This is topic Will I hear anything? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Dave Bird (Member # 490) on 04-02-2001, 05:34 PM:
Risking another dumb question, here goes. I like to thread up a trailer once in a while in my XL's, but my sound rack is still a mystery. So I'm wondering, in the interim,
where does the sound become audible? The exciters are working through the SH-1020's, I'm wondering if I connect the outputs (it's just mono) to a small amp and speaker, will I hear it? Or does it require the pre-amps and everything else?
Posted by Adam Martin (Member # 641) on 04-02-2001, 06:23 PM:
You will need a preamp to bump the signal up to line level for your amplifier in order to hear anything distinguishable. Just like a component turntable. I have an old radio shack mixer with a built-in phono preamp, but don't ask me where it is! 
You oughtta get a little preamp and use a drive-in speaker until your sound rack is complete!
Ken Layton is here somewhere ...
Posted by Ken Layton (Member # 133) on 04-02-2001, 06:44 PM:
Feed the solar cell to the microphone input of an amplifier.
Posted by Paul G. Thompson (Member # 655) on 04-02-2001, 07:15 PM:
In addition, parallel the solar cell with a 560 ohm resistor if you use a microphone amplifier. This will provide proper loading and impedance matching of the solar cell to the pre-amp.
A 1/4 or 1/2 watt resistor will do.
Posted by Barry Floyd (Member # 385) on 04-02-2001, 10:07 PM:
I'm somewhat confused....You mean you can go "directly" from the solar cell to a pre-amped turntable input on one of my DJ mixers? Where does the "cinema processor" come into play. I was always under the assumption that I had to have a cinema processor of some type to decode the output of the solar cell?
If this is truly the case.... why would I bother with a cinema processor in the first place?
In essence.....
I could feed the projector sound to "Channel 1", and CD players (you other guys refer to it as "non-sync")to "Channels 2 & 3", and still have the Microphone inputs available for paging and announcements. I could feed field speakers with the "Record Output", feed the transmitters with the "Master Output" and feed the concession stand and booth monitor with the "Booth Zone/Cue" output. Is this practicle or even feasible?
------------------
Barry Floyd
Floyd Entertainment Group
Nashville, Tennessee
(Drive-In Theatre - Start-Up)
Posted by Gordon McLeod (Member # 33) on 04-02-2001, 10:21 PM:
basically any low impedance microphone mixer will provide sufficent gain for the solar cell to drive a power amp.
It will not provide the correct frequency response though
Posted by Dave Bird (Member # 490) on 04-02-2001, 10:25 PM:
Barry, that's kind of the idea I had (at least for playing around in the garage). At a recently re-opened drive-in I visited last year, the owner had replaced scads of amps and racks for the former carbon/changeover field speaker/AM setup. He literally had the wires out of the SH-1020 to the FM transmitter with perhaps a small pre-amp, I didn't see it. The transmitter itself could accomodate the mic and non-sync inputs I think, and his booth monitor was a transistor radio hanging on the wall!
Posted by Adam Martin (Member # 641) on 04-02-2001, 10:52 PM:
AFAIK, if you're going for just left and right, you don't need to decode anything. If you want center or surround, you need a CP to decode the SVA matrix, but that's a strange idea for use at a drive-in.At the drive-in I did, we didn't use field speakers, so we went directly from the solar cell to the "projector" input on the transmitter. The transmitter also had a non-sync and a couple of mic inputs, too. We used a home stereo (tuned into the appropriate frequency) to run the speakers for the booth, concession and patio.
Sorry, I don't remember the make and model of the transmitter, but it was specifically designed for drive-in use.
Posted by Aaron Sisemore (Member # 145) on 04-02-2001, 10:53 PM:
>>You mean you can go "directly" from the solar cell to a pre-amped turntable input on one of my DJ mixers? Where does the "cinema processor" come into play. I was always under the assumption that I had to have a cinema processor of some type to decode the output of the solar cell?<<A Cinema Processor is only necesary if you are planning to extract 4 channels from a matrixed stereo print, and/or add the required noise reduction. Since you mentioned that it was a mono cell already, then yes it shpould work fine when properly preamplified. To improve the sound you might consider a 1/3 octave equalizer between the preamp and power amp, and using pink noise and an RTA adjust the equalizer to the proper freq. response curve.
Aaron
Posted by Paul G. Thompson (Member # 655) on 04-03-2001, 12:47 AM:
If the microphone input of the pre-amp is a transformer input, you will not need the loading resistor. If the pre-amp is not transformer input, the loading resistor is required. The solar cell wants to look into a load of 600 Ohms or so.
The solar cells will be too wild in gain and frequency response without the proper loading, and will sound like shit.
Gordon, I used a Shure Microphone Mixer with a Mono solar cell (Radio Shack $3.00 special) glued to a broomstick handle jammed into a Weber Syncro-Film Sound head. I was very impressed with the frequency response when I loaded it with a 680 ohm resistor. It made all the difference in the world.
Posted by John Eickhof (Member # 323) on 04-03-2001, 01:13 AM:
I have found that the later mono (kelmar) cells work best with about a 220 to 440 ohm bridging resistor, I think the nominal impedance of these cells is about 135-150 ohms...depends on light color temp & brilliance...------------------
John Eickhof President, Chief Slave
Northwest Theatre Equipment Co., Inc.
P.O.Box 258
Wendell, ID. 83355-0258
208-536-5489
email: jeickhof@nteequip.com
Posted by Dave Bird (Member # 490) on 04-03-2001, 08:30 AM:
Thanks so much fellows, off to the electronics store I go!You know, from the age of ten or so, I've torn apart all kinds of my dad's stuff (and pissed him off a couple times) like 8mm projectors, tape decks, radios etc. Inexplicably, did not take electronics in school when it WAS offered. I think I can get this little solar cell job done, but can anyone suggest some reading material to help with the principles of all this sound stuff?
Electronics for Dummies? Is there such a thing? Thank you again.
Posted by William T. Parr (Member # 677) on 04-03-2001, 09:19 AM:
Dave, Download one of the Dolby manuals in the Manuals section of Film Tech. Preferably the CP200 manual would be the best since it covers the Magnetic and optical domain. The CP65 would be a second best. Also if it is available download the Dolby MPU manual. All Dolby manuals do have a preface and documentation on how Sound is recorded and decoded. You can also visit John Allen's website at www.hps4000.com He does a majority of the Sound articles in Boxoffice magazine and has his articles archived on his site.
Posted by Barry Floyd (Member # 385) on 04-03-2001, 10:25 AM:
I've got "Kelmar" cells in all three of my soundheads... how can I tell if they are stereo cells or mono cells?Also.... after reviewing the manuals for the RCA 9030 soundheads.... I cannot find any wiring diagrams that tell you what to hook to where... anyone care to chime in?
------------------
Barry Floyd
Floyd Entertainment Group
Nashville, Tennessee
(Drive-In Theatre - Start-Up)
Posted by Ken Layton (Member # 133) on 04-03-2001, 10:42 AM:
A mono cell is enclosed in a black case with a glass cover over the front. A stereo cell is mounted on a clear-white plastic holder with the tiny solar cell (about 3/16") glued to the front without any protection to it's surface (they are very delicate).
Posted by Adam Martin (Member # 641) on 04-03-2001, 12:04 PM:
Am I correct in saying (generically) that a mono cell will have two wires and stereo will have three?Ken's right about the delicate thing ... I once had a film crash that tore the stereo cell to shreds.
Posted by Randy Loy (Member # 112) on 04-03-2001, 12:09 PM:
Dave, I had no sound with my Simplex SPS portable 35mm projector and I did what everybody here is saying and it works fine. The projector came to me with a cord with a 1/4" plug so I plugged it into the microphone jack on a Radio Shack PA amplifyer. When I got no sound I removed the side panel to see where the cord was attached inside. It was attached to a small board, probably a no longer working preamp, which was then attached to the solar cell leads. Upon the advice of a friend who is a projection and sound engineer, I simply removed the ends of the cord from the board, spliced and soldered them to the solar cell leads (with a resistor) and plugged back into the microphone input on the amp. Presto, glorius mono sound! 
Posted by Barry Floyd (Member # 385) on 04-03-2001, 12:24 PM:
By looking at my solar cells (if I remember correctly) the bracket that attaches to the soundhead casing is black w/ the word "Kelmar" on the side. Attached to the tip of the bracket is a clear piece of plastic or glass. Sounds like I have mono cells in all three machines?
If Adam is correct... 2 wires for mono and 3 wires for stereo.
------------------
Barry Floyd
Floyd Entertainment Group
Nashville, Tennessee
(Drive-In Theatre - Start-Up)
Posted by John Walsh (Member # 168) on 04-03-2001, 02:07 PM:
Also, by looking at the face of the cell, you should just be able to see the two halfs (L and R.)
Posted by Dave Bird (Member # 490) on 04-03-2001, 04:04 PM:
Okay, I now have my resistors (set of 680's and 220's, as have been suggested, we'll see what's best). So now, as I look at the gear side of the soundhead where the output wires connect, I can see where I need to be. There's two double-pronged poles labeled
"P E CELL" above "1" and "2" below. I'm assuming that the "2" is the common as the white wire is attached. So now, my only question is: Do BOTH wires get a resistor on their way to the mic jack? I believe they are Kelmar's (the power supply is), can't wait to hear that glorious mono sound! I'm so intrigued to play a B/W intermission reel I have, but don't dare till I'm a little stronger on threading!
Adam, I will indeed be using a drive-in speaker, which is what I use at the cottage relaxing out on the dock! Thanks guys....
Posted by Aaron Sisemore (Member # 145) on 04-03-2001, 05:52 PM:
>>So now, my only question is: Do BOTH wires get a resistor on their way to the mic jack?<<The resistor goes "across" the input, i.e. one end to the hot terminal and the other end to the common or ground.
Aaron
Posted by Gordon McLeod (Member # 33) on 04-03-2001, 08:35 PM:
The cell in your soundhead already has a loading resistor accross it (it is a pot mounted in the coundhead directly below the scanner)
Also the CP200 manual has no pertinenant info for this application and the HPS site has even less
In a drive in the advantage of the Smart Mod2B DI processor is that it has
1 NR for SR and A type (emulated)
2 3 issolated outputs for AM mono/Field Speakers mono/ and FM stereo
Posted by Ken Layton (Member # 133) on 04-03-2001, 08:57 PM:
A mono cell will have 2 wires, Black and Red, which may or may not be in a shield. A stereo cell will have 3 wires, Red (left), Black (common), and Green (right). If you get up real close to the stereo cell, you should be able to see the green and red wires actually soldered to the face of the cell.
Posted by Dave Bird (Member # 490) on 04-03-2001, 10:57 PM:
I see the resistor now in the old SH-1000 schematic (from 1941), I have a lot to learn in this area. BUT, I now have my glorious mono sound! It goes to the mic input in a cassette deck to amp to DI speaker. One heck of a hum when idle , but pretty good sound actually when the film goes through.
The hum is present whether or not the exciter lamp is on, so I think it's a ground problem (not ground at all at this point).
Posted by Ken Layton (Member # 133) on 04-03-2001, 11:16 PM:
Dave:
The shield of the cable is NOT hooked up at the solar cell end. You only connect the shield at the amplifier end of the cable.
Posted by Paul G. Thompson (Member # 655) on 04-04-2001, 12:00 AM:
The solar cell should be connected as a balanced input. Do not ground the shield at both ends. Ground the shield ar the pre-amp end.None of the wires on the solar cell should touch ground.
This may be causing your hum. (referred to as a ground loop hum).
Posted by William T. Parr (Member # 677) on 04-04-2001, 01:11 AM:
The Manual and website were a suggetion to his question about getting reading material on the fundemantals of sound and not a suggetion to his related project or equipment. I know some of the Dolby manuals have some bsaic information on how a dolby track is encoded and decoded through the matrix and this is what I was hoping to point him to. It may have been in the first generation Dolby equipment manulas CP 50 and 100 where it explained hoe the Left and Right channels were recoded and the Center and Surround channels were decoded out of the Left and Right channel.
Posted by Dave Bird (Member # 490) on 04-04-2001, 07:23 AM:
I'm not even using shielded cable right now, when I get some, I'll have to think about where to ground it, it's only running to a old tape deck that has no ground (two-prong plug). Will earth (wire) do? (Of course being very careful not to "ground" to the hot wire.) Thanks.
Posted by Gordon McLeod (Member # 33) on 04-04-2001, 08:37 AM:
I use Belden 9451 or 9452 cable for mag and cell lines
In Canada it is available through Electrosonic in Toronto
Posted by Paul G. Thompson (Member # 655) on 04-04-2001, 02:15 PM:
Gordon's suggestion will help you. If you are using unbalanced inputs on your pre-amp, a matching transformer would be recommended. Usually, those can be found in an electronics store.
Get a 1:1 ratio, 600 Ohms input and output.
If you do this, the loading resistor is not needed to terminate the solar cell.
Ground the 8451 or 8452 shield on the pre-amp end. If the preamp has an XLR connector, tie the shield to pin 1, the black wire from the solar cell to pin 2, and the red wire to pin 3.
If you are using a stereo solar cell, don't tie the red and green directly together. It'll load the solar cell down too much, and it may not work properly, or sound good.
Posted by Gordon McLeod (Member # 33) on 04-04-2001, 02:43 PM:
David there is a Eprad StarScope on ebay right now and for a drivein it would work since it will provide a pair of preamps,
A type nr and a left and right output for a stereo transmitter and the centre would run the am transmiter. The starscope has no gain riding logic on it matrix so this will work
You will need to get a stereo cell though
Posted by Josh Jones (Member # 447) on 04-05-2001, 12:45 AM:
OK, OK,
For those of you who do not know...
The surround channel is decoded by finding the difference between the right and left channels, using a voltage comparator or a differential amplifier. A phono input can be used to boost gain on the cell. If you do this the sound will be quite weak in treble and heavy on bass. This is due to the RIAA equalization curve built into the preamps circuitry. These devils like to hiss a lot as well. a mic input would be a better choice. If you do not load the cell, your amplifier will sound like it is clipping, or making clicking noises on peaks. the resulting stereo signal can be fed into a home theater reciever and use dolby pro logic decoding. the only thing you will be lacking is noise reduction, but if you can live with and occasional click pop, or period of hiss, you will be fine.FWIW,
Josh
Posted by Dave Bird (Member # 490) on 04-05-2001, 07:59 AM:
Ack, the StarScope's to be shipped within US only, go get 'em Barry!I now see though Gordon, from looking at the StarScope and the Smart MODII-DIT what you mean about the mono unit I have being "built-up". These Smart units look pretty slick. It would seem to me that should I ever get past the stage of running trailers in my garage, the way to go would be a new processor (will car stereos soon be "surround"???), stereo cells, lamps and lenses for the old XL's. (And of course, a qualified technician to install them, know any 
?)
Posted by John Pytlak (Member # 331) on 04-05-2001, 08:14 AM:
I think some of the high end car audio systems do matrix a "surround" for the rear speakers. And certainly some like to have a few kilowatts of subwoofer so you can hear (feel) them coming down the street. 
------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Posted by Sean Weitzel (Member # 244) on 04-05-2001, 08:41 AM:
I saw someone mention a retrofit kit for Stereo on a DeVry XD at one point. Anyone here have any recent info on this? I'd love to run stereo on my DeVry! [although Lowell Thomas's voice on some of my old variable density newsreels sounds so wonderfully rich on the OEM mono phototube and vacuum tube pickup/amp combo ]
Posted by Gordon McLeod (Member # 33) on 04-05-2001, 09:15 AM:
Josh the surround channel is not in fact the difference between the Lt and Rt channels but actually involves to 90 degree phase shifts if you want to decode them properly.
Also a phono preamp will be very shrill sounding due to improper cell loading
A solar cell need to see in effect a virtual ground to work properly
Posted by Josh Jones (Member # 447) on 04-05-2001, 10:25 AM:
As far as I know, The smart mod III used a differential amp to get surround. That's about all I know. I you use a phono pre-amp and use EQ all over the place, it doesn't sound that bad.Josh
Posted by Gordon McLeod (Member # 33) on 04-05-2001, 10:35 AM:
Most centre surround systems use just a differential amp
All 4 channel systems require a logic system and a proper matrix
Dave I have delt with her and she would probably ship it to you
Posted by Paul G. Thompson (Member # 655) on 04-07-2001, 01:53 PM:
Hey guys, I forgot to mention that a 10 MF NPO capacitor is needed to keep the DC off the control grid of the first stage of a vacuum tube pre-amp. Some amplifiers do not have a coupling capacitor in the first stage. Since the first stage is usually a very high gain, the small amount of DC on that control grid will upset the bias and possibly allow the grid to become positive with respect to the cathode.
The end result is audio clipping.
Sorry - my oversight.
Posted by Joe Schmidt (Member # 822) on 04-08-2001, 12:32 AM:
This is probably overkill for a drive-in, but if a stereo pick-up cell could be obtained and installed...{ Experience aligning a stereo solar cell using a Dolby test film and a dual-trace scope is probably essential first. With this experience, if you don't have a Dolby film and scope handy, it is possible to come doggone close with a 9KHz test film and multimeter ...}
Then, on the cheap a stereo setup for a drive-in booth and surrounding area if you have benches, etc. could be built up with opamp chips [2 on 1 chip about $1] for your preamp stage, feed outputs of these to the L/R inputs of a stereo amp. For the mono signal to FM transmitter use another opamp stage with 10K isolation resistors to each of your preamp outputs.
This is radically oversimplified; other parts will be needed with your opamp chips and if you don't have audio-circuit build-up design experience try to get local help from a techie to do it; still the cost of parts is almost zilch, it's practically like making something out of nothing. A Dolby CP-50 manual is full of apps using opamps if ya wanna see complete working circuits.
I've been out of this for so many years and don't even know if stereo FM xmtrs were ever used in drive-ins or not. Hope I'm not about to get shot for suggesting this...!
J.
Posted by Gordon McLeod (Member # 33) on 04-08-2001, 12:18 PM:
re Joe Schmidt's comments read the entire topic from start to finish and one will notice that fm transmitters are the defacto standard in most driveins.
I don't advocate the build it yourself route for the preamp since at some point someone else will probably have to fixed it. And with out documentation it is a nightmare.
Also there are many reliable professonal products that outperform what you are advocating doing
Posted by Dave Bird (Member # 490) on 04-08-2001, 08:29 PM:
Nah, she wouldn't ship it (too heavy she said), so I guess I'll join the United Drive-In Owners and buy the Smart processor! (I'm kidding, but I DID get an e-mail a while back, Smart was offering a deal on the drive-in units to members of UDITOA, so a little plug in case any of you needed one....)
Posted by Joe Schmidt (Member # 822) on 04-10-2001, 05:04 AM:
Mostly, I agree with Gordon, buy a regular system if you can afford it. But sometimes such is not readily affordable, depending upon circumstances. Building audio gear from scratch is NOT for everybody; however, if you can do it, an advantage is that you have complete control over quality and what goes in.If I design something, the goal is for it to run forever and never need service; because I want to go on to something else and not keep running back and fixing stuff. This was always, and still is, the design philosophy at McIntosh Labs.
But then, nobody's perfect. Last month I had to replace the stepping attenuator [volume control] on my C27 preamp. First repair needed since 1974. Did have to replace a couple of #1866 lamps along the way, tho.
Posted by Barry Floyd (Member # 385) on 07-10-2001, 10:48 AM:
I wanted to bring this topic back up as I've been working in the basement for several nights on my machines. The machine I am currently working on is a Brenkert BX-60 on top of an RCA 9030 soundhead. I've got Kelmar mono cells in the soundhead, and I do have a resistor bridging across the leads of the cell.
In the soundrack I've got a Numark DJ mixer with built-in phono preamps, a Numark twin tray CD player, and a Ramsey FM25 FM Stereo transmitter.
Once I got eveything wired up, film threaded, and the exciter lamps on, I flipped the switch and the sound from the projector is there... but very muffled and noisy - along with a nasty Hum. Grounding the sheilded cable to the mixer helps on the hum, but the sound is still muffled. Are both exiter lamps susposed to be on at the same time or just one? I don't see a way to light only one.
What am I doing wrong?
------------------
Barry Floyd
Floyd Entertainment Group
Nashville, Tennessee
(Drive-In Theatre - Start-Up)
Posted by Aaron Sisemore (Member # 145) on 07-10-2001, 12:36 PM:
>>In the soundrack I've got a Numark DJ mixer with built-in phono preamps<<there's part of your problem. Does it have XLR inputs for microphones? If so, try connecting the solar cell to the balanced in using two conductor + shield cable and connect the ground(shield) to the mixer side ONLY. This should take care of most if not all of the hum.
Are you using AC or DC to power your exciters? Sometimes running AC will cause a nasty hum with exciters.
Switching can be done is a number of ways: you can leave both lamps lit and switch the outputs of the cells, or you can leave both cells hot and switch the power to the lamps, or you can switch both together.
>>the sound from the projector is there... but very muffled and noisy <<
Check three things:
1. the cleanliness of ALL the optics from the exciter to the cell.
2. Condition of the slit lens (is it full of oil or dirt or both?)
3. Focus of the optics in relation to the cell.
Correcting any or all of the above three should eliminate the muffled sound.
As for the system you are planning on using for the projector sound:
First thing I would do is can the DJ mixer and get some kind of a system designed for cinema use.
Aaron
Posted by Gordon McLeod (Member # 33) on 07-10-2001, 05:33 PM:
One other problem with cheap mixers even if they are balanced input is they have no d.c blocking capacitor to block the dc offset of the solar cell. I you add a cap to block the dc it throughs the balancing off. As such a cap in each line is required. The best is a transformer balanced input
Posted by Will Kutler (Member # 770) on 07-10-2001, 05:43 PM:
I believe that the second exciter lamp is a spare. Download the 9030 book!Also keep the soundhead clean and free from excess oil spillage! This can ruin the optics --especially the slit lens!
There are some schematics in the 9030 book
Posted by Rick McCluney (Member # 642) on 07-10-2001, 07:34 PM:
Yes the second exciter bulb is a spare. In an emergency you could quickly slide the bracket out, turn it around and slide it back in.Rick
Posted by Aaron Sisemore (Member # 145) on 07-10-2001, 11:15 PM:
OK I assumed he was talking about changing over exciters on a pair of machines, of course as everyone else said the second exciter in the RCA soundhead is the spare bulb.Aaron
Posted by Barry Floyd (Member # 385) on 07-11-2001, 08:53 AM:
I knew the second exciter was the spare, but I still see no way to keep the second bulb from lighting. I've downloaded the manual, cleaned the front and rear of the slit lens and the face of the solar cell, but still muffled sound. I did manage to get the hum out of the sound with a grounding strap to the mixer.The majority of the drive-ins I've visited over the last several years use a DJ type mixer for their sound systems. I know the SMART MOD II DIT is specifically designed for this application, (and will eventually probably get one), but I already had this equipment on hand and thought this would be a temporary fix until I actually have a theatre to put this equipment in.
------------------
Barry Floyd
Floyd Entertainment Group
Nashville, Tennessee
(Drive-In Theatre - Start-Up)
Posted by Will Kutler (Member # 770) on 07-11-2001, 09:44 PM:
Double check that the slit lens is not damaged or filled with oil. Also focus the exciter lamp and slit lens, and align the lateral guide pressure roller per the manual.Make sure all the terminal ends on your wiring is good. It is best to swap cables. A multimeter(vom) can sometimes be misleading.
Make sure that none of your speakers are damaged.
Just check all of your wiring and components.--go over everything