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    SP12 preamp revisited

    tubes4hifi
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    Post by tubes4hifi on Sat Apr 13, 2019 7:40 pm

    Six years ago the SP12 was the top selling preamp in the Tubes4HiFi (VTA) product line, almost every person buying a VTA amp was buying the SP12.
    But 7 years ago the SP12 got a big brother, the SP14, and in the past 5 years or so the SP12 has almost been forgotten by buyers, as buyers were
    no longer looking for a "budget" tube preamp, but the very best tube preamp kit available, the SP14.   Maybe 100 SP12s were sold in 4-5 years.
    During the past 4-5 years well over 400 SP14s have been sold, more than 4x as many.

    But let's NOT forget the SP12.   The SP12 uses the EXACT same circuit design as the SP14.   But it uses the popular 12AU7 tube instead of the larger 6SN7 tube.
    The SP12 has a single power power instead of dual power supplies.   It only needs one power transformer.  The SP12 kit is $250 less than an SP14.
    ALSO, the SP12 is the ONLY VTA preamp that you can add an INTERNAL phono stage to.  The older PH12 phono stage has been replaced by a much superior PH14 phono stage,
    the PH14 can fit into the same chassis.  The improved PH14 phono stage also has it's own power supply, and it has an output buffer.
    The SP12 is definitely NOT a "budget" tube preamp, it's the smaller brother of the HI-END SP14, 3/4 the size and 3/4 the price, and when you add the PH14
    phono stage you can have a COMPLETE tube preamp with integrated phono stage, for LESS money than the cost of the SP14 preamp.

    Here's a link to a recent SP12 build . . . SP12 - 2019 build photos

    Here's a link to a customer review (back in 2011) SP12 review
    rustybutt
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    Post by rustybutt on Sun Apr 14, 2019 3:27 am

    I have an SP13 preamp that Troy built for me.  He managed to fit a PH12 phono board in the larger chassis with it.  I am very happy with it.  I managed to find some Brimar Mazda 6CG7 tubes and it's pretty sweet.  

    You can have your cake and eat it too...
    rustybutt
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    Post by rustybutt on Sun Apr 14, 2019 4:08 pm


    My SP13 is essentially an SP14 with 6CG7 tubes instead of 6SN7.   Smaller tube, smaller board.  Dead silent.  You might want to ask Roy for help on it or just unload it on US Audomart.
    wgallupe
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    Post by wgallupe on Sun Apr 14, 2019 4:51 pm

    rustybutt wrote:I have an SP13 preamp that Troy built for me.  He managed to fit a PH12 phono board in the larger chassis with it.  I am very happy with it.  I managed to find some Brimar Mazda 6CG7 tubes and it's pretty sweet.  

    You can have your cake and eat it too...

    I also have a 'Troy built' SP13/PH12. For tubes, I settled on NOS Tungsol 6CG7 for the pre and NOS Amperex 6922PQ for the phono.

    I recently added the Khozmo remote 64 step volume control (and new faceplate).

    Indeed, "it's pretty sweet"
    tubes4hifi
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    Post by tubes4hifi on Mon Apr 15, 2019 10:11 pm

    all these posts are WAY off topic, but since a few posts are from SP13 people, they should know I have a stash of about a dozen NOS RCA clear top 6FQ7 in stock
    that I will never use, so if interested let me know. Only about 8 SP13s were ever sold, so they are rare and a real gem.
    The SP12, SP13, and SP14 preamps are all totally dead quiet, except for a couple customers having 100db efficient speakers.
    The other 400+ customers are in audio heaven.
    That's a tough nut to fix, but no tears when you can sell it to someone else for $1000+ who has more common speakers.
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    mijohn

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    Post by mijohn on Tue Apr 16, 2019 12:03 am

    The most likely source of the hiss is noisy tubes in the gain stage, which are the pair of tubes (front and back) on the left.
    They need to be selected low noise types. You can use the noisy ones in the buffer stage where they won't be noticed unless they are really bad.


    Last edited by tubes4hifi on Mon Dec 30, 2019 4:08 pm; edited 3 times in total (Reason for editing : correct spelling)
    10-E-C
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    Post by 10-E-C on Tue Apr 16, 2019 6:44 am

    tubes4hifi wrote:all these posts are WAY off topic, but since a few posts are from SP13 people, they should know I have a stash of about a dozen NOS RCA clear top 6FQ7 in stock
    that I will never use, so if interested let me know.   Only about 8 SP13s were ever sold, so they are rare and a real gem.
    The SP12, SP13, and SP14 preamps are all totally dead quiet, except for a couple customers having 100db efficient speakers.  
    The other 400+ customers are in audio heaven.
    That's a tough nut to fix, but no tears when you can sell it to someone else for $1000+ who has more common speakers.

    I totally understand having some hiss in very efficient speakers, both sets of my speakers are at 99 db, it's a never ending fight to eliminate the hiss, but you can get close with rolling quiet tubes.
    I got tired of fighting the noise in my Klipsch speakers so I went another way in DIY audio. I built a Amp Camp Amp (ACA) SS class A 8 watt amp to drive my Fortes IIs. Its a Nelson Pass design and is very musical driving my Klipsch, of course I have a Sacks tube amp feeding the ACA and very happy with the setup, no noise at all.

    TM
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    rjpjnk

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    Post by rjpjnk on Fri Apr 19, 2019 1:06 am

    tubes4hifi wrote:
    The older PH12 phono stage has been replaced by a much superior PH14 phono stage,
    the PH14 can fit into the same chassis.  

    Roy,
    What is better about the PH14 compared to PH12?
    What are the dimensions of the PH14 board?
    I've been very happy with my SP12/PH12 combo, and currently have them both mounted in a 12" chassis. I like the compact size.

    btw, I have 99dB Klipsch Heresy speakers and do not hear any hiss at all on the line stage. Phono of course adds hiss, but I figured that is expected given the additional 40dB of gain. Would the PH14 be the same in this regard?
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    KSMITH

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    Post by KSMITH on Mon Apr 22, 2019 2:06 pm

    Tubes make no difference in the hiss.  Rolled numerous 6SN7 before putting it into mothballs. Just poor compatibility with horn speakers (read power supply). Will say no more on the subject as post deletions and subject diversion rule here.
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    Post by rjpjnk on Tue Apr 23, 2019 6:38 pm

    KSMITH wrote:Tubes make no difference in the hiss.  Rolled numerous 6SN7 before putting it into mothballs. Just poor compatibility with horn speakers (read power supply). Will say no more on the subject as post deletions and subject diversion rule here.
    Twisted Evil

    By hiss do you guys mean thermal noise? The comment about power supply above made me think perhaps not. Is there some other form of noise you think is coming from the power supply. I am curious to learn more about this. The only sort of noise I am familiar with due to power supplies are 60Hz line, 120Hz rectifier, and SS diode hash. Is there another one?

    If we are talking about thermal noise then I have this comment: Why should speaker efficiency alone be associated with hiss? It seems to me it is the combined gain of amplification and speakers that matters. At some point this overall gain is large enough that you can hear the thermal noise. So a more powerful amp would lead to hiss just the same as efficient speakers would. My understanding is that there is no way to remove this as it is a fundamental property of physics and is a function of bandwidth and temperature only.

    If changing to another amp reduces hiss then doesn't this simply mean the new amp has less gain?
    tubes4hifi
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    Post by tubes4hifi on Fri Apr 26, 2019 5:07 pm

    RJPJNK,
    yes, you are about 90% correct. Forms of power supply noise are 60Hz line, 120Hz rectification, and SS diode hash.
    In most amps or preamps, some of this noise is introduced into the amplifier stage thru either the filament supply or B+ HV supply.
    However, in my preamps, any power supply noise is sampled, inversely adjusted to the gain of the amp, and injected (summed) into the amplification stage,
    thus eliminating 99% of any power supply noise. However, other power supply noise can be from EMI radiated from the transformers, leaking into non-shielded audio paths,
    or inducted/transmitted by other wires (transformer leads, etc) and possibly picked up by internal elements inside the tube (plates, grids, filaments).
    Most of the time this doesn't happen in a well-constructed amp or preamp, using short wires, shielded wires, twisted pairs, and shielding where necessary.
    And yes, you're correct about amplification. So an amp or preamp with more gain is more likely to make that noise more apparent by the time it gets to the speakers.
    Super high efficiency speakers work better with very low gain amps/preamps
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    Post by audiobill on Thu May 02, 2019 6:16 pm

    Many of us feel that a dac sounds better with a preamp than without. More dynamic.

    After all, the transformers alone in an sp14 have more heft than a Benchmark DAC 3L
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    Post by audiobill on Fri May 03, 2019 9:07 am

    Well, my Grace m920 (a Sabre based dac/preamp, much like a Benchmark Dac3), a fully tubed and transformer coupled AudioNote dac 4.1LE or my PS Audio FPGA Directstream dac all benefited from adding Roy's SP14, whether through my M-125s or my dual Conrad Johnson Premier 140 power amps, biamping Magneplanar 3.6/r or PBN Montana EPS speakers....but of course YMMV.

    Best,
    richtp
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    Post by richtp on Mon Dec 30, 2019 3:35 pm

    Just out of curiosity, what are the dimensions of the board? Also what is required for high voltage and filament transformers? I hav been playing around with a Dynaco Pas for years and never really liked it. I think I may abandon it and start over with an SP12 instead.
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    Post by tubes4hifi on Mon Dec 30, 2019 4:12 pm

    Hi Rich,
    the SP12 board is 7.2 x 5.2" and uses an Antek AS-05T240 power transformer.
    I've had a few customers actually gut PAS3 or PAT4 preamps and put it in there if you're on a tight budget,
    although $160 for the PCB kit isn't really a huge deal. It's the custom chassis that costs $$
    www.tubes4hifi.com/pre11.htm
    richtp
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    Post by richtp on Mon Dec 30, 2019 5:14 pm

    I think I may go for it. Just have to figure out what to put it in. I have an old Pat preamp not being used it would be a perfect candidate. But maybe I will build a chassis. So many decisions haha. Thanks!SP12 preamp revisited Ddafa510
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    Post by deepee99 on Wed Jan 22, 2020 8:14 pm

    rustybutt wrote:I have an SP13 preamp that Troy built for me.  He managed to fit a PH12 phono board in the larger chassis with it.  I am very happy with it.  I managed to find some Brimar Mazda 6CG7 tubes and it's pretty sweet.  

    You can have your cake and eat it too...

    Indeed you can. One of those beauties adorns my man-cave. Recapped and loaded for bear.
    richtp
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    Post by richtp on Sun Feb 09, 2020 10:58 am

    Well, I took the plunge the kit arrived Friday (very fast shipping). I assembled the board last night. Now
    I need to decide what to use for a chassis. The board is very well made. I am impressed so far. Can’t wait to hear it in action.
    SP12 preamp revisited Bb953310
    pedrocols
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    Post by pedrocols on Mon Feb 17, 2020 12:46 pm

    Any updates?
    richtp wrote:Well, I took the plunge the kit arrived Friday (very fast shipping). I assembled the board last night. Now
    I need to decide what to use for a chassis. The board is very well made. I am impressed so far. Can’t wait to hear it in action.
    SP12 preamp revisited Bb953310
    richtp
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    Post by richtp on Mon Feb 17, 2020 5:11 pm

    Not a lot of progress. Been really busy at work. I have the PAT 4 chassis gutted and cleaned up. Figured out my layout. Now I’m deciding what stays and goes. Many of the switches and pots will go back in the chassis to keep the original look but will be nonfunctional. I was planning on etching my own board and making a new RCA board for the inputs and outputs but none of the boards I have are long enough. That was supposed to be my weekend project. I hope to work on it a bit tonight if I can manage to go home from work.

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