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Phase Fetish

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    Posted: 22 Jun 2012 at 6:10am
One of the more crazy fetishes in audio is the preoccupation by some of having absolute phase.

Absolute phase is about keeping the signal right side up from source to speakers (or headphones).

If the signal gets inverted (turned upside down) people reckon they can tell the difference, and that difference is because it's upside down!

Oh really?

So, we can all tell a difference if we upturn the signal? I wouldn't have thought that possible because all we're ever doing in audio ends up as vibrations in the air -- affected by room acoustics -- so is the signal in absolute phase when those air vibrations vibrate your hearing mechanism?

And what about some three drive unit speakers which have the mid range unit wired out of phase?

But I hear some saying it does sound different. Those who have a phase switch, and invert the signal say it sounds different. Are they crazy?

Well, actually they're not crazy. It can sound different. But not because the signal is the other way up.

It is about a thing called common mode distortion, which is a really bad way of putting it because it suggests all single ended inputs distort in this way.

A non-inverting input will distort as common mode distortion and so will an inverting input. But, most inverting inputs are run as summing amps ("virtual earths") which behave quite differently, and more often than not, an amp/preamp with a phase inverting switch uses this type of input for signal inversion. So as one has common mode distortion and the other doesn't, then by flicking the phase switch, one sounds different to the other!

In my own opinion I think the inverting summing amp input sounds better. But so far, I've never dared to make inverting amps because of the preoccupation with absolute phase.

In fact, it's nigh on impossible to do an inverting input phono preamp -- although some will point out that Dynavector do one. But has anyone tried it with moving magnet? Exactly! I will try and include more on this subject in the upcoming Phono Preamp Project Part 2.

Now, before anyone gets carried away, common mode distortion isn't the end of the world. It's only when you overdrive an input that you get common mode distortion, and I'm really careful to place volume controls ahead of any line stage that's not a summing amp. A magnetic phono cartridge is only capable of doing this at really high frequencies close to groove break-over, and because I know about it, I ensure it won't happen.

So let's not get in a tizzy about upside down signals and I'll get busy on something that inverts and you'll be the first in line to try it out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackinBlack Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jun 2012 at 11:47am
Graham, another fascinating observation and reasoned explanation of what is happening to the sound. I've spent over 40 years listening, observing and reading about the pursuit of believable and  honest reproduction of recorded material. I have never subscribed to the more expensive is better school and tried to spend within a sensible budget. If it sounds good to me, then I'm happy; understanding why it sounds good is a bonus! Many Thanks.

So, to the point, I have gone (spent) as far as suits my budget on Moving Coil cartridges and was just about to go back to Moving Magnet/Iron with a Genera for starters, but now you announce Phono Preamp Project part 2, will this be applicable to the Genera? Do I wait or just get on with it?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jun 2012 at 1:16pm
Originally posted by BackinBlack BackinBlack wrote:


So, to the point, I have gone (spent) as far as suits my budget on Moving Coil cartridges and was just about to go back to Moving Magnet/Iron with a Genera for starters, but now you announce Phono Preamp Project part 2, will this be applicable to the Genera? Do I wait or just get on with it?


Part 2 is about moving coil. I may add that I've absolutely no idea yet where to start on this part, but that's what happened when I started part 1 (the Genera). I'm going to try and make it fit the existing Genera PCB... LOL

There are no changes to the MM Genera Wink
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jun 2012 at 1:28pm
I don't know if it's the summing amp configurations I'm using on my digital work but "Streaming Lord Such" (John C's code name for the little USB streamer - he's a *cad!(man) Wink), and the grown up DAC, both different in one is op-amp and the other discrete, don't half pluck some extra detail out. There's a piece on Kate Bush: 50 Words for Snow, where I thought somebody was shouting me from the workshop door (hard right) - I jumped up from my seat to find nobody there. Played it again and yes, the same sound, that being using the HD250II on "Streaming Lord Such". Fleetwood Mac: Rumours, "Songbird" where the piano is so real with tons of space - listening using SR80's. Either it's because it's digital Ermm or I need to do more with summing amp configurations... interesting Smile


*meant in a kind way Wink
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BackinBlack Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jun 2012 at 3:38pm
Thanks Graham. I look forward to seeing the development of the MC version.
Meanwhile I shall revert to Moving Magnet/Iron cartridges, order for Genera coming up.

Regards Ian
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