8mm Forum


Post New Topic  Post A Reply
my profile | my password | register | search | faq | register | forum home
  next oldest topic   next newest topic
» 8mm Forum   » 8mm Forum   » Eliminating Hum in Eumig S 802

 - UBBFriend: Email this page to someone!    
Author Topic: Eliminating Hum in Eumig S 802
Dan Lail
Film God

Posts: 2110
From: Loganville, Georgia, USA
Registered: Jun 2003


 - posted November 15, 2010 10:34 PM      Profile for Dan Lail   Author's Homepage   Email Dan Lail   Send New Private Message       Edit/Delete Post 
I thought I would start a new topic on this since I had success in getting rid of the dreaded hum problem so many have had to put up with in the Eumig S 802. I took the back off and, using contact cleaner, sprayed the record function switch on the circuit board while pushing the red record button several times. Then I sprayed the pots and rotated them several times also.

Now the hum is gone and I have clean loud sound. This was done on an early model from the 1970's. Before cleaning, the hum was unbearably loud and the volume was very low.

 |  IP: Logged

Bill Brandenstein
Phenomenal Film Handler

Posts: 1624
From: California
Registered: Aug 2007


 - posted November 21, 2010 03:59 PM      Profile for Bill Brandenstein   Email Bill Brandenstein   Send New Private Message       Edit/Delete Post 
Dan, I have an 810D that hums and look forward to trying out your procedure on it! Thank you for posting.

 |  IP: Logged

Bill Brandenstein
Phenomenal Film Handler

Posts: 1624
From: California
Registered: Aug 2007


 - posted June 04, 2011 10:56 PM      Profile for Bill Brandenstein   Email Bill Brandenstein   Send New Private Message       Edit/Delete Post 
Well, that was a little while ago...

Just now played with this. Originally I had two electrolytic capacitors replaced, which took the hum from unbearable to noticable. Now I've used contact cleaner on the record switch, two pots, the volume controls, and the Normal/Super switch. Plus I checked the hum bucking coils.

The crackles are gone, but the hum isn't. I'm not sure it even got less. What did I miss?

 |  IP: Logged

Steve Klare
Film Guy

Posts: 6811
From: Long Island, NY, USA
Registered: Jun 2003


 - posted June 05, 2011 08:50 PM      Profile for Steve Klare   Email Steve Klare   Send New Private Message       Edit/Delete Post 
Bill,

You can't ever completely eliminate the hum. The thing is to reduce it to the point where it isn't intrusive and call it a day.

Is the hum you are experiencing through the projector's internal speaker or are you running it through an external amp and speakers?

There are two seperate problems associated with both of these, and you can completely solve one and not begin to solve the other.

[ June 05, 2011, 10:11 PM: Message edited by: Steve Klare ]

--------------------
All I ask is a wide screen and a projector to light her by...

 |  IP: Logged

Bill Brandenstein
Phenomenal Film Handler

Posts: 1624
From: California
Registered: Aug 2007


 - posted June 06, 2011 01:28 AM      Profile for Bill Brandenstein   Email Bill Brandenstein   Send New Private Message       Edit/Delete Post 
Aha! The hum has always been consistent either way in the past, so I've not tried it with an external speaker or line out yet.

After I posted, I think some of the contact cleaner continued to do its magic. The hum really isn't intrusive now but is still present -- sounds like just what you're describing, Steve. Thank you for the tip. More experimenting to come!

 |  IP: Logged

Michael De Angelis
Phenomenal Film Handler

Posts: 1257
From: USA
Registered: Jul 2003


 - posted June 06, 2011 09:59 PM      Profile for Michael De Angelis   Email Michael De Angelis   Send New Private Message       Edit/Delete Post 
Ahhh, the wonderful and reliable Hum-mig projectors.
[Wink]
A Friend told me that a notch filter would eliminate the hum.

Does anyone know how a filter can be constructed?

--------------------
Isn't it great that we can all communicate about this great
hobby that we love!

 |  IP: Logged

Paul Adsett
Film God

Posts: 4844
From: USA
Registered: Jun 2003


 - posted June 07, 2011 08:13 AM      Profile for Paul Adsett     Send New Private Message       Edit/Delete Post 
You can connect the output of the Eumig to a stereo amplifier through a 10 band Graphic Equalizer (obtainable from Radio Shack or Best Buy for about $90.00) and then notch the equalizer spectrum at 120hz (in the USA). This almost eliminates the 60hz mains hum, which is actually the first harmonic at 120hz. I always use an equalizer when showing super 8 films, as they are great for adjusting high and low frequencies for the very best otput audio. For example, you can totally tune out high frequency hiss and low frequency hum without affecting the quality of speech and music, and you can boost high frequency content on the muddy sound tracks of old films. So an equalizer is a great accessory for film projection in general.
The hum problem was totally resolved on the 900 series Eumigs.

--------------------
The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj

 |  IP: Logged

Steve Klare
Film Guy

Posts: 6811
From: Long Island, NY, USA
Registered: Jun 2003


 - posted June 07, 2011 09:34 AM      Profile for Steve Klare   Email Steve Klare   Send New Private Message       Edit/Delete Post 
The thing you run into when you connect a projector into a stereo amp is there is more happening than just the hum you hear in the internal speaker. Both the Aux. output on the projector and the amp input on the stereo are referenced to their chassis, but unless they are perfectly grounded there will be some extra voltage between the two chassis which winds up being part of the signal (ground loop).

I had a really bad ground loop because my entire home entertainment system is actually grounded through the cable TV coax which meets earth out in the garage 75 feet away. Even though the projectors are very well grounded themselves when I plugged everything together I got a nasty low frequency buzz even with the projector audio off. When the audio came on the projector hum just added on to this. It was actually better through the internal speaker.

I thought about this a long time, I took to sketching circuits in my notebook during meetings (I'm an engineer...I can get away with it!) I dragged a projector to work and put a 'scope on the speaker during lunch. Finally one day I decided to stop thinking and just build something and see what happened.

What I did is build a circuit board in a case that sits back with my amp. Its power supply plugs into the switched outlet on the back of the amp. 30 feet of shielded cable run to the table the machines sit on. If it's one machine the cable plugs directly in. If two I have a switch box. Two RCA connectors connect a short cable that runs to a spare input on my Amp.

Inside the box there are a couple of stages of op-amp circuits. Everything is double because this box is stereo capable.

Stage one is a differential amp. It takes the two conductors coming in from the machines and subtracts the voltage on one from the other. This breaks the ground loop by subtracting out the difference in ground voltage between the projector and the amp.

Stage 2 is a notch filter with the notch set at 60 Hz. I was going to do 120 and 180 too to get rid of the harmonics I measured on the 'scope, but I was concerned about wiping out the bass tones in music. 60 Hz represents more than half the total hum power, so getting rid of it gets me most of the way there anyway.

The very last thing before the output is a resistor to prevent damage from short circuits and a small capacitor to take out the hiss above 10 kHz.

I have been very pleased with this. With everything turned on and ready to go, you can hear hum if you put your ear about a foot away from the speaker and the room is very quiet (as I said: you can never completely eliminate it). Under any normal circumstances the hum is completely inaudible.

Building this setup has improved my enjoyment of watching films easily as much as going to a big screen. The sound through the big speakers is booming and the clarity has allowed me to understand dialog that was too muddy before.

--------------------
All I ask is a wide screen and a projector to light her by...

 |  IP: Logged

Michael De Angelis
Phenomenal Film Handler

Posts: 1257
From: USA
Registered: Jul 2003


 - posted June 07, 2011 07:57 PM      Profile for Michael De Angelis   Email Michael De Angelis   Send New Private Message       Edit/Delete Post 
I have a Eumig 822D and 810D machines.
The the treble control knob, that is behind the volume knob does not work and the films sound bassy.
I had a tech repair them and within a short time, the adjustment failed again. Thus, no treble sound.

Will the equalizer alone, correct the low tones?

--------------------
Isn't it great that we can all communicate about this great
hobby that we love!

 |  IP: Logged

Steve Klare
Film Guy

Posts: 6811
From: Long Island, NY, USA
Registered: Jun 2003


 - posted June 07, 2011 08:54 PM      Profile for Steve Klare   Email Steve Klare   Send New Private Message       Edit/Delete Post 
Hey Michael,

What did the tech do to fix the machine?

-and where did you get a movie projector repaired around here?!

--------------------
All I ask is a wide screen and a projector to light her by...

 |  IP: Logged

Michael De Angelis
Phenomenal Film Handler

Posts: 1257
From: USA
Registered: Jul 2003


 - posted June 07, 2011 10:50 PM      Profile for Michael De Angelis   Email Michael De Angelis   Send New Private Message       Edit/Delete Post 
Steve,

The projectors were serviced a long time ago, and
I never had anyone to look at them again.
On the two separate occasions and different service techs.

About 18 yrs ago, I was given the lead of a gentleman who once worked at Eumig USA. in New Hyde Park. After Eumig, this man went into a home furnishing business with his spouse. I begged him for his service, and he was reluctant because he was out of the business, and he had limited time. I don't know if he replaced a transistorized components on the 822.
The sound improved, but then it blew out again. Since then, the furnishing business has been closed.

About a year later, I was given another lead of a man in NYC. I think it was called Projector Workhouse. That man is out too, and the business is closed. He too fixed the treble control on the 810D. I brought the machine home, turned it on, ran about one minute of film, and the treble control blew out as it had on the 822.
I'm guessing that it was a very sensitive transistor component.
It was discouraging, and a waste of money.

A friend told me that he has a neighbor that works with electronics and the amps on these 700 and 800 series Eumigs are primitive and not very good.

--------------------
Isn't it great that we can all communicate about this great
hobby that we love!

 |  IP: Logged

Steve Klare
Film Guy

Posts: 6811
From: Long Island, NY, USA
Registered: Jun 2003


 - posted June 08, 2011 08:12 AM      Profile for Steve Klare   Email Steve Klare   Send New Private Message       Edit/Delete Post 
It sounds to me like they didn't get to the root cause of the problem: something was causing something else to fail. They replaced the something else but didn't fix the something!

It's like if your car's engine overheated and failed because your radiator is clogged up and they replaced the engine but left the old radiator. The new engine will overheat and fail too.

(This is when the mechanic says "They don't make 'em like they used to.")

I think if the failure of the circuit has removed most or all of the treble, the equalizer can't put it back. If nothing else what little is left behind is probably down in the noise level and if you boost it up the noise will come up too.

--------------------
All I ask is a wide screen and a projector to light her by...

 |  IP: Logged

Michael De Angelis
Phenomenal Film Handler

Posts: 1257
From: USA
Registered: Jul 2003


 - posted June 08, 2011 05:45 PM      Profile for Michael De Angelis   Email Michael De Angelis   Send New Private Message       Edit/Delete Post 
Steve,

Thanks for the insight, it all makes sense.

--------------------
Isn't it great that we can all communicate about this great
hobby that we love!

 |  IP: Logged

Bill Brandenstein
Phenomenal Film Handler

Posts: 1624
From: California
Registered: Aug 2007


 - posted June 08, 2011 06:51 PM      Profile for Bill Brandenstein   Email Bill Brandenstein   Send New Private Message       Edit/Delete Post 
My 810D doesn't have a treble control... or does it? The front knob is sound-on-sound dubbing level, isn't it? The second from the front is volume, of course; with the internal speaker, it does tend to be rather bassy, but sounds OK if I run it out to another speaker.

Time to break out the manual. Which, by the way, contains a schematic if anyone here can read those.

Some very good information there, Steve. With all due respect to Paul, I think the graphic equalizer option is the lesser one because it does result in the loss of a great deal of bass. But most of us don't have access to a notch filter (or could build one like Steve). I did once borrow an analog parametric equalizer (now retired from studio use) and got rid of 60, 120, 180, and 240 with tiny notches. Connected downstream to a separate amp and speaker, the Eumig never sounded better. I was hoping to not ever have to consider going to that trouble again.

 |  IP: Logged

Steve Klare
Film Guy

Posts: 6811
From: Long Island, NY, USA
Registered: Jun 2003


 - posted June 08, 2011 08:48 PM      Profile for Steve Klare   Email Steve Klare   Send New Private Message       Edit/Delete Post 
I think the two approaches are different, but either has plusses. For example if I don't like the way a soundtrack sounds I'm basically stuck with the treble and bass knobs on my amp as far as adjustment. Paul has a lot more adjustability when he needs it. Fortunately I seem to have gotten the recipe pretty good for most sound tracks.

Mine has a lot to do with the environment I show films in. Paul has a home theater, but I have (and share) a living room and a dining room. The fact that my sound system lives in the cabinet with my stereo means there is less stuff to set up and put away when my "projection booth" goes back to being the dining room table.

I also do remote shows, and the cable, the power supply and the interface box are small and very portable. All I need is for there to be a stereo at my destination.

One of the things I like most about my setup is for the most part it operates just as if I was just running the machine with the internal speaker. I have a set of standard pre-sets on the Amp that work well and I just adjust the volume on the projector.

The interesting side effect is now I can plug any audio device with a 1/8" phone plug into my stereo. Just after I got the thing working I plugged the laptop in, found some belching sounds on the Internet and nearly killed my 8 year old from laughing.

-oddly, my wife missed the comedy of the situation!

--------------------
All I ask is a wide screen and a projector to light her by...

 |  IP: Logged



All times are Central  
Post New Topic  Post A Reply Close Topic    Move Topic    Delete Topic    next oldest topic   next newest topic
 - Printer-friendly view of this topic
Hop To:

Visit www.film-tech.com for free equipment manual downloads. Copyright 2003-2019 Film-Tech Cinema Systems LLC

Powered by Infopop Corporation
UBB.classicTM 6.3.1.2