Yet another phase question

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Elrick
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Yet another phase question

Post by Elrick »

I have a PV7 that phase inverts, been running it for a few years using a couple dynakit Mark 3's. I just reverse the speaker banana plugs and all is well,

I've recently bought a powered sub woofer - BMW 25000. The signal goes from the PV7 to the sub and then to the mono blocks, which feed the stereo speakers. I run the subwoofer's phase switch at 180 for inverted and it sounds right. But I'm wondering if I should still be reversing the speaker inputs? I originally used it without changing the speaker leads (kept them reversed) and it sounded good, but after some beers the other weekend I changed them back to normal (reversed) and I also think that sounds right. And that's how I have them right now but I would like to get to the bottom of this.

Can anyone explain the correct set up when using this sub? I think I understand the idea of gain stages and how the phono circuit has two gain stages so it does not invert but the line stage has only one stage of gain so it does invert. Can i assume the sub woofer has two gain stages so it doesn't change anything? If that was the case I should put speaker cables back to reversed ??
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Re: Yet another phase question

Post by Elrick »

This is what the system looks like.

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Re: Yet another phase question

Post by admin »

Nice setup! As for the proper setup for phase, I would recommend you invert at the point of your subwoofer (Have 180 phase correction on), then invert between the amps and the speakers by switching negative and positive speaker cables. This should put both the speakers and sub in correct phase.

Just to be clear, you are running the RCA cables from the PV7 into the sub and then RCA's from the sub out to the amps, then speaker cables to the speaker, right?
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Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
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Re: Yet another phase question

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Hey, thanks for commenting. Yes, just to clarify, I am running the RCA cables from the PV7 to the sub, then to the amps and finally to the speakers.
If I'm reading you responcse correct that's how I had them originally. But actually it sounds better if I set the sub to 0 inverse and then keep the speaker's reversed. That's not what I would have expected but is what I experience.

The sub paperwork indicates most users will have the best results with the phase setting at 0. After reading that, and knowing my preamp is phase inverting I automatically assumed the setting for my application should be phase at 180, but it seems to sound best at 0. That's' why I'm stumped on this set up.
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Re: Yet another phase question

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At the end of the day go with what sounds best to you. Any chance you are getting some weird interference issues. You can try moving the sub around the room and see if you still prefer the settings.

The other thing you can try is if the sub has speaker wire inputs/outputs, you can try running the signal to the amps first, then the sub, then the speakers and see what happens.
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Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
Big Dog RJ
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Re: Yet another phase question

Post by Big Dog RJ »

Hey mate, just happened to come across this post.

I had this similar issue way back in the hey day and it never really bothered me after nearly 20 years...

What I learnt along the way, also from talking to Lew Johnson himself and of course Ed (head tech at the time) was the following:
1. The system as a whole should be "phase correct"- i.e. if any one component is phase inverting (this means the system is out of phase).
2. The number of phase inversions should be either Zero or an even number. (either 0 or 2)
3. For Example: if the preamp is phase inverting, and all other components are phase correct (the system is out of phase) this can be easily corrected by reversing the speaker leads only at the speaker terminals (not at the amplifier outputs).
4. Lew and Ed also told me since I was using maggies with external cross overs, the jumper leads from the cross over box to the panel must also be reversed, so this means that the entire "speaker terminal" ends are swapped in polarity. For the system to be in total phase.

Since you're using a sub that has a phase selector switch to compensate certain recordings that are out of phase, I can only suggest one simple thing.
Keep your sub phase switch at Zero (this means it is not trying to correct the phase to 180 or whatever). Reverse only at the speaker terminals.

If you are to switch your sub to 180, this means it is correcting the phase, which means it is inverting. Since your preamp inverts phase and the sub is now in 180 = a total of two which is an even number. Then when you change your speaker terminal ends back to normal, you are actually experiencing total correct phase in your system.

However, remember not all recordings are phase correct, therefore from the above config, with the sub at 180 & the cj preamp being phase inverted, and speaker leads in normal polarity = pretty good sound BUT not for all recordings...
Therefore, I would set the sub to zero phase (in order to make it neutral) and reverse only the speaker leads = "absolute phase" - this should give you the best possible sound overall.

The other thing is, going through your initial post I realized that you were after a few beers... anything out of phase after a few beers sounds pretty darn good to me. Infact, the other weekend, I was listening to my Quads and noticed after a few scotches something was not quite right in the middle imaging Re, to the soundstage. Later figured out that one of the Quads wasn't even ON!... This is what happens when you're actually enjoying music!
cheers mate and let us know how you find the overall sound now? If that doesn't satisfy you just throw the sub out and listen to pure clean music with just the B&W's. They look great BTW, have a good one.
RJ
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Re: Yet another phase question

Post by Elrick »

RJ , after a few sessions it was clear there are two settings that sounded correct.
A: Sub set at 180 degrees phase, and speakers normal.
B: Sub set at 0 degrees and speakers reversed.

I set the sub at 55 Hz so I don't over do it.

I like LP's, I'm using Denon stuff for phono. DP62L TT w/ a DL103r and a AU320 SUT into the PV7.
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Re: Yet another phase question

Post by Big Dog RJ »

Hey mate, Sorry for the late reply.
Ok, this seems logical and the two settings you have experienced is in absolute phase. That's good!

Just wondering, why do you need a sub? Isn't the bass from the B&W's adequate?
RJ
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Re: Yet another phase question

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RJ, I never thought I would need a sub and actually had bad impressions of systems that employed sub woofers, so I was reluctant to take the plunge and buy one. I'm not interested in using sub's for playing videos with earth shattering explosions or stuff like that. I'm strictly an old fashioned 2-channel stereo guy. I've ran the B&W's since new and just recently picked up my sub from Epay for good price. My sub was part of the same line up that B&W offered at the time I purchased my main speakers new, so I thought it might be a good fit.I liked the idea that this sub had plenty of power, (700W continuous w/ 1000W peak) so I thought it might help relieve some power from the main amps/speakers since my amps are only 60W tube power.

My impression now, after running them for a number of months is turning down the sub's crossover to about 50- 55Hz and adjusting the sub's volume to suite the music, the result is very nice, but not excessive. It completes the sound that I was lacking but not over doing it. Maybe it has something to do w/ my listening room situation as well. The subs are rated down to 20Hz while the main speakers are rated to 40Hz. I'm really glad I took the chance and added the the sub and it was WAY cheaper than replacing my speakers.
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Re: Yet another phase question

Post by Big Dog RJ »

Fair enough, that makes perfect sense. Yes, the B&W's don't do low bass so adding a decent sub with clean output will certainly be a good investment to your system overall.
Re. 60w tube power, that's plenty to drive fairly efficient speaker loads. Anything from a 4-8ohm load with an efficiency of around 89db and above is fine for tubes. Even a little 35w tube amp will do magic. As you are probably aware, tubes in well designed circuits will have plenty of current to drive the speakers, they also don't clip hard. At one point in time I was using just a small Cayin 35w tube integrated to drive an old pair of maggies mgIIIa, apart from near field listening, the musicality coming from the EL34's was marvelous!

Of course the larger cj monoblocks were in a league of its own but for the price of the Cayin, the value couldn't be beaten. It also depends on what you're after, to me it sounds like you are really enjoying your music with your tt & B&W's + sub and the pv7 seems to be the cherry on top. Since it's sounding great, don't change a thing, just sit back and enjoy those beers!
Btw what's your favorite beer? I just discovered an awesome smooth one from Japan called kirin.
Great yellow snow. ..
Cheers mate, RJ
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