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Thread: Nelson Pass B1 preamp build

  1. #101
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

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    A punt has been taken. A mumetal shield on route from China.
    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. #102
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 36,798
    I'm Geoff.

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  3. #103
    Join Date: Jan 2009

    Location: Sheffield - UK

    Posts: 6,072
    I'm Mark.

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    Ah, I’m sorry to say but I don’t think that will cure the issue - in fact I suspect the shield will cause exactly the same issue the lid does. I say this because the shield is essentially doing the same as the lid, just from an even more magnetically permeable material.

    100% Analogue

  4. #104
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

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    Quote Originally Posted by YNWaN View Post
    Ah, Iím sorry to say but I donít think that will cure the issue - in fact I suspect the shield will cause exactly the same issue the lid does. I say this because the shield is essentially doing the same as the lid, just from an even more magnetically permeable material.
    I suspect you'd be right BUT if it doesn't help, it can be used elsewhere. Not much investment either, £8 lol.
    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. #105
    Join Date: Aug 2012

    Location: Hartlepool UK

    Posts: 1,383
    I'm Alan.

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    Every system has to have at least 1 point were the chassis earth is connected to the signal ground
    Some pre amps have this as an earth lift switch where you can have it connected or not at the flick of a switch
    In some source components they have this connection and as long as that is connected to wont get a hum but if you have it in a source component and a pre amp you will get an earth loop and get a hum so you cant have it in 2 components.
    None of mine have this connection so I deliberately connected mine in the pre amp and the hum disappears

    So from your case earth run a wire to your star earth or signal ground and see if the hum disappears ?

    If you buy Mumetal plate and bend it, it may need heat treatment afterwards for maximum permeability

    Alan
    Turntable - Garrard 401/Jelco 750L/Ortofon Kontrapunkt B, Pioneer PLC 590, SME 3009/2 , Denon DL103R - DIY Paradise Phono stage - Reel 2 Reel Studer A810, Otari MX55,Tascam BR20 - Digital HTPC / Young Dac - Preamp - DIY B4, 821, Power Amp's DIY Voyager Mono Block, Speakers Tannoy precision 6.4 / Wilmslow Kit Volt BM220.8 / Scanspeak D2905/9500

  6. #106
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

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    Quote Originally Posted by 337alant View Post
    Every system has to have at least 1 point were the chassis earth is connected to the signal ground
    Some pre amps have this as an earth lift switch where you can have it connected or not at the flick of a switch
    In some source components they have this connection and as long as that is connected to wont get a hum but if you have it in a source component and a pre amp you will get an earth loop and get a hum so you cant have it in 2 components.
    None of mine have this connection so I deliberately connected mine in the pre amp and the hum disappears

    So from your case earth run a wire to your star earth or signal ground and see if the hum disappears ?

    If you buy Mumetal plate and bend it, it may need heat treatment afterwards for maximum permeability

    Alan
    I'll give it a go Alan,

    Thanks.
    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. #107
    Join Date: Oct 2016

    Location: Bolton, England

    Posts: 1,380
    I'm Andrew.

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    Quote Originally Posted by 337alant View Post
    Every system has to have at least 1 point were the chassis earth is connected to the signal ground
    No, it doesn't. Metal casework must be earthed for safety, unless it is double insulated. Zero volts doesn't need to be connected to mains earth. It doesn't need to be connected to the chassis either.

    Remember, this is just a buffer with unity gain. People put phonostages and mic preamps into steel enclosures without getting hum, so it should be easily possible here.

  8. #108
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

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    A keen eyed watcher (Mr Firebottle) has spotted that both the output and input are sharing the same common which is also connected to the Chassis. I'll cut the wire tomorrow and see if it helps.

    Geoff, you also stated this so you might be on to something!
    Last edited by Bigman80; 06-07-2018 at 22:17.
    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

  9. #109
    Join Date: Nov 2015

    Location: Wolverhampton

    Posts: 6,240
    I'm Oliver.

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    Quote Originally Posted by ijrussell View Post
    This is my DCB1 built by a friend for me. I went a bit foo with Khozmo attenuator, Audio Note Tantalum resistors and Mundorf caps but it's defintely worth it!

    That looks fantastic.

    So far today, the Khozmo & DCB1 have been a very good listen. I am very happy with it all so far, apart from the hum that has disappeared after unscrewing the lid and just resting it in place.

    Not overly happy with the RG316 as it sounds hard at times and a little etched but it's a characteristic of the cable I was aware of. UP-OCC is ordered and should be here next week. I'll rewire the thing when I get a chance.

    Also, any of you eagle eye watchers may have noticed that the fuse holder isn't connected. Thats because I didn't have a suitable fuse! One on the way. All will be done next week.

    I've given it a thorough workout today with my DIY valve phonostage and a Solid-state phonostage and the results are wonderful with both. Great soundstage, Excellent depth and very revealing. It's a pleasure to listen to.

    I really felt like I was taking a risk when I sold the Slagle but it was a blind punt I'm glad I have taken.

    The DCB1, a really really good preamp.
    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. #110
    Join Date: Apr 2015

    Location: Central Virginia

    Posts: 1,254
    I'm Russell.

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    Iíve got great respect for DIY gear. Iíve been wanting to build my own stereo for years! Iím sure it sounds just that extra bit better when you build it yourself. Nice thread and a great project!

    Russell

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