On Friday, February 17, 2012 07:07:39 PM Fons Adriaensen did opine: But at a 60 ohm impedance, that capacitance is considerable. I could put 20 volts P-P into a cable headed for our news dept, at say 15 kilohertz, and 200' away, I could only see 6 or 7 volts. And often sensitive to both crossover distortions and slew rate limits, one of the reasons I built a DA card years ago, 2 channel in 4 out each channel, and used TLO84's for all of it. I was replacing a rig that had heat sinked TO-5 bugs in it that had both crossover and slew rate limits much worse than the near gain of 1 op amps had at half the output P-P. Those were also a home brewed copy of something one of my employees made before I came in the door in '84, and in my attempts to build a working television station, that problem finally filtered itself to the top of the must do list about a year later. The biggest problem with the TLO84's was that those long cable runs made excellent antennas for EMP's, which caused then to self destruct in bags full every time the STL tower, a 255' pyrod self supported tower about 20 feet outside the back door, got tapped by a wandering lightning strike, so I had to keep TLO84's around in 3 stick quantities, but TLO84's are dirt cheap. The lightning strike was a many times annually event when you have 255' of steel sticking up. Likewise Fons, have a good evening. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> lisp, v.: To call a spade a thpade.

fons, gene, thanks for your insights, particularly about the problems of AC rms meters at audio frequencies - i was totally ignorant of this, and i'd have shot myself in the foot with this eventually. fons, after i read your remark i asked around, and yes, the ff800 does indeed use servo-driven outputs, so the voltage difference is intentional and no cause for concern. i'll definitely investigate the level differences between channels, but as you said, i'd better do that with a sound card rather than a meter. gene, would love to follow your scope advice (particularly for the beneficial effects on gonads), and i'm looking out for one, but i'm not really prepared to pay much. in any case, it's way sexier than one of those usb sampling gadgets sold for a scope these days... maybe i'll find a nice, simple one in a dumpster somewhere. nice to get you two guys into another discussion about signal transmission - very instructive! best, jörn btw: yes, the folkwang address seems to have expired at last. the la* lists were the last things i used it for, and i have now resubscribed from my own mail domain. so please ditch that old one from your address books if you want to get in touch off-list. -- Jörn Nettingsmeier Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487 Meister für Veranstaltungstechnik (Bühne/Studio) Tonmeister (VDT) http://stackingdwarves.net

On Sat, 2012-02-18 at 13:47 +0100, Jörn Nettingsmeier wrote: Get a Hameg with "Komponententester" http://www.dict.cc/?s=Komponententest

On Saturday, February 18, 2012 07:02:22 AM Fons Adriaensen did opine: Something I didn't consider in my first generation design since I was still learning myself, which although it had an output impedance at the TLO84 pin of under an ohm, then used 300 ohm per leg build outs. The next generation card, the main design change was to change that 300 ohm to 30 ohms. This then worked much better out in the newsroom, but was even more susceptible to the emp spikes the longer runs picked up. Since the card had to fit the cage, it never did grow the schotkey power diodes to the supply rails that would have absorbed those spikes, no room left on the the card for diodes that at the time (1984-85) were about 1/2" long & 1/4" in diameter. It would have taken 12 of them to protect the inputs as well as the outputs. These cards all had their own rail regulators (78-7915's) for +-15 volts as the cage supply was about 22 volts +-, filtered some but not regulated, good for about 10 amps a rail. 22 cards with 44 pin edge connectors in one 3 space high rack, it did have noticeable but tolerable heat output. The only place with enough farads available to dump the emp was the main rails, and a quick test of that idea using a bench supply showed that wasn't a cure as the output stage of the TLO84 was still destroyed when the output was pulled above or below the cards internal +-15 volts by about 2 volts, long before the schotkeys to the +-22 volt rail would turn on. Since they were very transparent & distortion measurements were difficult because it was well under .01% at 28v p-p output, and even with the emp problems, were 10x as dependable as another rack of Ramco DA's we paid 5 grand for before I came in the door, I made sure we had sticks of the chips, and bags of the capacitors on hand in case mother nature heard somebody call that stuff butter, and ran with it. At least the TLO84's were socketed, those quad 741's (4432's?) in the Ramco weren't. Those eventually were pulled out, they weren't as good sounding by a long ways. Those 4432's were so slew rated they weren't really any good above about a volt p-p out. Pure crap to my ears. With that slew rate clipping, the intermod turned your teeth on edge worse that fingernails on a slate blackboard. Downright fugly was how I described it at the time. Sounds like. In those cases I always figured the cable ohmage if otherwise impedance matched at the src, was a std factor of the load currents flowing, and with a nominally 10k load on the far end, a generally ignorable. Effectively un-terminated, it of course dependent on the src terms to absorb any 'vswr'. In any event, by then I had managed to obtain a function generator, and a 10 to 60 khz sweep actually looked pretty good at the far end, easily within about 5% of flat on the scope. Technically incorrect?, yes. Was better by magnitudes than what was there when I walked in the door?, hell yes. Which also had the effect of making a long 15 kilohertz rated line into one of the best 'brick wall' filters you've ever measured. Maybe a db down at 15 khz when they were done, a twenty mile circuit was down 90 db by 17 khz. And they never did get the S/SN below 48 db, so we eventually bought a subcarrier radio, which made 75db rather nicely. ;-) Yep, sure is today Fons, even for a 10 foot run between racks in our new digital control room. So now the problem is levels, digital doesn't come with a knob. The std, if there even is one, is ignored, which explains the commercials that are 20db louder than the program, nobody cares and we catch hell from the listeners. I don't believe that will be solved until the commish puts some real teeth into it, traces the violating material back to the production facility & then figures out a way to make them legally responsible so they can fine their ass & make it stick in court. Sure, we can re-encode if we have to, but there goes the lip sync unless we bucket brigade the video too. That also takes truly competent manpower most stations don't have near enough of. In many cases, it isn't even available to hire! This is one business where we often have to grow our own technical people. Then, hanging onto them becomes the next problem because its an industry wide problem and the head hunter business is alive and well. We are often caught in the "damned if we do, and damned if we don't" world, so we wind up playing it by ear, letting the ratings tell us how we are doing. IMO, that isn't always optimum. When I first started back in the '60's, where I worked often helped the 'other guy' stay on the air, based on the premise that if he went down and somebody else got that license, they might come in & spend some real money on physical plant and wipe us out of the market. A case of preserving the status quo was good business sense for us. Obviously to protect since this list covers the planet, and its largely historical anyway, that small market won't be named. :) Cheers Fons, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> You mean you didn't *know* she was off making lots of little phone companies?

On Sunday, February 19, 2012 10:17:31 PM Fons Adriaensen did opine: Actually, driving a 600 ohm load on the bench, the heat rise of the chip doing the output I was monitoring, was only barely detectable. Failures, when there were failures, were usually in tensies or so, in the wake of a passing thunderstorm that nailed the STL tower. Not in normal automation programming, its pretty much a hard digital switch. If we start fooling with it, lip sync problems rear up and byte us on the butt. The board with actual gain controls is only used during live newscasts, and in pre-production making of the files used in those newscasts (used to be tapes), there the gain is controlled usually by the reporter as he does the editing to get 5 minutes worth of the file from the camera's hard drive, down into a minute thirty or so package that tells the story as compactly as possible without leaving out any gory details unless they really are gory and next of kin hasn't been notified yet. Really overpowering to the point of digital clipping or even phase reversals, generally get flagged by the on duty switcher, and John will yell at the src the next day to make them redo the production with a normal audio level. We do probably 55% of the production in this market, the other guys do about 25-30%, leaving the national agencies doing the remaining stuff, and they are the worst offenders by far. It seems to me, that a scan of the file done ahead of time, or if its really fresh, the first time it airs, and using that average data to develop an average volume level, then run the audio thru a D/A which then feeds a multiplying A/D running at the same clock speed, with the multiplier being that whole program average loudness, should be able to do that fast enough that lip sync isn't a problem. Once determined, that digital gain value should somehow be tied to that file in such a way that it is applied before the first frame of video on subsequent playbacks. The IT & production managers are actively looking for something that would help, but so far, their searches have only managed to come up with stuff similar to the old analog frame synchronizers, at 5 digit and up prices. The system integration to make it work is, as I see it, a bigger problem than the hardware, which it seems to me could be thrown together for under a 200 bill a channel, and all four of the channels we would need could possibly be in one box. Or we could go 8 channels & be playing one file that needs massaged thru a 'preview' circuit to derive the gain that spot/program needs the next time it plays for real. Hardware, to me, seems relatively simple, but of course the devil that will raid the fridge and eat your lunch, is in the details. Even a digital gain control developing the A/D multiplier voltage would seem to me, to be something we ought to be able to buy for maybe $150/channel/box. That would give the operators a real time, darned near pure digital gain control. If somebody were to take a stab at this, I suspect, given enough noise made in our comm channels & industry rags, you might need a ladder to reach the side of the hog, for a while at least. We aren't a walmart sized market of course. The commission is about to take action if they haven't already, and this may force the issue, opening up a limited market, but one that could keep 10-15 people on a production line, busy for a few months. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> "From there to here, from here to there, funny things are everywhere." -- Dr. Seuss

On Fri, 2012-02-17 at 22:55 +0000, Fons Adriaensen wrote: Still very expensive. I only own an elCheapo multimeter, just good for coarse measurements. If I have trouble at home where something better is needed, I ask a friend who owns a measuring bridge and several oscilloscopes etc., if I do a job and something is "really" broken, in other words more than just a controlable voltage stabilizer needs to be calibrated, I ask to give it to a workshop. IMO it's not only expensive to own all the gear that sometimes is needed, it also takes too much space. If equipment is seldom used, it tends to fail at the moment it's needed. IMO an averaged audio engineer who does mixing, wiring and repairs without a big fuss, doesn't need such gear. - Ralf OT: I would like to own a Hameg oscilloscope with the so called "Komponententester" (translated perhaps something like "semiconductor tester"). I wonder if there's any other company offering this.