Posted by andy evans (A) on June 23, 2006 at 08:42:21

Hi there - Having a single LL1540 to play about with, I put it as an output transformer in one of my line stages, which has 12b4 in differential with a CCS set for 8mA per tube under each diff pair. Anode resistors of 10k, 170vDC on anodes, HT250vDC. I used a 2uF parafeed cap between pins 2 and 4 on the input and connected 6, 8 and screen of the secondary to earth. Ran a couple of 10k resistors from pins 5 and 7 into a shunt attenuator of 20k (250k pot with 22k across it). Simple as that. I wasn't expecting much, but it seems to sound very good, judging from the one channel I have up and running. Can't wait for another LL1540 to hear it in stereo. How does this setup sound to you? It's a very cheap solution! I don't see the LL1540 discussed much but I guess it has been used quite a bit in studios and pro audio. Comments appreciated, pus any suggested mods! Andy Evans

• Re: LL1540 in parafeed as output for line stage - KevinC 14:50:09 06/23/06 (2)
  In Reply to: LL1540 in parafeed as output for line stage posted by andy evans on June 23, 2006 at 08:42:21:

  Good for you! Sometimes the odd experiment takes me in a new direction, too.

  The LL1540 is a relatively high impedance transformer, so it's not really ideal for this service, but it's not off-the-wall either, largely because your attentuator doesn't load it excessively. Of course, the output impedance is essentially the value of your series resistors in your attentuator, so don't use long interconnects.

  If you use a higher mu tube, you can use a transformer in stepdown and use lower value series resistors and attenuator, too, to get the output impedance down.
  
  Kevin Carter
  K&K Audio
  www.kandkaudio.com
  
  

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  • Re: LL1540 in parafeed as output for line stage - andy evans 06:24:30 06/24/06 (1)
    In Reply to: Re: LL1540 in parafeed as output for line stage posted by KevinC on June 23, 2006 at 14:50:09:

    The LL1540 is a relatively high impedance transformer, so it's not really ideal for this service, but it's not off-the-wall either> >

    Hi Kevin - the thing that attracted me to the LL1540 was the high impedence, so I could use it after a tube stage. I guess it must be pretty much the only one out of the small line stage trannies that has a high enough impedence to follow a tube stage? Are there others before we go up to the medium size transformers which are quite a lot bigger (and double the price). Andy
    
    

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    • Re: LL1540 in parafeed as output for line stage - KevinC 05:26:40 06/26/06 (0)
      In Reply to: Re: LL1540 in parafeed as output for line stage posted by andy evans on June 24, 2006 at 06:24:30:

      I have used the LL1674/1676 for a similar purpose, as well as the LL1538XL, so there are others that work well, too, albeit at a somewhat higher price. Other less expensive lower impedance transformers such as the LL1530 should also work.
      
      Kevin Carter
      K&K Audio
      www.kandkaudio.com
      
      

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