Owner`s manual

listener defined low frequency bass impact without bass boom. This

circuit has been used in different forms in many products including

Rockford Fosgate Car amplifiers. Jim Fosgate received US patent

number 3,883,832 for this circuit in 1975. It is called a "SINGLE

ELEMENT CONTROLLED TWIN T FILTER" and has a much steeper

curve than a bass or loudness control. It changes frequency and

amplitude (Boost) with a single control. When the control is set in the

“Min” position, the boost is applied at a lower frequency than when

the control is set to the “Max” position.

In order to infuse the sound with a natural sound stage, Jim

integrated his surround circuitry design, part of his US patent

5,307,415 “Panorama Control” filed in April 1994. This circuit applies

an out of phase cross blend to create a sense of depth and space

and moves the dimensional soundstage outside of your head. The

control has “Min”, “Max”, and “Off” positions. In the center “Off”

position the surround circuit is bypassed so the signal is unaffected

and provides normal stereo output.

The Fosgate Signature Tube Headphone Amplifier’s elegant circuit

has the tube amplifiers, buffers, bass EQ, and surround processing

configured in a single stage. Negative feedback is applied around this

stage in a single loop. Output offset is controlled with DC servos,

allowing the video buffers to directly drive the headphones with no

output capacitors in the signal path. There is only one coupling

capacitor per channel in the signal path, and it is enclosed within the

feedback loop, thus capacitor colorations are eliminated. Distortion

and noise are below the threshold of hearing. The bandwidth is very

wide allowing audio signals to pass through without colorations.

Bandwidth is an amazing “ten times” the threshold of human hearing,

2 HZ to 200KHZ at -3DB.

The power supply is similar to the one used in our Fosgate Signature

Tube Phono stage. It uses separate oversize storage capacitors on

each amplification path of each channel to provide a rock solid supply

voltage without voltage regulators to affect the signal. The circuit is

configured so that audio signal from one channel cannot couple to

signal from the other, preserving soundstage width and depth. This

power supply provides the benefits of both dual mono and batteries

but in a simple AC powered circuit.

A 35 second muting circuit eliminates turn on/off thumps from the

direct coupled output circuit. Two stereo inputs and a stereo tape

output are provided for added flexibility.