CES 2013: Musical Surroundings and Fosgate Signature Headphone Amp
Jim Fosgate is an audio legend. Credited with the invention of the first car audio power amplifier, Dolby Pro Logic II, and the TATE II 101A quadraphonic decoder. Jim is evidently still at it, this time partnering with Musical Surroundings for the development of the Fosgate Signature Headphone Amplifier.
This is a hybrid amp using two 12AX7 tubes in an SRPP configuration as its input stage driving a solid state video buffer in the output stage. All well and good, but what intrigues me about this amp are two other features, its bass-boost and surround control.
More and more, we're seeing bass-boost switches on headphone amps. I actually think this is a good idea. I'd much prefer to have flat headphones and add bass with the amp (or equalizer), than have the headphones tuned with a bass boost. With a flat headphone, I think a 4dB bass-boost below 100Hz is about right to compensate for the boundary re-enforced lows, and chest and nasal cavity compression and bone conducted low frequency information sensed with full-range speakers in a room. When headphone manufacturers try to make a headphone with bass-boost, all too often the rise in bass can't be kept narrow band and the bass rise starts at much higher than 100Hz...and, of course, it is all too often boosted much more than 4dB. The patented Fosgate bass-boost circuit (pat. # 3,883,832) claims to deliver a steeper edge to the bass-boost and results in a less "boomy" response by limiting the boost to the very lowest octaves.
I've long been a proponent of cross-feed circuits in headphone amplifiers to improve the stereo image on headphones. You can read more about why you might want a cross-feed circuit here. The problem is, almost all cross-feed circuits come with compromises. The analog versions (HeadRoom, Meyer, etc) tend to taint the purity of the sound, and the digit ones tend to get over-thought and too many factors are added in like room reverberant cues and side wall echos (Dolby Headphone, SRS). However, some I've heard are extraordinary (SPL Phonitor for analog, and Smyth Realizer for digital) and lead me to believe there are some real gains to be had from this type of circuit for headphone listening. From a quick read of the patent (5,307,415), it appears this circuit is some type of "variable matrix decoder," meaning that it not only tries to identify the spacial information in the audio signal, but dynamically controls certain signal characteristics to maximize the directional information on and ongoing basis. Color me intrigued!
I'll let Garth Leerer give you the rundown. You can look more closely at this amp here.