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My Super 8 projector is located in my hallway and shoots into the screening room where I have my digital projector and A/V amplifier located. The RCA cable run from the projector, running through the interior walls, to the input of the amplifier is about 15 ft. The AV system is noise free when playing digital movies, CD's, and radio, but whenever I switch the input to the super projectors I get significant hum. This is not the fault of the GS1200 because I get zero hum when listening on headphones plugged into the same socket on the projector. So its probably a ground loop situation which I have so far been unable to fix. So I hooked up a $30.00 Blutooth transmitter to the projector and paired it with the Blutooth input of the A/V receiver. Low and behold I now get zero hum or noise through the speaker system! And the sound quality is really superb! The only drawback is a very slight loss of sound synch. probably equivalent to a couple of frames of film, which is detectable but not objectionable. A wired connection is the preferred way to go, but honestly this little Blutooth connection right now is a huge leap in sound quality for me.
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Last edited by Paul Adsett; September 17, 2024, 09:42 AM. -
Hi Paul,
This problem kept me from having an external sound system for a couple of years. I rigged up a connection between my projector and my amp, fired it up and got this horrific hum! As my wife put it: "What are you DOING down there!?". I decided to filter out the low frequency hum coming off the projector. Then it became kind of baffling! -now I had thin projector sound AND just as much hum!
I actually gave up and stayed on the internal speaker for a while: overall that sounded better than audio plus buzzy hum!
I had to get to the point where I realized the hum I was disturbing the household with had absolutely nothing to do with the projector audio (-and is usually worse than that hum.): it even shows up with the projector sound turned off. It's actually hum within the house ground-wiring that accidentally gets added into the audio signal we really want: a classic ground loop. I eventually figured out how to deal with this and the day I made it work was red-letter day in film collecting for me! (-kind of like the one you are having!)
The whole issue is somehow isolating chassis ground of the projector from the amplifier: just somehow sending the audio signal from one place to the other without the difference in ground voltage between the two points. You've done it wirelessly: no wired ground interconnection, no ground loop. I did it electronically: I built an op-amp circuit that subtracts the hot and return sides of the signal from each other. Since they both will carry the ground loop voltage, it's subtracted out and all you get is the audio you want. It is also possible to do it magnetically. There are these devices that can be inserted inline between the two devices called a "ground loop isolator" or "eliminator". These are an audio quality transformer that magnetically couples the audio signal across from one device to the other, but succeeds in having no electrical connection between the two grounds so the difference in grounds can't get past. Steve Osborne has sold these at times, maybe he still does. (Amazon has at least one.)
It's also possible to do this optically. A couple of months after I got the differential amp circuit I'm talking about above working, we had a ground loop issue where I work and I saw them fix it with a special opto-coupler that has compensation to make it function linearly: it can faithfully reproduce (for example) an audio signal without distortion. (Some folks would instead convert analog to digital and transmit through fiber-optics before converting back. I'm way too analog to try this!)
I was a little disappointed when I saw this. The circuit I built has a weakness: it's sensitive to the value of the resistor in the line-level audio output of the projector. For example, I got it to work very well with an Elmo ST (600 Ohms) but it failed spectacularly with a Eumig 800 Series (50,000 Ohms). I once tried it out with Doug's GS at CineSea (two 600 Ohm stereo channels together for an equivalent 300 Ohms) and made some hum publicly!
At this point, I had what I'd built inside a nice plastic case. I had weaned it off two 9 volt batteries and put it on a nice little power supply. I was too committed to it to start over so I lived with it until I got a mixer, compensated it to play nicely with that. Now everything plugs into the mixer and works just fine.
-but if I ever had to do it again, I would go optical and have it play nicely with anything. -
Hi Paul,
For some time now I have been using bluetooth to play back both super 8 and 16mm in my room. And although there is a slight 1ms or so delay, it is a small price to pay for the convenience of not having cable runs everywhere.
I am fortunate, on my 16mm it has a sprocket after the intermittent before the film enters the soundhead, so it is possible to control the amount of frames between the gate and soundhead, and this solves the problem.
For super 8 I found my Beaulieu works better for this than my GS. As the Beaulieu has two sets of heads, record/playback and a playback. Using the record/playback head as the main playback, this is set about three frames closer to the picture gate than the official playback head, and eliminate the problem.
My AV amp is used mainly for a DLP and television which can both be viewed simultaneously. The DLP is in perfect sync the TV is not. Only by ficking through the amps menu, by accident I found a audio sync control that allows for the audio responce time to be speeded up or delayed.
It could be worth looking Paul to see if your amp has this feature, as it could solve the problem.
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Steve (Klare), can you recommend a specific hum elimination device on Amazon that you think would solve my hum problem?
Steve (Lee), Wow that's a neat feature on the Beaulieu!
Yes my amp does have a feature to sync sound and picture, but I do not think it will help with the GS1200 or any other projector. Because the bluetooth is delaying the signal you need to advance the sound and there is no way of doing this electronically if the sound has not yet reached the sound head! The only way to do it is to get a shorter loop between the projectors gate and the sound head, as you have done on the Beaulieu. Presumably the sync feature on the AV amp can delay either digital sound or digital picture but it can't advance information that has not yet arrived!
It is interesting to note that I can detect zero audio lag when using blutooth headphones, but going through the AV amplifier to the speakers introduces a visible lag of about 40 to 80ms. I assume this is due to the additional sound processing circuitry in the amp.Comment
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Hi Paul,
This is very typical of what I see:
ZIOCOM Ground Loop Noise Isolator
It's this little two connection device that gets inserted in the offending line. You'll notice the input and output aren't marked: sometimes they say "You can connect it either way.", which is basically screaming "isolation transformer!!" to me.
It is a stereo device with Tip-Ring-Sleeve jacks. For monaural you can probably get away with just plugging into the Tip-Sleeve aux jack on a projector. If you want to bring two-track audio out of your machine, you'll need some kind of 'Y" cable on the projector side with two Tip-Sleeves to a single Tip-Ring-Sleeve, and then maybe something like a TRS to RCA "Y" cable to get it into your amp input.
It's certainly cheap enough to give it a shot, and with that series 600 Ohms in the projector Aux, even if the thing is s a dead short it can't hurt anything! (It's a passive device, so it has no power or voltage to zorch anything either.)
(Besides: Amazon calls it "nifty"!)
What's important to know about these is they are strictly for line level signal, not speaker power. Once or twice people I know have inserted them in amplifier-speaker lines to eliminate hum. Nothing gets hurt, but there isn't any sound either: they just can't pass any power.
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Brilliant hum fix, Paul!Comment
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Thanks for that link Steve. I will give that little ZIOCOM device a shot.
I also really like your idea of using an optical cable though. as that would definitely kill any electrical ground loop issues. I assume I would need the following items to do that:
1. RCA ANALOG TO DIGITAL OPTICAL CONVERTER
2. TOSLINK OPTICAL CABLE, 15FT LONG IN MY CASE
My Yamaha AV receiver already has an optical input port so I assume there is no need to also use a digital optical to RCA analog converter ahead of the receiver.
Do I have this right?Comment
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Paul,
When you get into digital circuitry, you are definitely leaving my comfort zone! I'm not really sure how that happened: I diddled with the idea of being a Computer Science/Electrical Engineering major in college, but that first CompSci course convinced me I wouldn't escape with my sanity (-and degree) if I went down that road! After that, working 40 years in industrial power conversion has basically made me an Amps and Volts kind of guy!
-so the best I can offer you here is "Yeah...sounds good!" (Actually it sounds like fun!) Hopefully there won't be any latency issues here as well.
It absolutely will dispense with any ground loops you have.
I have a young friend at work (Same college, 35-ish years later) he knows how to code and I know which end of the screwdriver is which! We help each other out.
(If you should happen to have any questions about Steam Power, I'm pretty good with that, too! It's like they are preparing retirement for me in a display case at some museum between the Pterodactyl and the Brontosaurus!)
How analog am I? I collect movies...on reels!
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Me too Steve! And I think you have raised a great point, namely that the latency of this type of analog to digital conversion (and back) is unknown and it might even be as much or greater than the Blutooth connection. Still your idea is intruiging and the ADC Converter is less than $20.00 and the 25ft optical cable would be about $25.00, so I am thinking about trying it out. As you say, definitely a fun thing to do.
My knowledge of steam trains is confined to having travelled on them - a lot when I was a young boy in the UK. I can still hear the puff puff of the local Cardiff to Penarth train as it struggled up the steep incline from Cogan station to Penarth, finally letting out an exhausted gasp when it pulled into Penarth station! I do have one super 8 sound train movie, The Train Driver, made by Pathe and its basically showing a train travelling from London to Manchester. Its a beautiful black & white print by Derann.Comment
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Well, this thing happened to me in college...I had to take this course called "Thermodynamics": it was a degree requirement. I had been warned about it a number of times! Some called it "Thermo-God-damn-ics" and a friend of mine literally washed out of engineering school because of it! (-failed it TWICE!)
-but it was like an academic kidney stone: I had to pass it!
So that semester I added a history course so I could stay in good academic standing if I blew The Course, and I showed up that first day prepared for the worst.
It turned out a lot of it was about steam power: I loved it!
At home that semester I fired up my Mamod stationary engine and appreciated it on a whole separate level than ever before!
-shame about my friend: maybe if HE had a Mamod, he'd be an Engineer now!
When I cook with my wife, we can't agree how a pot of water on the stove works (-yet I know how it works!)Comment
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Built my own steam turbine when I was a kid. Take an old metal soup can and bore 2 venting holes in the cap 180 degrees apart. Take a cork and fit four cardboard vanes 90 degrees apart and slanted at 45 degrees. Put a long needle through the center of the cork, and suspend it over the center of the lid with a bent Meccano strip. Put water in the can and bring to boil on stove. Just watch that thing wind up to about 1,000 rpm!Comment
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Childhood has changed so much!
I have a scar on my left knee that I got when I was 12 years old, stripping wire with flame! (-like NAPALM it was!).
-these days they can't even get dirty!
I make a point when I do brakes to talk my son into joining me: I think he owes it to himself to have something to scrape out from under his fingernails!
From what I am seeing, the general consensus on the latency of A/D converters is it's not significant enough to be noticeable.
These days with audio/video systems being so integrated It wouldn't have to be just our problem.
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Hi Paul,
If you have an optical input on your AV amplifier this will work.
I currently have my PC connected to an AV amp via optical, using a USB to optical converter, and it works great.
It's a shame that optical wasn't promoted more as an audio connection, as it has so many pros over wired. As steve has said, it is not prone to interference from static and mains grounding issues. It can be used on very long runs without dropout, and the signal is actually traveling at the speed of light. You can't get any better.
I have been tempted to install an optical output permanently in the back of both of my machines, and to find a way of powering them from within the projectors, so there is no extra power cables.
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Thanks so much for that info Steve, you have encouraged me to give optical connection a shot. If it works out I may try incorporating the analog= to =optical converter within the GS1200, plenty of space to do that now that I have removed both internal speakers ! (done to reduce weight and improve cooling for the 250w ELC lamp powered from external supply)Comment
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I found something here and the reviews say, the sound is really go:d
https://www.bol.com/nl/nl/p/allteq-t...2.ProductTitleAttached FilesComment
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