• Re: Want to built a 300B PP amp, Kevin please advise - KevinC 13:57:33 04/04/05 (3)
  In Reply to: Want to built a 300B PP amp, Kevin please advise posted by Louis Sit on April 2, 2005 at 23:55:00:

  Louis,

  The website schematic is not the latest version. I have designed several variants for different individuals who had specific requirements. What you will build depends to a large degree on your budget and specific needs (power, size, etc.).

  Basically I have three push-pull filamentary triode (300B, 32B) designs:

  monoblock or stereo PP 300B (about 16-25 watts / channel)
  monoblock PP parallel 300B (about 50 watts / channel)
  monoblock PP 32B (the one with 2A3 drivers) (about 55 watts / channel)

  The overall topologies are the same, but there are power supply variations, as needed, to address different tube choices and power levels. I'd be happy to e-mail any schematics you want. I would think twice about using the 32B tubes, though, as they are very expensive and do not ship very well due to the poorly supported plate structure. They're a terrific tube, otherwise.

  Having not ever heard the Karna, I can't comment on its sound. The other amps above all sound roughly similar within the constraints of their power ratings. The selection of audio transformer core material makes a much bigger difference than which tube is used. The new amorphous core output and interstages take any of these amps to a level beyond any commercial amplifier I have heard.

  I've not heard either the Sowter or the O-Netics transformers, so I can't comment on them. There are Lundahl transformers to fit any of these applications. They will undoubtedly sound different, but better or not is impossible to predict.

  It's easy to ship these to you in Hong Kong. If I don't have your choices in stock, it may take a few weeks to get them made and shipped from the factory, otherwise it can happen quickly.

  BTW, your English is better than that of many Americans'!
  
  Kevin Carter
  K&K Audio
  www.kandkaudio.com
  
  

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  • Re: Want to built a 300B PP amp, Kevin please advise - Louis Sit 01:32:26 04/05/05 (2)
    In Reply to: Re: Want to built a 300B PP amp, Kevin please advise posted by KevinC on April 4, 2005 at 13:57:33:

    Hi Kelvin,

    Thanks for your advices and support.

    It would be nice if you can email me your schematic for three variants for my reference. Email: louissit@hotmail.com

    Here is my idea:

    1. Output - I think 25W should be enough for me
    2. Output tube - Use normal but not super 300B like 32B so I can test different tubes easily
    3. Size - Monoblock would be nice
    4. Driver stage - no idea.....I heard that 2A3 is great, but which sounds better?
    5. Transformer - I would use all amorphous core transformers if possible
    6. Pre-amp - S&B TX102 or K&K line stage. Will the gain is high enough for S&B TX102?

    Sorry for many questions. Look forward to hearing from you soon.

    Best regards,

    Louis

    
    
    

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    • PP 300B monoblock questions - KevinC 10:23:39 04/06/05 (1)
      In Reply to: Re: Want to built a 300B PP amp, Kevin please advise posted by Louis Sit on April 5, 2005 at 01:32:26:

      Louis,

      The choice of driver tube is a matter of preference and some convenience. I find the 6BX7GT to be nearly the sonic equal in this application to the 2A3. However, the 2A3 is a bit of a pain to use to get that little bit extra. You need a separate filament supply, of course. If it's AC, then the amplifier output noise will suffer to some degree, even if you use "hum pots" to null 60Hz noise. A DC supply will make it quiet, but at a substantial extra parts count.

      How much gain you need in the line stage is dependent on your system specifics. From memory, the fully differential/push-pull amplifier has about 23dB of gain with the 6SN7GT/6BX7GT/300B and 1:1 input and interstage transformers. Connecting the input transformer for 1:2 step-up has minimal impact on the sound, but gives an additional 6dB of gain if it's needed. Unless you possess speakers with less than 88dB sensitivity, this should be adequate with any reasonable source to allow you to use either a TX-102 or Raleigh Audio line stage circuit.

      
      
      Kevin Carter
      K&K Audio
      www.kandkaudio.com
      
      

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      • Re: PP 300B monoblock questions - Louis Sit 21:11:22 04/06/05 (0)
        In Reply to: PP 300B monoblock questions posted by KevinC on April 6, 2005 at 10:23:39:

        Hi Kevin,

        Thanks for your schematic and advice.

        Could you send other two schematics for 2A3-32B and 300B parallel PP amp to me as well? I just want to compare them and decide which one I should make.

        Will LL1671 sounds better than LL1660S/PP in this application? I saw some post said so.

        Are the transformers for 300B filaments from Lundhal? If not, could you provide them for me?

        Best regards,

        Louis

        
        
        

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