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Thread: Nelson Pass B1 preamp build

  1. #1
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

    Default Nelson Pass B1 preamp build

    Hi all,

    After missing out on a Nelson Pass B1 preamp recently, I decided I'd have a look at building one.

    A quick chat with Alan alerted me to a B1 buffer being sold by Jazid (James) so I snapped it up.

    I've decided to try and reuse the case it's all currently residing in and get a black perspex sheet to replace the Aluminium front.

    I settled on an Elma 2 pole selector switch (same as in the Slagle I have just sold) which I felt was as good as it gets really for a selector switch and a Khozmo Stepped attenuator, which again is scant company at the top of the attenuation tree.

    2 shaft extension bars will enable mounting of the switches to be as close to the outputs and input as possible so this should keep the signal path extremely short.

    The hopes are that we can fit a 3 in 1 out configuration on the already slightly congested back panel. Luckily I have an expert to call on so that should be very beneficial.

    Hookup wire is still to be decided but I'd like to try and use the same as the existing wire.

    Any suggestions on what it is from the pictures?


    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK5 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken & Tesla Valves)
    Digital: NONE
    Amplification: Nelson Pass DCB1 & Monarchy Audio SM-70 Class A Amplifier
    Cables: Fisual S-Flex Speaker Cable & SPOTFIRE IC Cables & NEW SPOTFIRE Tonearm cable
    Speakers: Pioneer CS-77A

  2. #2
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

    Default

    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK5 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken & Tesla Valves)
    Digital: NONE
    Amplification: Nelson Pass DCB1 & Monarchy Audio SM-70 Class A Amplifier
    Cables: Fisual S-Flex Speaker Cable & SPOTFIRE IC Cables & NEW SPOTFIRE Tonearm cable
    Speakers: Pioneer CS-77A

  3. #3
    Join Date: Jan 2009

    Location: Sheffield - UK

    Posts: 6,072
    I'm Mark.

    Default

    Yeah, the hookup wire is solid silver in Teflon from HiFi Collective.

    100% Analogue

  4. #4
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

    Default

    Quote Originally Posted by YNWaN View Post
    Yeah, the hookup wire is solid silver in Teflon from HiFi Collective.
    Cheers mate,. I'll order a bit.
    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK5 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken & Tesla Valves)
    Digital: NONE
    Amplification: Nelson Pass DCB1 & Monarchy Audio SM-70 Class A Amplifier
    Cables: Fisual S-Flex Speaker Cable & SPOTFIRE IC Cables & NEW SPOTFIRE Tonearm cable
    Speakers: Pioneer CS-77A

  5. #5
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 503
    I'm Simon.

    Default

    Quote Originally Posted by Bigman80 View Post

    I settled on an Elma 2 pole selector switch (same as in the Slagle I have just sold) which I felt was as good as it gets really for a selector switch and a Khozmo Stepped attenuator, which again is scant company at the top of the attenuation tree.
    If you wanted to go mad, get a 34 or 46 step Seiden attenuator and stuff it full of Charcroft Z-foils! I believe the Seiden attenuators are the best if there is no budget (I haven't seen anything better).

    Here: https://www.hificollective.co.uk/cat...on-p-7254.html

  6. #6
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

    Default

    Quote Originally Posted by Simon_LDT View Post
    If you wanted to go mad, get a 34 or 46 step Seiden attenuator and stuff it full of Charcroft Z-foils! I believe the Seiden attenuators are the best if there is no budget (I haven't seen anything better).

    Here: https://www.hificollective.co.uk/cat...on-p-7254.html
    Hi Simon,

    Ha! Yes I did see that yesterday but over 350 on a volume control is outrageous and unfortunately budget has come in to the equation!

    I'm happy with the Khozmo
    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK5 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken & Tesla Valves)
    Digital: NONE
    Amplification: Nelson Pass DCB1 & Monarchy Audio SM-70 Class A Amplifier
    Cables: Fisual S-Flex Speaker Cable & SPOTFIRE IC Cables & NEW SPOTFIRE Tonearm cable
    Speakers: Pioneer CS-77A

  7. #7
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,381
    I'm Andrew.

    Default

    My opinion is that the current fad for so-called "shunt" stepped attenuators is based on a fallacy. Here's a quote from the HiFi Collective site:
    " ...we are proud to offer a version of the Glasshouse stepped attenuator range in SHUNT format...we are offering a choice of 7 resistor types, though bear in mind you can always buy the all important Series (load) resistors separately..."
    How is the series resistor any more of a load than the shunt resistor? Why would one be any more important than the other? Why doesn't it matter that the impedance seen by the source and the output impedance both vary other an extremely wide range?
    Absolutely none of it makes sense and makes me doubt the competence of those making and selling them.

    My advice is to buy a conventionally configured stepped attenuator.

  8. #8
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 503
    I'm Simon.

    Default

    That's one of the reasons why I went with a standard Series attenuator (Acoustic Dimensions 41 step).

    The other thing I did not like about the Shunt type is that if for some reason the contact fails or doesn't click into place right, the volume will not be attenuated at all so speakers will likely be blown (tweeter at least). I know the chances of it happening are very slim but contacts can get dirty after time.

  9. #9
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

    Default

    Quote Originally Posted by RothwellAudio View Post
    My opinion is that the current fad for so-called "shunt" stepped attenuators is based on a fallacy. Here's a quote from the HiFi Collective site:
    " ...we are proud to offer a version of the Glasshouse stepped attenuator range in SHUNT format...we are offering a choice of 7 resistor types, though bear in mind you can always buy the all important Series (load) resistors separately..."
    How is the series resistor any more of a load than the shunt resistor? Why would one be any more important than the other? Why doesn't it matter that the impedance seen by the source and the output impedance both vary other an extremely wide range?
    Absolutely none of it makes sense and makes me doubt the competence of those making and selling them.

    My advice is to buy a conventionally configured stepped attenuator.
    Hi Andrew,

    Thanks for the advice,

    I have purchased a series type which I understood to be "conventional" ? If it's not then so be bit. I will admit to naivety in regards to how they differ and why one would be better than the other. The advice I was given is that Series presents a constant load.

    Either way, it's all about how it sounds SO! how's about this.....

    If someone sends me a "conventional" stepped attenuator, I'll do a comparison and write it up.
    Analogue: Technics SP10 MK2 > Phonomac AT-1010 MK5 tonearm > Ortofon Kontrapunkt b > Bigbottle Jfet MC Valve Phonostage (Telefunken & Tesla Valves)
    Digital: NONE
    Amplification: Nelson Pass DCB1 & Monarchy Audio SM-70 Class A Amplifier
    Cables: Fisual S-Flex Speaker Cable & SPOTFIRE IC Cables & NEW SPOTFIRE Tonearm cable
    Speakers: Pioneer CS-77A

  10. #10
    Join Date: Aug 2011

    Location: Coventry, England UK

    Posts: 503
    I'm Simon.

    Default

    Yes, I believe a series type will appear as the same load towards the source, however it does vary it's output (a 10k based attenuator will be 2.5k at worst case (half volume on the dial).

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