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Old 15th December 2012, 08:14 PM   #11
Magz is online now Magz  United States
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The picture for a 2kHz square wave looks the same, just more compressed in the front of the waveform. I used 10kHz for the pictures because it's easier to see the ringing and the improvement on that scale.

When I run the signal generator cable directly to the scope probe I get a perfect square wave - any anomalies from the generator/cable pair should show up there, right?


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Last edited by Magz; 15th December 2012 at 08:18 PM.
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Old 15th December 2012, 09:49 PM   #12
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Originally Posted by davidsrsb View Post
Most sources don't generate square waves or anything much above 20 kHz, so the overshoot is unimportant
Ring like this is very audible. It needs damping.

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Old 15th December 2012, 10:04 PM   #13
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The ringing shown in your last picture is very minor, very high in frequency, seriously doubtful that you'll hear it. BUT... you've beautifully demonstrated how these circuits do have to be tuned for certain source impedances, and dropping the bandwidth (in exchange for getting zero overshoot) by secondary loading will make that a bit less critical.
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Old 15th December 2012, 11:29 PM   #14
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Yes, I'm happy with the way things look in the last picture - can't let my OCD take over...

I'm pretty sure that little bit of ringing left has to do with the leakage inductance of the Faraday shield between the windings. When I disconnect the shield from ground it disappears almost completely. I think I'll live with the little bit of inaudible ringing, though, for the improved common mode rejection the shield provides.
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Old 23rd December 2012, 04:34 PM   #15
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...BUT... you've beautifully demonstrated how these circuits do have to be tuned for certain source impedances, and dropping the bandwidth (in exchange for getting zero overshoot) by secondary loading will make that a bit less critical.
SY, this statement is SO true. I added an 800R resistor to the + inputs of the LL1676 input transformers, and the difference is profound.

The improvement in the sound is so startling that I had to recheck it on three different listening occassions just to be sure - and it's real. Going from the 10kHz square wave in picture #2 to the one in picture #3 above cleans up everything about the sound...from the deep bass all the way to the highest treble. It's remarkable!

In this case, the 10kHz square wave was the perfect diagnostic tool. Now, my digital source runs at 192/24 and has selectable low pass filtering from the standard CD brick wall at 22kHz to no filter at all, in 5 steps. I use one of the gentler filters (more HF information passed) so that may account for why the removal of an overshoot at 80kHz or so has such an enormous effect, but it certainly does.

So to summarize: LL1676 wired in 2||2:1||1 with a source impedance of 1k (200R + 800R) and a snubber of 2nF+850R on the secondary = perfect. Highly recommended.
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Old 24th December 2012, 02:07 PM   #16
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I have consistently found that ringing (peaking) out at about 60khz is extremely audible. Superficially it gives an airy extended top end - but fatigue rapidly sets in making the result unlistenable in the long run.

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Old 24th December 2012, 02:45 PM   #17
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I have consistently found that ringing (peaking) out at about 60khz is extremely audible. Superficially it gives an airy extended top end - but fatigue rapidly sets in making the result unlistenable in the long run.

Shoog

Agreed. It's much smoother now. I had some CDs that were just recorded bright, but even they are much more tolerable now - I haven't lost the sparkle of the top end, just the annoyance factor.
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