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Author Topic: Eprad Starlet/Starscope crosstalk. Lindsay Morris Expert Film Handler Posts: 233 From: Darlington, WA, Australia Registered: Sep 2002 posted 02-09-2004 12:38 AM                     Anyone out there who has had anthing like this with an Eprad processor?? I have noticed of late that mine which I have only had going since the start of this new season (November) that when playing Non Sync I can hear very low level non sync in the box monitor when it is switched to the surround channel.(I have set mine up so I can monitor all chans L R C & S but normally run on Centre only). From the manuual I downloaded from this site it seems that there should be NO Non Sync in Surrounds. As well when running film there is a similar level of voice crosstalk but more of a "splattered" type of signal than is evident from the non sync crossfire. From an audience viewpoint the crosstalk in the surrounds is quite low almost to a point of being inaudible unless you are sitting under a surround and then you hear it. There may well be two problems here as I suspect that the slit lens might just be a wee bit off azimuth but when I run some variable density soundtrack the sound is very clean in L R & C but it also breaks through into the surrounds. If the azimuth was off by much, normally, variable density sounds absolutely crappy and the distortion is quite audible. I have my suspicions that the Format card may have a problem as this started to happen after a few VERY hot nights a week or two back. Am going to borrow another Format card and do a swap and see what happens with another card in there but I just wonder if anyone has experienced this sort of problem in the past with the Eprad processor. Lindsay  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-09-2004 02:12 AM                     I had the Eprad Starbelch at the old Lido Theater in Mount Vernon, but never had a non-sync problem as you describe. However, I do remember some of the surround problems. I wonder if there is a difference in exciter lumination across the slit? I could be 100% incorrect on this. Just a guess. If you have a snake track, that should show that problem up. Been years since I delt with that thing, but it seems that the level adjustment is very critical with that unit. Make sure the processor is set up to exacting specifications in the manual, including gain adjustments, etc. Hopefully, your problem will go away or reach a tolerable level. As with similar processors of the past, it has been my experience the surround drive and decoding was very sloppy. Other than that, I am out of guesses.  |  IP: Logged Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 02-09-2004 04:46 AM                         |  IP: Logged Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 02-09-2004 04:49 AM                        Hi Lindsay You must use dolby tone to set the preamp levels otherwise funny things do happen. to lazy dig out the circuit at the moment, but both preamps must be spot on in level, the trim pot between the level pots can be used to trim out dialoge in suround on the bottom of the format card there is a pot to adjust the surround attack and decay this should be set so that the surround content fades in and out gently. Where there is no surround content rear should be as quite as a mouse. Ive been playing with the eprads for around 25 years and still consider them to be a good low cost entry into stereo sound. Regards Stan Gunn.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-09-2004 08:50 AM                     If there is NobSync bleed into the surrounds I would tend to lean towards to things Bad grounding and a faulty format board As for surround dialogue the only accurte way is to use a scope and check the azimuth it is very criticle on the eprad phase detector  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-09-2004 10:15 PM                     Stan, I have to admit...they do sound very good if they are kept in exact alignment.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-09-2004 10:16 PM                     Double post. Sorry.  |  IP: Logged Lindsay Morris Expert Film Handler Posts: 233 From: Darlington, WA, Australia Registered: Sep 2002 posted 02-09-2004 10:51 PM                     Thanks for the responses, Paul, Gordon & Stan. Will have to recheck the levels again but first have to replace the Dolby tone loop as the JGS portables I used at Newman trashed it. One thing I did not mention was that I am using a ACL laser in place of the regular exciter and I do have a loop of Cyan tone but am unsure if that is actually Dolby level. This is from some stuff being handed out by Atlab at one of the Movie Conventions a year or so back. It does not look that different to the old Dolby tone but it is not labelled as being Dolby tone so not real sure what I have there. I wondered if the laser might be overdriving the solar cell unit so I will switch back to incandescant as well and see what I get there.(I have kept the original exciter system intact and can simply swap the exciter brackets over.. one with a normal exciter lamp and the other has the new ACL on it powered from its own little power pack).... Did not totally trust the ACL's and wanted some form of backup Playing with it again yesterday it does sound like levels are way too high as if I pad back the output from the Cassette deck the x fire almost vanishes and the gain control on the Eprad has to go up a few more notches to about midway (5/6) rather than where it has been at 2/3. Have not run any film as this point but the preamp cards are not in the Non Sync circuit so tonight I will run some test tone and some film on the spare projector spot but wind the gain pots well down and see what gives there. It all sounds like inter mod like I used to experience on cable carrier systems (coax and copper pair) when levels went all pear shaped and the system was overdriving a line repeater or two and channels would splatter all over the place. There was grounding issue on the backplane to the EPRAD where the earth lead had been cut away when a replacement power trannie was installed as the original big hefty Eprad one had expired so the power amps were heaved out. The way in which the earth got to the screens of the signal leads was via the power supply and once it went so did the earth and I had a few hum issues to start with. The EPRAD is mounted on the front wall nice and handy to the machine and a nice short cable to the soundhead and then 6 long screened cables go over to the side wall to feed the power amps and pickup the Non Sync from the amp rack. The lack of earth soon showed up with some fairly strong hum until I tracked that down and replaced the few inches of missing wire. The puzzling thing is that it has only really just started and was not doing this when we opened for the season back in November. Will keep hunting.. thanks for the inputs Lindsay  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 02-09-2004 11:59 PM                     You might want to check your building electrical system's and equipment rack grounding. Something sounds kinda funky.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-10-2004 09:42 AM                     1 the eprad preamp was designed for very high gain typically the excitor lamp (9v4amp) had to be set for 4 volts to not overload the preamp With the laser or reverse scans there is less range of turn down possible On the preamp card the cell input loading resistor was 4.7K reduce it to 1K or 600 ohms to reduce the overloading of the preamp Your HF response of the cell will also change so you will have to do a complete a chain alignment If you hae overloaded the format card the fets could have damaged and become leaky as they do the switching Also the nonsync should not be routed through the projector 2 input It may be necassary to put a input trim pot on the nonsynce source to pad it down the buss level on the starscope is 300mv for 50%mod just like most dolby stuff  |  IP: Logged Lindsay Morris Expert Film Handler Posts: 233 From: Darlington, WA, Australia Registered: Sep 2002 posted 10-27-2004 04:21 AM                     Been a while since I had a go at the Eprad and finally gave it away in March as the season was about to end. I did try another Format Board.. exactly the same problem with Non Sync bleed into the Surrounds. Over the break period and the cinema not in use I dragged the Eprad out and home onto the bench and with osc and CRO confirmed that I was getting Non Sync into the surround chan and was the same on all Format boards I tried. I got a clue when I was doing an overall gain test of my Format board to the others which I did with Master Vol control full on and then measured the input sensitivity of each and every channel (L,C,R,S) and recorded the output of each channel. In doing this I did each NR/EQ board on its own and then all 3 plugged in and so on. I noticed that the Surround output jumped by 6-8dB whenever the Right NR/EQ board was installed. But as soon as you brought the Master control back a notch ot two the level went back to normal and stayed there and the only way to cause the sudden increase again was to unplug that board and shove it in again.(Hot swap) Got the "old shorter than normal eyes" out and had a good look at the board in case there was some components pushed together which I had missed.. result = Nil BUT there was 2 X 0.1uf caps with a broken leg each. Replaced those and the Non Sync bleed stopped. Checked the other 2 NR/EQ boards and found another similar cap on the Centre chan also O/C one leg so fixed that as well. Now with NO Non Sync bleed I reckon I may have fixed the sort of splatter I was getting in the surrounds from film dialogue. So back into the cinema bio box she went and fired up the 9khz test loop with the CRO on the soundhead O/P to check phasing and found that the phase relationship was about 30 deg out but try as I might no matter what I did to the slit lens azimuth setting there was no way those two sine waves were ever going to coincide. Checked the lineup of the ACL laser unit in case I bumped that and it was smidge out so readjusted that to just bring the laser slightly further towards the operating side. So then had equal light on both tracks... at least on a bit of white card taped to the drum it was equal. Checked the phasing again.. still out by 30 deg and looking closely it seems as though the laser beam was striking the very top edge of the solar chip so as a last gasp effort I loosened the cell holding screws and moved it up slightly so the laser beam fell about 1/3 of the way down the chip. Back to the scope and the phase had shifted quite a bit and all that was needed to get it spot on was a very slight tweak of the azimuth and BINGO both traces conicided. Convinced that now I would have NO dialogue bleed into surrounds I ran the Cyan Dolby tone loop and set the Eprad levels exactly right with all 4 LEDs on and then ran some film. Still had dialogue getting in, not as much however but still there and more annoying to me as I could always hear it but never had any patrons complain about it. The system is, as I understand it, is that when L & R are perfectly in phase and the same levels the surrounds do not have any output. So based on that I reasoned that a Mono print when run in stereo mode should in theory have NO dialogue in the surrounds. So grabbed a nice little short I have on trains with lotsa noises and dialogue etc and plenty of good music and set that going. There was some bleed into the surrounds BUT by ever so slightly adjusting the preamp gain pot on either L or R chan I could NULL that bleed down to NOTHING at all. Reckoned I had it nailed to the floor now so then ran the test reel I have and there was bits and pieces of various dialogue getting thru and maybe... just maybe that is the way is was mixed. But watching the screen action and listening very carefully I just could not work out whether or not it was just mixed like that. Am I correct in assuming that a Mono track played in stereo mode will give NO signal in the surrounds if the thing is set up correctly cos if so that is how I am going to bloody leave it!! Have noticed in another post or two comments re Cyan tracks and relative merits of Jaxlights, ACL laser units etc. What I have found with all my mucking about is I have not used a Jaxlight but opted for an ACL laser as it seemed to offer the best virtual "drop in" ease of installation (take out the old exciter and central base connection, slide the ACL unit down into where the exciter base used to be with the DC leads for the laser coming out of the old lampholder base and lock it in place as you would do with a tungsten lamp). Then adjust the laser height and azimuth by slackening the small locking screw in the tube that goes into the lampholder and once set carefully locking that into place. Peter Naples noted that they take a bit of setting up and he is spot on here but once set in place are quite stable. When running the Cyan loop Dolby levels on the Eprad LED display are almost exactly the same as if I ran the B&W Dolby test loop. There is only a slight difference which equates to just on one FULL turn of the preamp 40 turn trim pots UP if running B&W after setting it for Cyan loop.... Virtually NO Diffrence in level running the ACL laser with either Cyan or B&W test loops. The actual output levels going to the power amps remain the same as the NR boards are doing their job and the Master Vol control stays at the same point. So in theory when I run a Cyan print there will be no perceivable difference between that or Hi magenta or B&W... but I have not been able to get hold of a HiMag Dolby test loop.. doubt whether one actually exists. So does a Mono print give you NO surround signal??? and my tests have shown NO virtual difference between a Cyan loop and a B&W loop when using the ACL Laser unit. Go back to the old tungsten lamp with Cyan and I really have to wind up the proj preamps to achieve the correct Dolby level on the Format board (all 4 LEDs lit). There is certainly not enough grunt left in the Master Vol control to lift the Cyan level up if using a tungsten lamp. Normally I run the Eprad on 5 and probably could raise the power amp faders to compensate but the hum and noise certainly comes up. But with redlight and Cyan the tone is very clean. So for those hesitating on going to a red reader I would not wait around too much longer as I reckon you will be in big piles of poo if you cop a Cyan print out of the blue (pun intended)as most systems will probably not be able to compensate for the certainly lower level. As a "techie" type Indie I did not want the problem of having to stuff about madly trying to source a red light unit after I had experienced a disaster with a Cyan print. I wanted to be ready so that we had a smooth transistion and the ACL laser may have cost me $900(Aus) but I am now confident that Cyan will not give me any grief whatsoever. It did hurt paying out that $900 but it is now done and as an operating expense that can be written off against the business tax... same as a new Xenon. Just gotta do it to survive. As well the BXR 10V 5amp exciters are almost impossible to source here in OZ. I do not think that other countries are pointing the finger at America as being the villains in this switch to Cyan. It really has been the lack of Cyan test loops so that one could evaluate just what was going to happen and that would be where I think the industry has fallen down as to my knowledge there is still NOT supplies of the combined Dolby tone and Pink Noise available in Cyan. It seems totally logical to me that if "the industry moguls" wanted a switch to a new system they should have had all this test film out there and readily available from day ONE not 3 or 4 years down the track as it seems to be in OZ and I suspect in many other countries as well. In that way various industry folk could try and see EXACTLY for themselves what they were in for IF they did not switch to red light sources when Cyan became widespread. The best thing ATLAB did in Oz as to hand out samples of the Cyan track at the Movie Convention 2 years ago and that got a few of us really going.. others are still fence sitting hoping it is all a "furphy" and will go away. It won't Lindsay  |  IP: Logged

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