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Old 11th September 2003, 08:26 PM   #1
Beggar is offline Beggar  United Kingdom
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Default Gain/phase relationship of amps?


Just piecing together a few inverted LM1875 based tweeter amps for my newly built time aligned speakers, and then I had an annoying thought/questions, well 2 acutally

1) Because my tweeter and mid amps (both LM1875 based) have slightly differenet gains (22.2 dB mid, and 20.8dB tweeter) is there a phase difference between the 2 amps?

2) Is the phase shift caused by the input cap and resistor going to be significantly different, given that the tweeter amp has 4.7uf and 25.5K and the midrange has 10uf and 30K.

I think I can work out question 2 with enough time, provided my assumption that the input to an inverting amp is a virtual earth? (I left my electronics textbook at home, doh?) Although i have forgotten/dont know any formulae for calculating the phase response of a simple resistive-capactive network, so actually i probably cant :S

Here's a pic of the amp schematics...

Thanks for any help!

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Old 11th September 2003, 08:32 PM   #2
SY is offline SY  United States
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If I understand the context of your question, it's really, "Are these both minimum-phase devices?" And the answer is yes, they are. You don't need to take the amps into account for purposes of aligning driver acoustic centers- the phase shifts from the HP rolloff are negligible in the region of interest.
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Old 11th September 2003, 08:50 PM   #3
Beggar is offline Beggar  United Kingdom
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Cool, thats exactly what i wanted to hear!

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