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How do you know if your preamp has inverted the phase?

Its monday and I feel like asking a dumb question.
I read somewhere that out of phase stages in a preamp can cause some loss of listening pleasure.
So the dumb question is I have 2 stages in my preamp for phono (Ixys current reg on each anode with output of 1st stage off anode into grid on stage 2 (which also has an Ixys reg on it) feeding into an srpp line stage?
So what is the rule of thumb here?
Thanks
Nick
 

ray_moth

Ex-Moderator
2004-01-27 8:55 am
Jakarta
Rule of thumb is a grounded cathode stage inverts the phase; grounded grid and cathode follower do not. SRPP counts as a grounded cathode, so your preamp inverts phase twice (once in each stage), the net effect being no inversion.

If you believe it's possible to enjoy music more without inversion, this is good news for the preamp but what about the main amp?
 
2 stages in the phono section

Hi Ray_moth
I have 2 stages in the phono section. They each have an ixys current
reg on them. They are grounded cathode. So thats 2 and phase is inverted twice. The third stage (line stage) counts as a grounded cathode as well so shouldnt the preamp be out of phase when I am playing records. Come to think of it it should be out of phase when i am just using the line stage.
Does being out of phase mater?
I am using one preamp to feed a ss power amp and the other feeds my pp 6550 power amp.
Can anyone enlighten me on the relative merits of phase reversal and what if anything can be done to ameliorate it?
Thanks
 
Re: 2 stages in the phono section

duderduderini said:
Does being out of phase mater?
The answer is easy: listen to your system for a while (I suppose it's done already). Reverse the speaker cable polarity and listen again. Compare.
It is good to know that virtually every CD player having a single inverting opamp analog stage does reverse polarity.
 

ray_moth

Ex-Moderator
2004-01-27 8:55 am
Jakarta
The third stage (line stage) counts as a grounded cathode as well so shouldnt the preamp be out of phase when I am playing records.
Ah, there's a third stage! From your description I thought there were only two. In that case, when using all three stages, yes, it will produce an inverted output. Whether this will be audible is outside my experience but, as I said before, if you don't know whether your power amp inverts then all bets are off!

P.S. I'm a skeptic. I suspect it only matters if you think it does, like some people can imagine themselves a toothache :D
 
So what should i do now?

Hi Guys
I did the listening tests and found this
1. On my phono section with the polarity reversed on the speaker outputs, it suddenly becomes , to me anyway, a LOT more listenable.
BUT
2. The cd player sounds better with the polarity switched the other way
This ties in with the opamp stage in the cd inverting the signal and my 6sn7 srpp inverting to normal phase.
So given this, I really need either a new phono stage which remains inverted so that the srpp can invert it again OR I need two line stages. One which inverts and vice versa.
The phono stage i built uses 2 stages with e280f with an ixys current reg as i mentioned. the output comes off the anode of each stage. I really like this phono stage and would be loathe to change it. I figure a 3rd stage- perhaps a cathode follower might help. Is it right that a cathode follower is unity gain?
What suggestions do you guys have?
Or maybe i could just change the speaker wires over between cd's and vinyl
By all means speak your mind but go easy on me.. i dont have the tube guru minds of most here. No doubt some or all of my theory is flawed
Thanks
Nick
 
I use 3 stages in the phono, the passive RIAA eq is divided between them (bass boost between 1st and 2nd, treble cut between 2nd and 3rd). This arrangement is inverting, and the line stage is also inverting. So does the I/V converter after the DAC. I don't care about the tape and tuner inputs.

But how can we be sure that the correct polarity is maintained during the disc cut or CD mastering on every recording?
 

EC8010

Ex-Moderator
2003-01-18 7:57 am
Near London. UK
oshifis said:
But how can we be sure that the correct polarity is maintained during the disc cut or CD mastering on every recording?

You can't and it probably isn't. Suppose you had a snare drum, would you put the microphone above or below? (They're opposite polarities.) What's actually done is to mix both with one inverted. But which one? What about direct injection from an electronic instrument? Or the difference between a pressure microphone and a velocity microphone?

I believe absolute polarity is a function of asymmetric distortion in small loudspeakers, so one way round sounds better than the other, depending on track.
 
Re: polarity switches

duderduderini said:
this switch you speak of.. Would it be feasible to install?
Hi,
some amps may be very easy to modify like this, others may require an extra stage.
But in ALL cases extra switching and/or active stage will be required and the improvement you are looking for may be negated.
When it is already fitted then the possible deterioration will have occurred and comparison of phase/polarity is possible.
 
What you can not be sure of is the music source signal:

Microphone, microphone transformers, preamp, recorder, then editing studio, etc.
Consider all of these processes, and the wiring of the interconnects, some balanced, some not, some with wire reversals, one more inverting stage, etc.

What you can be sure of:

You are sitting in a concert, and two Bass Drum heads are facing you.
One drum is struck by a Mallet on the front side of the drumhead that faces you (that transient starts with a Rarefaction of air).
The other drum is struck by a Mallet at the back side of the drumhead that does not face you (that transient starts with a Compression of air).
Those two drums are in different phase at your seating position.

An oscilloscope will not tell you which way the drum was oriented versus the position of the microphone, because there are too many circuits, wiring, parts, and processes between the original performance and the playback system.
Oh, and which side of an open baffle woofer are you sitting on?
 
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Thank you, EC8010, for using the proper term, "polarity," instead of the improper term "phase."
Alas its universally known as phase of phasing in recording studio equipment, as in phase inversion switch, etc.
Same with opamp datasheets - early one's had problems with "phase reversal" when driven to the rails, so it is common to see claims of "no phase reversal" in such datasheets now.


"Phasing" is very important in studio gear as signals are often sent to effects units and then the result summed with the "dry" signal
again, which sounds very strange if the polarity is different. Mic inputs always have phase switches in studio consoles as positioning of microphones varies and sometimes you want to play with phase to get specific response patterns.


You won't change this usage now :)
 
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egellings

Member
2010-08-21 7:59 pm
CA
Only certain way I know is to hang a 2 channel scope on 'in' and 'out', feed in a sine wave, and take a look. Or if you can attenuate the amplifier's gain so that it is at unity gain, feed in a reasonable signal, say 100mV or so at a kHz or so, and differentially measure the input signal to output signal voltage. If it is very low, the amp inverts. If you see a large signal, the amp is non-inverting, and the input & output are summing constructively to give a larger voltage.
 

6A3sUMMER

Member
2016-06-07 6:50 am
Usually, a struck bass drum waveform is not symmetrical.

No matter which side is struck, typically it will have a large initial excursion in one direction (no matter whether you are on the pressure side or the rarefaction side of the drum head), and then a smaller excursion in the other direction, and it continues to alternate, and collapse exponentially.

Next, let's take the upright acoustic bass.
What is the direction of the first acoustic pulse if the string is pulled away from the neck, and then released to strike the neck, resulting in a "whack" sound?
This is a sound effect, but it still is a purposeful part of the music.
I do not know the answer as to the 'polarity' of the initial impact, but I bet the direction of the first pressure or rarefaction is always consistent.

Music is a variable.
So are recording plus playback systems.

Live music is what it is, live.
But . . . are you sitting in the audience; in the middle of the performers; or at the back of the stage?
All those sound experiences are different.

So now, when that same performance is recorded, what are the locations of the multiple microphones?
Nothing like that is very simple.
 
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