Pass BOSOZ Balanced Preamp
Welcome to the AudioShark Forums.
Results 1 to 10 of 10
  1. #1
    Senior Member
    Join Date
    Nov 2013
    Location
    Minnesota
    Posts
    1,129
    Post Thanks / Like

    Pass BOSOZ Balanced Preamp

    My son and I built a DIY Pass Labs Bride Of Son Of Zen Balanced preamp. He built the chassis out of wood (front panel is African Wenge and the sides are Maple. We had the circuit boards built professionally (gold plated circuits) and we both populated the boards with high end resistors (Shinkoh Tantalum, Audio Note non metallic tantalums, Talkman and a few other high end brands, some carbon Am-Trans for added warmth) and Mundorf electrolytics, Elna caps for power supply, Panasonic and Obbligato Gold Caps. The Balanced 4 pole Selector switch is a Seiden from Japan, all gold plated silver contacts. He is using a Balanced 4 pole Blue Alps motorized remote controlled volume pot 10kohm (the weak link but if he likes the sound he will replace it with $400 Remote controlled Khozmo ladder type pot). The Obbligato Golds will eventually be upgraded with the Clarity caps that he has in his Pass B1 buffer we built. On the rear wall you can see dual gain pots.

    Currently, it is being wired up and tested by an EE friend. I wired the Pass B1 but this is a little over my head. We will be putting a shield around the 2 torroidal transformers. I will post a review in a few weeks when it is broken in.

    My Gear- Mains System-Pass X250 amp, BAT VK-51se preamp, Luxman DA-06 DAC, Magnepan 1.6's, Thorens TD-145 TT, Dual Martin Logan Subs, Vintage Luxman T-110 Tuner, Other systems- Parasound A21 amp,Van Alstine Ultra Plus Hybrid tube DAC and Preamp, Magnepan MMG's, Monitor Audio S1's, PSB B6's, Def Tech Pro Monitor 1000's, Velodyne sub, Adcom GFR-700 AVR, Music Hall 25.2 modified CDP, Cables by Cardas Parsec, AQ Columbia DBS 72v, Wire World.

  2. Likes joeinid, Mr Peabody liked this post
  3. #2
    Super Moderator
    Join Date
    Apr 2013
    Location
    NY
    Posts
    16,388
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    Can’t wait to see photos and read your thoughts about how it sounds. Pretty amazing.
    Joe

    Avantgarde Duo XD, Klipsch RB-75, Klipsch RP-160M, JBL 590.

    Accuphase E-650 w/ Dac, Job INTegrated, Naim Supernait 2 w/ HiCap-DR.

    Conrad Johnson GAT2, Wyred 4 Sound STP-SE Stage 2, Misho Myronov Wooden pre, Linear Tube Audio MZ2.

    First Watt SIT-1 monos, Misho Myronov Wooden amp, First Watt SIT-3, Luxman MQ-300, Job 250 Monos, Valvet E2se, NuForce STA200, AkitikA GT-102 amp, Cary 300B SE monos, ASL Wave monos, Dennis Had 45 monos.

    Lumin U1 mini, ModWright Ultimate Sony XA-5400ES, Audio Mirror Tubadour III NOS R2R Tube Dac w/ upgrades.

    Burmester 948, McIntosh MCLK12, Kimber Kable, Siltech, Cardas, Avanti Audio cables.

  4. Thanks Mechnutt thanked for this post
  5. #3
    Senior Member
    Join Date
    Nov 2013
    Location
    Minnesota
    Posts
    1,129
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    Thanks Joe,

    It was a fun build and more adventurous than building the Pass B1 which sounds great by the way but it has no gain and it is not balanced. The BOSOZ has a lot of gain and is supposed to sound better then the original non balanced BOZ preamp. I could have done some of the wiring but not all of it. Plus I could not have put it on a scope and tested it. My EE friend already found that one of the MOSFET's were bad so he replaced them all with matching pairs.

    We used a lot of higher end boutique caps and resistors and they do have better sound quality than most cheaper parts. The question is, will it sound better than the sum of the parts. You never know. When we built the B1 I used a relatively expensive TKD remote pot and it was too sibilant and bright but had great detail. I swapped in a much cheaper remote Blue Alps pot and the sibilance and brightness disappeared with just a slight sacrifice of detail.

    Anyone want to buy a TKD 2511 MC remote volume pot?
    My Gear- Mains System-Pass X250 amp, BAT VK-51se preamp, Luxman DA-06 DAC, Magnepan 1.6's, Thorens TD-145 TT, Dual Martin Logan Subs, Vintage Luxman T-110 Tuner, Other systems- Parasound A21 amp,Van Alstine Ultra Plus Hybrid tube DAC and Preamp, Magnepan MMG's, Monitor Audio S1's, PSB B6's, Def Tech Pro Monitor 1000's, Velodyne sub, Adcom GFR-700 AVR, Music Hall 25.2 modified CDP, Cables by Cardas Parsec, AQ Columbia DBS 72v, Wire World.

  6. #4
    Super Moderator
    Join Date
    Apr 2013
    Location
    NY
    Posts
    16,388
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    Lol, the brightness and sibilants would kill me but I’m so happy you found a remedy. Just like a great recipe, a balance of flavor is the key. Well done!
    Joe

    Avantgarde Duo XD, Klipsch RB-75, Klipsch RP-160M, JBL 590.

    Accuphase E-650 w/ Dac, Job INTegrated, Naim Supernait 2 w/ HiCap-DR.

    Conrad Johnson GAT2, Wyred 4 Sound STP-SE Stage 2, Misho Myronov Wooden pre, Linear Tube Audio MZ2.

    First Watt SIT-1 monos, Misho Myronov Wooden amp, First Watt SIT-3, Luxman MQ-300, Job 250 Monos, Valvet E2se, NuForce STA200, AkitikA GT-102 amp, Cary 300B SE monos, ASL Wave monos, Dennis Had 45 monos.

    Lumin U1 mini, ModWright Ultimate Sony XA-5400ES, Audio Mirror Tubadour III NOS R2R Tube Dac w/ upgrades.

    Burmester 948, McIntosh MCLK12, Kimber Kable, Siltech, Cardas, Avanti Audio cables.

  7. #5
    Senior Member
    Join Date
    Nov 2013
    Location
    Minnesota
    Posts
    1,129
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    I think if all goes well with this build, we may try and build the Pass First Watt F-5 turbo amp (50 watt at 8 ohm version or possibly the 100wpc mono blocks) some time next year. I will have to run it by my EE friend as I will need some help with that one. It would be a great winter project.
    My Gear- Mains System-Pass X250 amp, BAT VK-51se preamp, Luxman DA-06 DAC, Magnepan 1.6's, Thorens TD-145 TT, Dual Martin Logan Subs, Vintage Luxman T-110 Tuner, Other systems- Parasound A21 amp,Van Alstine Ultra Plus Hybrid tube DAC and Preamp, Magnepan MMG's, Monitor Audio S1's, PSB B6's, Def Tech Pro Monitor 1000's, Velodyne sub, Adcom GFR-700 AVR, Music Hall 25.2 modified CDP, Cables by Cardas Parsec, AQ Columbia DBS 72v, Wire World.

  8. #6
    Senior Member
    Join Date
    Nov 2016
    Location
    Arizona, Idaho
    Posts
    125
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    It’s great you found a project to work on with your son. I think the time together with him is worth just as much or more than the preamp.
    Gary
    Accuphase E-650; Lumin A1; Tannoy Canterbury GR

  9. Thanks Mechnutt thanked for this post
    Likes joeinid liked this post
  10. #7
    Senior Member
    Join Date
    Feb 2016
    Location
    west Michigan
    Posts
    453
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    Very cool indeed.
    Interested in your opinion on this piece after some time with it.
    Yes, we tend to gravitate to the "exotic" parts for our builds hoping they will give us an edge. And sometimes they do.
    What is most interesting with Nelson's stuff is that the parts he uses are rather generic.
    He seems to concentrate more on circuit design than magic parts.
    But I'm like you, got to put in those premium parts..
    Keep us posted on your "family" project.
    My System:
    A trusty old Pioneer PD-65 as a Transport, Lumin A-1, a Merrill Heirloom T.T. as sources. A Lampizator DAC to PAD Cables to a SP-14 Tubed PreAmp, Pass XA30.5 , Fusion speaker cables, AudioKinesis Zephryn 46 Speakers. pair Rythmik F-12 subs, EP2050, Kaplan Power cables, Hydra power conditioner, Two dedicated 20Amp power lines. DIY corner traps and Acoustic Geometry Curves for room treatment.

  11. Thanks Mechnutt thanked for this post
  12. #8
    Senior Member
    Join Date
    Nov 2013
    Location
    Minnesota
    Posts
    1,129
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    Quote Originally Posted by jadedavid View Post
    Very cool indeed.
    Interested in your opinion on this piece after some time with it.
    Yes, we tend to gravitate to the "exotic" parts for our builds hoping they will give us an edge. And sometimes they do.
    What is most interesting with Nelson's stuff is that the parts he uses are rather generic.
    He seems to concentrate more on circuit design than magic parts.
    But I'm like you, got to put in those premium parts..
    Keep us posted on your "family" project.
    Will do.

    Nelson Pass made all his kits with off the shelf cheap parts. He wanted to keep it cheap for people. There are thousands of pages on the DIY forum on all his kits, many seeing improvement in better quality parts. We used high end caps and resistors in the Pass B1 build with success. Caps made the most difference but resistors helped tune the tone and transparency. Naked Z foil resistors have great clarity and impart more air in the input and output stages. Carbon resistors add a little distortion perceived as warmth. Shinkoh and Audio Note Tantalums are more organic sounding. Middle and top of the line Clarity caps have tight powerful bass and no brightness. They are better than the obliggato golds but more expensive.(the golds have a huge almost 3D sound stage and warmth but bass is a little lighter and looser and they are relatively inexpensive for a boutique cap) We would have used Duelund or Jupiter caps but the chassis would have needed to be much bigger.

    By the way, my EE who also repairs broken audio gear says the design of the BOSOZ is a little funky and there are simple things that could have been done to do make it more user friendly putting it together without sacrificing the sound. The design though is over 20 years old however.

    Whoops, lost track of my point. A friend of mine built a B1 with different high end parts and his sounds great as well but different at the same time. So you can clearly tune your gear with different caps and resistors.
    My Gear- Mains System-Pass X250 amp, BAT VK-51se preamp, Luxman DA-06 DAC, Magnepan 1.6's, Thorens TD-145 TT, Dual Martin Logan Subs, Vintage Luxman T-110 Tuner, Other systems- Parasound A21 amp,Van Alstine Ultra Plus Hybrid tube DAC and Preamp, Magnepan MMG's, Monitor Audio S1's, PSB B6's, Def Tech Pro Monitor 1000's, Velodyne sub, Adcom GFR-700 AVR, Music Hall 25.2 modified CDP, Cables by Cardas Parsec, AQ Columbia DBS 72v, Wire World.

  13. #9
    Senior Member
    Join Date
    Nov 2013
    Location
    Minnesota
    Posts
    1,129
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    Tomorrow we finally get the finished preamp. My EE friend tested it and adjusted it. He says that it is very detailed and transparent with a large sound stage. I will post a review in a few days once it starts breaking in. It will take at least 100 hours for the caps to settle in.
    My Gear- Mains System-Pass X250 amp, BAT VK-51se preamp, Luxman DA-06 DAC, Magnepan 1.6's, Thorens TD-145 TT, Dual Martin Logan Subs, Vintage Luxman T-110 Tuner, Other systems- Parasound A21 amp,Van Alstine Ultra Plus Hybrid tube DAC and Preamp, Magnepan MMG's, Monitor Audio S1's, PSB B6's, Def Tech Pro Monitor 1000's, Velodyne sub, Adcom GFR-700 AVR, Music Hall 25.2 modified CDP, Cables by Cardas Parsec, AQ Columbia DBS 72v, Wire World.

  14. Thanks joeinid thanked for this post
    Likes joeinid liked this post
  15. #10
    Senior Member
    Join Date
    Nov 2013
    Location
    Minnesota
    Posts
    1,129
    Post Thanks / Like

    Re: Pass BOSOZ Balanced Preamp

    I finally heard the finished product last night. I was shocked at how good it sounds. I was not expecting it to sound this good. It had great detail, air and transparency with space between instruments. Bass is punchy and fairly tight. Piano sounds natural and has excellent decay. Vocals are textured. The top end is smooth with an airey quality. It is neutral sounding and it has a huge, almost holographic soundstage with depth. My son commented that he was hearing things in recordings that he had not heard before. Once it breaks in some more, I will put it in my system to compare it to my BAT preamp. I would bet that it sounds as good if not better.

    However, there are some issues that need to be fixed. There is a low hiss coming from both speakers that is not related to the volume level. There is also a hum when the phono section is playing and there appears to be a ground loop issue.

    One other thing about the preamp, it draws .5 amps and after you turn off the preamp, music will still play for about 4-5 minutes do to the energy storage.
    My Gear- Mains System-Pass X250 amp, BAT VK-51se preamp, Luxman DA-06 DAC, Magnepan 1.6's, Thorens TD-145 TT, Dual Martin Logan Subs, Vintage Luxman T-110 Tuner, Other systems- Parasound A21 amp,Van Alstine Ultra Plus Hybrid tube DAC and Preamp, Magnepan MMG's, Monitor Audio S1's, PSB B6's, Def Tech Pro Monitor 1000's, Velodyne sub, Adcom GFR-700 AVR, Music Hall 25.2 modified CDP, Cables by Cardas Parsec, AQ Columbia DBS 72v, Wire World.