Little Bear t10 v2.5 Preamp quality upgrade so far

Discussion in 'Audio Hardware' started by coltlacey1, Jul 25, 2015.

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  1. E.Baba

    E.Baba Forum Resident

    Mine didn't even come with one so I bought a locally sourced one with right angle plug for convenience. From what I've read elsewhere the power supply cables are rubbish and I'd advise to replace them. Your problem just points out how bad it is.
    Using the cheapest of every thing again. Just as well it's cheap and can make a decent sound depending on how far you want to do your own building.
     
  2. Michael Sutter

    Michael Sutter Forum Resident

    Location:
    Holbrook, NY
    I actually got the supplied cable to work but I had to really make sure it was seated deep into the socket. In any case I ordered a 10ft cable from Monoprice to run it behind my desk since the one supplied is a bit on the short side. Next up, replace these cheap tubes with some Electro-Harmonix 12AX7s. Or maybe I'll go NOS, I honestly have no idea yet.
     
    E.Baba likes this.
  3. E.Baba

    E.Baba Forum Resident

    Anything will improve it.
     
  4. Michael Sutter

    Michael Sutter Forum Resident

    Location:
    Holbrook, NY
    I'm actually pleasantly surprised by the stock tubes, while they aren't top notch they are definitely not unusable. But yeah definitely wanna replace them.
     
  5. E.Baba

    E.Baba Forum Resident

    Maybe you got a fluke good set, but I bet you prefer whatever else you put in.
     
  6. Michael Sutter

    Michael Sutter Forum Resident

    Location:
    Holbrook, NY
    Now I'm looking at some used GE or Sylvania tubes. Maybe RCA if I can find a good enough deal. NOS is a bit too pricey but used seems like a good option and I hear they last decently long anyway.
     
  7. Michael Sutter

    Michael Sutter Forum Resident

    Location:
    Holbrook, NY
    Update: There was a very good deal on a gain-matched trio of Voskhod 6N2P tubes. NOS from 1979, Soviet-made. Reviews online sounded promising, and for the price it was definitely worth a shot.
     
    latheofheaven likes this.
  8. E.Baba

    E.Baba Forum Resident

    IME they have a very 'clean' sound. I had 16 of them ! I had 2 LB and a double -up on the order. I had the Military spec ones. Long life /heavy duty determined at the factory for heavy use. You can tell by the extra long part number. I'm including 4 with each of my LB I'm sellng; and still have some left over.
    Sky is the limit with NOS. It's a matter of set your own high price. Don't go too far or you're overcapitalising on what the LB can actually make use of. Remember it is entry level. I've kept mine in case I get into glass again later.
     
  9. Michael Sutter

    Michael Sutter Forum Resident

    Location:
    Holbrook, NY
    Thank you for your help so far. Do you think it's worth replacing the 6Z4 rectifier tube in this? Will it provide any appreciable increase in sound quality? I can't even find a suitable replacement for it that isn't Chinese made, and it seems to be a different kind of tube than the American 6Z4.
     
  10. Michael Sutter

    Michael Sutter Forum Resident

    Location:
    Holbrook, NY
    Just plopped in the Voskhod 6N2P-EV tubes, and while they still need to be broken in a bit, it's already evident that they are built much better than the Chinese stock tubes and are not nearly as noisy.
     
    latheofheaven likes this.
  11. draganm

    draganm Forum Resident

    Location:
    Colorado
    I had a lot of noise problems with my T10 as well, could not have it anywhere near my equipment rack or other electronic devices. The AVR was especially bad at making it hum, pretty loudly at that. I wound up putting it on it's own little stand off to the side of my AV rack, and unfortunately knocking it off one day while vacuuming. :(
    Broke one phono jack off, which the manufacturer was kind enough to send me a free replacement, but I needed to fix this issue. The plastic case was already starting to look like crap with spider cracks thru most of the panels . I had always intended to put this unit in a metal case so this was the catalyst that finally got that project rolling. Nothing too fancy, a Jameco Valuepro SY0207-R is $10. + $8. shipping and an Astrodyne TDI fused and shielded power input module (PIM), part number 082.01001.00 , $18. with shipping. I know that's putting a $36. case on a $100. amp but it was easier than selling this and buying a new T11.

    It's 2 machining op's to cut the lid for the tubes to stick up, transformer vent holes, and for the RCA jacks in the painted Steel lid. 1 more to cut the PIM hole in the AL base piece. Let me know if you need the CAD files to do this (you'll need a milling machine or have a machinist friend).

    Electronically, this requires some soldering skills as I removed the AC port on the board and the little red power button, replaced with leed-wires and a jumper respectively. Tested it last night, it's dead quiet, really happy.

    I have some cool pics, but can't seem to attach them without hosting on a 3rd party site?
     
  12. draganm

    draganm Forum Resident

    Location:
    Colorado
    alright, maybe not so much interest in this unit anymore, but in case someone down the road decides to improve theirs,
    some pics from a registration-less hosting site
    cheers
    [​IMG]
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    [​IMG]
     
    Old Rusty and 33na3rd like this.
  13. draganm

    draganm Forum Resident

    Location:
    Colorado
    one more pic, an "action shot" LOL Not having the RCA jacks and AC power port on opposite sides of the box anymore really improves fit into AV rack (power chord moved to long side of box)

    [​IMG]
     
    H8SLKC and Al Smith like this.
  14. Michael Sutter

    Michael Sutter Forum Resident

    Location:
    Holbrook, NY
    The Voskhod 6N2P-EV tubes have been awesome and completely outperforming expectations. Highly recommend if you need a bang-for-your-buck tube.

    I just replaced the Chinese rectifier 6Z4 tube with a NOS Soviet, 1980s era Reflector 6C4P-EV tube and it's noticeably reducing the hum this unit is known for.

    The Little Bear T10, plus about $30 invested in Soviet replacement tubes, has been an AWESOME value for the price.
     
  15. I hear ya, I run Voshkod 6J1P-EV tubes in my tubed phono-stage & they sound phenomenal. Bang for the buck, indeed.


    [​IMG]
     
    H8SLKC likes this.
  16. draganm

    draganm Forum Resident

    Location:
    Colorado
    honestly I didn't hear any difference with a Russian rectifier tube a friend gave me, but it's nice to have a spare. Otherwise my T10 came with 12AX7's for the audio portion, no plans to change them.
     
  17. These may do the job but they are made of aluminium so I don't know if they will really shield the tubes from EMI coming from the transformer, covering them with several layers of tin foil may do the job, what do you think? I'm thinking about getting them for my EAR 834 CLONE and cover them with thin foil, as tubes are inside the preamp and not visible this looking bad is not an issue.
    VENTED CANS MILITARY SPEC. (SUIT ECC82/12AX7 B9 SIZE) | eBay [​IMG]
     
  18. draganm

    draganm Forum Resident

    Location:
    Colorado
    Tin foil is really Aluminum foil, so those cans are the commercial solution to using AL foil. They will function as complete EM shielding, no need to add anything except maybe some form of leed to ground the shield to either the case of the device or the circuit board ground plane. Careful that your ground wire doesn't short out any other components, use an insulated wire .
    if your clone is already in a metal box then this shield might not have any additional benefits.
     
    Kiko1974 likes this.
  19. Yes, tubes are inside the EAR 834 clone, but the transformer (a toroidal one) is very close to them 'though it's encased in metal but there are plenty of other electronic components surrounding the tubes and both components and tubes are "on the open",unshielded.
    Some tubes hum more than others on my EAR 834 clone Phono preamp and as it uses three tubes and every one of them does something to both channels, not the classic configuration where one tube amps only one channel. And matching different tubes are a real NIGHTMARE on this Phono preamp,specially if a 5751 tube is used as a V1 tube that does most of the amp, V2 does RIAA de-eq and some more amp, and V3 is used as a "buffer tube" on a cathode follower configuration to reduce impedance and distorsion, the specs of this Phono preamp say to use a 12AX7 tube but I read that using a 12AU7 tube gives better results and I agree and that's whay I use as a V3 tube. But here comes the X File: as I said it's a nightmare to get a combination of three tubes that doesn't hum as hell but with some match and test this is got, excep for Hitachi or Hit Ray (a Hitachi and Raytheon joint venture in the 1960's, tubes were made by Hitachi) tubes, no matter how I match them, a 12AX7 as a V1, a 12AX7A as a V2 and a 12AU7 as a V3, except for the V3 which I always use a 12AU7 tube, one can do all the combinations that want with Hitachi tubes that the hum is very low, and sound is excellent using Hitachi tubes on this Phono preamp. The edge have it a pair of Hitachi 7025 tubes I have that are extremely quiet both with hum and noise and their sound is outstanding. I got them NOS for dirty cheap money, 40 $ including shipping to Spain. I'm always hunting more of these Hitachi 7025 on ebay but no luck for the moment.
     
  20. E.Baba

    E.Baba Forum Resident

    I got fed up with the LB. To be fair I was trying to to run two mc tables into it. Not really what it's for. Too many boxes and too much hum to keep away from other gear.
    I got a battery powered custom phono and then a Project tubebox.
     
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