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Daniels Audio
Bluebird ZPS
Mountain Bluebird ZPS

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MSRP USD $2390

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 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.