Review: Pass B1 Buffered Preamplifier

Al M.

VIP/Donor
Sep 10, 2013
4,513
351
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Greater Boston
#1
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.
 

MadFloyd

Member Sponsor
May 31, 2010
2,424
19
38
Mass
#2
Al mentioned in the above post that he tried his new Pass B1 in my system to get additional perspective on whether it was transparent or not.

I have to say that I was pretty certain that it was NOT going to be transparent. In my system, a change of power cable or interconnect makes a very audible difference. I've also been auditioning several high end preamps and comparing them against the output of my Vivaldi DAC and each one has a distinct sonic signature. Well the Pass B1 impressed me. It was very difficult to tell the difference between my DAC direct and going through the Pass B1. You would think the addition of another interconnect alone would result in a change, but the character of the Vivaldi came through seemingly unaltered.

For a $1,000 this unit is high value to anyone who values transparency to the source. Of course not everyone wants that - many are willing to give up a little transparency for some glorification of the music that a preamp can offer, but in Al's case he really doesn't need that - his unique amps are incredibly musical and he isn't after any sonic changes so the B1 is a great solution.

I think it's really good to know this product is available and at a reasonable price to boot.
 
Jan 29, 2012
1,213
330
83
#3
Al mentioned in the above post that he tried his new Pass B1 in my system to get additional perspective on whether it was transparent or not.

I have to say that I was pretty certain that it was NOT going to be transparent. In my system, a change of power cable or interconnect makes a very audible difference. I've also been auditioning several high end preamps and comparing them against the output of my Vivaldi DAC and each one has a distinct sonic signature. Well the Pass B1 impressed me. It was very difficult to tell the difference between my DAC direct and going through the Pass B1. You would think the addition of another interconnect alone would result in a change, but the character of the Vivaldi came through seemingly unaltered.

For a $1,000 this unit is high value to anyone who values transparency to the source. Of course not everyone wants that - many are willing to give up a little transparency for some glorification of the music that a preamp can offer, but in Al's case he really doesn't need that - his unique amps are incredibly musical and he isn't after any sonic changes so the B1 is a great solution.

I think it's really good to know this product is available and at a reasonable price to boot.
I've owned several of Nelson's First Watt amps and they are simply amazing, regardless of price. If you have a high efficiency system you own it to yourself to try Nelson's products.
 

Al M.

VIP/Donor
Sep 10, 2013
4,513
351
83
Greater Boston
#4
Al mentioned in the above post that he tried his new Pass B1 in my system to get additional perspective on whether it was transparent or not.

I have to say that I was pretty certain that it was NOT going to be transparent. In my system, a change of power cable or interconnect makes a very audible difference. I've also been auditioning several high end preamps and comparing them against the output of my Vivaldi DAC and each one has a distinct sonic signature. Well the Pass B1 impressed me. It was very difficult to tell the difference between my DAC direct and going through the Pass B1. You would think the addition of another interconnect alone would result in a change, but the character of the Vivaldi came through seemingly unaltered.

For a $1,000 this unit is high value to anyone who values transparency to the source. Of course not everyone wants that - many are willing to give up a little transparency for some glorification of the music that a preamp can offer, but in Al's case he really doesn't need that - his unique amps are incredibly musical and he isn't after any sonic changes so the B1 is a great solution.

I think it's really good to know this product is available and at a reasonable price to boot.
Thanks, Ian, for giving your perspective! It was a fun and informative session. And your system sounded phenomenal. The fact that it sounds so incredibly open was another acid test for the transparency of the Pass B1, but it passed with flying colors.
 

Al M.

VIP/Donor
Sep 10, 2013
4,513
351
83
Greater Boston
#5
I've owned several of Nelson's First Watt amps and they are simply amazing, regardless of price. If you have a high efficiency system you own it to yourself to try Nelson's products.
Interesting that you say that. I have high efficiency (92 dB) monitors that are really easy to drive even by my parallel push-pull triode amps of 15 W/ch. I had already thought about trying the First Watt J2 amp of 25 W/ch, which only costs 4 grand. Just the external power supplies for my excellent amps cost that much, but perhaps the First Watt amp could be another incredible surprise.
 
Jul 22, 2010
385
16
18
SF Bay
#6
Great find Al. This is a great tool to use if you go to a fixed output analog signal. The 4000SV and this passive preamp could be just the ticket. You can add a tuner or stream through your Alpha 2 dac.

My Nagra PLL power supply is kaput so I bought a schitt passive pre to tie my over on my 2 channel tv system. It's a fine piece for $49. Passive pre amp make a lot of sense if the source and amp meet the requirements.

Before I went Spectral preamp and amp I auditioned the Esoteric C-03. The pre has multipule gain settings and the zero gain was awesome! Increasining gain was great for rock and then dial it back to zero for jazz.

Enjoy!!
 

cjf

Member
Nov 19, 2012
332
3
18
#7
Its a shame that almost none of these passives come in balanced configuration. Probably a dumb question but, why is that?

The SQ difference between balanced and single ended everytime I've tried it is significant in favor of balanced.
 

PeterA

Well-Known Member
Dec 7, 2011
5,551
445
83
North Shore of Boston
#8
Its a shame that almost none of these passives come in balanced configuration. Probably a dumb question but, why is that?

The SQ difference between balanced and single ended everytime I've tried it is significant in favor of balanced.
Great question, cjf. I was thinking of asking Al to bring the Pass B1 over to my system to compare it to my Pass XP20, but then I realized that my ICs to my amps would not work as they are balanced. I suspect the reason this is single ended is that the balanced circuit requires more parts and would add cost to the unit, but that is only a guess. Don't balanced circuits also increase gain by 6dB?
 

ddk

Industry Expert
May 19, 2013
3,911
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Utah
#9
Great question, cjf. I was thinking of asking Al to bring the Pass B1 over to my system to compare it to my Pass XP20, but then I realized that my ICs to my amps would not work as they are balanced. I suspect the reason this is single ended is that the balanced circuit requires more parts and would add cost to the unit, but that is only a guess. Don't balanced circuits also increase gain by 6dB?
Because you can't have balanced without an extra amplification leg, which is why you have your 6db gain or a transformer in line with the signal. You can use adaptors with Al's pre for testing the good ones don't degrade the sound but you might need the gain stage with your Magicos.

david
 

PeterA

Well-Known Member
Dec 7, 2011
5,551
445
83
North Shore of Boston
#10
Because you can't have balanced without an extra amplification leg, which is why you have your 6db gain or a transformer in line with the signal. You can use adaptors with Al's pre for testing the good ones don't degrade the sound but you might need the gain stage with your Magicos.

david
Thanks David. That makes sense. Can you share a link to the better XLR/SE adaptors? I'd like to try Al's unit in my system. I have tons of gain from my phono also.
 
May 30, 2010
15,305
593
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Portugal
#11
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. (...)
Al M,

Can you tell us more details about what is exactly the DC-coupled 2015 version ? As far as I remember there was the original Pass designed capacitor coupled B1 and then a modification carried by DIY people, the DCB1. I would love to have more details on your 2015 Pass version.

A picture of the inside of your unit would be greatly welcome!
 

ddk

Industry Expert
May 19, 2013
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424
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Utah
#14
Thanks David. That makes sense. Can you share a link to the better XLR/SE adaptors? I'd like to try Al's unit in my system. I have tons of gain from my phono also.
Purist & Cardas make audiophile ones, Neutrik makes similar ones for a fraction of the price available everywhere, just google XLR to RCA adapter and a lot of them will pop up. Alternatively buy a run of Radio Shack interconnects, I promise your system won't blow up :)!

david
 

ddk

Industry Expert
May 19, 2013
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83
Utah
#15

Folsom

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Oct 26, 2015
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#16
Yes I specifically chose one with a high quality transformer from that specific manufacturer so that it could be done properly. Adapters have a good chance of introducing a lot of noise, or worst case scenario even damaging equipment (not very common, but with some of the equipment out there wouldn't be a surprise). He also wants less gain. The transformer keeps more benefits of the balanced cables up until you get to the transformer, if you use an adapter all the benefits are lost for the whole cable.

if you're afraid of transformers in the signal path you should throw all your Lamm tube amps in the trash. :cool: Plus all the best volume controls are based on transformer technology, in the form of an autoformer. Unless tested by you specifically with that unit, I'm going to chalk this up to unwarranted fear because of other bad experiences not necessarily related.
 

ddk

Industry Expert
May 19, 2013
3,911
424
83
Utah
#17
Yes I specifically chose one with a high quality transformer from that specific manufacturer so that it could be done properly. Adapters have a good chance of introducing a lot of noise, or worst case scenario even damaging equipment (not very common, but with some of the equipment out there wouldn't be a surprise). He also wants less gain. The transformer keeps more benefits of the balanced cables up until you get to the transformer, if you use an adapter all the benefits are lost for the whole cable.

if you're afraid of transformers in the signal path you should throw all your Lamm tube amps in the trash. :cool: Plus all the best volume controls are based on transformer technology, in the form of an autoformer. Unless tested by you specifically with that unit, I'm going to chalk this up to unwarranted fear because of other bad experiences not necessarily related.
Actually I am a Jensen dealer and am quite familiar with their products, I have this unit and aware of its qualities. I love their phono SUTs for high-end but we used this one and their other ISO-max products in HT, PA and larger multi-monitor advertising installs where ultimate sound quality isn't critical.

david
 

Folsom

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Oct 26, 2015
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#18
I'd like to see a direct comparison done, by ear, since you used it in situations where one would never know the difference. The gear with all the funky balanced, single, and bi-phase on XLR is as problematic to a test/experience as any device could be.
 

ddk

Industry Expert
May 19, 2013
3,911
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83
Utah
#19
I'd like to see a direct comparison done, by ear, since you used it in situations where one would never know the difference. The gear with all the funky balanced, single, and bi-phase on XLR is as problematic to a test/experience as any device could be.
I test everything in my system first before using it in a client install. ISO-max products are extremely effective tools for ground loops and nearly always needed in PA and sound reinforcement when we have to deal with mismatched equipment and may runs of extension cords and power strips but do have a sonic signature which I find unacceptable in a high-end system. (EDIT) Unless one has persistent ground loops that they can't eliminate!

david
 

Folsom

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Oct 26, 2015
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#20
Have you tried Lundahl problem solvers? They make larger better transformers but I haven't seen them in a product just for conversion. It wouldn't be cheap as they cost more than Jensen by a good bit.
 

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