From: Cybermonk (cybermonk@amptone.com) Date: 8/12/2000 3:15 AM Subject: Re: Power attenuator, not simple dummy load I have done a little experimenting with a dummy cab as a power attenuator. I have two speaker isolation cabs, one of them heavy-duty. I have also put a raw unmiked speaker in blankets inside the heavy-duty box, making it truly silent (3 a.m. silent). The good news is that you can immediately try putting a speaker in blankets as a load. Use a single low-wattage guitar speaker as your monitor speaker. Choose your resistor placement so that the amp sees pretty much only the load speaker. In parallel with the load speaker, start off by putting a 500 Kohm pot in series with your monitor speaker. Both speakers are 8 ohms. The amp expects 8 ohms. I used a Radio Shack A/B/C box to compare the sound when the load is a speaker vs. a resistor. There was a strong difference in EQ, but the loss of dynamics with the resistor was difficult to hear. Now instead of the 500 Kohm pot, put in whatever value of resistor causes your monitor speaker to receive 1 watt. This will be quite loud, the same as perhaps 16 dB attenuation with a significantly saturating 50-watt Marshall head. This is using an actual speaker as the load. You should think of a power attenuator as actually two components, like the Harry Kolbe products. It's a load splitter, and a full dummy load. The dial directs a portion of the amp's power to the full dummy load, and a portion to the monitor cab. Now, you can use the Kolbe "The Attenuator" for your load splitter, and instead of attaching a resistive dummy load on one of the output branches, attach a speaker in a blanket. The Power Brake is like the Kolbe The Attenuator and the Kolbe Silent Speaker jammed together in one package. You could modify the Power Brake. Instead of using its built-in reactive dummy load, ignore that and push instead a speaker in a blanket. Or, use the Power Brake's knob as a Balance knob to set the relative volume of two conventional cabs on stage. Most anyone here can try that dummy speaker, resistor, monitor speaker experiment right away. Does it sound better than a Hot Plate or Power Brake pushing the same speaker with the same intensity? Based on common reports of how various amp gear behaves, I would expect the speaker in a blanket to make a better-sounding load than a conventional attenuator product, despite use of a resistor to regulate how hard the monitor speaker is pushed. Quiet cranked-amp tone techniques always boil down to how many degrees of compromise, how many increments of dynamic depth you lose. If we agree that speaker distortion is important, then there is no way a 5-watt amp can possibly sound as good as a 22-watt amp, when pushing the same single low-wattage speaker. So the question is really, what compromises the tone less -- a 5-watt amp, or a 50-watt amp into a power attenuator, or a 50-watt amp into an isolated dummy cab? You could also use asymmetrical speaker impedances -- dummy cab is 4 ohms, monitor cab is 16 ohms. http://www.amptone.com - power attenuator FAQ START NEW THREAD REPLY PREVIOUS LIST Read 138 times From: R.G. Date: 8/15/2000 4:40 PM Subject: Re: Power attenuator, not simple dummy load If we agree that speaker distortion is important, then there is no way a 5-watt amp can possibly sound as good as a 22-watt amp, when pushing the same single low-wattage speaker. But the big question is - do we agree? And whose ears do we use as a standard? So the question is really, what compromises the tone less -- a 5-watt amp, or a 50-watt amp into a power attenuator, or a 50-watt amp into an isolated dummy cab? Again, by what standard? Whose ears? Some people might think tone is less compromised by listening to a 2" speaker driven by an integrated circuit. Not my idea, theirs, and equally valid. Speaking of which - how *do* you measure "tone"? What units? And what instrument do you use to measure it? Is it single-dimensional or multidimensional? If multidimensional, into what subfactors do we split it to measure? There are no absolutes in this mess. There are only opinions unless you have the numbers - and numbers are precious hard to find when you're talking about what one person likes and doesn't like. START NEW THREAD REPLY PREVIOUS LIST Read 99 times From: Michael Hoffman (hoff@amptone.com) Date: 8/16/2000 11:50 PM Subject: Re: Power attenuator, not simple dummy load There's a general consensus on the Net that speaker distortion is an important factor in amp Tone. Also, what I call "speaker smoothing" is important. The worst, thinnest, grainiest sound is when the speaker is barely moving - say, 20 mW. Then around perhaps 1W you start getting some speaker smoothing. Then around perhaps 20 watts with a 25-watt speaker, you get speaker distortion. Consensus about tone is like a statistical bell curve. There are shared and dominant ideas. Sure, a small fraction of people have very different ideas, but there is some concensus or some groupings of opinions into which most people fall. There are recognizable standards for what sounds good -- that is not to say there is no divergence of views, opinions, or preferences. There is no need to throw up our arms and say that no agreement can be reached - that would be an unwarranted extreme relativism. I have not tried a 2" speaker. I would like to experiment with the 5" speaker in the Micro Room speaker isolation cabinet with built-in power attenuator. I have recently identified key units of Tone. When you cut out or simulate any major component in a classic amp rig, something is lost. You can lose a degree of dynamic depth or lose a distortion component such as preamp distortion, power-tube saturation, or speaker distortion. As you move time effects from post-mic toward the front of the amp, you introduce increasing degrees of "intermodulation distortion", as the delayed signal conflicts with the immediate signal in a distortion bottleneck. The best Tone (or a rig for the widest tonal palette) has: o All 4 degrees of distortion: preamp distortion, power-tube saturation, output transformer distortion, and speaker distortion. o Minimal intermodulation distortion (the most would be time fx before the amp, introducing a degree of I.M.D. at each distortion stage). o Full dynamic depth. Requires transparent preamp distortion that allows all notes of a chord to come through. Requires power-tube saturation response. Requires a hard-driven speaker. Requires direct power-tube/speaker interaction with no dummy load in between. I am not a relativist and do not say that all ideas about Tone are equally valid. There is an evident concensus, or predominant groups of concensus, about what sounds good. There are other choices besides "absolutes", "numbers", or "opinions". There are guidelines, principles, and common ideas about Tone. One missing component for concensus is amp tone MP3s. Having these will not create universal concensus, but will help tremendously toward presenting evidence publically, just like we can all critique the amp tone on a standard Hendrix album. http://www.amptone.com/amptonemp3s.htm When I first started a comprehensive online research pass about the pros and cons of power attenuators, I felt that there was a radical divergence of opinions on whether they suck Tone or work well. But now that I've mulled over the various postings and mentions from Web pages, I think there is a clear consensus, with minor variations in opinions about the degree of Tone-suck contributed by various aspects. I summarized this concensus about Tone and power attenuators in the Power Attenuator FAQ. http://www.amptone.com/powerattenuatorfaq.htm The consensus is that power attenuators suck some degree of Tone, and that this is partly due to the speakers being under-driven, and partly due to the lack of direct dynamic interaction between speaker and power tubes. The "debate" becomes merely about degrees: how *much* Tone is sucked, and how much of that suckage is due to under-driving the speakers, and how much is due to changing the load from a speaker to a dummy load. Another statement of concensus about Tone is the "Single Coil Manifesto" at the bottom of the Harmony Central Guitar Forum FAQ. http://www.nema.com/guitar/text.htm There is definitely a consensus, and standards -- this doesn't mean that there is an absolute and narrow concensus. One important standard is the standard traditional studio chain: preamp distortion, power-tube saturation, speaker distortion, mics, mixer, time fx. When trying to get good sound at low volume, people often try to deviate from that standard and it's certain that Tone is sacrificed; it's only a matter of how many degrees of Tone are sacrificed. START NEW THREAD REPLY PREVIOUS LIST Read 97 times From: SpeedRacer (Joe@ObsoleteElectronics.Com) Date: 8/17/2000 4:11 AM Subject: Re: Consensus? Consensus based on what? Folks on the 'net all sorta figure it sounds like a reasonable explanation of something they don't really understand? (and no one really does IMHO) We need research and facts IMHO. There's a consensus on the 'net that IMHO is equally flawed regarding OT saturation and tone. But hey, everyone thinks it's a reasonable guess at what's going on, nevermind no one has really taken a hard look. FWIW I *don't* think OT saturation sounds good, or is a good and necessary part of tone. Real OT saturation sounds lousy. What many people attribute to OT saturation is something else entirely - but they never bothered to really examine what it was they were hearing. It becomes "fact" because no one knows any better and no one questions it.** Sounds like a dangerous concept doesn't it? Probably just BH curve non-linearity effects in the core if I had to guess (don't quote me!). I'll offer this: Our OEI OT's do not saturate at full output (65W typically at 430V B+) and seem to sound OK to most folks. In your tonal model any amp using them would be lacking in one of the components of good tone. I should probably go post a warning on my web site. ;-) DR Z's OT's don't saturate. I'll betcha $5 Randall Aiken's don't either. Something to think about, or at the very least the disembodied rantings of the dissenting member of the 'net community. :-) This consensus thing is a slippery slope. It just seems that where a lack of real research is present, tone gets ascribed to everything *but* the thing that is responsible. Chassis material, transformer orientation, phase of the moon, etc. Like we used to say around the garage when trouble shooting cars, "is there gas in the tank? is there a spark?". Look for those before you go digging into some esoteric possibility.. The simplest answer is probably the correct one. Wattage ratings of speakers have little or nothing to do with distortion levels at output. They have to do (as most limits in engineering seem to) with heat and the dissipation of same. How fast can I clock my CPU before it dies? How hard can I brake before my disks melt? And how hard can I drive my speaker before the coil melts, deforms, goes open or is otherwise damaged. 25W RMS through the coil is all the mfr feels is safely tolerable before some kind of damage will occur, not a limit on where the distortions of the cone & motor will become objectionable.. To some degree, power ratings are just marketing. People want to buy 25W Celestions, so they label them as 25W speakers, never mind the fact they can take a *heck* of a lot more power than that. You can design a speaker to clip all over the place while never getting to it's full power rating - simple mess with the coil geometry.. A sine input translates to forward and reverse motion.. and if the cone cannot move far enough to recreate that wave form you have clipping. AFA low power levels sounding weak and buzzy, that could have as much to do with the work of Mssrs Fletcher & Munson as anything else.. (everything sounds heavy in the high mids at low levels. It's nature.) I don't mean to single you out on this speaker distortion issue but I've heard it all over the place and I personally think it's dead wrong. I would welcome someone to actually do some measurements and show some facts one way or the other. Consensus is a fine thing if based in reality. It is quite another when it is no more than a shared opinion with no factual basis (that I can see anyhow). I think in this latter case, it is in fact highly counterproductive and misleading. ** actually not quite true. I've seen RG, Randall & KG try to make this case a bunch of times to their credit. It was likely one of the three that got me to take another look at my own "assumptions". START NEW THREAD REPLY PREVIOUS LIST Read 77 times From: Steve A. (steve_ahola@yahoo.com) Date: 8/17/2000 5:35 AM Subject: Re: Consensus? Speed: Probably just BH curve non-linearity effects in the core if I had to guess (don't quote me!). Oops! I just quoted you... sorry! (What does BH mean?) Maybe you can define "saturation" so that we are all on the same page. I try to grasp concepts on an intuitive level so I think of OT saturation as being that non-linear distortion that you get when you pour more "juice" into the tranny than it can handle (as though it were a container)... A small OT will saturate sooner than a larger one (assuming that the impedances are correct, etc.) So is OT saturation something different than that? (When I think of an amp with OT saturation I think of the cheap small amps that blues guitarists would play on the streets of Chicago back in the 50's and 60's. Not necessarily a *good* sound but a distinctive sound. Of course I was never there and the sound on the recordings I have may have more to do with *tape* saturation than OT saturation... ;) ) Backing off from the term "saturation" your OT's are regarded very highly; do they respond/react differently (or non-linearly) at full output than they do at lower playing levels? Regardless of the terms used, the "consensus" will probably agree that a cranked amp sounds different (if not better) than it does at lower playing levels [let's ignore clean sounds for a minute- okay?]. We know that output tubes and speakers respond differently when the amp is cranked up; is that also true of an OT like one of your OIE's? Educate us, Joe! --Thanks! Steve Ahola START NEW THREAD REPLY PREVIOUS LIST Read 91 times From: ken "bigassguitaramp" gilbert Date: 8/17/2000 2:28 PM Subject: Re: Power attenuator, not simple dummy load fine and dandy, but what IS speaker distortion? is it the collapse of the magnetic field as the back-emf works against it? this is supposedly much of the sound of alinico speakers, after all. is it the breakup modes of the cone itself? this is supposedly much of the sound of celestions, which--by and large--use the same cone materials from model to model. what is speaker smoothing? at the mW level the speaker is actually REMARKABLY linear. how about we just use speakers which are less efficient? i know two easy ways to do this: a) with a speaker that has a permanent magnet installed, mount another magnet on the back, out of phase with the existing magnet. this will buck the magnetic field, lessening the magnetic flux in the gap, thus providing less force to the speaker when the ampere-turns of the coil produce flux of their own. if you wanted this sound permanently, you can just whack at the back of your permanent magnet with a hammer until it loses enough magnetism to be perfect. course, then you'd have to have it refluxed if you wanted the old sound back. b) design speakers with field coils, like they used to, wherein an electromagnetic coil (preferably current driven) produces the static magnetic field against which the voice coil's flux operates. thus you may obtain a continuously variable level of magnetic flux in the gap, and therefore variable speaker efficiency and ultimate acoustic output power. hell, make it MIDI switchable for all the techno-geeks. and what's all this bunk about IMD? shit man, the distorted guitar signal is ALL ABOUT IMD! that's where the art of tuning the distortion stages comes in--it's the art of blending the various orders of harmonic distortion as well as IMD. who DOESN'T want chords that are thick and chunky--in essense, greater than the sum of their parts? your idea of how to GENERATE IMD is way off the mark. how many enginnering texts have you owned, read, and struggled to understand? all you need to have IMD is two different frequencies. it happens with the harmonics of a single string. it happens with the residual ripple of the power supply's 60Hz and associated higher harmonics. you can't STOP it from happening, and why would you want to? there's an amp out there with a "fat" control which deliberately injects 60Hz signal to be mixed with the guitar signal in order to generate IMD, and thus a "fatter tone." When trying to get good sound at low volume, people often try to deviate from that standard and it's certain that Tone is sacrificed; it's only a matter of how many degrees of Tone are sacrificed. who the fuck are you--seriously--to say that "tone is sacrificed?" to YOUR ears, perhaps. i've done crazy shit with tubes that sounds wonderful; like having a 600W tube amp, it's hardly "standard." how many folks use van scoyc phase splitters, fully balanced interconnects, cascaded cascodes with variable local NFB loops, all active tone controls, constant current sources for cathode followers, or the like? (i know of ONE whacked-out dude like that.) judging by the obsession with quiet amp tone, i'd say if you heard my rig you'd a) shit your pants right off and b) run from the room in terror. that's the standard reaction, after all. wait--there's one more that comes right after that: the inevitable desire to have a rig just like it. that happens all the time too. maybe to be a standard i just need to build more of them? tympanic membranes--FEAR ME! kg START NEW THREAD REPLY PREVIOUS LIST Read 49 times From: GFR (gfr@cepel.br) Date: 8/17/2000 4:40 PM Subject: Re: Consensus? While I can't prove that speaker distortion is crucial to good tone (and I don't think it is), I think I can give an example (with some technical basis) that it can sound good. I've got a cheap, small, ss washburn practice amp. If I connect its speaker to a hi-fi amp, the sound is heavily distorted even at very low output levels (besides the lack of highs). If I plug the Washburn into any of my other (bigger) cabinets (that don't sound distorted with th hi-fi amp) its sound is entirely different (altough it can be just different frequency responses). The Washburn sounds much better with his own small, distorting, speaker. Also, I can give you some distortion curves for a couple of speakers taken at different power levels. All the curves I've seen show the distortion skyrocket as the power increases, specialy at low freqs. ALL speakers distort a lot, some just distort even more... START NEW THREAD REPLY PREVIOUS LIST Read 59 times From: Michael Hoffman (hoff@amptone.com) Date: 8/17/2000 6:49 PM Subject: Re: Power attenuator, not simple dummy load >What does "speaker smoothing" mean, given linearity at low wattage? At the mW level a guitar speaker may be linear. Speaker smoothing starts at around 1 watt, when the speaker is no longer linear. If using a power attenuator at high attenuation, or a 1-watt tube amp, it is better to push 1 speaker to 1 watt, to push it into smoothing, than 4 speakers to 1/4 watt each, at which point they would sound grainy and thin. I reserve the term speaker distortion to refer to pushing the speaker hard. >For quiet speaker distortion, you could use less efficient speakers... mount another magnet on the back, out of phase... design speakers with field coils; you may obtain a continuously variable level of magnetic flux in the gap, and therefore variable speaker efficiency and ultimate acoustic output power. Weber has a parameter-controllable speaker, but I can't find it now at WeberVST.com. I like the idea of MIDI control. We can expect more gear that has an all-tube path but realtime MIDI control of cabs, tube types, and conventional settings. >You could make it MIDI-switchable. I'm very interested in the Weber research such as coneless speakers and a compact speaker/mic transducer in a box. >For Rock, intermodulation distortion is desired. There are two different types of intermodulation distortion. 1. Distortion voicing is concerned with intermodulation of one frequency and another. With 2-note chords such as a fifth, the frequencies produced by the guitar are related and the intermodulation sounds good when forced through a distortion bottleneck. 2. When using a short echo before distortion and bending a single note, this produces intermodulation between the immediate signal and the delayed signal, in which there is a slight divergence of pitch such as a half-step, which produces unmusical beats that produce jarring arbitrary overtones. The most dissonant sound is playing a complex chord that has dissonant intervals, together with echo placed before all distortion stages. That would have intermodulation between one original note and the others, and intermodulation between the direct and delayed notes. The most harmonious sound is playing a simple chord or single-note run with harmonious steps, with echo placed after the miked amp. In certain conditions these two forms of intermodulation distortion are the same. Play a 2-note interval chord with a root and a half-step up from the root. Or, alternate between playing the root by itself and the half-step up note by itself, all through an echo. Either way, both notes (the root and the half-step up) will be present at the same time, and if you feed that narrow interval through the distortion bottleneck all at once, the dissonance of that chord will be multiplied. If you play a single-note run of notes into echo then distortion, any of those notes can be present together, forming an interval that collides in the distortion bottleneck, splattering quasi-random overtones all over, unlike placing echo after distortion. >What exactly do people mean by "speaker distortion"? http://www.webervst.com/spterm.html - speaker terms - "Breakup -- Context: It doesn't break up quite as smoothly as I like. Description: Below a certain frequency, say 900hz, the cone vibrates as one piece, much in the same way a piston goes up and down in an engine. Above that 'piston band limit' frequency, the cone vibrates in sections. By the time a wave travels from the apex at the voice coil all the way out to the edge of the cone, a new wave has started at the voice coil. Think of a series of ocean waves. One comes in and crashes against a sea wall, the sea wall generates a new wave that starts back out into the ocean where it meets a wave coming in, they crash together, and for a moment it looks like a stationary wave going up and down, but not travelling. The same thing happens on the surface of the cone. The result is comb filtering and other anomalies that create the texture of the overall sound. Interestingly enough, this all takes place between around 1 and 4Khz, where our hearing is most sensitive. If you look at a speaker plot, you'll notice the response of the speaker is fairly smooth until it gets in this region. Although some mathematics can be applied to the design of breakup characteristics, most information found on the subject uses phrases such as 'years of experience', and 'empirical data.'" "Crunch -- Context: Definitely a crunchy speaker. Description: Crunch is that sound you hear when you have the volume high enough to hear definite breakup patterns in the speaker, yet they seem well controlled as well as enhance the overall texture of your tone. Sometimes a very slight amount of flabbing due to loss of control of the cone can actually add texture and crunch to the overall tone and is desireable. Of course, too much flabbing is perceived as a stuttering in the tone and sounds like the tone has holes punched in it. Very annoying as well as disruptive to the texture of the tone." START NEW THREAD REPLY PREVIOUS LIST Read 47 times From: Mark Buckingham (buckinm@rocketmail.com) Date: 8/17/2000 7:12 PM Subject: Re: Power attenuator, not simple dummy load b) design speakers with field coils, like they used to, wherein an electromagnetic coil (preferably current driven) produces the static magnetic field against which the voice coil's flux operates. thus you may obtain a continuously variable level of magnetic flux in the gap, and therefore variable speaker efficiency and ultimate acoustic output power. hell, make it MIDI switchable for all the techno-geeks That's a pretty cool idea, and really simple too. Would varying the strength of the field coil change the reflected impediance back to the amp though? START NEW THREAD REPLY PREVIOUS LIST Read 47 times From: R.G. Date: 8/17/2000 7:23 PM Subject: Re: Power attenuator, not simple dummy load There's a general consensus on the Net that speaker distortion is an important factor in amp Tone. Show us the numbers, don't gloss it over as an opinion. Consensus about tone is like a statistical bell curve. No, it's not. Define "consensus". There are recognizable standards for what sounds good Elucidate the standards, and the number of people agreeing, and your methods for coming up with them, please. The best Tone (or a rig for the widest tonal palette) has: Please, define "best" and "tone". All 4 degrees of distortion: preamp distortion, power-tube saturation, output transformer distortion, and speaker distortion. Describe for us how these differ, and more importantly why they differ. Is the same waveform going to sound the same if it's derived by coming through a tube as through a transistor? How about a tranformer as opposed to a tube? While we're at it, what's a "degree" of distortion? Is that just how the distortion was arrived at? Does that matter? Why? Where are the numbers? Or shall we just blather opinions? I am not a relativist and do not say that all ideas about Tone are equally valid. Why not? How can you say what another person hears. While we're at it, how do you know what another person hears? And how do you know what they like? There are other choices besides "absolutes", "numbers", or "opinions". There are guidelines, principles, and common ideas about Tone. Define guidelines, principles, and common ideas as you've used them here, and as they relate to "tone" so we have an unambiguous picture what you mean. The sense I get is a fluffy, foggy slush of general clumping together. I kind of think that when someone won't state the numbers, they don't have them. Even the people who do state the numbers may have made them up. Let's see something other than handwaving. these will not create universal concensus, By golly, that one is right! When I first started a comprehensive online research pass about the pros and cons of power attenuators, I felt that there was a radical divergence of opinions on whether they suck Tone or work well. But now that I've mulled over the various postings and mentions from Web pages, I think there is a clear consensus, with minor variations in opinions about the degree of Tone-suck contributed by various aspects. Did you arrive at this divine inspiration by osmosis, by counting on-line opinions, by in-depth interviews with whomever wanted to say anything, by statistically valid research techniques, or by an epiphany? Did only you receive inspiration or did others get The Word as well? Are there Others in the world? Or could only you receive The Word? There is definitely a consensus, and standards -- this doesn't mean that there is an absolute and narrow concensus. Show us the numbers. Handwaving gets old. START NEW THREAD REPLY PREVIOUS LIST Read 45 times From: R.G. Date: 8/17/2000 7:41 PM Subject: Re: Power attenuator, not simple dummy load At the mW level a guitar speaker may be linear. Speaker smoothing starts at around 1 watt, when the speaker is no longer linear. If using a power attenuator at high attenuation, or a 1-watt tube amp, it is better to push 1 speaker to 1 watt, to push it into smoothing, than 4 speakers to 1/4 watt each, at which point they would sound grainy and thin. I reserve the term speaker distortion to refer to pushing the speaker hard. Neat stuff. Can you show us the research that indicates this? Do you have distortion versus power level charts? For how many different kinds of speakers? Do all speakers do the same thing? How do we select for "better" speakers? Do the speaker characteristics affect this? How does it scale with speaker size, voice coil size, mass, compliance, cone resonances, and cone materials. I love to find new, hitherto unsuspected scientific truths, so please point me to where I can find the data. I **know** you wouldn't stoop to handwaving and blathering. There are two different types of intermodulation distortion False. There are either one or an infinite number of types of intermod, depending on how you define it. Intermod is produced by any nonlinear process acting on two signals at the same time. Yes, I *do* have references. The exact nature of the nonlinearities may be infinite. When using a short echo before distortion and bending a single note, this produces intermodulation between the immediate signal and the delayed signal Nonsense. Intermod is intermod. What you're trying to say is that a delayed signal can produce intermod with straight signal. Of course. This isn't some new natural law. Look at your examples - The most harmonious sound is playing a simple chord or single-note run with harmonious steps, Nonlinear processes on single notes are just nonlinear, there is no intermod as there is no other signal to intermodulate with. Simple chords produce the fewest number of intermod products, and delays on single note runs produce **exactly** the same result as simple chords. Big surprise - it's the same frequencies added together to be intermodulated. If you play a single-note run of notes into echo then distortion, any of those notes can be present together, forming an interval that collides in the distortion bottleneck, splattering quasi-random overtones all over, unlike placing echo after distortion. Yes...? And the point is? START NEW THREAD REPLY PREVIOUS LIST Read 34 times From: ken gilbert Date: 8/17/2000 8:17 PM Subject: Re: Power attenuator, not simple dummy load well, i can tell you that it WOULDN'T change parameters like voice coil inductance, or DCR, or the Qms, or the Xmax... essentially you would be decreasing the BL of the motor assembly--that's the product of the length of the voice coil in the magnetic gap (L) and the magnetic flux density (B). therefore, decreasing the motor strength would make Qes go up. ironically, there would be an INCREASE in efficiency due to the increase in Q (there would be, in effect, less losses), but this would be offset by the decrease in motor strength. i'm at work now, but when i get home i'll dig out my loudspeaker design cookbook and perhaps some old texts on field coil speakers. then i can comment more fully on the subject of impedance. kg START NEW THREAD REPLY PREVIOUS LIST Read 28 times From: Brian (bthome@wsunix.wsu.edu) Date: 8/17/2000 8:59 PM Subject: Re: Consensus? Steve; The BH curve is the magnetic hysteresis (sp?) envelope. I think B is the coercive magnetic field (ie in the primary windings), and H is the resultant magnetic field (ie in the core). This could be backwards. I can't really draw one for you here, but it has a pretty distinguishable shape. It has to do with the fact that magnetics do not follow the same path in both directions. They "remember" the magnetic field that they have been given as they are coerced the other way. So it looks like an envelope instead of a straight line. (how am I doing here?, It is kind of hard to understand w/o the diagram) OT saturation is where more B does not result in more H. This is magnetic saturation of the core. The bad part of this is that for a part of the AC waveform, no more field is coerced onto the tranny core, which means that the primary is at a dead short. **BAD** This leads to overheating in the transformer primary, and kills it. Saturation tends to add an ugly, harsh distortion to the signal. I think the early marshalls had this problem. like jimi hendrix on live at winterland, where he goes on talking about how many amplifiers he has left. I believe the OT's were saturating and the amps would just die on stage. (not sure about this, but I think I remember hearing this.) BT START NEW THREAD REPLY PREVIOUS LIST Read 37 times From: Michael Hoffman (hoff@amptone.com) Date: 8/17/2000 9:17 PM Subject: Re: Power attenuator, not simple dummy load A general tone principle, accepted by strong consensus, is that echo sounds more musical when placed after distortion. This placement reduces unmusical and uncontrollable intermodulation distortion. Some intermodulation distortion is desirable and musical, such as when playing chords into distortion. But intermodulation distortion which is produced by direct and delayed signals reaching a distortion stage is difficult to control and tends toward random, chaotic intervals. The dissonance of these random intervals is exacerbated when they are put through a distortion stage. Therefore, there is widespread agreement that for general purposes, echo should be placed after distortion. This agreement is reflected in online discussions and articles about effects placement and in product designs such as guitar preamp/processors. Echo before distortion is considered a special effect rather than the standard placement. Also, everyone is used to hearing natural venue echo after distortion, such as when a distorted amp is played in a large hall. So there is agreement that for a natural sound, echo goes after distortion. The fact that speaker response varies and there is no hard numbers for amp tone heuristics does not reduce the practical value of those heuristics. I would love to see more research on low-SPL speaker distortion. The industry is collectively moving toward greater interest in the contribution of guitar speakers toward amp tone. In the late 80s through mid 90s, the industry was foolish and wishful enough to hope for cranked-amp sound from preamp tubes in conventional preamp circuits. Then from the late 90s to now, such as the Rack era with dummy loads and cabinet simulation filters, people hoped to get cranked amp sound through power-tube saturation driving a resistive or reactive dummy load, such as the Palmer PDI-03, 05, and 09. We found though that the speaker emulators don't sound as good as speakers. They are convenient and controllable, but unconvincing. Now, speakers are starting to gain respect and more people are becoming interested in them. Now I emphasize the contribution of preamp distortion and power-tube saturation and speaker response. If you try to simulate any of these, with today's technologies, the simulation is not convincing -- that includes the "simulation" that occurs with heavy attenuation from a power attenuator. http://www.amptone.com START NEW THREAD REPLY PREVIOUS LIST Read 24 times From: dutch (pylot@aztec.asu.edu) Date: 8/17/2000 9:36 PM Subject: Re: Consensus? I can't really draw one for you here, but it has a pretty distinguishable shape. It has to do with the fact that magnetics do not follow the same path in both directions. They "remember" the magnetic field that they have been given as they are coerced the other way. So it looks like an envelope instead of a straight line. (how am I doing here?, It is kind of hard to understand w/o the diagram) It's a "dog leg" or "s-curve" shape, with the resting point being the center of the "wiggle" in the curve. ________ N / / V / / ^ V / / ^ / / -------------------+---+-------------- / / V ^ / / V ^ / / S ___/___/ Kinda like that, if memory serves me.... The magnetization curve follows one leg up and the other down when you switch states.... BTW, magnetic hysterisis is the reason that tape decks use amplitude-modulated RF to record audio rather on tape rather than directly recording it as AF.... C ya, Dutch START NEW THREAD REPLY PREVIOUS LIST Read 21 times From: Eric H (ehensel@abac.com) Date: 8/17/2000 9:43 PM Subject: Re: Power attenuator, not simple dummy load Doesn't Weber VST have something like this available already? -Eric START NEW THREAD REPLY PREVIOUS LIST Read 21 times From: Brian (bthome@wsunix.wsu.edu) Date: 8/17/2000 9:50 PM Subject: Re: Power attenuator, not simple dummy load the Emag series is a field coil speaker. I didn't see it in the price list though, maybe noone is buying them? I would like to try one someday, but the ol' budget won't allow that right now. BT START NEW THREAD REPLY PREVIOUS LIST Read 25 times From: SpeedRacer (Joe@ObsoleteElectronics.com) Date: 8/17/2000 10:05 PM Subject: Re: Consensus? What does BH mean?) it's basically the operating curve of the core material. Without getting into magnetics, look at it this way: You have an input signal going into a "function generator" and which acts on that signal to yield a resultant output signal. This f(x) can be a tube with a characteristic curve for example.. it's the "funhouse mirror" the input signal bounces off of to create the output. In an output tranny, the BH curve is that mirror since the signal is coupled magnetically.. from the primary into the core and the core to the secondary. The properties of the core determine the "translation" if you will, of the signal. An average curve slopes up, more or less linearly (and there are techniques for creating more linearity by stacking different ways) A factor which affects *where* on the curve you are operating is the flux density which is basically a function of how much signal current is around the core. So yes, trannies act differently as the signal increases. More flux takes you up the BH curve. Too much flux and you have problems.. Maybe you can define "saturation" so that we are all on the same page. Saturation in a tranny core is where the core collapses due to being overloaded with flux. The BH curve rises to a point, levels off a bit and then plummets if you hit it too hard. It makes a big mess, electrically speaking. I try to grasp concepts on an intuitive level so I think of OT saturation as being that non-linear distortion that you get when you pour more "juice" into the tranny than it can handle ..precisely my point though.. someone has arbitrarily decided where that point *is* without actually finding out. Every amp will be different based on freq band pass, OT design, B+, tubes used, etc. Some amps *may* do it, but to say that it's a part of great amp tone across the board I think is a bad assumption based on bad info. You're almost certainly distorting the output tubes, but that doesn't mean the OT is also overloaded. - It could be.. but again (beating that horse just one more time for practice!) it's a bad assumption IMHO without any factual basis. In many amps, tonality is altered greatly by a loss of functionality in the -fb loop. (and resulting mid boost generally) and of course the complex dance of the output tubes against the speaker.. Of course I was never there and the sound on the recordings I have may have more to do with *tape* saturation than OT saturation... ;) certainly.. running into the 'red' was SOP at many studios back when.. the Beatles insisted on it. Great compression on tape (you get a nice bit of HF rolloff with that too). No way to know what's the mic coloration, amp, tape & eq, mastering lab, etc. We know that output tubes and speakers respond differently when the amp is cranked up; is that also true of an OT like one of your OEI's? I'd be quite a liar if I said I knew all the specifics of what it does in every amp etc.. :) The reaction of the output section is wildly complicated and while I have observed certain behaviors which appear transformer dependent I can't say for sure that those are absolute qualities and inputs from the magnetic circuit. (eg: does the tranny contribute this tonal element or does it stimulate a reaction in surrounding components?) I can say that in a 1986/1987 style circuit with EL34's (or KT66), different trannies can have enourmous effects on tonal elements such as freq response, harmonics, dynamics, and whether or not the bass mushes out. The real trick is optimizing your design to emphasize the qualities in the amp circuit you want. They just need to work together well. It's not cut and dried thing.. more of a negotiation. A dance. ;-) little more garlic, little less cayenne... and again, Stephen is the chef. I do the dishes. ;) As far as education, I'm really the knife at the gun fight around here! Maybe RG or Randall can step in and really answer some Q's. Also, both of their web sites contain great tranny info in plain understandable Engish. START NEW THREAD REPLY PREVIOUS LIST Read 27 times From: SpeedRacer (Joe@ObsoleteElectronics.com) Date: 8/17/2000 10:18 PM Subject: Re: Power attenuator, not simple dummy load how about we just use speakers which are less efficient? i know two easy ways to do this: ..or just make the gap wider. :-) Or the magnet weaker (charge it less).. on the FC solution, WeberVST has been working on something along these lines for a while. The FC model has a lot to reccomend it IMHO. I personally can't wait until someone gets this technology going again. and what's all this bunk about IMD? shit man, the distorted guitar signal is ALL ABOUT IMD! AMEN ! ! ! ! ! ! Preach on brother Ken! (people - ever wonder why some amps have no note definition on close intervals (or even have nasty S&D tones?) and some amps you can hear the individual notes ringing out, close intervals don't generate dissonant tones and the whole tone just grooves? IMD, IMHO. It's all about it. Call me a True Believer. ) START NEW THREAD REPLY PREVIOUS LIST Read 24 times From: Carl Z (summit@theramp.net) Date: 8/17/2000 10:30 PM Subject: Re: Consensus? Boy, where do I start in this thread! I think that no real true consensus can ever be reached regarding tone. It's just too much based on personal taste. Some people think Carlos Santana's tone is great others think it sucks. A lot of people think Fender's distortion is where it's at and other's like the sound of CF's clipping. Nobody's right and nobody's wrong. It's just a different set of views. I think what we do have is a set of paradigms that we've developed over the years to define what the ultimate tone is and that's probably based on the Fender and Marshall sounds with their derivatives. So, deviations away from this baseline will sound lousy to most people. As for OPT's, I prefer to have a fairly transparent design and let the amp do most of the work. I believe a good transformer can contribute to a great tone, yet at the same time a good one can also rob the tone. It' all about the intent of the design and it's implementation. This area is definetly seat of the pants, gut instinct engineering. I ought to tak a picture of the pile of trannies I went through before I got mine right. :D As for the argument regarding trying to quantify everything I'm starting to come to the conclusion that it's really a pointless endeavor that will cause an incredible amount of frustration to the engineer that lives for hard fast numbers. Things such as musicallity and tone are too personal and subjective to say that this thing sounds better than that thing. I've said it before and I'll say it till I die, do enough engineering on the circuit to make sure you're not running outside of the design limits of the components and tweak till you're cross-eyed. Components do have a sound and that sound is neither good nor bad, just different. Basically what we've got is an entire system of preamp, power amp, transformers, speakers and enclosure that equally contributes to the overall sound. Lot's of different ideas as to how to skin the cat and if the end result sounds good then it's right. I'm starting to lose track of what I'm talking about and where I'm trying to go here so I'll shut up now. Carl START NEW THREAD REPLY PREVIOUS LIST Read 23 times From: Peter S (Tele52twang@aol.com) Date: 8/18/2000 12:02 AM Subject: Re: Power attenuator, not simple dummy load I love the way you guys lose me in these technical discussions. I can fix just about anything(probably anyone can with proper motivation). I have a good, well trained musical(being raised by classical musicians saw to that) ear so I can tune or voice just about anything. I can get a good sound out of even the worst junk guitar and amp combination, because I try not use the gear to get my sound, instead I think of an electric guitar as different type of acoustic guitar. I can build killer amps(to suit my taste anyway), but when things start getting really technical I get lost because I can't retain all of the technical information and it becomes time to crack the books again. SpeedRacer......don't kid yourself you know more than most people out there. There are a few things that I THINK I know to be true about "good" amp tone(what I think is good). I want an amp to have a good balance of preamp and power amp distortion. I want plenty of IMD....it's a BIG part of what I percieve to be great tone. I want a transformer that doesn't allow the bass to mush out when the power tubes are cookin'. I don't want my speakers to flub out. In my newest prototype amp, I AB'd a couple of great sounding OT's that have been with me a long time against an OEI 50watt OT. I don't know why the OEI OT sounds MUCH BETTER than these other two trannies, but it sure does and not just to my ears...Several very accomplished musicians were VERY IMPRESSED with the sound of the OT...even my wife, who after 15 years doesn't really pay much attention when I fire up a new amp went out of her way to come into the lab and comment on how beautiful it sounds. I think what this tranny does is allow the tubes to speak without getting in the way. Note definiton and harmonics....even when the amp is cranked wide open is astonishing. And yes......the amp sounds awesome, even when attentuated -16db with a THD Hotplate. Peter S START NEW THREAD REPLY PREVIOUS LIST Read 12 times From: R.G. (keen@geofex.com) Date: 8/18/2000 2:12 AM Subject: Michael, please don't put us through this. Michael, please do us all a favor and go back to the usenet news groups. I really do try to be civil, but your blathering psuedotechnobabble and unsubstantiated preaching about your version of having seen the One True Way sets me off more than I can put a damper on. I will question every unsubstantiated handwaving generality you put up here and take issue with every bit of nonsense you post. You know pretty well from our earlier interactions that I can back up every one of my assertions with numbers, references and hard facts, and you have yet to do so with any of your stuff. Please don't put this island of sanity in a blindly out of control network through this. Either be prepared to back up every assertion you make or quit preaching here. Your style and approach of reading all the posts on everything and collecting whatever supports your view has not changed over the years. Blindly yelling your opinion does not make it right. You know, the really, really bad part of your style of discourse is that it gives a bad name to the occasional thing that you get right. Go ahead and collect every usenet post or your responses to them that you like, and post them on your web site. That space is yours, pollute it any way you like. Please don't do that here. START NEW THREAD REPLY PREVIOUS LIST From: Steve A. (steve_ahola@yahoo.com) Date: 8/18/2000 3:25 AM Subject: Re: Consensus? Speed: Many thanks to you, Brian and Dutch for your explanations! (I better save your posts to disk so that I can study them later.) I see that "saturation" is probably not the right word for us to use! Sort of like talking about a preamp or power tube "distorting"... we all like distortion- right? [That's a joke- many guitarists like a clean sound!] But some forms of tube distortion are just plain ugly (I don't have the exact terms handy but I've read them here...) The good type of tube distortion would be like the good type of non-linearity (or whatever that might be!) exhibited in a great OT... As far as education, I'm really the knife at the gun fight around here! I've heard only good things about your trannies so I appreciate hearing what you have to say on the subject! --Thanks! Steve Ahola