2. amps-preamps
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Phase Inversion in Preamplifer?

I just bought a used Audible Illusions 2D here on a'gon. This will be my first venture into separates. I've learned that AI preamps have inverted phase, so it's recommended that I switch +/- polarities at the speaker-amp hook-up. OK. But according to AI literature the phono stage of the preamp is NOT inverted, only the output stage is. So, since I listen to both vinyl and CDs, what do I do? Should I reverse speaker wire polarity or not?

Incidentally, the amp I'll be using is an ATI 1502 -- still haven't been able to find out if it inverts polarity or not. But based on my (limited) research thus far it appears that phase inversion is a design of preamplifiers more than power amplifiers. Is that right?

Thanks,
Rich
winegasman
clio09
3,353 posts
 
Sugarbie - you're correct about phase inversion and polarity. In my case, while it is called a polarity switch on my phonostage, the manufacturer suggests it is used to invert phase.
autio
42 posts
 
Clio09,
I just wanted to be sure that when you made the statement
" voice phase tests swapping the speaker leads made no difference to my ears. However, swapping IC leads did"

That you understand that swaping speaker cables chage polarity in each individual channel, while swapping Interconnects just swaps channels r l
clio09
3,353 posts
 
Autio, re-reading my post I did not make myslef clear. Swapping the speaker leads at the amp binding posts (+ to - on each channel) I could hear no difference, meaning the voice on the test CD stayed centered and was well imaged. However, with the speaker leads wired correctly, swapping the RCA leads at the amp inputs so that L from preamp output goes to R amp input and R preamp output goes to L amp input, I could hear a difference. The voice on the test CD was not centered, instead appearing as if it were coming from different areas.
sugarbrie
3,854 posts
 
If a system is out of phase you are more likely to hear differences at the frequency extremes, not in the center midrange like vocals. Affects the bass the most in my experience.

I would think having the right channel out the left and vise-versa would ruin the focus/image. Assuming the singer is in the center....
The voice would normally be to the left of the right channel microphones and to the right of the left channel microphone.
Switching the channels puts the sound of the voice on the outside of both channels instead of in the center.
phd
1,301 posts
 
When both speakers are not wired in phase this will of course effect the sound, more noticeably the bass. But if all minus & plus connections between your amp & speakers are correct, and you insert a phase inverting preamp, at this point it will take a very good ear to hear the differences because some recordings are phase inverted (as mentioned above). Personally I would not be too worried over a phase inverting preamp & making corrections. I was told that in order to manufacture a phase correct preamp it will require additional sound degrading circuitry.
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