Does the Crown K2 inject delay? How to test? - diyAudio
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Old Yesterday, 04:14 PM   #1
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Location: Madison, WI
Default Does the Crown K2 inject delay? How to test?

I've come to suspect that my Crown K2 is actually injecting some delay into my subwoofer!

I've recently refurbished an Adcom GFA-555 II, and as an acid-test, hooked it up to my subwoofer. (A TC Sounds 15" in a 14CuFt, 15Hz ported sono-tube)

The Adcom seems to sound better on the sub! Punchier, more even and smooth. I am always wary of my own bias, so I took some measurements with REW. Leaving the microphone in the same position, and matching levels, I observed a deep null at around 65Hz. (The null is different in different mic locations) Well, the Adcom showed 6db less null!

So, I put the K2 on the scope, and played test tones through it, comparing the input to output. At 20KHz, with the input and output super-imposed, it looks to be about 120 degrees off. But I don't know if it's worse than that! It could be several cycles.

How could I measure this delay precisely? Do I need something like a pulse generator? I thought about making a WAV file with pulses every few milliseconds or something.

Is a small amount of delay inherent to the design of a switching amplifier?
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Old Yesterday, 11:34 PM   #2
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OK, I came up with my own way to measure. I made a recording of music with source in the left channel and amp output on the right. (I made a voltage divider to convert speaker to line level.)
Then I opened the wav file in Audacity.

Everything is delayed by 2 samples, or 2/96000 of a second, or 0.02ms.

0.5 degrees! Nothing, really. That solves that. The K2 is a fine subwoofer amp.
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Old Today, 05:50 AM   #3
djk is offline djk
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"The K2 is a fine subwoofer amp. "

"The Adcom seems to sound better on the sub! Punchier, more even and smooth."

One of these statements is wrong.

So you think the Crown is OK, even though it doesn't sound as good as the Adcom?
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Last edited by djk; Today at 05:53 AM.
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Old Today, 07:24 AM   #4
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I suspect I was hearing things... Biased by affection for an amp that I had put a lot of work into. But maybe it does sound better. I'll hook up the AB/X switcher and see.

It doesn't explain the 6db difference in the bass null at 65Hz that I measured at that position, but maybe that was just sample variation.

One thing that was interesting, the response from the Adcom showed slightly more output around 8Hz! (Yes, the sub has measurable output down here.) This aligns with Crown's specification of an 8Hz 3rd order filter. From 11Hz and up, the Crown and Adcom measured the same except for that null. That's what got me thinking there was a delay. Seems not.
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