quote: Marin Zorica

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In my sound setups at local cinemas i don't use a stereo solar cells for reading analog stereo sound, but i use photo diode (small BPW 34 photo diode 2 in pair each for each channel!!!) and i get very low crostalk between channels (when i run Cat.No.97 L-R test film i get oscilogram like in manuals (this i telling because some people keep saying i can't get ok L-R cross talk with this method of reading optical stereo sound!!!)), but i wonder what is a frequencies response for optical readers with exciter lamp (here we use 6V 5A exciter lamps)????, here some projectors don't have good slit lenses but till now i menage that replacing from projector to projector (where i can get this lenses, and what is coast??), and what is proper width and thickness of slit???, and what power of light is needed for sound reproduction without distorzion, does light intensity effect on distorzion because i have distorzion in higher amplitudes, also does sound reproduction with and without Dolby SR, or Dolby A sound same, what is difference, what would be results if i put any cat.no.22 (A type NR) between pre amp and power amp in my audio chain.

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And this is mine L-R crostalak:


What do You think, ideas??
 

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Posted by Gordon McLeod (Member # 33) on 01-30-2005, 04:59 PM:
 
First off slit height determins your hi freq cutoff it is a mechanical lowpass filter
.4mil slit was the standard for years
A photodiode may have impedance matching issues with some preamps and that can be a cause of distortion as can the issue of frequency response of the device itself
 

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Posted by Michael Schaffer (Member # 1204) on 01-30-2005, 05:48 PM:
 
Good readers, a calm hand and a little patience often get you a flat response up to 10-12kHz and a nearly flat response up to 16kHz with a little slit loss EQ. You can do the math when you calculate how long each wave in any given frequency is when you take the length of film passing through the projector every second and divide it by the frequency you wish to still be able to read. A slit bigger than the wave will miss it.
 

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Posted by Marin Zorica (Member # 1716) on 01-31-2005, 04:43 PM:
 
Yes, slit high is very critical factor in high frequncy cut-off.
What is a input impendance of solar cel input on cinema processor???
Maybe i cando impendance matching with transformer?
What ybout that Ernemann Laser Audio red lkaser with optics???
I saw it, and are they ok, ther are too expensive but maybe one thay i get money for them!
Ok, does also distance of solar cell from film, and solar cell angle depends on high frequency cut-of??
And, what about oscilogram of L-R crosstalk in my post upper, is it ok?

Thanks!
 

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Posted by Steve Guttag (Member # 268) on 01-31-2005, 08:22 PM:
 
A good solar cell preamp will present nearly a short circuit to the solar cell for best frequency response. Many do not have that low but still quite low.

Steve
 

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Posted by Michael Schaffer (Member # 1204) on 02-01-2005, 03:06 AM:
 
What do you mean by "present to"? I thought the preamp simply amplifiers the signal voltage generated by the solar cell. Please explain!
 

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Posted by Marin Zorica (Member # 1716) on 02-01-2005, 05:36 AM:
 
Yes i'm wondered too.
How you mean short circuti, s it maybee because to get higher curent thru cell or what??
OK, in basic what would be a input impendance of good cell preamp?
Anothe rthing i'm wondered what are rise and fall time of quality solar cell?
And also an output voltage'
 

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Posted by Gordon McLeod (Member # 33) on 02-01-2005, 09:27 AM:
 
A solar cell is a current source When it is driven into a high impedance source it becomes a voltage source and the distortion goes up
The best preamps always treated the solar cell as a current source and had a minimal input impedance
A photodiode is a different animal and I don't have any info on it
 

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Posted by Marin Zorica (Member # 1716) on 02-01-2005, 12:25 PM:
 
On preamps i have here, it's got 15V voltage on solar cell input conector, it's mean i got unbalanced input for cell, and when i measure voltage on ground and hot pin on input conector i got 15V!!!!!!
Preamp is factory designed and it's for solar cells, does enbody know's for what that voltage is used for????
 

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Posted by Gordon McLeod (Member # 33) on 02-01-2005, 01:26 PM:
 
A solar cell does not require a DC bias voltage and I question the term factory designed as I know of no one who bias them
A photodiode will require a bias as it will also require a dc blocking component
 

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Posted by Marin Zorica (Member # 1716) on 02-01-2005, 03:36 PM:
 
Why photodiodes need bias voltage????

It's also mistery for me what is bias doing in this mine preamp, ok, but bias with 15V, i don't think hat is good?

Also does distance of cell from film effect on high frequency cut-off and distorzion?
 

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Posted by Gordon McLeod (Member # 33) on 02-01-2005, 03:46 PM:
 
is this a actual cinema audio preamp if so who made it
sounds like a mic preamp and the phantom power is on
 

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Posted by Marin Zorica (Member # 1716) on 02-01-2005, 04:47 PM:
 
Gordon, yes this is cell pre amp, yes it's thrue that is strange but now i conect cell thrue 1uF capacitor and it works but i'm stil curious about distorzion and high freq. cut-off.

Sorry for bugging guys, but can you tell me also does distance of cell from film effect on high frequency cut-off and distorzion?
 

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Posted by Gordon McLeod (Member # 33) on 02-01-2005, 05:03 PM:
 
what is this preamp from?
 

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Posted by Marin Zorica (Member # 1716) on 02-01-2005, 05:09 PM:
 
Sorry don't know, bur maybee it's fault somewhere in preamp???

But i'm not so woried in preamp, but i'm stil woried does also does distance of cell from film effect on high frequency cut-off and distorzion?
 

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Posted by Michael Schaffer (Member # 1204) on 02-01-2005, 05:13 PM:
 
Thanks for the clarification. The original formulation was actually quite clear already, only I somehow read "feeds to" instead of "what the solar cell circuit is seeing as resistance".
 

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Posted by Marin Zorica (Member # 1716) on 02-02-2005, 05:10 AM:
 
Sorry for bugging guys, but can you tell me also does distance of cell from film effect on high frequency cut-off and distorzion?

Thanks!
 

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