• Re: All Lundahl Transformers - 417a Preamp - Mr. Stone 00:07:57 12/05/03 (4)
  In Reply to: Re: All Lundahl Transformers - 417a Preamp posted by Mr. Stone on December 04, 2003 at 22:46:04:

  Hi Folks,

  Do I need to add a load resistor at the LL1660 output? THanks so much!

  Cheers
  Mr. Stone
  
  

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  • Re: All Lundahl Transformers - 417a Preamp - KevinC 07:14:28 12/05/03 (3)
    In Reply to: Re: All Lundahl Transformers - 417a Preamp posted by Mr. Stone on December 05, 2003 at 00:07:57:

    You can experiment with load resistors. I find that they are useful for reducing high frequency resosnances (> 20kHz), but must be used gently, because they also tend to drain the sound of life when they are too low. It's best to adjust by listening.
    
    
    

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    • Please define too low ? - akltam 00:15:00 12/06/03 (2)
      In Reply to: Re: All Lundahl Transformers - 417a Preamp posted by KevinC on December 05, 2003 at 07:14:28:

      Kelvin,

      I am now experimenting LL1654 in a 5K:150ohm configuration. And I am using 470 Ohm. Is that too low ?

      Alan
      
      

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      • Re: Please define too low ? - Dave Davenprt 05:51:33 12/06/03 (1)
        In Reply to: Please define too low ? posted by akltam on December 06, 2003 at 00:15:00:

        Hello Alan,

        "Too low" is a subjective evaluation. Start with no resistor, then a large resistor, several K, and then a small resistor, hundreds, and compare the difference in sound. Which is better? Then try a third resistor that is closer to that chosen. Which sounds better? Keep this up until you find the value of resistance that gives the best sound.

        Now, there is another factor involved. Things will change as the components break in. So you will have to repeat your experiment after several hundred hours of music.

        Dave
        
        

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        • The breakin problem. - akltam 07:15:59 12/06/03 (0)
          In Reply to: Re: Please define too low ? posted by Dave Davenprt on December 06, 2003 at 05:51:33:

          Dave,

          In fact that is the most troublesome thing that can happen and the DIYer that have to deal with. After you try another value of resistor, and then how can you remember few hundred hours ago with another.

          I was using a 1660/25mA before I try to use the LL1654. Immediately I found that the LL1654/40mA does not do too well in the treble section. (without a terminating resistor) And I knew at that time I cannot expect a new output transformer to be at its best. It was such an agony that I have to wait for it to break in. Time move so slow while you wait.

          Then I try different configuration and also I don't need too much gain, I use the LL1654/40mA with the 5K:150 configuration plus using a 470 ohm resistor on the secondary. It doesn't sound good at first. (that is what I found). After some time, it seems that it does improve. I then use a signal generator to test the response of this 1654 with 6C45(running at around 36-37mA). It was indeed pretty flat from 22Hz to 20K. The interesting thing is as soons as I get it down to 21Hz, the gain dropped. (haven't got time to test the band beyond 20k)

          Too little time, too lazy to try some other values of resistors.

          Thanks for sharing your experience.

          Alan
          
          
          

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