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Looking for any advice on trying to correct an audio imbalance issue with an EPRAD Starscope. The audio coming from projector 2 sounds spot on, however on changeover to projector 1 the audio seems to be muffled in higher frequencies. Does any one have any insight as to what the cause could be and the best way to try to get the audio balanced out? We are operating at a drive-in and are broadcasting out sound via an FM and AM transmitter.
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Wow, you have a Starscope that is still running??? Honestly you should pick up a used CP65 from ebay and junk that Starscope.
Still, the first thing you could quickly try is to flip the optical input wires between projector 1 and 2 on the back of the Starscope and see if the muffled audio then comes in when the processor thinks it's on projector 2, or if the muffled audio stays physically locked to the physical projector 1. If it stays with the physical projector, likely someone knocked your optical A chain out of alignment during threading (or perhaps a film jam). -
do what brad suggested, was this a sudden problem? if the problem remains at the same projector, examine the slit image by placing a white card at the film plane, if the slit image is yellowish, foggy or has a rainbow around it, the lens has taken in oil and needs to be replaced, simplex and rca soundheads were notorious for this, it will cause severe hf loss and muddy sound, if the slit is bright white and sharp, check with test films. the azimuth and focus would need to be adjusted. i have new .8 mil narrow slit lenses in stock. they will give much improved hf and clarity in the sound. of course, rule of thumb...take a clean q-tip and clean both ends of the slit lens before going further, a chunk of dirt or residue can block the lens too!Comment
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Thanks for the advice! This has been an ongoing issue, we initially attributed this to an aging LED due to a major drop in audio volume and fidelity, so the voltage on the preamp had been turned up to try and compensate for this with only short term improvements. However before this season started we had the LED replaced with a new one, the level is now the same between the two projectors but the HF issue is now very apparent. We do have Component Engineering reverse scan LED analog only sound readers installed in a Simplex SH-1000 sound head.Comment
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Did the tech replacing the LED run the full set of test films? Buzz track, focus(pink noise), Slit uniformity, and finally Dolby tone? Did he check azimuth and use an RTA to look at the HF response? If any of those were skipped, then that tech owes you a free return call to fix the issue, which is likely nothing more than the focus on the reader was moved during the LED swapout.Originally posted by Michael Drumbore View Post
Another (in this case, perhaps better) possibility is that the LED is too close to, and actually rubbing on, the film as it passes over the drum. That is an easy mistake to make when doing an LED swap (it caught me my first time doing it) and also needs the tech to return and do it right. DO NOT run any film with the LED touching it, it will scratch the film! You can thread up some film and visually check to see if the LED is touching the film itself, gently pull the film tight over the drum as you look.
Either way, call the tech back and have him (or her) fix what they forgot to do.
I had never seen any electronic failures in either CE or Kelmar reverse scan readers that would cause HF loss, so it has to be bad alignment/adjustment related.
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I would check the focus and azimuth of the reader The starscope preamp typically depending on vintage use a common slit loss was common between both projectors
Also try the back up preamp by rotating the preamp cardComment
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The only thing I have seen happen on a few reverse scanners is oil in the pickup lens. And those were early scanners.Comment
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I would be curious as to how they impedance match the reverse scan reader to thestarscope preamp
The impedance of the starscope was 4KComment
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