Recently I bought the Pass B1 (DC-coupled 2015 version), which is a buffered passive preamp that uses JFETs and no capacitor in the signal pathway. It does not amplify the signal, but it provides impedance matching (output impedance is 125 Ohm). My amps with their about 100 K input impedance and sensitive input can be steered by a simple passive potentiometer, my subwoofer (via line input) cannot.
A few pictures:
http://www.renohifi.com/First/B1Full.htm
(Mine came with black volume knobs.)
I need the Pass B1 for testing DACs/CD players with fixed rather than variable output (my current DAC, the Berkeley Alpha 2, has a variable digital output). This buffer will allow me to audition the Schiit Yggdrasil DAC or, perhaps sometime in the future, the Spectral 4000 SV CD player. Signal amplification is not required since the 2 V standard output signal from digital is sufficient to drive most amplifiers, including mine. High gain phono stages should also work well through the Pass B1.
For context of the review, my system is described here:
http://www.whatsbestforum.com/showthread.php?17334-My-minimonitor-subwoofer-system
with speaker and rack update here:
http://www.whatsbestforum.com/showthread.php?17334-My-minimonitor-subwoofer-system/page5
(post # 48)
First I established that the digital volume control of my DAC, as well as the extra interconnect between passive pre and amps, are sonically transparent. I did so by comparison of running:
a) the variable output of the DAC straight into the amps,
b) the variable output of the DAC through an unbuffered passive stepped attenuator set at max (to check the extra interconnect)
c) the DAC at max volume through the passive stepped attenuator with volume attenuation by that device.
All three options sounded identical; volume matching was done carefully with SPL meter.
Doing this test worked because my amps have an input impedance of about 100 K and need very little signal to feed them; therefore there is no loss of dynamics by an unbuffered pot. However, the pot performs badly when it also has a sub to feed; as expected, the Pass B1 is unfazed by that. I did the test without the sub being connected.
Having established that the digital volume control of my DAC, as well as the extra interconnect between passive pre and amps, are sonically transparent, I proceeded to assess the effect of the Pass B1. Comparison was:
a) running the variable output of the DAC straight into the amps
versus
b) running the DAC at max volume through the Pass B1 with volume attenuation by that unit.
In both cases the subwoofer was now connected as well, as opposed to the unbuffered pot test. Connection was either to the DAC output or the Pass B1; volume matching again was done carefully with SPL meter.
I heard no difference on anything, again from (deep) bass through midrange to treble. No differences in dynamics or rhythm & timing (rock!) either. There are also no electronic artifacts, no distortions. (I let the Pass B1 burn in for three days before doing the final comparisons.)
Just two critical examples for the preservation of sonics by the Pass B1:
1. The timbral texture of solo violin in my system is now so immensely detailed (after recent cleaning of my contacts with DeOxit Gold) that it compares rather favorably with top analog. Every little transient by the bowing, the rosiny texture, all the micro-oscillations of the strings and vibrations of the soundbox of the violin, were preserved through the B1.
2. Spatial depth and soundstage in my system/room are excellent, a focus of admiration by audiophile friends coming over. The Pass B1 changed absolutely nothing in the spatial presentation of performer being upfront, way in the back, or somewhere in between. Hall information is also the same. That means the B1 fully preserves the tiny signals that inform about the spatial clues and does not alter them in any way. How these fragile signals can easily be suppressed by electronic noise became clear to me when I switched from the internal power supplies of my amps to external ones (BorderPatrol MB), which are much more noise-free and finally allowed me to hear all that spatial information.
After careful comparison, I have given up on finding any sonic signature of the Pass B1 in my system (if there is one, which is likely, it's negligible). This buffered passive preamp is sonically transparent to me, I am enormously impressed. Moving my listening chair two inches back or forward, or rotating the tube traps somewhat between absorptive and reflective side makes a difference for the sound, this unit doesn't.
This was just my system. I have heard the unit in an even higher resolving system, that of Madfloyd, with similar results on a power amp with less sensitive input. This will be discussed in follow-ups to this review.
Given all the above, the Pass B1 will certainly not stand in the way of my testing of CD players/DACs with fixed output, sonically transparent as it is. For the price of just $ 1K, this unit is an incredible steal. It is the perfectly neutral and transparent preamplifier for digital and a high gain phono stage.
A few pictures:
http://www.renohifi.com/First/B1Full.htm
(Mine came with black volume knobs.)
I need the Pass B1 for testing DACs/CD players with fixed rather than variable output (my current DAC, the Berkeley Alpha 2, has a variable digital output). This buffer will allow me to audition the Schiit Yggdrasil DAC or, perhaps sometime in the future, the Spectral 4000 SV CD player. Signal amplification is not required since the 2 V standard output signal from digital is sufficient to drive most amplifiers, including mine. High gain phono stages should also work well through the Pass B1.
For context of the review, my system is described here:
http://www.whatsbestforum.com/showthread.php?17334-My-minimonitor-subwoofer-system
with speaker and rack update here:
http://www.whatsbestforum.com/showthread.php?17334-My-minimonitor-subwoofer-system/page5
(post # 48)
First I established that the digital volume control of my DAC, as well as the extra interconnect between passive pre and amps, are sonically transparent. I did so by comparison of running:
a) the variable output of the DAC straight into the amps,
b) the variable output of the DAC through an unbuffered passive stepped attenuator set at max (to check the extra interconnect)
c) the DAC at max volume through the passive stepped attenuator with volume attenuation by that device.
All three options sounded identical; volume matching was done carefully with SPL meter.
Doing this test worked because my amps have an input impedance of about 100 K and need very little signal to feed them; therefore there is no loss of dynamics by an unbuffered pot. However, the pot performs badly when it also has a sub to feed; as expected, the Pass B1 is unfazed by that. I did the test without the sub being connected.
Having established that the digital volume control of my DAC, as well as the extra interconnect between passive pre and amps, are sonically transparent, I proceeded to assess the effect of the Pass B1. Comparison was:
a) running the variable output of the DAC straight into the amps
versus
b) running the DAC at max volume through the Pass B1 with volume attenuation by that unit.
In both cases the subwoofer was now connected as well, as opposed to the unbuffered pot test. Connection was either to the DAC output or the Pass B1; volume matching again was done carefully with SPL meter.
I heard no difference on anything, again from (deep) bass through midrange to treble. No differences in dynamics or rhythm & timing (rock!) either. There are also no electronic artifacts, no distortions. (I let the Pass B1 burn in for three days before doing the final comparisons.)
Just two critical examples for the preservation of sonics by the Pass B1:
1. The timbral texture of solo violin in my system is now so immensely detailed (after recent cleaning of my contacts with DeOxit Gold) that it compares rather favorably with top analog. Every little transient by the bowing, the rosiny texture, all the micro-oscillations of the strings and vibrations of the soundbox of the violin, were preserved through the B1.
2. Spatial depth and soundstage in my system/room are excellent, a focus of admiration by audiophile friends coming over. The Pass B1 changed absolutely nothing in the spatial presentation of performer being upfront, way in the back, or somewhere in between. Hall information is also the same. That means the B1 fully preserves the tiny signals that inform about the spatial clues and does not alter them in any way. How these fragile signals can easily be suppressed by electronic noise became clear to me when I switched from the internal power supplies of my amps to external ones (BorderPatrol MB), which are much more noise-free and finally allowed me to hear all that spatial information.
After careful comparison, I have given up on finding any sonic signature of the Pass B1 in my system (if there is one, which is likely, it's negligible). This buffered passive preamp is sonically transparent to me, I am enormously impressed. Moving my listening chair two inches back or forward, or rotating the tube traps somewhat between absorptive and reflective side makes a difference for the sound, this unit doesn't.
This was just my system. I have heard the unit in an even higher resolving system, that of Madfloyd, with similar results on a power amp with less sensitive input. This will be discussed in follow-ups to this review.
Given all the above, the Pass B1 will certainly not stand in the way of my testing of CD players/DACs with fixed output, sonically transparent as it is. For the price of just $ 1K, this unit is an incredible steal. It is the perfectly neutral and transparent preamplifier for digital and a high gain phono stage.