8mm Forum: Where's The Hum Gone?

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Posted by Maurice Leakey (Member # 916) on July 20, 2014, 05:47 AM:

Years ago I bought new a Eumig 807D. The hum was very noticeable and the amp didn't have much "punch". For my public shows I bought a Craven amplifier, supposedly with a built-in hum filter.

Yes. It not only amplified the projector's output it also amplified the hum to an unacceptable level.

A year or so later it was replaced for public shows by a Bell & Howell DCR which had enough output and even on maximum there was only a slight trace of hum which was quite acceptable.

Recently I have bought a Eumig 810D HQS [High Quality Sound].

Where's the hum gone? No trace of hum and the amp delivers bags of volume. What have the wizards at Eumig done?

It's a nice kit in a fitted case with separate external speaker and a daylight viewing screen.

Posted by David Ollerearnshaw (Member # 3296) on July 20, 2014, 06:08 AM:

This could be the give-away. High Quality Sound.

Eumig did have a poor reputation for hum, one of the reasons I bought ELMO ST1200 (plus 1200ft spools). With the arrival of the High Quality Sound series the reviews seemed to get better on the sound front.

Currently looking for a standard 8 projector myself.

Posted by Steve Klare (Member # 12) on July 20, 2014, 07:35 AM:

The Eumig 800 series has absolutely miserable internal grounding. When I was developing my sound system I was measuring the voltage between the chassis and the ground at the outlet of various projectors to figure out how bad the ground loop could be. A couple of Elmo machines were running well under .1V, but my Eumig 800 series was about half a volt.

The thing is this voltage winds up mixed in with the audio signal when you run it out to a well grounded external amplifier and the hum can be awful.

If I remember right the problem came down to the ground line running to the power transformer instead of the the projector chassis and the grounding of the chassis was only as good as the contact at the transformer mounting points.

At the time I griped this publicly and found out I'm not the only one to see it.

I set that machine aside as far as the sound system, but I think a couple of star washers installed between the transformer and frame would really improve that contact.

Posted by Andrew Woodcock (Member # 3260) on July 20, 2014, 07:53 AM:

Unbelievable that even in the era these were made, such a basic design flaw would be overlooked and sent to market. Really poor on Eumig's design and marketing teams behalf. Just as well they got it sorted in the later years or else they would probably have gone out business much sooner than they actually did.

Posted by Steve Klare (Member # 12) on July 20, 2014, 11:18 AM:

Kevin F. said he actually got a mild shock off of one of these because this voltage grew so large.

So it isn't just an audio quality issue, but a potential safety issue too.

Posted by Brian Fretwell (Member # 4302) on July 26, 2014, 05:03 AM:

I remember my old 710D had two coils mounted on flexible steel arms that were supposed to have been adjusted during manufacture to reduce the hum. They didn't!

Posted by Rob Young. (Member # 131) on July 26, 2014, 09:46 AM:

Yes, Brian, but if you find a used 710 or 810, it is worth moving those coils to try and reduce the hum.

Often they get moved over the years and you can radically reduce the hum with slight adjustments.

Although it never disappears altogether, as others have pointed out, it was a pretty poor design.

Posted by Osi Osgood (Member # 424) on July 26, 2014, 12:09 PM:

"Where has all the humming gone ...
Long time passing ...
Where has all the humming gone ...
Long time ago ...
Where has all the humming gone ...
Gone with good techs everyone ...
When will it ever run?
When will it ever ... run? "

[Big Grin]

Posted by Paul Adsett (Member # 25) on July 26, 2014, 12:23 PM:

He's back! [Big Grin]

Posted by Osi Osgood (Member # 424) on July 26, 2014, 12:34 PM:

Yeah, but I gotta go home, I can't play anymore, the wife calls!

Coming honey!! [Smile]

Posted by Graham Ritchie (Member # 559) on July 26, 2014, 01:41 PM:

Don't forget folks, that song has a strong reverence to those that have lost there lives in "war" and should not be altered in any way for humour....Its a song that has certainly stuck in my mind since first hearing it way back in the 60s.

Take the time to watch "Where Have All The Flowers Gone?" sung by Marlene Dietrich live at the Royal Variety Performance 1963...its on you-tube.

Graham.

Posted by Erik Snel (Member # 4017) on January 10, 2015, 11:05 AM:

i know for a fact that the 60o silent series also have ground problems because the metal of the transformer has current too. i know this because it freakin hurted when i touched it by accident. so this may be helped if i better connect the tranfsormer to the ground point of the power inlet? same goes for the sound models is have [Smile]

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