974. There were literally NO amps that could come remotely close to the performance that this preamp provided. While David did design two power amplifiers (100 wpc & 200 wpc @ 8 ohms and slewed at over 1000 V / uS ), he never put them onto the market for some reason.
Even with the quality of parts used and the extreme amount of forethought that went into the design of the 511, it had a base price of $499. Keep in mind that there were several preamps retailing for appr $1000 or more in that era. Most of those were loaded with bells and whistles but couldn't get out of their own way sonically.
In stock form, the 511 sounds extremely clean, fast and detailed. Many fans of "musical" components find it to sound "lean" although it is not harsh by any means. Much of this can be corrected by simply replacing some of the original factory wiring with current offerings. I've also upgraded all of the RCA's and replaced the power supply caps and a few within the audio circuitry since the unit is now well over 15 years old. I have several of these units. Some with the factory optional Burr Brown circuitry ( who had heard of Burr Brown back then ??? ), various phono options and faceplates & cabinetry. My Brother uses one in his quad-amped system and my Father will be replacing his Counterpoint tube preamp with one of these once i'm done upgrading it. After comparing the AGI to my Fathers' Counterpoint in his system, my Mother called the Counterpoint "a piece of junk".
As such, many of you have probably never heard of this unit. It was not widely distributed and not pushed real hard by many of the "audio salons" that did sell it. Due to its' very reasonable price, there just wasn't a big profit margin involved. On top of that, there would be little need for "upgrading" into another preamp once the customer bought something like this. Even if it was sonically and mechanically excellent, it became kind of a "tainted item" in the eyes of many audio retailers. I know several "industry" people (manufacturers, reviewers and shop owners) that have these units. Even though they may not be using them, they simply won't sell them for some reason.
While David still services his units, he left audio to go into designing safety / security / monitoring systems for Nuclear power plants. He currently has contracts in several states and plays with audio as a sideline. Some of you might remember him as the "creative force" behind blind listening tests as he built the first ABX boxes that were ever available on the market.
Hope you folks found this "rambling" interesting and learned a little about this "blast from the past". Given that "super fast / ultra widebandwidth / low noise" circuitry has been around for over a quarter of a century in designs like this, how far have we REALLY come ??? Sean
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