8mm Forum: Sound Level out of my ST-1200HD

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Posted by Agnello Guarracino (Member # 97) on August 05, 2003, 09:55 AM:

I have just acquired an Elmo ST-1200HD and am having difficulties getting an acceptable sound level out of the twin track moni outputs.

Experimenting at the weekend I discovered I can get a quiet sort of sound level out my amp, but I am driving the amp at about 80% of max, eventually the amp over loads and shuts down.

I stuck a pre-amp box in the middle, and this time even with the pre amp turned down as low as it can go, I get a very boomy sound with my main amp volume at about 5%, if I turn the main amp up just a little, the boom increases exponentially which doesn’t make for a good audio experience.

I am wondering if this problem comes down to the fact that the output of the projector is 16ohms whereas most modern hi-fi equipment likes dealing with 4-8 ohms.

Any suggestions?

Posted by John Clancy (Member # 49) on August 05, 2003, 10:12 AM:

One thing I find which always sorts out this sort of problem is to change the machine for a GS-1200. Don't be such a skinflint in the future and spend a bit more money. And once you've done that you can re-record my films for a change!!!

Posted by John Whittle (Member # 22) on August 05, 2003, 10:29 AM:

Are you running the speaker output of the projector to the input of the amp? If so you are overloading the input and trying to compensate by adjusting the level controls. What you need to do is make up a pad in the output line from the projector to the amp and then you can run the projector volume control properly and the amp control properly. Why the intermediate preamp? That just makes matters worse.

You can buy a pre-made cord with a pad at many electronics stores (in the US Radio Shack sells them). The pad consists of two resistors, one in line with the signal and one across the signal to ground. Lots of values will work but you can start with 6.8K in line and 680 ohms to ground. You may need to experiment a bit in your situation. (The line out on the Eiki 16mm projector is just 7.5k/7.5k but that may be specific to that part of the circuit.)

John

Posted by John Clancy (Member # 49) on August 05, 2003, 10:35 AM:

The pre-amp Ag is using is because the sound level from the moni outputs is so low. The theory was a pre-amp would boost the sound level - it does. Unfortunately it boosts it so much the amplifier clips. Without the pre-amp the sound is so low the amplifier has to be turned up full to get a decent level which can be heard (not a good idea). So what is required is something that will boost the volume or something that will convert the 16ohm moni outputs to 8ohms.

Perhaps a mixer would do the job?

Posted by Henry Perangelo (Member # 40) on August 05, 2003, 11:59 AM:

I would consider a "Pyramid Adjustable Line Output Convertor" in between the projector and the Amp. This will convert the 16-ohm
projector line output to Line Level, which is what your Amp wants!

This item is only US:$8.40 and can be ordered from: http://www.mcmelectronics.com, part number:60-480 (do a search) once you are on the site.

I have had great success with both 16mm & 8mm projectors hooked up this way.

You may consider (also) throwing a mixer/equalizer into the mix to get really great sound ...

Best of luck,
-Henry-

Posted by Tony Milman (Member # 7) on August 05, 2003, 01:59 PM:

John,

How can you say such a thing about the ST1200HD? Must admit the sound from the built in speaker is LOUD but I have not yet got around to solving the output issue either. Perhaps, Agnello you can let me know if you solve it? I admit to resorting to the GS 800 for stereo films

Tony [Big Grin]

Posted by Mal Brake (Member # 14) on August 05, 2003, 02:39 PM:

I have been using ST1200HD's for 25 years, good workhorses except for that low output on the moni. For presentations in halls I used to feed the signal from the 3.5mm line-out next to the speaker socket on the side of the machine. That gave precise control over the output level albeit in mono. I was lucky in having an old stereo amp for home use that had a selector control for different senstivities so I was able to match the projector to the amp with nothing in between. However a couple of years ago I picked up a GS1200 (for £300) and the line out is much better on that machine.

Posted by John Clancy (Member # 49) on August 11, 2003, 08:01 AM:

I know Aggers has followed Henry's advice and has got hold of a little box of tricks for about £10 which sounds like it has done the job. He'll update us when he's confirmed the level is now okay on all his amplifiers. Could be good news for all you ST-1200HD owners out there.

Posted by Tony Milman (Member # 7) on September 12, 2003, 12:46 AM:

Agnello,

Do you have an update for us other 1200 owners?

Tony

Posted by Agnello Guarracino (Member # 97) on September 15, 2003, 05:55 AM:

I bought a little box of electronic tricks from a local hardware store. It is a speaker line output convertor only cost 10 quid.

It is supposed to be used in an in-car sound setup, the idea being that if you have an older head unit that doesn't have line outs and you wish to add a separate car amp for more bigger speakers or a sub you can take the speaker out wires, pipe them into this little box and then you get a line level output out the other side, and it seems to work just as well with my 1200 HD too.

I just needed to solder some jack plugs onto the input wires and that was it.

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