lalochezia

it’s been a busy month! and lots of preparations for the next year… and christmas is imminent. i love christmas. the lights, the tree, the music and the food. my kid loves it too and we (her and i) still know jul tomten (the xmas elf – santa) and his kin are a part of it. christmas has just a mild connection to christian history for me and the pagan solstice and or magical stuff of that is what i enjoy most. mainly, it’s the time spent inside (in the dark) with family and friends, and the small lights and spirits holding back the end, of everything.

it doesn’t have to be big to make a critical difference at the end…

Phillips AD 3800 M

today will be a medley of things i am thinking about… more spread out than usual.

the image above is of an interesting driver… it’s an 800 ohm “full range” driver for table radios. Phillips developed this, and others like it, to be used with a transformerless amplifier made with a “totem pole” output stage that used EL-84 or EL-86 minature power pentodes. this driver is more closely related to a headphone element than any standard loudspeaker. the voice coil’s DCR is about 600 ohms and the maximum dissipation is 4 watts, which would entail 56 V RMS and 70 mA RMS across an 800 ohm load. anything after is destruction. this one has a small slug of alnico magnet to form the motor.

i have no idea yet what the maximum usable sound pressure is, or what kind of bandwidth one can get out of it… it was used in a table radio! but just the possibility of driving it directly with tubes is so appealing all by itself, it  doesn’t really matter. i simply need to find out! it might be an interesting midrange driver in a widerange horn system, too?

i was chatting with Tim (de Paravicini), as he has some experience with this family of drivers, and he pointed me to the amplifier design most often used together with them. see below: from Frank’s Tube pages.

“SRPP” pentode power stage

i am lead to wonder beyond this driver, and have often wanted to try sixteen 3″ or 4″ 8 ohm, or 16 ohm, drivers in series – it could even be 2″ sound bar type drivers – this is a simple way to try it. 128 ohms would require more current than 800 ohms, but that can simply mean swapping out the EL-86s for a pair of EL-509s or 6KG6s… maybe a bit more B+, or a composite hybrid, but that would be all!

but that is a clever little bit of Phillips kit right there! instead of re-inventing the wheel, it’s worth working a bit with this arrangement, and see if something a bit better can come out of it? i like the single input “SRPP” totem pole idea… of course it can be lower distortion and more efficient if both the lower and upper are driven separately… in this case, as soon as the lower tube clips, all is lost. but for a modest effort, there is much to recommend this circuit. it’s wide bandwidth, open loop and a simple distortion spectrum. a rule of thumb, for me, is if it sounds decent without any optimization, it will just get better with some attention to detail.

i can think of two obvious methods to bring it into a bit more polish: one is to add a shitload of gain in front and use negative feedback to clean it up… and the other is a sneaky hybrid, which takes advantage of some complimentary feature from the solid state universe to accomplish the same thing. i love this kind of exercise.

first up, the amp… a conventional two stage feedback circuit is the basic idea. i love the russian 6P41S, or euro EL-500! what a great overlooked little gem. vertical amplifier tubes are quite often hifi. this would be an instant upgrade in performance as it has considerable peak current for a smallish tube. of course the upper tube will need it’s own heater (or use UL-84s or other “line voltage” heater tubes from the TV tube world), but many toroidal power trans are made these days with dual secondary windings… it’s a simple thing to take care of. both the L and R channels can be supplied at the same time. the addition of one transconductance amplifier stage (with a 6E6P or similar VHF pentode) along with the power tetrode SRPP output stage and nfb back to the cathode and it’s a done deal. two stages is simple to compensate, and there is no inductive component to fight with other than the load. one possibility might be to include C3 in the feedback loop?

C3 can be sized for “full range” operation, or for midrange up… 4.7uF or 8uF is typical for the range. the mains supply is so easy in this case! a 230 volt secondary will provide exactly the right range, and it’s easy to adjust. a one to one power trans will work perfectly… and a simulation of the way i would do it yields a THD with 2 volts pp input (70 V pp output) of 0.05 % and yes the push pull action reduces even order harmonics…you can see the typical push pull distortion spectrum in the fft sweep below. that will do 85mA peak and 50 Volts RMS output. just under the 4 watt threshold that will destroy the driver.

the 6E6P has it’s high gain buffered with DC feedback returned to the screen for stability. feedback is returned from the output to the cathode. simple. one improvement might be to buffer the screen supply? but it adds more parts…

two stage SRPP tetrode OTL amp (with coupling cap)
2V peak to peak in, 140V pp out… across 800 ohms

this is a good start! i would love to hear from anyone with experience using simple otl amps with medium Z loads. 100 to 1000 ohm loads. except for headphone amps, there aren’t too many loudspeakers for this sort of thing.

forensic satire

of course if i was to dream out loud about the system of my dreams, it would involve a wideband loudspeaker of high efficiency, augmented with some kind of subwoofer, to keep the first two octaves out of the middle… i have come no closer than a four way, at the level of performance i want. i have spent some quality time with the best “wide range” horns of the movie palace epoch, and i do love them. especially the Western Electric 12-A. but they are far from perfect. still WAY better than most, all the same.

so, there will be a horn involved in order to get the efficiency, but does it have to be a long one? short horns are much much easier to get some bandwidth out of… mass cut-off is hard limit. you need a few grams at most, of moving mass, to get any kind of high frequencies out of a long horn. like a WE-555… but amplitude ripple and “horn sound” are a constant fight. a short wideband horn is something to study closer.

i’ve been looking at alternative drive systems as well as experimenting with much shorter horns. ribbon drivers save weight by eliminating the voice coil. the diaphragm is the current carrying element… so there is a built in efficiency with ribbon drivers. but the impedance, while generally resistive, is in the milliOhm range. this implies a transformer… as directly driving milliohms is a brutal job. i have no problems with a coupling transformer! as long as it gets me where i want to go.

so these are my next two threads of research: driving very short horns with ribbons (and maybe planar magnetic elements?), and construction of large ribbon drivers with extremely powerful motors.

electrodynamic ribbon motor
testing
90° conical horn for 32″ of ribbon driver.
planar magnetic drivers for testing

so this will be an ongoing set of projects for the winter… it will be interesting to see where they go.

machine gun

PTSD – post traumatic stress disorder…

yeah… i have that. had it since i was a kid. i managed it with booze and drugs, but that started and then stopped working fairly young. believe me, if that shit doesn’t stop it, nothing will. not blinky lights, or chemical lobotomy… not electroshock!  i have involuntarily tried. over a long period of many years, i have gradually learned to simply live with it, and it is always a part of me, more or less. i am pretty sure that i will go to my grave over-sensitive to the world in terms of fear of the next blow, and what i am prepared to do when it comes.

i will see that beating take place, while no one is looking. watch the quiet theft. i seem to have hate radar, and feel your resentment at the same time, or before you do… i will wake up when the fire truck or the meat wagon turns onto my street. i know the caliber of the gun that’s fired. i will know where the dope is and who has it and what it is without getting close to it, seeing it or smelling it. who has the weapons and who is the mark. and identify with the broken ones… at least the irretrievably broken ones: i am one too. they are my people, along with the wild dogs and the crows.

the best thing about PTSD is that one usually does well in crisis. helpful even. i am still alive and shouldn’t be! big or small, i’m ready now and waste no time on outrage. and if you’re with me, and you move quick, you probably survive too. that’s good, right? but the flipside is a very hard time with the normal day to day. and whatever that is, i don’t believe it. well it is, frankly, unbelievable! normal takes a lot more work, than violent chaos ever will. and that is normal…

Charles Bukowski famously noted that one of the most obvious things about stupidity is confidence… intelligence makes doubt neurotically obvious. that’s all the justification i need. in any case, chaos does makes things simple for someone with PTSD. no time for anxiety! that always comes later. guaranteed.

why am i telling the world this? seems risky, and who actually gives a fuck?

there is a speed that is crucial to living with PTSD – full tilt. pedal to the metal… poppers! Bolivian marching powder. speed that shit up, captain! nitro methane mixed with gasoline! we all need a turbo sooner or fucking later. today! 5 steps ahead of the shot to the head. working out the odds, plan X and Y (a, b and c were so fucking yesterday), and spooling the film back and forwards to find that mistake you ARE going to make. grind those teeth…. speed mixed with a good dose of ridiculous superstition, and general negativity! yeah, it can be exhausting, but it isn’t going to stop, ever. so just get on with it. and swear like a barmaid!

god fucking dammit. fuck that shit!!! and fuck you while you’re at it. fuck!

wow. so much better already! what the fuck! what just happened there?

the french philosopher, and critical theorist, Paul Virillio, made a remarkable insight into the fundamental nature of technology. the “integral accident”. in technological terms: the invention of the ship also invented the shipwreck. the train: derailment. the car: the car crash. whatever you think of Virillio, and i like his thinking a LOT, in fact a great deal of thought goes into the prevention of the integral accident these days… modeling, simulations and pressure groups. millions of dollars of engineering budget… insurance analysis… an entire ecology of fear and worry. and also a military industrial complex and the insane rationality for it’s existence! but anyone and everyone with PTSD know the words to that song! we see that movie over and over again, every time we close our eyes. the libretto, committed to memory. that music is our soundtrack. you guys are behind schedule.

all the simulation and worry in the world CANNOT remove the possibility of car crash from the existence of car. the one is an unremovable part of the other. as my mother always said, “stop worrying so much about what you can’t do anything about, and start doing something about the shit you can!” (i really hate it when she says that…). well, sometimes all that can be done is swear like a NYC sewer! and laugh. well, airbags… they never prevented an accident ever.

laughter and swearing are such a powerful combination. i have never experienced anything that works better for my crazy mind than these two. it definitely interrupts that mad oracle of violence and injury that constantly plays in the background. and best of all, the relief is so perfect that i don’t really give a fuck what you think about it. no it doesn’t “last”, but neither does anything else. yeah i know it puts some people off, and it also means i have limits on the company i keep… and “reduced employment possibilities”. but i’m cool with that. i respect my crazy. it’s not easy but all i have.

in no way do i want to imply that swearing and laughing in any way change the implications of violence or catastrophe! nothing changes. people do violence to one another, and accident or natural disaster happen. accident for no other reason than that it does. death and suffering are mysterious components of living. and when it happens to you or your loved ones, which it can or will, it’s a truth you will spend the rest of your days with. i know that for a fact.

but laughing at the horror is still power. yes, a soft power and not a particularly linear sort of force, by any measure. but still, a power. when it is least expected or considered, it often does it’s best work. i know that too.

merry fucking christmas!