Everyone asks what "note flipping" is, and this is a small example I just clipped from one of my clips. Listen when the blues lick is released to the root. (A) Right at 4-5 seconds, then I cut the clip. You hear the note one way as soon as its released, and then you hear it start to "flip", or change phase. This is why years and years ago i used to wonder if Dumble built a phase shifter into his amps. Its all OVER the Blue line recordings, and 183 does it in spades. This was my Tworock Artist doing it.
Does anyone know WHAT in the circuit makes this happen? Dumble must have known, because this is one of the main characteristics that first attracted me to Dumble amps. I have never heard any other amp do it, or at least to anywhere NEAR the degree of what i call the great Dumbles. You can actually control it more or less on 183 by how hard you pick the note. SOOOO fine!!!!! Any electrical engineers here who know what is causing this circuit wise? Is there anyway to ENHANCE it? The TwoRock Emerald Pro is the only amp I know that can possibly out flip the Dumble at this one specific thing. WICKED cool! I have played many Dumbles that did not do this at all, as well as many clones.
I've noticed this in my amps too, and I think I know what causes it.
If you were to measure the preamp supply voltages after you hit a note, you will see them drop by 20-40 volts compared to their idle value. This changes the operating characteristics of all the preamp stages by dragging the load lines closer to the origin. When you let the input signal from your guitar decay, the filter caps charge again and the preamp voltages rise back up, so the load line expands outwards again. The harder you hit the note, the larger the drop is, so that's how you can "control" it.
The load line paired with the tube curves essentially determines the character of the distortion by telling you what the shape of the transition from the linear region to the nonlinear region of operation will be, and where it will be. Therefore, this sag changes the character of the distortion dramatically. You will get a different harmonic spectrum emerging when the note is first hit and the supply voltages are lowered compared to when it's decaying and the voltages are higher. I think this is what you're hearing as "note flipping"
This happens more dramatically in the Dumble circuit compared with other amplifiers because of the topology itself, but the amount of voltage sag is largely controlled by the size of the dropping resistor between B+3 and B+4. Notice that the "typical" schematic value here is 15k - much larger than the typical dropping resistor you would see in say, a Fender. But 183 has a 22k here - which translates into even more sag than your average Dumble style circuit.
One simple way to enhance the effect would be to increase that 22k to something larger - maybe 33k. Of course, this would also lower the idle plate voltages and change the sound of the amp overall.
FWIW, I have not explored this in much depth. I have been away from my workshop since May of this year and haven't even had an electric guitar with me since then. These are just my thoughts based upon how I understand the operation of the Dumble circuit.
Last edited by dave g on Thu Dec 02, 2010 11:12 pm, edited 1 time in total.
dave g wrote:I've noticed this in my amps too, and I think I know what causes it.
If you were to measure the preamp supply voltages after you hit a note, you will see them drop by 20-40 volts compared to their idle value. This changes the operating characteristics of all the preamp stages by dragging the load lines closer to the origin. When you let the input signal from your guitar decay, the filter caps charge again and the preamp voltages rise back up, so the load line expands outwards again. The harder you hit the note, the larger the drop is, so that's how you can "control" it.
The load line paired with the tube curves essentially determines the character of the distortion by telling you at what voltage the tube clips, and how sharply. Therefore, this sag changes the character of the distortion dramatically. You will get a different harmonic spectrum emerging when the note is first hit and the supply voltages are lowered compared to when it's decaying and the voltages are higher. I think this is what you're hearing as "note flipping"
This happens more dramatically in the Dumble circuit compared with other amplifiers because of the topology itself, but the amount of voltage sag is largely controlled by the size of the dropping resistor between B+3 and B+4. Notice that the "typical" schematic value here is 15k - much larger than the typical dropping resistor you would see in say, a Fender. But 183 has a 22k here - which translates into even more sag than your average Dumble style circuit.
One simple way to enhance the effect would be to increase that 22k to something larger - maybe 33k. Of course, this would also lower the idle plate voltages and change the sound of the amp overall.
FWIW, I have not explored this in much depth. I have been away from my workshop since May of this year and haven't even had an electric guitar with me since then. These are just my thoughts based upon how I understand the operation of the Dumble circuit.
Hey Dave, that is a fantastic theory! I do not understand everything, but from what I do know, it makes a lot of sense, especially seeing 183 has the 22K. It would be really interesting for someone to play around with that and see if they could accentuate that even more. Do you know the Emerald Pros circuit at all? It would be nice, because that amp does it to the max as well. Thanks so much for taking the time on this. It has always really interested my ear, and brain!
I think a lot of things affect that phenomnem.
The transformers, the filter caps (especially the plate filters), how well the transformer is regulated and the speed at which the caps recharge since the amp is basicially running from the energy stored in them.
The whole enchilada.
That's why you see those guys with the massive sub-woofers in their cars using huge capacitors across their batteries, to handle the current draw when there is a lot of bass.
If they don't use those, the headlights will dim with the beat!
Structo wrote:I think a lot of things affect that phenomnem.
The transformers, the filter caps (especially the plate filters), how well the transformer is regulated and the speed at which the caps recharge since the amp is basicially running from the energy stored in them.
The whole enchilada.
That's why you see those guys with the massive sub-woofers in their cars using huge capacitors across their batteries, to handle the current draw when there is a lot of bass.
If they don't use those, the headlights will dim with the beat!
True, but I think that by far the two dominant components in the preamp power supply are the 15k/22k resistor and the filter cap associated with that node. The resistance of the PT windings is negligible compared to that dropping resistor, although arguably the "upstream" effects would become more apparent when playing at high volumes.
Yes, tweaking the values of that dropping resistor and the filter cap on that node would allow you to change how quickly the note "flips", and how much.
IMO, this preamp "sag" is really the secret sauce to this circuit. I believe that it is also responsible in large part for the "bloom", the touch sensitivity of the overdrive, and the ability of these amps to have a lot of sustain and compression without resorting to the techniques found in most high gain amps (like hard clipping multiple stages)
markr14850 wrote:Tag, does this happen equally at bedroom and at "dogears" levels?
I ask because the sag from the power tubes is going to be much different under those two conditions.
Interesting thought, but from my understanding of this it's preamp sag.
I've measured the preamp voltages under load. With a 400Hz sine wave input and OD engaged, master on 0 on a dummy load. The voltage on V1 plate drops 20-30V with signal as opposed to without. Turning up the master makes no difference.
It's also interesting to watch the sine wave changes as you raise and lower the input signal. The peak AC voltage doesn't change much, but the shape of the distortion does.
This all makes since when you realize that lower preamp voltages tend to sound duller, higher voltages have more complex harmonic structure.
Mr Dumble wrote:Everyone asks what "note flipping" is, and this is a small example I just clipped from one of my clips.
Another great example is Carlos' lead tone on "Smooth". Several of his sustained notes flip pretty dramatically.
I hear that more as feedback, no?
I don't think so, I think that's notes flipping, because I often hear this when I'm a volume too low to feedback.
EDIT:
For example listen to the last note of the opening solo. It fades out fairly normally, so that's not feedback IMHO, but it does flip (I like to think bloom into harmonics)
Ok, I see what you mean. I thought you were talking about the sustained notes like the ones around 1:30 to 1:35. I think I definitely hear those as feedback.
In any case, notice the 33k dropping resistor in the Mk 1's preamp supply...
markr14850 wrote:Tag, does this happen equally at bedroom and at "dogears" levels?
I ask because the sag from the power tubes is going to be much different under those two conditions.
I cant say equally, but 183 does it pretty much dead on with what I hear in Fords amp in the studio at what I think would be pretty loud, and 183 and my Quinn clone do it right down to very low volumes.
Bob-I wrote:
Another great example is Carlos' lead tone on "Smooth". Several of his sustained notes flip pretty dramatically.
I hear that more as feedback, no?
I don't think so, I think that's notes flipping, because I often hear this when I'm a volume too low to feedback.
EDIT:
For example listen to the last note of the opening solo. It fades out fairly normally, so that's not feedback IMHO, but it does flip (I like to think bloom into harmonics)
Its not feedback for sure. 183 and my Quinn do it at whisper volumes. I do hear it a little on that Santana solo for sure, although its very mild. Must not be a great Dumble.
Its all OVER the Blue line recordings, and 183 does it in spades. This was my Tworock Artist doing it.
