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Author Topic: Distorzion in analog sound Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 04-01-2004 04:44 AM                     Ok, i've been constructing a pile of preamplifer for optical sound but latest was good, but i got a lot distorzion is sound expecialy in high sound levels on film, can cause of this could be a distance of exciter lamp or lamp optics from film??, i don't use stereo solar cells becose they are very very much expensive (if somebody have a one or pair after instalation of all reverse scan readers and don't know what to do with, send it to me), i use a two photodiode (one for each chanel) they are siemens BPW 34, but i don't think that couse of distorzion is they becose in other cinemas they sound good, and this is not firs amplifier that not work fine, projector is Ernemann IV here's link for datasheet of photodiod http://www.udt.com/Datasheets/Products/BPW-34.pdf if you have soem ideas will be cool to sold this problem  |  IP: Logged Mike Blakesley Film God Posts: 12767 From: Forsyth, Montana Registered: Jun 99 posted 04-01-2004 12:17 PM                        Morin I can't answer your question but you need to be more descriptive in your thread titles. Using just one word is referred to as a "teaser" and makes it hard to search the older archives later for specific information. There is more on this in the F.A.Q. One thing you don't want to do is get the moderators upset at you, or they might send Phil Hill to your house. You don't want that to happen. (P.S. I'm kidding with this paragraph....I hope.)  |  IP: Logged Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 04-02-2004 03:29 AM                     Mike thanks for advise!!!!!!!!!  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 04-02-2004 04:40 AM                  "Oh My"... Dear Diary: I have been "ordered" to Montana this next week... I will be in Texas in May. >>> Phil  |  IP: Logged Chris Hipp Phenomenal Film Handler Posts: 1462 From: Mesquite, Tx (east of Dallas) Registered: Jul 2003 posted 04-02-2004 10:22 PM                     Yeah, Phil has to bust Mr Miller for not saying 2004 in the Walking Tall thread. Even though the tail of the print CLEARLY says 2003.  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 04-02-2004 10:30 PM                        The head says "14 13 12 11 10 9 8 7 6 5 4", would you like that included too? Or how about we just include the release year. Marin -- you could be getting distortion from all of the things you mention. Have you ensured that your pre-amp (which it sounds like you built yourself) isn't faulty and can handle the input level?  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 04-03-2004 06:04 AM                  ...and then I've been "ordered" to Hamilton Ontario Canada to take care of "business." >>> Phil  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-03-2004 09:13 PM                     The distortion is most likely caused by the impedance of the input stage of your preamp  |  IP: Logged Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 04-04-2004 04:18 AM                     Gordon, yes the impedance may be coursing distorzion, but what is impedance of input for cell, maybe i can balance this with input transformer or similar, because i use photo diodes don't you think i could bias them with couple of volts, would that help??  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-04-2004 10:06 AM                     It looks like it is a current not a voltage device so possibly a high impedance transformer in serries with the bias supply never used one but I beleive the old ernamann preamp was 4.7K for a photodiode some how that sticks in memory from the distant past (no snide comments please)  |  IP: Logged Gilbert Travin Expert Film Handler Posts: 101 From: Villeurbanne / France Registered: Jan 2004 posted 04-06-2004 04:44 AM                        Hi Marin ! Sources of sound distorsion may be : 1 - the photodiodes are not biased correctly : they must be "reverse" mounted with a DC biasing ; 2 - gain of preamp is too much important ; you obtain saturation at great levels ; 3 - impedances don't match ... good luck !  |  IP: Logged Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 04-06-2004 08:53 AM                     >>>> 1 - the photodiodes are not biased correctly : they must be "reverse" mounted with a DC biasing ; 2 - gain of preamp is too much important ; you obtain saturation at great levels ; 3 - impedances don't match ... >>> 1. i try to reverse polarized photodiodes, but i only get higher signal, but distorzion stay same, how can i biased photodiodes well, anyone have schematic, or advice for this? 2.The gain is ok, i think, i tryed preamp with microphone and it work perfectly. 3.for impendace i don't know, what should be impendance??, Also soud is quite good at low levels is only distorzin at higher levels. Can the reason be a light source from exciter lamp??  |  IP: Logged Gilbert Travin Expert Film Handler Posts: 101 From: Villeurbanne / France Registered: Jan 2004 posted 04-07-2004 04:23 AM                        Hi Marin ! The good biasing of photodiode is explainated in ... the data sheet ! You need a resistor in serial with the photodiode for biasing. The value of the resistor is given (with the DC value of biasing) in the datasheet ! The photodiode signal must be connected to the preamp thru a capacitor, of course. The impedance is the "resistance" of a reactive-component (capacitor or inductor) when used with AC current. Also, there is a difference of phasis between current and voltage. With DC current the impedance of capacitor is infinity and the impedance of inductor is zero. For a resistor, impedance = resistance. To find a solution at your problem, you must use an oscilloscope to verify where the distorsion appears ... Good luck !  |  IP: Logged Edward Jurich Master Film Handler Posts: 305 From: Las Vegas USA Registered: Jul 2003 posted 04-08-2004 08:12 AM                     You might try adjusting the bias on the diode but if it's distorting only on high levels your pre-amp input may be overdriven. A simple fix may be to just lower the light source (exciter lamp) some, this will reduce the audio level and operate below whatever is being saturated.  |  IP: Logged Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 04-08-2004 08:28 AM                     No, the input is not overdriven because even if I lower gain of pre amp the sound is distorzed, even if i lower the exciter lamp light, but now after set the slit lenses, the sound is ok, and distorzion is small, but even I sold problem i wonder does color of light effect to quality of sound (because all reverse and led readers had red light??), I think the reasons of my problem was in projector reader, but even I think the sound my bee more better, but fact is my projector i Ernemann IV and is very old like slit lenses optic what is in them.  |  IP: Logged

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