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Question for Kevin

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I was wondering what your recommendation would be for those of us who have DACT 10K stepped attenuators who don't find it financially feasible to replace it with a S&B TX1022 but would like the advantages of an input transformer while using it in a single ended type of circuit like the Espressivo design.
Would it be the Lundahl LL1544a or some other input transformer, since I would not need any balanced features.
Thanks,
Anand.

Follow Ups:

Re: Question for Kevin - KevinC 13:49:45 07/04/03 (13)
Anand,
Either the LL1544A or the LL1676 would be my choices. I haven't done a head-to-head listening test of these, so don't ask me which I prefer. On first principles I would probably choose the LL1676, because of the larger core, however, I have used the LL1544A in numerous amps as an input transformer and been very pleased with the results.

Kevin Carter
K&K Audio
www.kandkaudio.com
- Re: Question for Kevin - AnandR 16:39:18 07/04/03 (12)
  Well...you did use the 1676 for your own linestage kit design didn't you? That pretty much sums it up for me. The only caveat is as long as my output voltage on my cd player isn't like 5V rms (it isn't). But there's always the 1544a if that situation arises (I recall this being discussed a long while ago re: input transformer for the Amity and Auroras).
  Can you give me an idea how the 1676 would be connected (those lundahl pdf schemas get me all confused!) in the Espressivo circuit since this is a single ended and not balanced design?
  I figure you haven't done a head to head comparison of the TX102's with the a DACT+Lundahl input transformer have you?
  Thanks,
  Anand.
  - LL1544A vs. LL1676 - KevinC 18:13:34 07/04/03 (11)
    The LL1676 will handle a substantially greater level than the LL1544A. In this case it IS all about size...
    I haven't compared the DACT + LL1XXX to the TX-102.
    For the LL1676, make the input side the two "2" windings in parallel and the output the two "1" windings in series and you will have a 1:1 input transformer.
    
    Kevin Carter
    K&K Audio
    www.kandkaudio.com
    - Re: LL1544A vs. LL1676 - AnandR 21:50:36 07/04/03 (0)
      Let me see if I have this right...
      For a 1:1 input transformer,
      Input side: Connect 2 to 4 and 1 to 5, so that the 2/4 combo is your positive and 1/5 combo is ground.
      Output side: Connect 6 to 9 and 10 to 8 so that 7 is positive and 10/8 combo is ground.
      Let me know.
      Anand.
    - Re: LL1544A vs. LL1676 - AnandR 21:46:20 07/04/03 (9)
      Well...lets see if I have this right, (I don't know what you mean by "2" and "1")
      For 1:1 input transformer,
      Input side:
      Connect 2 to 4 and 1 to 5. Then the 2/4 combo is your + and the 1/5 combo is your ground.
      Output side:
      Connect 6 to 9 and 10 to 8 so 7 becomes your + and 8/10 becomes your ground.
      Anand.
      - LL1676 wriing for 1:1 - KevinC 03:38:56 07/05/03 (8)
        
        In Reply to: Re: LL1544A vs. LL1676 posted by AnandR on July 04, 2003 at 21:46:20:
        
        No, that won't do what you want. Try this:
        For the input side connect 7 to 9 and designate that the "+" input. Connect 6 to 10 and call that the "-" input. For the output connect 1 and 4. Designate 2 as the "+" output and 5 as the "-" output. Ground pin 8.
        
        Kevin Carter
        K&K Audio
        www.kandkaudio.com
        
        Superb results with LL1676 in 1:1 mode - Lynn Olson 17:54:42 07/07/03 (4)
        
        In Reply to: LL1676 wriing for 1:1 posted by KevinC on July 05, 2003 at 03:38:56:
        
        I was at Gary Dahl's place and did some additional testing(12K load per half-secondary), and the 1:1 LL1676 is the best I've seen for input and phase-splitting applications. Performance at HF is dramatically better at 1:1 than 1:2 ratio.
        
        At 1:2, small phase deviations appear around 10kHz, and amplitude mismatch is about 5% at the same frequency - OK but not wonderful. (The smaller LL1544A is quite a bit better in that regard.) The effective HF limit is about 70kHz.
        With Kevin's 1:1 connection (posted above), HF performance of the LL1676 is in another league altogether, and superior to the LL1544A. The best I've seen from any transformer. HF first resonance is at 160kHz (!), and phase-match viewed on XY and dual-trace mode is visibly perfect up to and beyond 100kHz. It's uncanny to rotate the oscillator knob from 500Hz to 5kHz, and the next decade higher, with no visible change to the XY display, just a straight line, no tendency to open into a loop at all. Overlapping traces in dual-trace mode shows better than 1% matching through 50kHz and above.
        The most severe test is a dual-trace 10kHz square wave, with harmonics out to 90kHz and extreme sensitivity to phase rotation of the harmonics. This is where the 1:1 connected LL1676 pulls ahead of the LL1544A, with both square waves almost entirely overlapping. By comparison, the LL1544A shows noticeably different ripple patterns for each half-secondary, and the dissimilarity with the 1:2 LL1676 is quite obvious.
        So hat's off to Per Lundahl and Kevin for this achievement! All that and amorphous too!
        
        Re: Superb results with LL1676 in 1:1 mode - davidvair@hotmail.com 12:31:48 07/10/03 (0)
        
        In Reply to: Superb results with LL1676 in 1:1 mode posted by Lynn Olson on July 07, 2003 at 17:54:42:
        
        Dear Mr. Lyn, I have a 1544A input transformer for my amps now and I am very interested in what the measurements are for its performance in both 1:2 and 1:1 modes are. Would you be so kind as to inform me here?
        Thank you very much,
        David Vair
        
        Re: Superb results with LL1676 in 1:1 mode - Maciek P 04:15:35 07/08/03 (2)
        
        In Reply to: Superb results with LL1676 in 1:1 mode posted by Lynn Olson on July 07, 2003 at 17:54:42:
        
        Hi,
        Did you measure the max RMS voltage swing for a given distortion level for that configuration?
        Maciej
        
        Yes - Lynn Olson 13:18:14 07/08/03 (1)
        
        In Reply to: Re: Superb results with LL1676 in 1:1 mode posted by Maciek P on July 08, 2003 at 04:15:35:
        
        Very high overload limits from what I could tell. No THD measurement, just looking for gross distortion on the scope. The 1:1 LL1676 was good for 6V rms at 10Hz (!!!), and 15 or more volts from 20Hz on up (!!!). The HP generator was only good for 15V rms, so I didn't go further. Huge amount of headroom.
        
        I should also add that at more normal voltages of 2V rms, the square-wave at 10Hz had no visible tilting or roll-off, so the small-signal performance must have been good to 3 Hz. Pretty remarkable for a transformer ... 3Hz to 160kHz.
        
        Re: Yes - AnandR 05:07:39 07/09/03 (0)
        
        In Reply to: Yes posted by Lynn Olson on July 08, 2003 at 13:18:14:
        
        Well...I'm convinced, its like having no transformer there at all, but with all the advantages of galvanic isolation.I just put my order in :-) and will hook it up to the DACT 10K-2 for the Espressivo. I'll probably order another pair for a set of Amity's in the near future. If this is such a good trannie, imagine how good the Lundahl 1674 is in Kevin's output stage for current output dacs!!!
        Anand.
        
        Wow!! - gdahl 23:05:17 07/06/03 (1)
        
        In Reply to: LL1676 wriing for 1:1 posted by KevinC on July 05, 2003 at 03:38:56:
        
        Hi Kevin and Anand,
        After reading this, I wired up a LL1676 that way and checked its performance on the oscilloscope. Fantastic results!!
        These babies were flat from 5 Hz to 120 kHz! Phase splitting was as perfect as I've seen over the entire bandwidth. I will be converting my Aurora amps to the Amity circuit, using the LL1676's at the input.
        I was going to use DACT attenuators between the LL1676's and the ECC99's, but now I'm planning to use the DACT CT101 line stage, with the attenuator at its input.
        Gary Dahl
        "So many tubes, so little time..."
        
        Re: Wow!! - davidvair@hotmail.com 15:29:36 07/16/03 (0)
        
        In Reply to: Wow!! posted by gdahl on July 06, 2003 at 23:05:17:
        
        Dear Mr. Dahl,
        I understand that you and Lynn are excited about the new Lundahl input transformer LL1676. I have a 1544A input transformer for my amps, and I am very interested in what the measurements are for its performance. Do you happen to know what are its measurements in both 1:2 and 1:1 modes? Would you be so kind as to inform me here?
        Thank you very much,
        David Vair
        
        Re: LL1676 wriing for 1:1 - AnandR 07:04:06 07/05/03 (0)
        
        In Reply to: LL1676 wriing for 1:1 posted by KevinC on July 05, 2003 at 03:38:56:
        
        Thanks. I guess I got the entire thing reversed, I paralleled connected the wrong 'side' of the transformer, but at least I got the idea down!
        Anand.

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