geetarpicker wrote:I think that phase can have effect on controlled feedback. That said, I don't think there is one good way and one bad.
Recently I was experimenting with trying to get a particular note on my LP to sustain through my Wreck. I was trying to find the absolute lowest volume level (with a power attenuator in line) I could get away with and still get the note to predicably sustain. I found that this one particular note was easier with the phase reversed by using a rewired speaker cord. I also found that some notes sustained better with the phase "as is", and other notes worked better with the phase reversed. It's frequency dependent. I'm almost considering making a switch box to control this on the fly for song to song control, but making this safe without putting the amp in standby is the issue.
In other words moving your guitar position in relation to the amp, the phase of the amp AND the particular notes themselves all play a part in high volume and/or high gain sustain.
Glen,
From my experience with home theater installs, I can tell you for sure that what you are seeing gets worse with smaller rooms, and lessens with larger ones.
I'm sure you realize this, but you might be wasting your time with a phase switcher, unless it's for studio use only for example. I guess it's useful on stage, assuming you have time to work out the setup and mark some X spots on the stage with the feedback note written on them as how the big boys do it.
i've read in an interview with ken fisher, that he states the amp is in phase, counting three gain stages plus phase inverter, and this was specifically design that way because of harmonic bloom and feedback easily...hope that helps.
I still believe that the effect of phase on guitar sustain is note dependent. A simple backwards wired speaker cord can be used to swap the phase and then you can see for yourself which you prefer for the keys and notes you are playing.
And to add something to what Glen was talking about. Other things like if the cab is a sealed back,or open back cab,will make a difference in how the speaker is moving in phase,in or out. You can hear a difference in this effect also.
i've read in an interview with ken fisher, that he states the amp is in phase, counting three gain stages plus phase inverter, and this was specifically design that way because of harmonic bloom and feedback easily...hope that helps.
If I knew more about the tech side I could figure it out. But the PI produces two signals of opposite phase...but then each 'phase' is amplified by the power tubes (which invert)...and then it goes through the OT and I don't know if that inverts or not.
I guess I just assumed that that whatever the input to the PI is...the output from speaker is in-phase with that. So then it's just a matter of considering the preamp...odd number of inverting stages results in the output out-of-phase with the input and an even number of them results in an in-phase output.
I built a phase changing foot pedal and use it in the speaker line. I only switch while the strings are muted. I can tell a difference usually in the feedback and yes the notes that respond do seem to change with the phase. But after a half hour or less I find that one setting generally responds quicker and feedbacks easier and that is the way I set my cab up for that amp. I am pretty sure my Trainwrecks are both in phase normally wired. My Glaswerks is backwards. My Bassman has one channel in and one out
908,
Does your Glaswerks have an active loop (D'lator or equal)? An ODS with no active loop has four inverting gain stages before the PI but the D'lator has one inverting stage so it inverts it again. That's actually where I started with all this...Dumble and clone owners noticed the difference in response when they added the D'lator to the equation. No active loop = use a regular speaker cable; With active loop = use polarity-reversed speaker cable.
Yea, I have a BF Bassmn too and I even modded it to have the 6G6 Bass channel (the one with the cathode follower shoehorned between first stage and first tone stack). So I have the channels out-of-phase with each other...but most BF Fenders with Reverb are like that anyway.
In terms of absolute phase between input and output an Express and Liverpool are both inverting (a Rocket isn't).
I've no idea why Ken stated that they are absolute phase, because they're clearly not.
That being said, I think the phase issue is relevant to what you're playing, and where you're playing it. You can get one note that sings forever in one position and is dead when the phase is swapped, and I'm quite sure you can get exactly the opposite happening with another note/position combination.
An interesting discussion. If the amp is playing through one speaker or a cabinet with all speakers wired in phase I can see where there could be an effect on sustain and feedback on different notes whether the speaker is pushing or pulling at the initial sound due to the frequency of the tone and the distance from the source. Move and you change that phase relationship. From an audio engineering aspect a single point source would be in phase with itself. Now if two cabinet were used and one were pushing and the other pulling I could see major issues there. Phase cancellation and probably a hollow sounding tone with little bottom end. Same effect with multiple mics on a cabinet at different distances. Proper phase is very important. I don't personally think the phase issue being discussed in this particular case will effect the tone so drastically. Wire one of your stereo speakers out of phase and we are talking major phase cancellation. But wire them both out of phase and you probably wouldn't notice a big difference as they would be in phase with each other.
The Glaswerks does have a built in Dumbleator not sure if it is the cause of the phase change.
It was noticeable that certain harmonics were more active when the guitar was in phase and others when it was out. But I would say that the fundamental note responded more when the speaker and guitar was in phase. At least I assume it was in phase. Really you can just ignore it and you'll be fine or if it interests you make a switch box or a phase reversal cord and give it a try.
Fischerman wrote:Yes, the output is out of phase with the input. For guitar amps with a long-tail PI:
even number of inverting stages before PI = output in-phase w/input
odd number of inverting stages before PI = output out-of-phase w/input
In some amps with a switchable effects loop...the amp might be in-phase without the loop and out-of-phase with the loop (or vice versa)...then you have to know if the effect(s) in the loop reverse phase.
sorry to bump an extremely old thread, but i couldnt find the answer in other amps.
if i wanted to do a 2 channel amp, with two separate inputs, and use an a/b/y box like the bad cat/matchless stuff, and i had one channel that had 3 gain stages, and another that had 2 gain stages, i can just tie the into the opposite sides of the PI and run them together?
