Ken's interpretation of amplifier phase

[Jackie Treehorn]

I've been tweaking the Rocket and something I've noticed is that it seems to get more sustain and higher harmonic feedback with the output's polarity inverted, in other words, the output's polarity reversed with respect to the input. Playing with matched polarity tends to sustain on the fundamental, but not quite as long. This observation was somewhat mind blowing because all of my other amps seem to like to play with the input and output matched. I actually became convinved I must have the transformer backwards, so I checked by applying feedback to the other end of the PI and by playing a signal generator with a diode in series of one end (asymmetrical output) to see if the transformer was backwards. It wasn't. I'm going to have to do a rehearsal with the reversed polarity to know for sure whether it's better.

But, it got me thinking about Ken's article on the difference between the Tweed Bassman and the JTM45. I don't have it in front of me, but he states that the Marshall plays out of phase and the Trainwreck (I'm thinking he means Express/Liverpool) plays in phase. Of course, if you follow the number of inverting stages, this is just wrong. I'd kind of thought it was Ken being eccentric, but now I'm trying to understand more seriously why he'd say that. Maybe he's not neccessarily talking the matching of the input to the output.

One aspect that comes to mind is the symmetry of the signal itself. In an Express, there are two inverting stages before the asymmetry whereas the Marshall is one. The marshall and the wreck would then clip opposing sides of the guitar's signal. Perhaps Ken is talking about a phase relationship between the clip and the speaker output?

I'm wondering if anyone has any thoughts or perhaps a forum member has an insight from a conversation with Ken.

[paulster]

I've often wondered why Ken described the Express and Liverpool in this way as they're clearly inverting amps.

The Rocket, of course, can be either inverting or non-inverting depending which way round you wire your OT primaries since it doesn't have global NFB and I'm not 100% sure we know whether Ken had a preference for them to be configured inverting or non-inverting across the amp as a whole.

[geetarpicker]

Either way in my experience the phase of the sound coming out of the speaker cabinet can effect the sustain but it's note dependent. Of course even guitar body position is important to explore as it also effects the phase of the sound physically hitting the guitar. Point is having the phase one way can make controlled feedback great on certain notes, and dead on others. Then you flip the phase and the notes that are favored/cancelled totally change. In the studio I regularly employ a speaker cord that is wired with opposite phase. Then if I'm having an issue getting sustain on a certain note on a solo I'll swap the speaker cable, effectively swapping the phase and most of the time helping any sustain issues. Lately in the studio I sometimes work the sustain off the playback monitors cranked loudly, then I can easily swap the phase by hitting the phase switch on my studio preamps. Fun stuff, but earplugs required!

[2tone]

If you play the Rocket in a two amp setup with either the Liverpool or Express, it will be out of phase if facing the same direction. It will work better if the Rocket speakers are facing the Express speakers with player in the middle. Matchless finally put a phase switch on the back of their amps for similar reasons. If using one Express and one liverpool in stereo, they should both face the same direction to the player. Of course if using effects ect this can invert the signal too, and it becomes more complicated...

[paulster]

If you play the Rocket in a two amp setup with either the Liverpool or Express, it will be out of phase if facing the same direction.

That depends how you wired your OT primaries as you can put them round either way on a Rocket since there's no global negative feedback and it will work fine.

It will work better if the Rocket speakers are facing the Express speakers with player in the middle.

Actually, you'd want the front of the Express/Liverpool cab facing you and the back of the Rocket cab (assuming it's open) facing you to get around this problem. Phase and anti-phase are about compressions and rarefactions of the air so it doesn't matter whether the cabs are in line facing you or either side of you facing you, they'll still retain the same relative phase.

[2tone]

If you play the Rocket in a two amp setup with either the Liverpool or Express, it will be out of phase if facing the same direction.

That depends how you wired your OT primaries as you can put them round either way on a Rocket since there's no global negative feedback and it will work fine.
True... But I think Ken always wired the Rocket OT's the same..

It will work better if the Rocket speakers are facing the Express speakers with player in the middle.

Actually, you'd want the front of the Express/Liverpool cab facing you and the back of the Rocket cab (assuming it's open) facing you to get around this problem. Phase and anti-phase are about compressions and rarefactions of the air so it doesn't matter whether the cabs are in line facing you or either side of you facing you, they'll still retain the same relative pha
se
.

Phase cancellation from standing waves will be different whether facing each other or on the same wall... One player may prefer one setup over the other..

[rooster]

Yeah, that article was in the Guitar Player mag that addressed the story of Marshall. Ken's article is really saying the wrong thing regarding the phase of the Bassman vs. the Marshall because the amps are identical electrically. So then he starts talking about the speaker hookup and Jensens vs. Celestions, how Jensens are reversed at the basket..... but then I wonder if Fender connected the Bassman in a way that followed the speaker markings or the 'forward phase' way? I've owned two examples many years ago but I was never interested in how the speakers were hooked up stock - if my examples were stock. Anybody?

Anyway, what Glen says is spot on refering to feedback and how to counteract the dead notes that a room can present sometimes. Pretty cool. I have a little plastic box thing with a big AC amp switch built into it to reverse the phase when needed. Same idea as Glen, just different.

Too, when you use the Cliff or Rean style plastic jacks you can just reverse the connections. Not a problem since they are isolated.

OK, then back to the first post, yeah, at best, when Ken talks about how the 'happy accidents' of phasing and how a particular amp might even be richer in harmonics than one wired opposite? Well, I don't think we are talking about anything more than what Glen is refering to - mating a particular cab with a particular room.

[Richie]

depends on what bassman your talking about. Look at the layouts or schems. I think Ken may have been thinking of a certian model. Which the leads of the OT are reversed to normal fenders.
http://www.ampwares.com/amp.asp?id=27

look at the layouts, AA165 and AB 165 and AA864, notice the OT lead marking in the layout.

The wiring of the speakers in most combos, the speakers moved in. The JBLs were weird too, most think the red would be positive,and black neg.
Not by JBL. [ask them] Black is pos,and red is neg in the JBLs.
I had a twin here years ago, and was watching the movement to check the phase. the speakers were in phase with easch other, but they moved in. Maybe the reason was they were open back cabs.

I know i load the combos like that,and the closed back cabs, speaker moving out. Then you get into folded horn cabs and reflexed,maybe some speaker gurus could speak up about what they think.

But, as some have said, you can try it, listen and see what you like or what works for you.

[tubedogsmith]

Either way in my experience the phase of the sound coming out of the speaker cabinet can effect the sustain but it's note dependent. Of course even guitar body position is important to explore as it also effects the phase of the sound physically hitting the guitar. Point is having the phase one way can make controlled feedback great on certain notes, and dead on others. Then you flip the phase and the notes that are favored/cancelled totally change.

This is what I've found as well. It happens with pretty much any guitar but with something like a 335 it is really enhanced. Some notes will just die one way and switch the connection and they take off like a big ass bird!!!

[rooster]

Richie - Er, I was speaking of the Fender Bassman that Marshall copied and made into their 'Plexi' model, the Bassman built in 1959, 4/10s, etc..

Intersting that you know that about the BF amps, yes, that's true. They are reversed at the speaker jack. Still remains to be known if the Jensens in the 2/12 cab they sold with it were wired forward or backwards. I have never pursued this.

I have this article at the house. I will scan it and post it here, give me a day.

[Richie]

I kind of figured that i was just mentioning sometimes when people say the word "bassman",unless you do know which model/yr they are talking about,can get their wires crossed..


all the real 59's and some earlier that i have had here the speakers moved in. Just like the jbl loaded later twin and other combos. Like you i never tried all the others to see. I might start doing a closer check.
But i have heard the fender speakers were backwards to what one would think.

Maybe its because marshall switches flip down to turn the amp on,and up to turn it off.. fenders and american amps up is on,down is off.. but maybe because one chassis the tubes hang down,the others are up.

and the marshall or english amps,the inputs are on the other end compared to fenders No wonder its hard to figure out which end is what.

Ok back to the real world. As some have posted,there is a difference in the sound and how they react. Something you can hear and is not mojo.
I don't think many have messed with it much or tried it to see what happens. Or one way is better or worse. It will aslo matter what type cab is used,open or closed.
There are a few other things in amps i'd like to try,just to see what effect it has.

[Jackie Treehorn]

Now I've done a rehearsal and a gig with the reversed phase and I'm confident it's an improvement. The bigger coupling caps in the output section make a lot more sense to me now. Before, I was thinking of lowering them. It's a brighter, tighter, more complex tone with the phase reversed. There's definitely more bloom and sustain. My EF86 high gain mode works better now, too, because that one switches the phase again back to in phase output so it gets some more girth in the mids, whereas before, it could get a bit screechy.

One thing I've noticed, at least in my own builds, is that after I tweak/adjust for maximum feedback, I'll get a lot of feedback one way and very little the other. After switching phase on the rocket, I tried some of the adjustments I had previously abandoned and got better results with the phase reversed. I was just playing the amp and now the non reversed phase doesn't seem to have many redeeming qualities. I may flip the transformer leads next time I've got it open, so I don't have to use a phase reversed speaker cable.

[geetarpicker]

One tip that comes from experience! Always be careful with a speaker cable wired for inverted polarity. On the speaker side IF the plug has a metal shell it will be HOT on the outside compared to common ground. So if you touch it while playing or have a mic cord XLR connector drap over it at a gig you could have a short and/or get shocked. Not good for the amp OR you. What I do with switchcraft style plugs is wrap the barrel on the inverted side to insulate it, just in case. Long story but once I got shocked by the full 100 watt speaker output of an Ampeg VT22 combo aka V4 head, ouch!!!

[paulster]

Yep, same as me. Red heatshrink over the plug indicates a reversed phase plug and has the advantage of insulating it.

I'm still trying to find the blurb from Ken where he said that the Express and Liverpool were non-inverting amps in the first place. I'm sure I would have filed it because it was so peculiar on amps that are so obviously inverting!

[Jackie Treehorn]

One tip that comes from experience! Always be careful with a speaker cable wired for inverted polarity. On the speaker side IF the plug has a metal shell it will be HOT on the outside compared to common ground. So if you touch it while playing or have a mic cord XLR connector drap over it at a gig you could have a short and/or get shocked. Not good for the amp OR you. What I do with switchcraft style plugs is wrap the barrel on the inverted side to insulate it, just in case. Long story but once I got shocked by the full 100 watt speaker output of an Ampeg VT22 combo aka V4 head, ouch!!!

also important to make sure the reversed phase plug is at the speaker if using the airbrake, too, otherwise the whole enclosure would be hot.

The article, JTM45 vs Tweed Bassman, with Ken's statement on the phase of the amps is in the second book by Gerald Weber, Tube Amp Talk for the Guitarist. The one with the Mullard EL37 on the cover. I can't seem to find my copy at the moment to scan...