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Author Topic: Drive-In FM Transmitter: Identification, Manual, and Volume Problem Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 08-18-2004 12:40 PM                        The board on the end is the stereo generator. You can adjust the modulation level by the blue pot closest to the corner. The board with the two heat-sinked transistors is the transmitter. As Gordon says, frequency is controlled by the settings on the dip switch. By the voltage regulator, there's a place for a jumper that will raise the voltage to the "final". If the jumper isn't there, it only puts out around 100mW. The stereo gen doesn't have a lot of headroom, so incoming levels are a concern. As the transmitter has no compressor/limiter, I'd imagine things can get interesting for the listeners if you get the clipping resolved. As there's no indication of outside padding in there, how the ratshack amp feeds it sounds like an interesting place to start! I've got manuals & schematics for all that stuff. If you can wait for me to get my scanner going, I'll email it. Otherwise, if you send me an address, I'll copy this stuff & mail it to you. Jack  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 08-18-2004 01:33 PM                     I would appreciate a copy of them scanned as well thanks  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 08-18-2004 02:20 PM                     Since this is a cinema related application, could you add those diagrams to the manuals section? I would bet that someone turned up that power amp or even got a feedback which sent the audio input op-amp into rapture. The microphone is awfully close to the Boom Box field monitor. KEN  |  IP: Logged David Buckley Jedi Master Film Handler Posts: 525 From: Oxford, N. Canterbury, New Zealand Registered: Aug 2004 posted 08-18-2004 02:40 PM                        quote: Paul Trimboli When you say there are earthing points all over the place, well they all earth back to the metal case? I always thought that is correct? Nope, thats earthing done real bad. There should be a single ground point for the whole assemblage, to which each earth wire returns. This is called star earthing. The principle is to stop currents circulating throught the earth system. Such circulating currents can lead to all kinds of problems, from hum superimposed on the signal, to instability.  |  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 08-18-2004 04:51 PM                        I agree, the grounding is all messed up. Looking at the board it was clear the dips were the frequency selectors. First thing to do is to do something about the Rat Shack amp. Not too worried about feedback as that radio is used for non-sync music, but you never know. Would appreciate the manual in any form convenient to you Jack. If you'd prefer I can scan them for you if that is easier. Thanks again everyone.  |  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 08-21-2004 01:25 AM                        I received the manual and schematics for the transmitter (via FedEx International Priority, BTW -- thanks so much Jack!) today and was able to adjust the gains on the stereo board and on the FM exciter, both were fairly low. I also added a transformer between the preamp (I love Electrosonic, ordered at 5:15pm, out the door at 6:30pm, had it at 10:00am) and the soon to be thrown out mixer amp, which helped a little. The big problem is the impedance mismatch between the mixer amp and the transmitter though. I'm in the process of tracking down a good mixer that has a pair of XLR inputs, a 1/4 mic input, a composite RCA input for non-sync (or just another 1/4 input), and 600 ohm or 10k ohm stereo outputs. I'd love to install a real cinema processor with noise reduction, but unless I can get one real cheap I don't think it's in the budget since they'll be spending $2100+ to upgrade their analog readers in their Century R3s-- which reader is yet to be decided on (it'll be either BACP or Kelmar). For anyone who's interested, the transmitter as it's currently set up has a power output of 250mW. Moving a single resistor changes the power output to 500mW.  |  IP: Logged Josh Jones Redhat Posts: 1207 From: Plano, TX Registered: Apr 2000 posted 08-22-2004 04:06 PM                        I built a 5 watt VCO transmitter several years ago from scratch that didnt use heat sinks that big! Although considering the technology, at least you have PLL Josh  |  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 08-29-2004 10:41 PM                        At least they won't have to worry about it overheating when the booth hits 40 degrees in the summer. In case anyone is interested, here's the input/output specs for the mixer I bought, a Yamaha MG10/2. Which is a realy nice board for the $159 it cost me. I actually went in to order a Soundcraft Spirit Notepad, which is similar, with fewer channels, a plastic rather than metal case, and nearly twice the price. Hopefully I'll get some time to install it sometime this week.  |  IP: Logged

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