• I did it! - MaciekP 11:58:14 06/04/04 (5)
  In Reply to: LL1674 as a parafeed 4:1 output posted by MaciekP on May 27, 2004 at 01:36:21:

  

  Hello,
  I used LL1674 as a parafeed output of my Audio Note DAC 2.1x in 4:1 config.
  I tried it with Jensen tin foil 1uF cap and Audio Note PIO copper foil 0.47uF. Jensen was a nightmare, poor transparency, poor HF and bass, but 0.47uF AN sounds great with deep bass, very good MF, HF, timing...just fantastic. So even 0.47uF can be good if a cap is good. I didn't have any other coupling caps, so maybe big plastic like Kimber or Aricap 2uF would do the job also.
  I hear better notes separation and transparency, but not lean at the same time. I'm a bit supriseed it works in a AN circuit...

  Maciej
  
  

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  • Have you tried listening with the transformer connected - Bas Horneman 08:51:56 06/07/04 (3)
    In Reply to: I did it! posted by MaciekP on June 04, 2004 at 11:58:14:

    to the plate of the bottom tube instead of the cathode of the upper one?

    Cheers,
    Bas
    
    

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    • mod picture - MaciekP 09:22:20 06/07/04 (0)
      In Reply to: Have you tried listening with the transformer connected posted by Bas Horneman on June 07, 2004 at 08:51:56:

      

      my modified DAC2 with LL1674s at the back wall
      Maciek
      
      

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    • Re: Have you tried listening with the transformer connected - MaciekP 09:10:36 06/07/04 (1)
      In Reply to: Have you tried listening with the transformer connected posted by Bas Horneman on June 07, 2004 at 08:51:56:

      No,
      I think that it is a nature of SRPP to get the voltage from the upper tube cathode. Maybe I should try it...
      If it was Mu stage yes, it shoul be connected to the lower tube anode. Can someone more skilled comment it?
      Maciek
      
      

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      • Actually a typical mu-stage is tapped from - Bas Horneman 09:48:35 06/07/04 (0)
        In Reply to: Re: Have you tried listening with the transformer connected posted by MaciekP on June 07, 2004 at 09:10:36:

        the cathode of the upper tube as well. Just like the SRPP...

        But I was simply curious..if you have tried and listened to it otherwise...

        
        
        

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  • Cool! Really love it when people report back on their - Bas Horneman 08:46:35 06/07/04 (0)
    In Reply to: I did it! posted by MaciekP on June 04, 2004 at 11:58:14:

    adventures!

    Cheers,
    Bas
    
    

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• Re: LL1674 as a parafeed 4:1 output - Dave Davenport 09:55:04 05/27/04 (3)
  In Reply to: LL1674 as a parafeed 4:1 output posted by MaciekP on May 27, 2004 at 01:36:21:

  Let me take a shot at this since I have experience using the LL1674 in a parafeed configuration.

  1. Can you estimate what is the max Rp of the tube to get the good LF with LL1674 in parafeed 4:1 configuration?

  I use a pair of 6N1P in bridged parafeed, each tube has 4400 Ohms nominal plate resistance. Double this for the two in series. The bass is fine. I haven't noticed much if any change in the bass with different tubes.
  
  2. What is the recommended min. capacitance of parafeed capacitor

  There are several formulas available but I have not found one that gives consistent results. The only way I have found to find the right value is build the circuit and measure the very low frequency - less than 20 Hz, response.
  
  3. What resistor value is the best for secondary termination, if any?

  This is a controversial topic. I prefer the sonics with no secondary termination.

  4. What is the max output voltage for this transformer ratio?

  It depends on frequency. I did measure it but I don't recall off hand my measurement. I do know that it is totally adequate for preamplifier output use. However it is not enough for use as an interstage.

  
  5. Do I really need a plate choke?

  Well, if you are going to parafeed you need some kind of high impedance load in the plate circuit. That is the definition of parafeed. You can use a large resistor, a choke, or a constant current source. I prefer a CCS.

  Dave

  
  
  
  

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  • Re: LL1674 as a parafeed 4:1 output - MaciekP 10:15:21 05/27/04 (2)
    In Reply to: Re: LL1674 as a parafeed 4:1 output posted by Dave Davenport on May 27, 2004 at 09:55:04:

    thanks,

    2. What is the recommended min. capacitance of parafeed capacitor

    There are several formulas available but I have not found one that gives consistent results. The only way I have found to find the right value is build the circuit and measure the very low frequency - less than 20 Hz, response.

    
    Is 0.47uF a good starting point?

    4. What is the max output voltage for this transformer ratio?

    It depends on frequency. I did measure it but I don't recall off hand my measurement. I do know that it is totally adequate for preamplifier output use. However it is not enough for use as an interstage.

    
    If it is about 22V at 20Hz in 1:8 ratio, so the primary should handle 2.5V...and it is probably something I should expect from the output from 4:1 config I think.

    Maciek
    
    

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    • Re: LL1674 as a parafeed 4:1 output - Dave Davenport 17:56:10 05/27/04 (0)
      In Reply to: Re: LL1674 as a parafeed 4:1 output posted by MaciekP on May 27, 2004 at 10:15:21:

      Hi Maciek

      Sorry that I left that out. Kevin's response was correct.

      Dave
      
      

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    • Re: LL1674 as a parafeed 4:1 output - KevinC 10:19:57 05/27/04 (0)
      In Reply to: Re: LL1674 as a parafeed 4:1 output posted by MaciekP on May 27, 2004 at 10:15:21:

      I would start with something more like 2-4uF. The maximum measured output (just prior to transformer saturation) for a parafeed 6N1P driven LL1674 connected 4:1 is 4.5vRMS at 20Hz. I didn't measure it at a higher frequency.
      
      
      

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