Re: Sound Phase Inverter Software 21
Teodolinda Mattson
Can anyone explain why when I record are jam sessions that after a certain amount of time the recording starts sounding like there is effects being added and the guitar starts to sound like it's off in the background with a twang effect. I am clueless
I've recently made a comparison between Rde and Oktava mics placed right beside each other and matching their gain pretty well on the mixer. When you added the signals without phase reversal, most of the bass was gone.
Now the point here was for comparison purposes, so the end product contained either one or the other, but if I had wanted to create a musically useful product by combining two microphones, I'd have been pretty annoyed (my mixer doesn't have phase inversion switches, but my DAW has). Also when switching in full sound, a phase mismatch would cause loud clicks.
In contrast, there is the trick of tying two microphones to each other, sing straight into one, and combine them phase inversed. That make most sound from a larger distance cancel and helps against acoustic feedback.
Before you go to a pricy output set of tubes and a possible need to rebias the amp think about a simple phase inverter change. There are no amp adjustments necessary when you change the phase inverter.
It makes sense that the phase inverter is very important. It's feeding the signal from the pre-amp into the power-tubes and has to make that signal change very cleanly, without adding any distortion. At least that's the idea for an amp running very cleanly.
With a lot of amps we rely on the pre-amp stage to provide the distortion, so the power-amp tubes really should only amplify. But, there's a really nice distortion you get when the power-tubes are getting pushed, and, according to that article it's the phase-inverter that is responsible for that sound. So, making sure that tube is in good shape is important otherwise the output-stage distortion will be weak or flabby sounding instead of fat, like it should sound.
In any case the tube will have about the same effect as any other tube in the chain. Any tube will have more of an effect the harder it is driven. All tubes will behave approximately the same if they are kept in in their linear range. Even bad tubes can sound good if not driven hard enough(All physical devices behave linearly within some range).
The reason why some tubes do work better typically have to do with the type of circuit the amp is built around rather than the tube itself. I know this sounds contradictory but the point is that some circuits happen to be out of spec and some tubes can handle it better(or worse depending on your perspective). What this means is that it's more of a problem with the circuit itself than something special about the tube and instead of changing the tubes you can fix the circuit. Of course it's easier for people to change tubes rather which is why you get so many people doing it and claiming some tubes are better than others.
Given that there are only like 4 vacuum tube manufacturers left in the world and 99% of the tubes you see are just rebranded versions goes to show that tubes don't make all that much of a difference.
The idea is that the pre-amp is where you get your distortion by overdriving the tubes there. Unfortunately this can happen in the PI too trying to get more gain which causes them to distort. Because of the circuit difference it will distort differently which will have a different effect.
If you are comparing PI tubes make sure you are driving them as hard as the amp allows to get the real difference else they will all sound almost identical(i.e., the whole point of saying they are operating in the linear region).
Apologies for answering my own question, but after performing some empirical experiments the answer in short is: yes. A phase inverter has an effect on the tone of your amplifier. I performed some experiments with the following tubes:
I matched all the following combinations for the PA and the PI in my Orange AD-30R and recorded a clip of me playing (almost) the same riff with my Les Paul R8. The settings and volume were identical on each clip, and they were recorded through a SM-57 into an Apogee Duet with Logic Pro on my Macbook.
After I have A/B'd these clips, I can tell that there are obvious differences between all of them. Take the two clips with the JJ's for the Preamp tube for example. There is a very noticable harshness to the clip using another JJ in the PI, while the Mullard is less so--fatter and more evenly spaced. There is, of course, also the fact that the Mullard is a 12AT7 and the JJ is a 12AX7. That could attribute to the fatter sound due to higher headroom and a much lower gain rating.
Wish I could listen to those audio files, but the links seem to be broken. I've recently gotten a Bugera V55HD that has the same setup - 3 12AX7's, 2 being for the gain stage, and the 3rd being a phase inverter.
I've always replaced all 3 12AX7's in my amps in the past, but now it seems the 2 12AX7's has to do with tone, while the Phase Inverter 12AX7 affects how easily the amp is overdriven and how much distortion it has. While I might not want a lower powered tube in the gain stage tubes, it's possible something like a 12AT7 or 12AU7 might produce more desirable breakup and distortion characteristics...
Only a few people realize this, but every single tube in an amplifier affects the sound of that amp, and even fewer realize that even though a brand new set of tubes may have the same identifying part numbers and may even be from the same manufacturer and the same batch of tubes, they are not all created equal when it comes to gain capability and frequency response. The best results usually come about by matching the tubes up with each other as far as gain characteristics are concerned and then giving the matched tubes a listen while installed in the chosen amplifier. When compared with any number of other tubes of the same type and manufacture in a given amplifier, There will be tubes that stand out as desirable in the way they sound, and others that just don't seem to offer anything special in the way they sound. It can involve extra time and money to purchase a number of tubes from which you can select the ones that perform best for you, but if you want the absolute best performance from your amplifier, this is one way to get it. Then again, I suppose not everyone requires top performance.
Itsy features independent left and right channel phase inversion switches and a corresponding correlation (phase) meter for checking the phase of your stereo signal. At +1 both L+R are in-phase, and means you have a mono signal; at -1 the signal is entirely out-of-phase. Stereo signals will typically be between -0.5 and +0.5. The phase controls can be applied to the stereo inverter, or the phase section can be split from the stereo inverter and used on a second signal instead.
Simple question. Amp uses 3 preamp tubes, 2 power tubes, and one rectifier tube. Want to put a 12at7 in the phase inverter to get more clean headroom (I hear that's the best placement to achieve that goal). How do I find out which tube that is?
It shouldn't have any affect on your sound. But remember we don't really know your amp. You can try but changing the PI shouldn't do anything and if you have a reverb or vibro on that amp it's using 1/2 of V3 and that may make for a bad sound... Just try it and report back.
Try the 12AT7 in the PI. People have this simple belief that 12AT7's will run cleaner power amps because of their lower gain, actually 12AT7's have a lower internal resistance than than 12AX7 and put out almost 10 times the current. It is the extra current will drive power tubes more before it starts to break up, allowing smoother OD and or touch sensitive dynamics, and you'll get less PI distortion.
The 5751 is a tube specifically designed to be used in 12AX7 applications, with a gain rating of 70, similar to a correctly biased 12AT7, and a internal resistance and current output closer to the 12AX7.
Going for extra headroom with tube swaps is a exercise in futility. people never need :just a little more headroom," to get noticeably more headroom in gig/jam situations, usually you need to double the wattage output or move to a more efficient speaker that gives you the equivalent (moving to a speaker that is 3 db more sensitive is roughly the same as doubling the power amp wattage).
I dont know if this will really get you where you want to be to be honest. Try it by all means but it might not work out like you expect. Also this is assuming its a long tail pair PI, if its a cathodyne (or something wacky) then using the wrong type of tube could yield some pretty ugly results.
actually-- that's only paritially true. adding an at where there was an ax can increase your headroom pretty gigantically in a phase inverter. its in no way a MINOR difference, to tell the truth-- and depending on how the amp is set up-- it can totally transform the response of the thing.
the tough part about locating your PI without a tube diagram is that at times you'll have things like verb or tremolo drivers. for instance-- v2 is the PI in a fender hotrod deluxe (just found this out this week with a friends amp). i'd google it, or call the manufacturer-- but i think putting an AT in your phase inverter is a great place to start-- and CERTAINLY way better than putting an AT in any driver positions.
I have a Signex CP44 unbalanced patchbay in which I've wired some sockets in parallel, so splitting the signal is no problem. On the returns, could I use balanced cable and swap the hot and cold pins to create the phase inversion, or would this not work, as the original signal and patchbay are unbalanced?
Technical Editor Hugh Robjohns replies: The technique you're referring to works by adding some of the right-hand signal to the left-hand channel out of phase and some of the left-hand signal to the right-hand channel out of phase. You can read the original article on-line at www.soundonsound.com/sos/oct00/articles/stereomix.htm, but I've included the original diagram here for easy reference. Many phase-inversion tricks aren't mono-compatible, but one advantage of this widening technique is that when the left and right channels of the final mix are summed to mono, the effect disappears without causing any problems.
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