Audio Out for Eumig 824 Sonomatic

[Ethan Knightchilde]

Unfortunately this has been a futile effort. I checked the fit to the projector, checked the pins to the wires, soldered according to balanced (2 to ring and 3 to tip), checked with the ohmmeter to be sure all was well after the operation, plugged it all in, got a pleasant projector hum through the speakers and then… nothing. No film sound through the speakers at all.

[Ethan Knightchilde]

To clarify, I used what this connector labels as 1 and 2 because the 1 pin at 3 o’clock would mate with the 3 female connection at 9 o’clock on the projector. I also tested from the projector housing to the ring connection and got a reading on the ohmmeter.

[Steve Klare]

We're not done yet, Ethan!

It's possible that your mixer expects a connection not tip and ring, but tip and sleeve. If your mixer jack is TS and you plug something TR into it, there will be no connection.

Maybe if you unsolder the connection from pin 2 and move it to the sleeve terminal (you could even temporarily jumper it with a clip lead), your audio will come through.

When this connection is correct, you should be able to unplug the machine from power, plug your new cable into the machine only, and measure between 50,000 and 100,000 Ohms on the two connected terminals on the 1/4" plug (Just like at post #33). That's how you can be sure you are connected to pins 3 and 2 on the 5 pin DIN. The 1/4" TRS terminal that's supposed to be connected to pin 2 should also measure a very low resistance to the projector chassis and the grounding pin on the power plug.

[Ethan Knightchilde]

Ok. Move pin 2 from ring to sleeve. I’ll give it a shot later tonight or tomorrow. Thanks.

[Ethan Knightchilde]

That worked! Although there is a horrible background hum. :/

[Steve Klare]

Welllll....

That's not completely unexpected here. These Eumig 800 series machines have a lot going for them, but hum performance is not exactly their strength!

What's also going on here has something to do with how we hear these things with modern ears. Modern audio systems have extremely low hum, and we are used to them sounding that way. Then we plug in something built while the Berlin Wall was still years from falling and the hum is irritating! Maybe when we were little kids it would have sounded much better: things all around us just naturally hummed. A dear old film-friend of mine decided he liked the hum. (We all cope in our own ways!)

In setups like this: hum basically comes two ways: ground loop (common mode) and audio system (differential mode). Hopefully your mixer's balanced inputs have nullified any ground loop hum.

You can tell which is which this way: audio system hum rises and falls with volume, ground loop noise is there even with the amplifier turned "off", since it actually originates in the ground wiring between the projector and the amp.

What happens when you mess around with your volume level?

The audio system noise (NOT ground loop noise) exists at least partially because there is a very sensitive magnetic sound head which is subjected to stray magnetic fields. Eumig put hum buck coils in series with the head which are bathed in the same stray magnetic field and hooked up so that the voltage they pick up is equal and opposite to the head and should cancel out the hum voltage headed to the amplifier. Since yours is a twin track machine, you will have two (Post #42 in this thread). If you move these around to optimize their position in the field, you can fine-tune this cancellation. I've never had a lot of luck with this (maybe mine is as good as it gets!), but if you search here and in the Archive forum for "hum buck coil", maybe you can find wisdom far beyond my own.

There may be something easier you can do right now. If your mixer is like mine, it has a little bit of frequency equalization built in. There are knobs marked "high", "medium" and "low", and "low" is marked "60 Hz.". This would be a happy coincidence if it wasn't on purpose! 60 Hz. is the North American power line frequency and the root of all evil where hum is concerned.

If you have a control like this for the channel your Eumig is plugged into, maybe you can take the edge off the hum if you dial this control back.

Could be the big capacitor in the audio circuit: I changed mine, if it helped, it didn't help nearly enough. I've seen others report the same results too.

[Ethan Knightchilde]

Hum increases with volume and yes, the mixer has the 60 Hz knob. I’ll try that out tomorrow. I worry the sound will seem “tinny” if I turn that knob all the way down, but it’s gotta be better than that loud hum. (Sounds like an old radio console warming up but it stays that way throughout.)

[Ethan Knightchilde]

Well that did it! There is still hum of course, but nothing like what it was with the 60 at a normal level. Turning up the mids a bit and the highs down some gives an acceptable sound.

Thanks all for your help. I’d never have been able to do this without your advice.

[Steve Klare]

My pleasure! I was pretty well set up to help you here: I did the exact same thing myself maybe 10 years ago.

My experience with hum is as time passes, you acclimate to it. My sound system has an active notch filter between the mixer and the amp, so with an Elmo projector at normal volume settings the hum is pretty much gone. (-with my Eumig? Not so much!) If I travel with the same machines, I leave all the complications home and operate unplugged. At first the hum through the internal speaker sounds downright awful: second or third night I barely notice it anymore! The only thing different is my own perception of it.

Besides, I operated that way something like a decade.

Strange: hum is actually useful to me. When I first turn everything on I grab a mixer knob and turn it up to levels I would never use with a sound track. If I don't hear any hum, something is wrong!

[Ethan Knightchilde]

I don’t mind some hum. That’s just part of the experience. Old radios and record players had the same thing. But this was LOUD. I mean, it was overbearing and competed with the soundtrack. Nothing like that came from the projector speaker or even using the Elmo speaker connection. Turning off the low end brought it down to a reasonable level that was easy to acclimate to!

[Brian Fretwell]

ONe advantage of 50Hz mains a lower frequency hum that means you neeed to cut the low end even lower and miss less.