Dumble note flipping caught on sound file!

[mdroberts1243]

You know that is Dr. Ika as he is called, right?

I for one am just a bit skeptical of that clip.

How can something bloom or feedback without speakers?

I think I agree... sounds a lot like the characteristic feedback I hear all the time from the amps... not what I imagined as sag-induced bloom at all. But just my $0.02.

[ericlee]

You know that is Dr. Ika as he is called, right?

I for one am just a bit skeptical of that clip.

How can something bloom or feedback without speakers?

I think I agree... sounds a lot like the characteristic feedback I hear all the time from the amps... not what I imagined as sag-induced bloom at all. But just my $0.02.

Sorry Sir, your $0.02 and Tom's scepticism are wrong.
I hope I’ve explained everything in previous post.
I guess you’ve missed it or having a problem to understand it.

Bloody sceptics

[Structo]

That's fine.
But, can you explain how the bloom happens without the feedback loop to speakers or amp?

Where is the loop?

I believe there must be an interaction of the guitar and amp to cause this.
Either acoustically or possibly magnetically, as in magnetic flux of the amp reacting with something external.

Or perhaps it is something internally in the amp that causes it.

I don't know, that is why we are having this discussion.

I don't mean to offend you when I said I am skeptical.
It's just that anybody can post an audio clip and make any claim they want.

Because since I don't know you or your character, then I have nothing to base the acceptance of your claims on.

[vibratoking]

That's fine.
But, can you explain how the bloom happens without the feedback loop to speakers or amp?

Where is the loop?

I believe there must be an interaction of the guitar and amp to cause this.
Either acoustically or possibly magnetically, as in magnetic flux of the amp reacting with something external.

Or perhaps it is something internally in the amp that causes it.

I don't know, that is why we are having this discussion.

Tom. I'll take a stab at explaining the theory even though I don't have firsthand experience with recording bloom in the way that ericlee did.

Anytime a signal passes through a circuit with reactive components, Ls or Cs, there is a phase shift that occurs. It means that a sine wave would appear to be delayed in time from it's original form. If you sum a sine wave and a copy of itself that is delayed by 0 or 360 degrees, you will end up with a signal that is twice as big as it was. Summing that same signal with itself but delayed by 180 degrees results in no signal. Rather than explain this further, go to this website and look at the animation under the heading of:
"Two sine waves travelling in the same direction: Constructive and Destructive Interference"
http://paws.kettering.edu/~drussell/Dem ... ition.html

This interference is the same as summing or adding two sine waves together.

First, there are two types of feedback that we are discussing. One is the classic feedback such as GNFB in a circuit. It has nothing to do with speakers, volume, and pickups. The other is the feedback that we are familiar with as guitarists.

The main point is that when a signal is passed through a circuit that causes phase delay and then returned back to the input as in classic negative feedback, then there can be a potential for instability in the circuit. This instability happens to be very severe if the feedback signal is delayed by 180 degrees and is as big as or bigger than it was as the input. The amount of phase delay at each frequency can be different. So that a 1kHz signal will have a particular phase delay and a 2kHz signal could have a very different phase delay. It could happen that the 2kHz signal is fedback 180 degrees out of phase and big enough in amplitude that the instability happens which might cause the note to bloom. It could bloom out of control without any speakers or it could bloom for a brief moment if the circuit is on the edge of instability and a bias shift of some sort causes the circuit to move back away from from the instability point. All this is very theoretical, but it can happen in a system that is very well tuned to the edge of instability.

There is a theory in this thread that states that the bias voltages sag as signal is applied. It could be that the bias voltage sag causes a load line change, which in turn causes the stage to become more stable.

For instance, a note is played. It is amplified and the second harmonic is fedback in an unstable way which causes the note to bloom. At some point after the blooming is heard, the bias voltage sags causing the amp to move away from instability.

Disclaimer - I have not verified this. It is theoretical only.

I have verified last night that I can get certain notes to bloom, in a small way, on most of my guitars, unplugged.

I hope this helps. If not we can discuss it further if you like.

[wjdunham]

I really tried resisting the urge to jump into this discussion, but alas... here are my thoughts on the subject, don't take them too seriously

On the subject of feedback inside the amp, there are plenty of feedback loops created by the interactions with the power supply stages, and within a stage caused by the close physical routing of plate, grid and and cathode wires on the preamp tubes. The layout of these wires has been shown to affect the tonal characteristics of an amp, particularly with regard to sustain and bloom. The amp is also generating lots of it's own harmonics, the balance of which can be tuned by things like the twiddling the gain knobs for each stage, PI balance, tube selection etc... So, my long winded take on why I believe we can see feedback without any speakers being used. Parasitic oscillations are an extreem case here, while generally not a problem in the audio band, the amp is oscillating or "feeding back" all on it's own, luckily we know how to get rid of these oscillations. How to get controlled feedback in the audio band that can be modulated at the players command is the art few have mastered.

Of course, the amp is only one part of the overall system, but an important part in taking the content of a note generated by players fingers and guitar, and amplifying or otherwise emphasizing certain frequencies, and having this emphasis vary over the time frame of a note. I believe this is one important reason why a "hand wired" amp has a life of it's own, and most PCB amps seem rather flat and lifeless. All of this stray inductance and capacitance in the wires, and the coupling/feedback loops and phase delay they create, give the amp it's life. Also why every amp is a bit different.

the psychoacousticts part I believe is very important factor in all this. The brain is very sensitive to the frequency balance in a signal, it's what allows us to differentiate a persons voice and be able to hear every voice as unique, no matter how small the difference in the frequency content. It's why amp building is such an art, VERY small differences in the frequency balance have a big affect on how we perceive the amp. When it comes to bloom, it's this subtle shifting of the frequency/phase balance of a note from fundamental to harmonics that seems to sound so good to our ears...

OK, I feel better now.

By the way, 180 degrees is "out of phase", 0 or 360 degrees is "in phase" and 90 degrees is 90 degrees out of phase, neither here nor there...

If you sum a sine wave and a copy of itself that is delayed by 180 degrees, you will end up with a signal that is twice as big as it was. This is called in-phase. Summing that same signal with itself but delayed by 90 degrees results in no signal. This is called out-of-phase.

[Structo]

Yes, I have studied that theory. In fact somebody here posted a link to a Hi Fi site that talked about the loops inside the tube amp starting with the power supply filters.

You touched on something that I have kept meaning to ask.

How much does the lead dress affect this phenomenon?

We know that HAD liked to place the plate wire and cathode wires of the second and fourth stage in a close parallel fashion on the floor of the chassis.
Most of us were taught not to do that because it could make the amp noisy or unstable.

Yet many feel this lead dress imparts some of the legendary Dumble tone.

Perhaps it is a phasing thing as far as the flipping is concerned but the part that is hard to understand is why does the note stall on that tone instead of blooming into the second harmonic?

[wjdunham]

Tom, it's absolutely a feedback loop, many of them actually. I think the most important is the V1 plate wire running next to the V2 grid wire, since this is in-phase (two inverting stages back to back), this will have an effect on the sustain - I have seen posts from many pro builders on this site (Brandon, Tony, Henry) stating that running the three wires (V1 plate, V2 plate, and V2 grid) parallel for a few inches increases feedback and sustain. The V2 plate running next to the V2 grid is negative feedback, probably tames some harshness similar to a very low value snubber?
Bill

[Reeltarded]

I don't want to be here.

"Bloom" happens shortly after a struck note. (or not) Has nothing to do with what is being described here. It's in the lows.

That crying harmonic thing is not bloom. It's nice, but it's not "bloom". It's "That crying harmonic thing". That splatting preamp is not bloom. It's gnarly, but it's not "bloom". It's SPLAT.

I like the splat (starved pre) when it can be controlled, especially when followed by bloom (fundamental amplitude expansion) and that crying harmonic thing. (that crying harmonic thing)

"Note flipping" is the splat *almost* about to happen barely.

Parsimonious vernacular. Practice makes perfect.

[vibratoking]

Bill. You are correct. I went back and fixed my post about in and out of phase. I think some confusion can come from inverting or non-inverting.

Reeltarded. One of the things that I am trying to accomplish here is nomenclature and definition of these phenomenon. Without that, there is no meaningful discussion due to the confusion. Care to post a clip of each and suggest a name?

[CHIP]

Tom, it's absolutely a feedback loop, many of them actually. I think the most important is the V1 plate wire running next to the V2 grid wire, since this is in-phase (two inverting stages back to back), this will have an effect on the sustain - I have seen posts from many pro builders on this site (Brandon, Tony, Henry) stating that running the three wires (V1 plate, V2 plate, and V2 grid) parallel for a few inches increases feedback and sustain. The V2 plate running next to the V2 grid is negative feedback, probably tames some harshness similar to a very low value snubber?
Bill

I thought the V1b plate wire was run parallel to the V1a and V1b cathode wires.

[wjdunham]

I thought the V1b plate wire was run parallel to the V1a and V1b cathode wires.

You're right, my description of the topology was not correct - the effect is though, V1B plate wire to V1A cathode wire coupling = positive feedback loop. Same for V2 as well. Thanks for pointing that out.

[markr14850]

V1B plate wire to V1A cathode wire coupling = positive feedback loop.

The cathode is effectively at AC ground, so there shouldn't be much effect.

[Reeltarded]

Reeltarded. One of the things that I am trying to accomplish here is nomenclature and definition of these phenomenon. Without that, there is no meaningful discussion due to the confusion. Care to post a clip of each and suggest a name?

Sure! I get that. The problem is some of the ones we are using are established to mean something else already.

Bloom. Make your amp loud, strike the lowest G note. In the second after the attack subsides, the fundamental takes over and "blooms".

The crying comes from the 2nd/3rd order harmonic content.

The splat happens to me most often with a Fender style front end starved for voltage. The more energy the note has, the deeper the splat. It soiunds as the low-mids version of something not passing the key jangle test one might use on microphones. I use variacs on larger amps for much the same effect.

If you balance the "bloom", the "crying", and the "splat" just so.. it sounds like it's "flipping". I have a Bassman head that does all this pretty well without much gain at all.

What about a splat control on the front to control that dropping voltage? I can't wire anything more complex than a patchbay, and I think electricity tastes terrible.. but hey... someone here must be good with a soldering iron.

[Max]

If you would be so kind, please explain to me how psycho-acoustics applies in any significant way to blooming, flipping, straining, etc...

Hi vibratoking,

the science of Psychoacoustics IMO applies in a significant way to "blooming" (just as an example for a whole universe of existing and/or possible linguistic descriptions of the tone of an amplified electric guitar), because "blooming" is a linguistic metaphor for a certain kind of human perception of certain air pressure stimuli and not for a certain kind of physical data resulting from measurements of all the objective physical parameters of these air pressure stimuli.

Now the science of Physics explains why and how precisely a certain kind of plugging a string of a Stratocaster leads to a certain kind of measurable air pressure stimulus.

And the science of Psychoacoustics explains how precisely the human sound perception relates to these air pressure stimuli and why - as an example - the human sound perception system may perceive a dynamic difference in the volume (amount of air pressure) as a difference in pitch and/or timbre (frequency of the air pressure).

So in the human sound perception

- tremolo may be perceived as vibrato
- exactly the same frequencies may be perceived as warm and pleasing which may be perceived as sharp and shrill only after raising the volume or changing the dynamics of their presentation (swell and decay times)
- some frequencies may be (more or less) "suddenly" perceived in the sound only when a note decays because other frequencies may have decayed at this point to an extent that they loose their masking effect
- etc.

But please understand that these are only examples with all the advantages and disadvantages of all examples in general and especially regarding a complex science like psychoacoustics.

And if after reading one of the two books I linked to in my previous post as an example you should still be completely sure that psychoacoustic effects -like masking just as an example - play no part at all in the perception Mr Dumble tried to describe with the metaphors "blooming", "straining", "note flipping" or however else, please feel free to think so.

I am personally rather happy that this is (as it should be IMO) a colorful world and so it would be completely fine with me - as it would further add to all these interesting colors of our different opinions and approaches - if our opinions should remain different concerning this topic even after you should have studied the science of psychoacoustics.

Cheers,

Max

[CHIP]

Max,
You often bring a different approach to explore our quest. Thanks.
Great post.