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Impact of phase inversion by preamp

This will be my first post on this forum so I thought I’d pose a question I’ve always wondered about.  I have a Conrad Johnson Premier 18LS preamp that I’ve been extremely happy with since first acquiring it some years ago.  This is a solid state single ended, single stage design that inverts the phase of the input signal at the output.  The manual states that you should reverse the connections to the speakers to account for this.  Obviously this is easily done but I really can’t see how it would really matter as long as things are connected consistently between the left and right channels.  I’d be interested to hear what others have to say on this subject.
ligjo
bdp24's avatar
bdp24
9,417 posts
 

This subject has been brought up a number of times, and every time it is once again pointed out that many (most?) loudspeakers have their two or three drivers wired in opposing polarities. As an example, the midrange driver will be opposite the woofer and tweeter (Wilson's, I believe). Reversing the polarity at the pre-amp will result in each driver then being opposite of what it was. What remains constant is that different frequency bands are being reproduced by drivers in polarities opposite each other. Which frequency bands do you want in "correct" polarity? Wire your speakers (or flip your pre-amp control) so as to achieve that.

But as almarg said above, many recordings are themselves already of mixed-polarity, so what does it matter?! If you play a single-polarity recording through a single-polarity loudspeaker, phase reversal should be more audible than in the above scenario. Phase reversal of the Sheffield direct-to-disk LP's is more audible than of "normal" recordings, and many of the Sheffield's are themselves in reverse polarity (a snare drum strike creates rarefaction, not compression). Sheffield recommended the playback system polarity be reversed when playing their LP's.

ieales's avatar
ieales
1,201 posts
 
many (most?) loudspeakers have their two or three drivers wired in opposing polarities
hopefully to correct crossovers phase shift and not arbitrarily.

It is more than the bass that is affected. Percussion has very steep transients, sometimes exceeding 20KHz on tape and LP. On quality phase coherent systems, the effect is clearly audible by some. Not all are sensitive to it.

Expanding on what Al said regarding polarity flip circuits, even in fully balance circuitry, they are seldom in themselves inaudible. This can be demonstrated by reversing loudspeaker polarity and listening to the A:B, which is quite likely C:D.


atmasphere's avatar
atmasphere
11,577 posts
 
In a balanced preamp the phase switch simply redirects the inverted phase to the non-inverted circuitry and vice versa. Its completely passive.
With many recordings the correct position is inaudible, owing to the recording being multi-tracked and mixed. The phase may be different depending on the instrument playing! So usually you only hear it on true stereo recordings, those done with only 2 or 3 mics (the latter being the Mercury process or Decca stereo tree, that sort of thing). The problem is that 50% of all recordings regardless of the media are not in absolute polarity while the other 50% are. Switching your speaker cables around to deal with this is a pain which is why we included the switch since we were making a balanced line preamp anyway.
You just have to try it and see. I seem to hear it easier with brass instruments.
ieales's avatar
ieales
1,201 posts
 
In a balanced preamp the phase switch simply redirects the inverted phase to the non-inverted circuitry and vice versa. Its completely passive.

Nothing is completely passive. The more revealing the circuitry, the more it exposes component 'flaws'.

Experience with phase flip switches in active and passive balanced hardware often left something to be desired in terms of routing and hence inaudibility.

Making both halves of a balanced circuit identical is EXPENSIVE. Add in tube vagaries and the probability of a sonic delta is fairly certain. Not to all listeners, but to some.

Decades back it was demonstrated there were distinct sounds in a system on the same source:
  1.  Normal polarity to speakers
  2.  Invert channel A at source* and speakers - same Φ as 1
  3.  Invert channel B at source* and speakers - same Φ as 1
  4.  Invert both A&B at source* and speakers - same Φ as 1
*Balanced out - polarity swapped with identical but inverted polarity cables.

Theoretically all should sound the same, but they didn't. If one subscribed to OOPS, at least 2 & 3 should sound the same, but they didn't. It was postulated that the loudspeaker is an asymmetric load and depending on the other hardware, affects the sound.

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cleeds
5,646 posts
 
ieales
Nothing is completely passive. The more revealing the circuitry, the more it exposes component ’flaws’.
Semantics. There is passive circuitry, and there is active circuitry. There’s no value in confusing the two.
Experience with phase flip switches in active and passive balanced hardware often left something to be desired in terms of routing and hence inaudibility.
Whose experience? With what hardware?
Decades back it was demonstrated there were distinct sounds in a system on the same source ...
When was that, and by whom? Where was the demonstration, what were the source and other components used?
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