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Old 24th February 2006, 01:09 AM   #1
back is offline back  Greece
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Default adjustable time delay

hi i need an analog adjustable time deay in the range off 20-500 microseconds.

can anybody point a schematic?

thank you
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Old 24th February 2006, 01:39 AM   #2
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Over what frequency range? Most analog delays are only good over a certain frequency range

IE: If we had a circuit with an analog delay of 1usec over 20Hz - 20kHz, and we used it outside of that range (let's say 30kHz), the delay would not be 1usec anymore (could be more or less).

Another issue is that analog delays usually have amplitude gain nonlinearity over frequency (in our previous example, the voltage gain at 20Hz is probably not the same as the voltage gain at 20kHz).

==> Are you sure you can't digitize your source and use a digital delay? I would think that a digital delay would probably be MUCH more accurate and precise.
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Old 24th February 2006, 10:29 AM   #3
back is offline back  Greece
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i didn`t know that.

i want to use it to the output of a crossover.
the frequency ranges are 300-5000 for the mid and 5000 -20000 for the tweeter.

i don`t want to digitize it again.

i was looking for a way to improve quality easily.

if it can`t be done i will wait to get a digital xover.
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Old 24th February 2006, 11:26 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
an all pass filter will give you a time delay.

Do a search on filters and on all pass and you should find many.

I would expect most could be made adjustable, but you would need to change at least 2 poles so a switched adjuster may be necessary rather than a ganged pot.
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Old 24th February 2006, 11:54 AM   #5
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If you want to achieve a constant group delay over a large (but still restricted) frequency range you will need a very high-order allpass.

Regards

Charles
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Old 24th February 2006, 12:10 PM   #6
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http://www.linkwitzlab.com/filters.htm#4
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Old 24th February 2006, 12:31 PM   #7
back is offline back  Greece
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thank you all for your help.
i don`t want to aplly phase correction only but real time delay
over the entire range of each driver.

i guess that is called group dealy?

i think that the linkwitz link is all i need i will study it when i have more time.
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Old 24th February 2006, 12:54 PM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
I think that time delay equals phase correction in these allpass filters.
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Old 24th February 2006, 01:08 PM   #9
dnsey is offline dnsey  United Kingdom
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Why not just align the drivers? At most, you need 20cm difference.
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Old 24th February 2006, 01:29 PM   #10
mazurek is offline mazurek  United States
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One trick you can use to let you get away with less allpass stages is to delay the mid and invert its signal relative to the tweet. This worked out perfectly for me, as I already needed an inverting gain on the tweet.
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