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Posted by Michael Wright (Member # 1387) on December 12, 2008, 05:37 AM:
Hi, I have just joined the forum and have a question about hum on this machine. I know Eumig have a bit of a reputation for this problem, but this one is really bad. I have heard of hum bucking coils but I can't see anything in the projector that looks like a coil near the sound head. Can anyone tell me what I should be looking for or other tips to improve the situation. Thanks MIKE
Posted by Steve Klare (Member # 12) on December 12, 2008, 05:50 AM:
Hi Michael,
Try looking under the soundhead: in other words between the head and the baseplate of the machine.
These machines tend to be hummy and any amount of twiddling with the coils will not cure it completely. With mine it's actually better to play it through the internal speaker as a larger external speaker has better bass response and will aggravate the problem.
Posted by Paul Adsett (Member # 25) on December 12, 2008, 09:05 AM:
Hum was the plague of the Eumig 800 series. It can be reduced by adjusting the position of the little hum-bucking coil situated right underneath the sound head. Remove the side cover and set your projector to play with sound, but with no film, and turn the volume control way up. Carefully move the hum bucking coil around to minimize the audible hum level.
Another way is to feed the output of the 807 thru a 10 band graphic equalizer and then to an external amplifier, and notch the equalizers filter settings at 120 hz.
Posted by Steve Klare (Member # 12) on December 12, 2008, 09:35 AM:
Hi Paul,
Have you found that the 120 Hz. notch effects bass tones in music?
I've played around with passive filters and found that by the time I get enough roll off to really knock down the hum, music starts to sound tinny.
A graphic equalizer is an active filter, and would be much more frequency specific (narrower band-stop). At the least it should allow more of the frequencies other than 120 Hz. through.
Posted by Paul Adsett (Member # 25) on December 12, 2008, 10:55 AM:
Hi Steve,
The way I set up my Yamaha 10 band graphic equalizer is to notch down -6db at 120 hz, while actually boosting the bass levels by +6db at 30,60, and 240 hz. The hope is that this produces a very sharp 12 db notch around 120hz so you don't lose too much bass. It certainly works a lot better than a simple bass control. I only do this when running my Eumig 820. On my version 2 GS1200 there is no significant hum, so I do not notch out at all at 120hz. But for my older version 1 GS, I do notch out the hum just on track 2, which has an audible level of hum. I also use the equalizer to boost treble levels on 'muddy' sounding mono film tracks, and I also totally notch out (-12db) all films at 16khz to eliminate hiss. All told, I find the equalizer a great tool for improving the playback quality of super 8 sound tracks.
Just to note, that the hum problem on the Eumig 800's was essentially eliminated on the later 900 series machines, where the transformer was located much further away from the sound head, and they also improved the shielding of the head.
Posted by Bill Brandenstein (Member # 892) on December 12, 2008, 11:54 AM:
Really the answer is a parametric equalizer. Unfortunately a piece such as Klark-Teknik's DN 410 still is worth a little bit of money. The advantage is making the notch TRULY narrow, plus you can do it at several frequencies without making the whole sound range tinny.
I've never actually tried this. But it might be worth a try.
Posted by Martin Jones (Member # 1163) on December 12, 2008, 12:44 PM:
There are simple, but VERY effective notch filter circuits around using Operational Amplifiers and resistor/capacitor combinations. Using these, it's possible to obtain 40dB (or better) reduction at specific frequencies. 50, 60, 100, and 120 hz are the important ones (depending where you live).
As suggested, these are used between the Line Out jacks of the projector and an external amlifier and speaker.
As I've said before, commercial "hum filters" intended to go in the speaker leads are USELESS.
Martin
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