Audio General AGI 511 High Speed Preamplifier w/Phono

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General:
This is a hard-to-find audiophile grade preamplifier originally designed in 1974 and produced until 1990 by Dave Spiegel.

This is the only product that Audio General made, and it is amazingly well built! A peak inside shows great attention to detail, good layout, and nice parts quality.  

The 511 preamplifier also has a surprisingly warm sound! It's clean, clear and fast, but warm too.. This preamp has a neutral tone and plays with precision, but without sounding sterile.

We've carefully tested this unit in our lab and long term test ring and it's working super nice.

Ownership:
Single Owner

Connections:
RCA inputs and outputs

General Sound:
Neutral sound with little to no coloration

Cosmetic Condition:
7/10 = Good. One or two minor scratches. Well Maintained.. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab and listening room.

Included:
Just the unit and power cord.

Packing:
Will be packed using our highly developed in-house process and custom packing materials.Specs:
Voltage: 105-130V, 50-60Hz, 5W 
Features: Tape 1 and 2, Phono, Tuner, Aux, Dubbing, Mono, Tone Send, Volume, Balance

Dimensions:
14" x 9-3/4" x 5 1/4"

Weight:
13 lbs.

Approximate Age:
1980

Recommended Cables:

Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Testing Process:

We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCB’s for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.

When we first power on a preamplifier we connect its RCA output to a Sencore PA81 Power Analyzer which simulates real world loading conditions and gives us an oscilloscope interface. The first order of business is checking that the volume control works smoothly throughout its entire range with acceptable channel balance. This is accomplished by feeding a 1KHz sine wave into one of the preamp’s line level inputs while monitoring the preamp’s output on an oscilloscope. We then switch to a 1KHz square wave to test the tone controls, loudness function, and filters where applicable. During this step we are watching for equal alteration of the test signal by both channels. This also helps us identify dirty controls that will need treatment. Once the basic line stage functions are verified, we test each input individually. This is especially important for devices that use relays to select their sources. If the preamp is equipped with a phono stage we test that as well. We use an inverse RIAA filter which allows us to feed a reference test signal into the phono input with the proper RIAA equalization and level. A square wave or sine sweep is used to verify that the device’s phono stage is faithfully reproducing the RIAA curve. If the preamp under test has balanced inputs and/or outputs these are tested as well.

We finish up our bench testing with a listening test with our bench amplifier and reference speakers. During this test we check for hum or hiss that may not have shown up in earlier testing. We also check that all of the tone controls and filters perform as expected. If the preamplifier has remote control functions these are also tested. Preamps with tube circuits or complicated power supply topologies are connected at our long term test rig for extended stress testing under real world conditions.