8mm Forum: Elmo ST1200HD and stereo playback... The final word.

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Posted by Jan Bister (Member # 332) on May 21, 2006, 01:23 PM:

Well, we all know it already - the Elmo ST1200HD provides monitor outputs for both tracks, allowing stereo playback through an external amp... but the output level is pathetic (and I'm being nice here!!). I found the result of connecting my own stereo amplifier disappointing, and any plans of developing in-line preamps or even ways to grab the signal directly off the Elmo soundheads have failed to come to fruition as well...

So I'm going to try a new approach... a headphone amp that I just bought which I'll be plugging into my "real" amplifier (rather than headphones) to get a sizable gain in output level. We'll see how this works out so watch out for an update, hopefully next week. [Smile]

Posted by Sam James (Member # 477) on May 21, 2006, 01:59 PM:

Jan,
I was literally sitting down to write about how, having reduced the level of hum from my st1200, I had tried and failed to get anything like reasonable sound from an external amp and speakers, when I read yours.
The machine's great, the picture's wonderful, the sound's crap. I bought a pre amp (mentioned in previous posts) to boost the signal, but all it did was increase the level of hum.
Last night, in desperation, I plugged a pair of Sony Walkman external speakers directly into the headphone socket and although the result wasn't breathtaking, I did have reasonable sound coming from both the projector and the external speakers. Tomorrow I'm going to hook up the speakers that I bought for the computer which are of a far better quality and have their own woofing and tweeting box to see if I can get a better noise.
Of course I realise that it's never going to be DVD equivalent, but surely it's can be better than what I've currently got.

Please let us know how you get on with the headphone amp.

Thanks, Sam

Posted by Mal Brake (Member # 14) on May 21, 2006, 04:18 PM:

I must be one of the lucky ones. I use a 40 year old stereo amp that has 3 levels of input sensitivity so I have excellent stereo sound from the ST 1200HD and the GS, plus two channel mono for an Eumig 710D and an Elf 16mm.The same amp also handles the non-sync music via CD.
Mal

Posted by Jan Bister (Member # 332) on May 21, 2006, 04:18 PM:

I suppose the Elmo sound is quite good if you're not looking to get stereo playback - I've used the internal amp with a speaker placed near the screen and got booming sound, loud and nice.
What kind of preamp did you try? The one I went for is said to be a very high-quality unit, capable of a 600% gain and with a signal/noise ratio of more than 100dB. (Also notice this is not a phono preamp which would be a huge mistake to try and use with the ST-1200HD, as phono preamps use RIAA equalization for turntable cartridges and boost bass levels massively.)
I do have to add that my Elmo doesn't exhibit any hum problems (which makes me lucky I guess), so I'm having high hopes right now...!

Posted by Tassos Laudas (Member # 588) on May 21, 2006, 04:28 PM:

Although i don't have any experience with the particular projector, and supposing no one would spend hours trying to solder sound head with wire heading to a stereo cassette player's amplifier -which should definitely help things though-when having this 2 outputs' option, i would suggest trying the aux (high) inputs of a high gain dj mixer, the one supposed to drive an high current amplifier. These mixers are cheap ,could cost even less than 100 usd as far as i know. As i'm a d.j. i have used a couple of mine accepting signal from headphone output of my st1200d with very nice results in both cases.

Posted by David Storm (Member # 509) on May 21, 2006, 05:45 PM:

A DI-box like ART ZDirect will solve this problem. You can also use it to connect speaker outputs from a projector to the amp. Behringer DI4000 is probably a good choice if you want a 4-channel rack unit. You need two ZDirect for stereo playback.

Posted by Jan Bister (Member # 332) on May 21, 2006, 08:58 PM:

That's the thing with the ST-1200HD, though - there is only one speaker output. It already comes with a separate AUX output as well but the only way to grab both tracks separately is through the low-level monitor outputs.

Posted by Dan Lail (Member # 18) on May 21, 2006, 10:33 PM:

Jan , I asked the same question back in 2003. Try doing a forum search using- How Do I Use The Preamp Out On An ST-1200?

You're on the right track though.

Hope this helps. [Smile]

Posted by John Clancy (Member # 49) on May 22, 2006, 02:45 AM:

Well said Dan, we've been through this so many times before. Agnello Guarracino came up with the solution. Here in the UK it costs around £10. He purchased a car hifi box o' tricks that converts speaker connections into full level hifi line outs. Simple.

Posted by Kevin Faulkner (Member # 6) on May 22, 2006, 03:49 AM:

As has been said before many times on this forum the only, way as others have said, to get stereo out of the ST1200HD is to use the monitor our sockets. You will only get mono sound from one track or the other or a mix of the two out of the headphone jack or aux out.
The monitor sockets give quite a low level output and will need some sort of amplification before feeding into an external amp, otherwise the input will need to be fairly sensitive but dont use a magnetic pickup input as this will give quite bad sound.

Hum and noise can be reduced bu moving the Hum Cancel Coils under the heads for minimum noise.

What we have to remember is that the monitor outputs were never designed to be fed into an amplifier but to be used for track to track transfer so were designed for feeding into the ST's own inputs which are quite sensitive.

Kev.

Posted by David Storm (Member # 509) on May 22, 2006, 07:54 AM:

Jan, what I meant to say was that you can connect the ST-1200HD monitor outputs to the DI-box, it will convert virtually any audio output to a line level signal.

Posted by Chip Gelmini (Member # 44) on May 22, 2006, 09:27 AM:

I have 4 ST1200HD units and they all are superb. Never ever had a problem with low sound coming from Moni 1/Moni 2.

Because I use two machines for changeovers, there are 4 A/V switchboxes attached between the projectors to the Dolby Pro Logic decoder. All of these boxes are electric power, which I guess boosts the signal somewhat.

The first box after moni inputs I use as a mono-stereo switch. I do not have to swap cables.

The second box serves as a sound changeover via remote control, between machines.

The third box selects movie sound, or background music before a show.

The sound reaches the Pro Logic Decoder (not a receiver, just Dolby PL).

The sound is equalized left and right channels only.

The sound passes through a pair of Carver TF CB15 power amps, @ 100 watts per channel. These amps handle left, right, center, and subwoofer.

The surround output from the Dolby PL is amplified by an Onkyo 80 watt per channel amp (also not a receiver).

When running a show, Dolby PL volume is set to about 11:00am volume setting.

The average peak sound coming from Die Hard explosions of Nakatomi Plaza hit just about 0.3 of one watt.

Obviously, I have never connected the projector merely from the backs of the moni leads straight into the back of an amp. So maybe I might have your same problems. But I really don't know.

What I do know is my sound coming from these machines is great. I would strongly recommend all ST1200HD users to take a good look at what they are using for amplification, as well as how it is installed.

Remember that most headphones will not monitor Dolby PL correctly, as there is no center speaker to the headphones. Any 5 channel effect would be just that, a simulation. If using headphones, best to turn off Dolby PL, and use standard stereo mode from within the Dolby PL device.

Helpful hint: Your local Radio Shack store will sell and stock most standard cables for these connections to be made. Do not forget splitters, so that (i.e. aux out) both speakers behind the screen receive the same mono signal. If you run aux out and only the left speaker is getting the signal and the right speaker is dead, the splitter solves this problem. You can get it to connect at aux out at the machine, or you can attach to the back of the amp input (mono female to double male RCA).

Not to offend, but that's all I can think of to comment in this thread.

CG

Posted by Dan Lail (Member # 18) on May 22, 2006, 10:07 AM:

Great post Chip! I use those a/v boxes too for smooth fast connections.

John, I really do need to try one of those car hi-fi boxes.

Kev, what are the hum cancel coils under the heads? [Eek!]

Posted by Kevin Faulkner (Member # 6) on May 22, 2006, 11:59 AM:

Dan, Under the head block you will see 2 small yellow coils or should I say coils covered in yellow plastic sleeves on twistwd wire. There is one for each track. Put the machine into forward with the lamp on full. Turn up the vol and with the machine set to track one move the coils about by hand or with a non metal item. You will soon see which coil changes the hum. Move it about till you get the least hum. Once you have done this change to track two and repeat with the other coil.
Dont man handle these coils too roughly but you may need to move them quite a bit and even untwist the wires they are on or even tighten them up more. With a lot of rough movement it is possible to snap the wires.
Give it a go...you will be surprised at the results and how quiet you can make the sound on these machines.
This applies to all the Elmo sound machines. They all use the Hum cancellation coil technique for reducing the level of hum.

Kev.

Posted by Dan Lail (Member # 18) on May 22, 2006, 12:19 PM:

Kev, that's fantastic advice. I'll give it a try the next time I plug in the ST-1200. Also, I'll tweek the sound on the ST-800.

Posted by Kevin Faulkner (Member # 6) on May 22, 2006, 03:13 PM:

Go for it. [Smile]

Let us know how you get on.

You can get the GS1200 to be virtulally silent at full volumme by adjusting its coils.

Kev.

Posted by Adrian Winchester (Member # 248) on May 22, 2006, 04:45 PM:

"They all use the Hum cancellation coil technique for reducing the level of hum."

What puzzles me is why didn't Elmo staff do this before each projector left their premises, or is it a matter of further adjustment being needed after years of use?

Posted by Kevin Faulkner (Member # 6) on May 22, 2006, 05:35 PM:

Not quite all machines use that technique some do it in the circuitry such as some of the Noris machines.

I think that the Elmo factory probably set these machines up on a different supply voltage to ours and even frequency?

Certainly machines that have come from Europe and set up for 220V have needed adjustment after changing to 240V for UK use. I think it's down to the different flux levels in the mains transformers.

Does anyone know what the frequency and voltage is for Japan?

Kev.

Posted by Jan Bister (Member # 332) on May 22, 2006, 10:31 PM:

Japan uses 100V (not 110V) at 60Hz.

David:

quote:
Jan, what I meant to say was that you can connect the ST-1200HD monitor outputs to the DI-box, it will convert virtually any audio output to a line level signal.

I had a look at one of these and from what I understand (maybe I'm wrong here?) it's designed to attenuate any signal down to line level, not apply gain to weak signals to bring them UP to line level. If I'm mistaken, by all means let me know... And what does the term "DI-Box" mean, anyway? [Confused]

Kevin:

Brilliant advice about those hum coils, I have to remember that. [Smile]

I don't have any hum problems myself, more of a hissing thing going on, however I just recently demagnetized the soundheads so that should further improve things.

Chip's setup sounds interesting, although I remain skeptical about his claim that even peak signals such as explosions/rumbling only demand 1/3 of a single watt out of his amplifiers. Could it be that whatever display is showing the "watt" usage is not actually related to the power amp itself, but to some part of the pre-amplification stage?

Posted by Kevin Faulkner (Member # 6) on May 23, 2006, 07:47 AM:

That may well explain why these european machines can be made quieter. I wonder how Elmo took the voltage and frequency into consideration when making this very precise adjustment?

Kev.

Posted by David Storm (Member # 509) on May 23, 2006, 02:56 PM:

Jan, Yes that is correct, the signal is attenuated so that the output impedance matches the input impedance. Boosting the signal will only result in more noise.

DI-box = Direct Input box. They are commonly used to connect guitar amps, keyboards and other equipment to mixers and PA-systems. The "car hifi box" John mentioned is basically the same as a passive DI without balanced outputs.

Posted by Jan Bister (Member # 332) on May 23, 2006, 10:23 PM:

I must confess that I don't even understand impedance... have tried many times to educate myself and always walk away confused. I do understand that it's sort of the AC version of resistance in a DC circuit, and that there's a relation between current and voltage that somehow defines impedance... but I remain hopelessly confused.

And how would boosting any signal result in increased noise, unless that noise is present to begin with? Case in point, a turntable needs serious preamplification/equalization before it even reaches line level, which is further amplified to power speakers or headphones... yet the whole system is capable of an impressively low noise floor - if you play a silent portion of a record, it truly is silent (other than the typical slight crackle associated with vinyl)... I don't see why it shouldn't be the same way with the Elmo's monitor outputs.

Posted by Paul Adsett (Member # 25) on May 24, 2006, 09:20 AM:

I tried Kev's trick with the coils on one of my GS1200'S, and it removed just about all the hum on track 1 and reduced hum quite a bit on track 2. I use a 10 band stereo graphic equalizer to 'notch out' the small residual mains hum in the 60hz band.

Posted by Jan Bister (Member # 332) on May 24, 2006, 09:07 PM:

Well, I got my Pocket Amp 2 in the mail tonight [Smile]

so this weekend will see me try it out on the Elmo and then I shall report my findings here. Standby for further details [Smile]

Posted by Jan Bister (Member # 332) on August 13, 2006, 05:31 PM:

Has it really been almost 3 months again? I wish I could just take a one-year vacation from work right now, and work through my to-do list from start to end. [Big Grin]

But anyway - I finally got around to doing a first test run with my Elmo, the Pocket Amp 2 and a stereo film (incidentally my new print of FREEWAY FRENZY). Will post photos later, but for now suffice it to say I have the pocket amp hooked up to the twin monitor outputs, and a 50ft(!) RCA audio cable running from the pocket amp's output to my main amplifier's tape input, all the way up by the screen.

AND IT WORKS!!!

The (battery-operated) pocket amp does a great job pre-amplifying the Elmo sound to line level, so I only need to turn the main amp's volume up to about 11 a.m. to get loud, room-filling stereo sound. Noise and buzzing levels are pleasantly low as well - but better yet, I'm apparently able to start & stop the projector without the resulting 'pop' causing the main amp to shut down the speakers and go into overload protection mode (previously a problem I ran into). It looks like the pocket amp is able to limit those loud pops and prevent them from overloading the main amp. Woohoo! [Smile]

Anyway, as promised - photos to come. [Smile]

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