Film-Tech Forum ARCHIVE: Solarcel cause of bad sound?

This is topic Solarcel cause of bad sound? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Patrick de Groot (Member # 858) on 09-26-2006, 03:17 PM:

A short question: can a malfunctioning solarcel be the cause of harsh/shrill analog sound? It's a red led reader. Our tech already checked the settings, but I can't hear any improvement...
equipment: Cinemeccanica vic 8, Dolby CP65

Posted by Gordon McLeod (Member # 33) on 09-26-2006, 03:52 PM:

I would check the LED if it is the wrong distance away from the film plane it can cause trouble plus I have had the preamp module on the reader fail

Posted by Cameron Glendinning (Member # 3516) on 09-27-2006, 04:14 AM:

Sorry if this sounds stupid, but doing your dolby levels with old or damaged test film can make it shrill, proper balance is vital for good analogue sound.

So with a vic 8, when converted for red light, was the solar cell moved to where the white light was once produced? If it was the cell is huge and easy to see the alignment or any cell damage (very improbable).

A raperound or not removing tape at the end of the film can do two things to a vic 8 depending on its cell installation, push the led out of place, so the beam misses the solar cell. Or can crack the solar cell if its still inside the film drum.

Both of the above will make the sound shrill.

Posted by Nick Scott (Member # 2850) on 09-27-2006, 05:35 AM:

Is it a new red led or has it been in place for a while?
I Have a DP 75 Hooked to a CP 65 and after a few months of use with a red led i couldnt even get a dolby tone. The sound was awfull had to run it at around 8 on the fader,i changed the led and all was fine, so your led could be about to die.

Posted by Dave Macaulay (Member # 813) on 09-27-2006, 09:55 AM:

Why do you suspect the solar cell?
There are dozens of things that could be at fault.
What "settings" did your tech "check"? To me, "checked the settings" means SFA. Did he "check" the amplifier gains to see if the knobs still pointed to his scratch marks, or did he do a proper A and B chain alignment?
Whar red LED reader are you using? Only the JaxLight and similar conversions use the original solar cell and most use a separate preamp to boost the reduced cell output. Reverse scan systems have an integrated pickup and preamp. The preamps can fail giving distorted sound or a wiring problem can do the same.
Anyway, to answer: maybe a cell malfunction could make your sound "shrill" but that's the last thing I would check - standard troubleshooting practice is to start at the problem... i.e. the speaker the bad sound is heard from - and work back through the system to find the problem.

Posted by Patrick de Groot (Member # 858) on 09-27-2006, 02:35 PM:

Don't know what the tech checked. He said he would look at it. What I have done is a Dolby tone adjustment; switch cards with another CP65; change output voltage of adapter of LED; adjust amplifier outputs; readjust to Dolby tone; it didn't help. Non-sync music sounds ok. LED is on sound drum. Well maybe I can check some sugestions given here. Thanks.

Posted by Randy Stankey (Member # 64) on 09-27-2006, 02:49 PM:

This is a bit of a non-sequitur but I have a question.

Why are they using red LEDs?

Blue or even green LEDs produce photons with higher energies. Higher energy photons emit more electrons when they impinge on the surface of a solar cell. (Or CCD cell.)

Wouldn't the emission of MORE electrons be beneficial? Wouldn't that mean that less preamplification is necessary? Woudn't that produce a better signal/noise ratio? Wouldn't that solve some of those problems that using LEDs for the exciter causes?

Even if it doesn't eliminate the use of preamplification, wouldn't it mean less preamplification is required?

Just thinking... [Roll Eyes]

Posted by Dave Macaulay (Member # 813) on 09-27-2006, 04:06 PM:

If the solar cell is in the sound drum, you must have a JaxLite, LaserLens, or something similar.
I would look at parts of the CP65 only used for film sound, the optical preamp and matrix board don't affect non-sync at all.
Check the sound in bypass mode. This uses vary little of the CP65 circuitry, just the optical preamp card as I recall and maybe the output card. If it sounds OK - remember it will be mono and (probably?) have the Academy curve equalization applied which cuts frequencies above 2kHz... but you should be able to tell if it's OK - then your problem is past the cell and preamp card.
Try format 01 Mono (definitely has academy curve applied) does it sound bad? This skips the matrix card.
Try turning the centre channel amp off. Centre carries a LOT of film sound but isn't normally used for non-sync: a speaker or amp problem on C makes film sound bad while N/S sounds OK.

Posted by Patrick de Groot (Member # 858) on 09-28-2006, 02:30 AM:

The LED is in the sound drum.
I will check your suggestions! Thanks.

Posted by Cameron Glendinning (Member # 3516) on 10-01-2006, 10:13 PM:

Hi Patrick, Have you visually checked the solar cell yet. Its so big you can see if its alligned, How old is your dolby loop and how long is it?