Audio General Inc. (A.G.I.)

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[edit] Preamplifier

511A

AGI only produced one product over a 14 year span and it was their 511 / 511A preamp. Many of the folks that were into audio way back when will remember this preamp as it was written about in most every "underground" audio mag along with glossies like Audio during that time frame. If i remember correctly, J. Peter Moncrieff stated "this is the only product made that has ever challenged the residual noise floor of our test equipment".

Control amplifier which David Spiegel of AGI who tackled the subject of high-speed-izing of amplifier with an awareness of the issues announced as a concrete result of the research.

The high speed circuit which shows the numerical value of more than slew-rate 250v/microsec, [ less than Ries / fall time 0.01microsec ], and less than time delay 0.0035microsec,By realization of the ultra wideband width which amounts to 50MHz or more, phone amplifier begins TIM (transient intermodulation distortion), and is free completely from generating of slewing induced distortion.

The circuit device is added so that distortion by an inter-modulation may not arise in connection with the power amplifier which is not quick out of a transient response. Moreover, the big ability to adapt over various conditions of a load side has been acquired by an output with a low Output load impedance and a margin.

The capacitor plug-in socket which enables a setup of the optimal load conditions over a phone cartridge is carried in the input side.

The TONE SEND function and the DUBBING switch are carried.

Setting all up is finished only using the superior parts of Military Specification. Moreover, all magnification elements are mounted by the plug-in system by the socket plated with gold.

The exterior uses the product made from stainless steel also for the setscrew of chassis covering. Moreover, wooden cases are attached.

Gain 33.0dB±0.25dB (1kHz) Input impedance 47kohm (90pF) Maximum permissible input 160mV(1kHz) Output load impedance Rec out: 220ohms Maximum-except-take-off level 7V/10kohm Frequency response RIAA deflection of less than ±0.25dB Phase characteristic + 12 degrees-4 degrees (20Hz - 20kHz) Signal to noise ratio 88dB or more (10mV, 1kHz, IHF-A) Distortion (at the time of 5V/10kohm) THD: 0.005% or less (usually 0.001% or less, 20Hz - 20kHz)

                                      IMD: 0.005% or less (usually 0.001% or less, the SMPTE method) 

characteristic Slew rate: More than 250v/microsec Ries / fall time: Less than 0.01microsec (2 Vp-p) Time delay: Less than 0.0035microsec

<High-level amplifier part> Gain 18.7dB±0.25dB Input impedance 38kohm Output load impedance 47ohms Maximum-except-take-off level 9.5V/10kohm 6V/600 ohm Frequency response 20Hz-20kHz±0.1dB Phase characteristic + 1 degree-3 degrees (20Hz - 20kHz) Distortion (at the time of 5V/10kohm) THD: 0.005% or less (usually 0.001% or less, 20Hz - 20kHz)

                                      IMD: 0.005% or less (usually 0.001% or less, the SMPTE method) 

characteristic Slew rate: More than 50v/microsec Ries / fall time: Less than 0.25microsec (10 Vp-p) Square-pulse dealt: 2% or less (20Hz, 1000-ohm load) <Others> Power source AC100V (90V-111V), 50Hz/60Hz Power consumption 5W Dimensions Width 354x height 132x depth of 243mm Weight About 6kg Attachment Wooden case

Incorporated Zobel Networks to minimize transformer ringing / AC noise, star grounding to minimize ground loops, 24 Karat Gold plated Berryllium copper contacts for all signal connectons, Allen Bradley Mil-Spec pots, poly and tantalum caps, metal film resistors, coined silver contacts in the switching, etc... As one can tell, the quality of signal and components used were of utmost importance.

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