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Old 25th July 2005, 01:58 AM   #501
andy_c is offline andy_c  United States
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Default Update

Well, I finally found out what the "problem" was with my Squeezebox SlimServer software not playing the LTSpice output file. The "problem" was a short between the headsets (figuratively speaking) . Turned out I had inadvertently swapped the LTSpice WAV files, one of which was a one-for-one copy of the input, the other being the error voltage.

The error voltage file was nothing but silence. At least, I couldn't hear anything. So I was actually listening to the error voltage file, which was actually playing silently, when I thought I was experiencing playback errors when listening to the input.

So the result of listening to the error voltage via Squeezebox->Benchmark DAC->Sennheiser 580 headphones was complete silence. Even though a transient response shows glitches at the beginning of, say, a sine wave starting at t = 0, this is a result of the non-bandwidth-limited nature of such a signal. When a bandwidth-limited test signal is applied, it appears that the presence of the output inductor is inaudible - at least for this particular source material and simulated loudspeaker load.
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Old 25th July 2005, 02:53 AM   #502
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Hahahaha Andy,

"The error voltage file was nothing but silence. At least, I couldn't hear anything. So I was actually listening to the error voltage file, which was actually playing silently, when I thought I was experiencing playback errors when listening to the input."

Maybe it'd be more audible with the music playing?



Cheers,
Greg
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Old 25th July 2005, 03:05 AM   #503
andy_c is offline andy_c  United States
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What's even funnier is that I didn't discover this until after I had written code to figure out the values of the missing byte counts in the LTSpice WAV file headers, and write out a new file with these numbers put back in. Turns out that the players seem to ignore these numbers anyway, and just read data until end of file is hit.

That's what writing software will do to you .
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Old 25th July 2005, 03:07 AM   #504
Jorge is offline Jorge  Brazil
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Default The error voltage file was nothing but silence

Or could it be that just a small damped inductor doesn't matter?

There's a smell of ABX in the air...
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Old 25th July 2005, 03:16 AM   #505
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Hi Andy,

That calls for some beer therapy?

I remember, in about 1970, doing a huge integrated amp PCB layout on a light table with tapes and donuts using those SOT23 plug in small signal BJTs popular then, and after about a weeks work I was checking it over and discovered that ALL the transistors were mirror image pinout and the routing was ****.

I was gutted.



Cheers,
Greg
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Old 25th July 2005, 03:34 AM   #506
andy_c is offline andy_c  United States
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Default Re: The error voltage file was nothing but silence

Quote:
Originally posted by Jorge
Or could it be that just a small damped inductor doesn't matter?
It's beginning to look that way isn't it? Maybe a capacitive load would give some sound in the error voltage file. I'll try to think of some music with lots of transients and other high-frequency stuff also. I picked the Steely Dan selection because the recording quality is very good - not so much on whether or not it contains many transients.
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Old 25th July 2005, 03:50 AM   #507
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Tom Waits "Rain Dogs" has a lot of sharp clatter.

Could be a witch-hunt.

Cheers,
Greg
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Old 25th July 2005, 08:11 AM   #508
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Hi Andy,

A completely new crossover generated series resonance voltage will still be clearly audible at minus 60dB, so can I suggest you increase the gain of your 'E1' error detector in Post#496 to this level.



Cheers ........ Graham
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Old 25th July 2005, 10:49 AM   #509
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Hi Andy,

A non-obvious oversight is still possible, or could it be that 16/44.1 has insufficient resolution to convert error waveform ?

Did you run a steady sinewave test ?

I have set up exactly the same as your Post#496 circuit in my simulator, and there is a notable 80mV error voltage, at minus 34 degrees, for 1V~10kHz steady sine input.

Any 10kHz music component could not fail to generate this -22dB differential error potential, and it should be resolvable.


Cheers ........ Graham
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Old 25th July 2005, 09:50 PM   #510
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With the lack of clarity of the diagrams it is impossible to comment.

BUT - and I hope this is not trouble. I have been familiar with Mr Hiraga's philosophies since about 1970, and his sometimes debatable views on feedback.

Let me be kind and just state, if this happens to be part of the debate. (I have joined recently and am unfamiliar with past post):

With negative feedback PROPERLY APPLIED it is certainly possible to design an amplifier with inaudible distortion under normal operation, meaning only low order harmonics. (Example: 2nd = 0.008%; 3rd = 0.006% and all higher buried in the noise at 0.001%) - this particular example for a 70W unit with 28 dB of negative feedback.) As a check, removing the feedback increases the harmonic components by the feedback factor, indicating that things behave as intended.

Power supply influence can certainly be critical and is indeed an often overlooked source of irritation. Somehow I would also be interested in the article results in readable form. (It bothers me that no Y-axis scale appears to be given, unless that was in the text.)
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