Line Stage Preamplifiers
The Bluebird ZPS preamplifier is a wide bandwidth (~1.2 MHz), Zero Phase Shift DC coupled amplifier. Actual phase shift at 20 kHz, referenced to DC, is less than 40 micro degree (0.00004
° ), compared to 30° for an amplifier with a -3 dB bandwidth of 50 kHz and 0.2° for a 6 MHz (@-3 dB) amplifier. Similarly, frequency response is +2 mdB (0.002 dB) @ 20 kHz, compared to -0.3 dB and -0.04 mdB for 50 kHz and 6 MHz amplifiers respectively. The corresponding total distortion is thus 50 to 400 times smaller than for conventional medium to narrow bandwidth audio amplifiers and three times smaller than for a wideband 6 MHz amplifier. Only a 20 MHz amplifier has similar total distortion characteristics. Although a 20 MHz amplifier would have similar total distortion as a ZPS preamplifier, it would not sound anything like it. For a 20 MHz amplifier all the distortion is due to phase shift, whereas for the Bluebird ZPS, it is all due to amplitude response. The fact that phase distortion is a lot more noticeable than amplitude distortion explains the difference in sound.The distortions listed above refer only to the amplifier section. Switches, volume controls, internal cabling, ... can increase the distortion by significant amounts. Though these distortions are small and add little to the already large distortion of the 50 kHz amplifier, adding these numbers to a ZPS or a 6 MHz amplifier can easily increase the total distortion by an order of magnitude at 20 kHz. Note, however, that since these added distortions are mostly due to phase shift, their audible effects would be significantly more pronounced for an amplifier with no phase distortion, than for one with no amplitude distortion. The careful selection of connectors, switches, and wiring insures that the added phase distortion from these component will be negligible at all audible frequencies The volume control thus remains the only significant source of added distortion for the Bluebird ZPS. In spite of the added phase distortion due to the volume control, the Bluebird ZPS preamplifier has less distortion from input to output than the amplifier section alone of most wideband preamplifiers! When the phase distortion due to switches, input connectors, cabling, etc. is added to these other designs, the total distortion of the Bluebird ZPS is orders of magnitude less than the phase distortion alone of all competing designs. Thus, the Bluebird ZPS preamplifier offers vastly better definition, detail, timbre, dynamics, image (specificity and size) than any other preamplifier.
The Mountain Bluebird ZPS preamplifier is a two box version of the Bluebird ZPS preamplifier. Housing the power supply in a different enclosure than the amplifier section of the Bluebird, results in a significant reduction of power supply noise (60 Hz in the USA). This noise is due to electromagnetic coupling of the rectifier switching noise and the power transformer stray fields as well as mechanical coupling of transformer hum to the amplifier section via the preamplifier’s enclosure. In addition the separate power supply permits increasing the power supply’s capacitance by approximately 30%. This added capacitance coupled with the reduction of power supply noise allows for a more defined and articulate bass, an improved soundstage and better transient response. The use of Vishay resistors, OFC connectors and our Omega wiring throughout the Mountain Bluebird further improve on the already stellar performance of the Bluebird ZPS.
Daniels Audio Corporation
1001 N. Humphrey Avenue
Oak Park, IL 60302
Phone (708) 383-3319
FAX: (708) 383-3230