Does a Lerpoole 15 watter invert phase?

[RCGPNY1]

Was just wondering if the Lerpoole 15 watter inverts phase? Over this past weekend I hooked up my Marshall JTM50(with 6V6's) and my Lerpoole 15 together using a Divided by 13 Switchazel A/B, A+B box.
When I combined them, there seemed to be less bass than with either of them alone...so I'm thinking they are out of phase with each other. I was under the impression that Marshalls invert phase.

[geetarpicker]

You might try swapping the speaker wires on one cab just to see if it sounds better. You could instead make a reverse phase speaker cable, but you then have to be careful to somehow insulate the plug barrel on the reverse side as it would have the hot signal on the metal sleeve.

[Colossal]

You might try swapping the speaker wires on one cab just to see if it sounds better. You could instead make a reverse phase speaker cable, but you then have to be careful to somehow insulate the plug barrel on the reverse side as it would have the hot signal on the metal sleeve.

I added a phase flipper switch to my 4x12 for this very purpose. Signal comes into the cab from the amp via a Switchcraft jack then into a DPDT on-on switch and from the switch to the speakers. Up is phase flipped, down is normal phase/unchanged.

[martin manning]

To answer the question, a Liverpool does invert phase, and a JTM45 (or JTM50) does not, so yes there will be some cancellation. Later Marshall's with cascaded input stages do invert since there is an odd number of inverting gain stages before the PI.

[geetarpicker]

You might try swapping the speaker wires on one cab just to see if it sounds better. You could instead make a reverse phase speaker cable, but you then have to be careful to somehow insulate the plug barrel on the reverse side as it would have the hot signal on the metal sleeve.

I added a phase flipper switch to my 4x12 for this very purpose. Signal comes into the cab from the amp via a Switchcraft jack then into a DPDT on-on switch and from the switch to the speakers. Up is phase flipped, down is normal phase/unchanged.

Excellent idea!

I've noticed when going for controlled feedback in the studio changing the phase has a definite effect on what notes sustain more strongly. Sometimes during a recording session if I was going for controlled feedback on a particular note (with difficulty) I would first experiment with angles and proximity of the guitar to the cab. If placement or angle still wouldn't work I'd also try reversing the phase of the speakers. I have an inverted speaker cable that I sometimes use, but the toggle switch on the cab is an excellent idea.

Same thing goes for PA monitors. Sometime swapping the phase can help feedback issues before even messing with the EQ. Typically nicer mixers have phase switches on each channel, and many sound guys don't know that trick. Anyway in that case the goal is less feedback obviously, but with guitar it is still an interesting tweak even in a single cab setup. That said, I've personally never heard any difference in tone by reversing cab phase in a single cab setup but in a multi amp/cab setup phase can be critical.

Anyway, pardon my side track on the subject!

GK

[Colossal]

Very cool Glen, I always enjoy your comments.

I can post the switch wiring arrangement if you or others are interested.

[vibratoking]

I am interested in how you mounted the switch. Is it sticking out the back or did you recess it in some way?

[RCGPNY1]

I've toyed with the idea of a phase switch on speaker cabs since I first started using 2 amps together...seems like its the way to go. Better off using a jack that does not ground to the jackplate..as we dont want to pass our signal through that. Funny...in the Marshall book...they claim that a JTM45 does invert phase...they cite that as one of the differences between the JTM and the bassman-that the bassman doesnt. It wouldnt be the first time that book was in error.

[Colossal]

I am interested in how you mounted the switch. Is it sticking out the back or did you recess it in some way?

The switch is mounted on a vintage looking Marshall jack plate (the round ones) just below the main jack plate, so the switch is recessed. I enlarged the jack plate hole to 0.50" to accommodate the switch's threaded bushing. There is just enough meat left for the lock nut to cinch the switch down tight onto the jack plate. It fits tight up against the plywood back cover. I used a medium/heavy duty NKK S-series switch; plenty of beef.

Oh, and to RCGPNY1's comment, I used isolation washers on the Switchcraft input jack.

[RCGPNY1]

To answer the question, a Liverpool does invert phase, and a JTM45 (or JTM50) does not, so yes there will be some cancellation. .

Hmmm...Ken F. always claimed the "wrecks" to be "phase coherant"..that they do not invert phase....In the Marshall book it is stated that Marshalls do invert phase, at least JTM 45's . Suffice to say they are out of phase with each other and I need a Flip switch like Colossal suggests

[martin manning]

To answer the question, a Liverpool does invert phase, and a JTM45 (or JTM50) does not, so yes there will be some cancellation. .

Hmmm...Ken F. always claimed the "wrecks" to be "phase coherant"..that they do not invert phase....In the Marshall book it is stated that Marshalls do invert phase, at least JTM 45's . Suffice to say they are out of phase with each other and I need a Flip switch like Colossal suggests

In Michael Doyle's History of Marshall it says Steve Grindrod stated that "Yes, the sound is 180 degrees out of phase, relative to a Bassman..." (pg. 21). That is just not true. You can easily see that by looking at the schematics, and also that the speaker output is in phase with the instrument input.

[pdf64]

Martin, I seem to remember reading that early Marshalls wired their amp's speaker output jacks flipped, so it would be of the opposite polarity to a 5F6A Bassman, which used RCA speaker outputs that necessarily connected the shield to the amp chassis.
I'll see if I can find a reference for this.
Pete

[martin manning]

Pete, look at the feedback loop in the JTM45- same as the 5F6-A.

[pdf64]

Agree, the polarity flip would be due to the implementation, in which the schematic ground / chassis is connected to the speaker jack socket's tip terminal, signal 'hot' to the socket sleeve terminal.
Obviously it's only possible with an isolated socket type, eg Cliff.
I've googled but it's not been conclusive. From chassis photos, some apparently original ones are wired in the normal manner, ground to sleeve, but with others it's unclear, kinda looks like black wires to tip, coloured to sleeve.
I'll carry on, maybe raise it on a Marshall forum.
Pete