8mm Forum: Adding an Audio Mixer Panel

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Posted by Steve Klare (Member # 12) on December 15, 2014, 12:56 PM:

I’ve been messing around lately incorporating a mixer panel as the front end of my sound system.

The Behringer Xenyx 802 Mixer: honorary cinema gear!

What this thing does is take two monaural audio signals and two stereo signals and blend them together into a single stereo mix that is then available at line level to amplify or record or whatever the user wants. In my case I amplify it and shoot it into the speakers when I'm showing films.

At first glance this might seem like greatly overcomplicating things, but for better or worse, real world Super-8 sound gets awfully messy, and this actually helps simplify things a lot.

If you are using a single projector connected to an amp, and your sound is nice, you absolutely don’t need this. Unfortunately, things didn’t stay that simple for me. For example, my favorite mode of operation for years has been two machines side by side. When I built an interface between a single projector and my stereo amp, I was happy as a clam until I reverted into changeover mode. At first this was stopping, turning off the amp, re-plugging into the second projector, repowering everything and starting up the new reel. This is the very opposite of a seamless changeover!

I‘ve been running on a box with a selector switch: better, but a long way from ideal.

What the mixer does for me in this case is add (mix) the two projector audio signals together into a signal sent out to my amp at whatever levels I like. I turn them both up to normal levels as a changeover approaches, do the changeover at the machines and turn the level of the empty machine down before that obnoxious end of film signal comes booming through my speakers.

Another issue is the classic twin-track to stereo dilemmas of Elmo projectors. My audio interface is stereo capable, but I’ve rarely ever used it this way because stereo operation is such a pain it the butt! This panel greatly relieves this pain!

The twin track outputs on the GS-1200, ST-1200HD (and maybe the GS-800?) are fixed volume. This is no big deal if you have a volume control on your amp, but it still is for me because my amp is 15 feet from the machines and a good 30 from the screen. I really need that control close to where the audience is sitting so I can judge how loud “loud” really is. Otherwise I might get tired from all this walking back and forth and give up! “YES, I KNOW IT’S VERY LOUD, BUT I’VE HAD A LONG DAY AT WORK AND I JUST WANT TO LAY ON THE COUCH AND WATCH A FILM!!....I’M SORRY, OFFICER!!!”

This panel puts a volume control right next to the machines, as a matter of fact: several volume controls (more on that later…).

When I first hooked my ST-1200HD into my stereo, running my first true stereo presentation, I was feeling awfully pleased with myself until I started a second reel (monaural), and all of a sudden I only had sound in the left channel (…so much for ego!). You see “monaural” and “left” are the same sets of jack contacts and the setup was doing exactly what it was supposed to do. The problem was that there was no “right” soundtrack on the stripe to drive those speakers.

To solve this I'll give a twin track machine one stereo input and one monaural input and use the individual level controls to choose which. –no swapping cables, just flexibility.

The ST-1200HD twin track outputs are pretty wimpy level wise: with this I have a pre-amp for them and can bring them up to a comparable level with the other signals I’m operating with. I chose this particular panel because it has enough inputs to do this for two twin track machines. There are other panels in the series with more inputs (plus one with fewer), but I’m hoping it will never get more complex than this!

All four inputs each have a simple equalizer: low, mid and high ranges. I’ve noticed my ST-1200HD sounds muddy on some films. I’ve been able to make these sound a lot brighter by boosting the mid-range up. The upper range is beyond the high frequency capability of most Super-8 mag sound tracks and all of my machines, therefore it is basically a knob for choosing how much hiss comes through the speakers. Naturally I’ve decided to keep these controls turned all the way down.

One important thing this does specifically for me is coping with a fault I unknowingly built into my interface box. I discovered after the fact that my home made audio interface is very touchy about the value of the resistors in the line level outputs of the projectors connected in. It is “tuned” to the 600 Ohms in the monaural auxes of an Elmo ST. Hook in anything else with a different resistance (For example: Doug Meltzer’s GS-Xenon at CineSea and my Eumig 800 series all the time) and now I have ground loop hum. I believe now that I’ve compensated my interface for the output resistance of this panel (it hummed at first too...), I should be able to connect basically ANY line level device to the input and have the speakers stay as quiet as church mice where ground loops are concerned. (Stay tuned: I haven’t tried this yet.)

Each monaural channel has a “pan” knob. Normally this sits dead center and the channel is equal in right and left speakers. (This is so a vocalist can be placed in each channel, actually). Being that I have a pretty wide screen I figure I can now show two films simultaneously with the sound tracks in their own speakers. Granted, this is a disturbing idea, but someday I will get bored and almost certainly try it!

Even with all these good things (and even that just plain weird thing…) this is real life: so there are drawbacks here.

This is basically 6(+) independent audio channels for the input and two(+) for the output (there is other stuff I will never, never use). Each stereo channel is not a nice, standard 3 conductor phone plug like most consumer electronics, but instead two monaural channels (with independent jacks) working together. Also, the Elmo audio connection standard is 1/8” (3.5mm) plugs (my standard too, BTW) and this unit is based around ¼” jacks and plugs. Choosing to go this way means a symphony of adapters and short cables and the sanity to keep them sorted out in your brain and connect them where they should connect.

There are also A LOT of knobs here. Sitting in front of this thing is like discovering your new car has 3 brake pedals, 5 gas pedals and 2 clutches! If you start counting with the volume controls on my projectors and finish with the one on the amp, each audio channel can now have as many as 5 volume controls associated with it!

Life with this NASA-like thing is basically fiddling with each of these, appreciating what they really are meant to do, finding a good level they can stay at and ignoring all except maybe one per channel plus the main (mix) volume. Simplicity is a great source of sanity in our lives, and even here it is achievable!

It pays to remember the operating environment is usually DARK and not friendly to fiddling with this many knobs all the time!

It doesn’t take a lot to get started here. This runs around $65.00 (plus all that cabling..), and there is a simpler model that runs fifty-ish. As a bonus it is available brand new and all over the place, unlike a LOT of the stuff we need!

I’ve had mine almost a year. I got it at a time when I didn’t have time to really explore it, and set it aside. This last week I’ve been really digging into it and am more and more pleased every time I do!

Posted by Osi Osgood (Member # 424) on December 15, 2014, 01:15 PM:

Steve ... you have my admiration!!!!

Could that be equally used to mix and then record magnetic super 8 tracks as well?

Posted by Steve Klare (Member # 12) on December 15, 2014, 01:35 PM:

Thanks, Osi!

It's generally useful for a lot of different varieties of messing around with multi-track audio. It's intended for a small portable setup like a garage band (it has two mic inputs) as opposed to the immense, expensive mixer panels a recording studio or an arena concert would need.

Just by a happy coincidence it also does exactly what I needed!

I wanted to build something like this, but at this price and this level of function I would work weeks to produce something a tenth as nice. (Just not worth it...)

Posted by Graham Ritchie (Member # 559) on December 16, 2014, 01:10 AM:

That looks good Steve...the only mixer I have at the moment is a four channel "mono" in and one mono out. Mike Kent from Film Making days did it as a DIY job back in the 70s so I made one, and has worked really well.

However I do like the idea of mixing both stereo and mono, and in particular the stereo out. I must look out for one. The last time I used the mixer, was our wee DVD on the cinema where young Chris recorded the dialogue separate onto a tape in the "quiet room", while viewing the final DVD. The mixer was brilliant for the job of backing off the sound of the projectors etc and bringing in the dialogue. Oh also used it for the you tube-video on the Ernemann 2.

A good sound mixer is must these days for all kind of things... will have to look out for one of those units, it does look. [Cool]

Posted by Andrew Woodcock (Member # 3260) on December 16, 2014, 05:22 AM:

I remember reading that very edition of Movie Maker only a week or so ago!
Quite primitive by modern day standards but obviously from what you are telling us very effective all the same!

Posted by Steve Klare (Member # 12) on December 16, 2014, 07:59 AM:

Graham,

These mixers are very easy to find. This one came from Amazon. They are also available at local music stores, and there are usually quite a few on E-bay.

The key to buying these internationally is there may be only one model of each mixer for the whole world, but if you get one from someplace else it may not come with the right power supply for your local AC connection and house current. You can buy the power supplies separately, but why complicate life?

The microphone inputs are intriguing...

I could plug in a mic., turn up my speakers and never lose an argument again!

...then again there are TWO inputs, aren't there!

"I don't like your tone of voice! Turn down your midrange now or so help me, I'll boost my bass!"

Posted by Graham Ritchie (Member # 559) on December 16, 2014, 11:48 AM:

Hi Steve

There is a good music store in the central city... I will chat to them after the holidays [Smile]

Graham.

PS Andrew... Mike Kent was with "Film Making" not "Movie Maker" and was a great DIY person who also wrote a very good book...I still have it somewhere. [Smile]

Posted by Steve Klare (Member # 12) on December 16, 2014, 01:06 PM:

As I said: mine is a simple mixer for simple applications.

Meet Big Brother: (...yet far from the biggest)

In our terms this is four twin track projectors operating in mono/stereo mode plus enough spare inputs to mic. a barbershop quartet! (OH! the cabling!)

(What a show that would be!)

I DO like those sliding controls, though!

Posted by Graham Ritchie (Member # 559) on December 16, 2014, 09:41 PM:

Now we are talking [Smile]

...I want the "big brother" just to play with the sliding things [Cool]

never mind plugging it into anything [Wink]

Posted by Steve Klare (Member # 12) on December 17, 2014, 10:50 AM:

Manufacturer's suggested retail for this panel is $569.99 US ($379.99 on sale right now)

Go for it, Graham!

The nice thing with these panels is as long as you establish good standard settings for things like the amplifier and projector volumes, this could centralize your audio operation to a single place.

In my dream home cinema this sits in a recessed shelf between the two projectors, inside my dream projection booth/editing room/film vault...

(There's a small steam powered railroad out in the dream back yard...but that's another story!)

Posted by Gary Crawford (Member # 67) on December 17, 2014, 02:36 PM:

That's a great solution to so many problems. All I have is two little Radio Shack mixers...to handle left and rights of the two elmo 8mm machines in the booth and a cd player, and two 16mm projectors. And yes..the output from the st1200 monitor jacks is VERY wimpy...even when mixers are full force. And , like you,Steve, my actual power amp is in the screening area, not the booth.
Now normally I wouldn't do what I am about to describe, but the signals from the st's are SO wimpy that I thought I'd try this and it has worked beautifully. I know about impedance and the bad things that can happen, but I tried plugging the projector outputs into the MIKE jacks of the mixers. Result: perfect levels...AND somehow...better highs and lows overall In this case the projector levels are so low there is no overdriving, no distortion and no clipping. I don't thing the levels coming out of those st1200's are much higher than what you'd get with a powered condenser microphone, anyway.
Also....I started using the old wireless baby monitors in the booth. Transmitter in the actual screening room , receiver in the booth...and now I have at least a pretty good notion of levels in the screening room right from the gitgo. Works pretty well...and I can also hear my audience saying "turn it up" or "turn it down" and react to it quickly.
But I do envy that mixer set up of yours, Steve!!!!

Posted by Steve Klare (Member # 12) on December 17, 2014, 04:16 PM:

-and there's human nature hard at work!

I envy YOU for having a booth to project from.

The joy of this mixer is it really isn't much to envy. It's pretty affordable and once you get past its complexity it's actually pretty easy to live with.

It isn't really that complex either, it does fairly simple things but it does them multiple times. If you got rid of all the controls that duplicate what others do on different channels it would be 10 knobs max!

-then again, does the world really need a single channel mixer? It wouldn't be much more than a preamp with a fancy tone control!

Posted by Graham Ritchie (Member # 559) on December 17, 2014, 10:32 PM:

Actually those prices are pretty good, although I cant see my financial advisor "the wife" agreeing to any of it....but its a nice thought [Smile]

Posted by Steve Klare (Member # 12) on December 30, 2014, 05:03 PM:

I moved onto another stage of this experiment today.

Earlier I mentioned I have an interface I built which is intended to get rid of the hum caused by ground loops, but unfortunately it fails more or less miserably if driven by anything but the 600 Ohms in an Elmo ST Aux output.

The Elmo GS Auxes are also 600 ohms, but they are stereo, so effectively they are 300 Ohms: hum. The mixer itself is 120 ohms per channel and also hummed until I hung an extra 1080 Ohms in each channel and shut it up. (A GS-1200 aux pair should work fine with 600 ohms added per channel)

Today we faced the ultimate: a Eumig 800 series. This character has a whopping 50,000 Ohms in series with the aux! This is about 80 times what I need it to be to make that circuit work right.

The theory is that the mixer itself can cope with ground loop issues and as long as the mixer plays nice with the interface box I should be OK.

I made a cable to patch the Eumig Aux. into the mixer, and I'm pleased to say it works quite well, especially compared to what it was like when I plugged in directly.

The differential hum (what you also hear through the machine's internal speaker) was worse than with an Elmo, but I was able to bring that into line with the bass control on the mixer. It's only noticeable when the sound track is very low or silent.

The nice thing about this is because of the disagreements this machine has had with my sound system it has been sidelined for a while. Now what is my original sound machine will be getting more screen time.

Next: Operating an ST-1200HD in stereo (with monaural option)

-makings for the new cables have been shipped and I'm very interested when I get the mail these days!

[ December 30, 2014, 06:51 PM: Message edited by: Steve Klare ]

Posted by Steve Klare (Member # 12) on January 02, 2015, 05:17 PM:

A package showed up from Digikey today with two 3.5mm monaural cables (one for left, one for right).

After I soldered on the 1/4" plugs for the mixer end we now have stereo!

(Even came out the correct channels on the first try...but then again I had a 50/50 shot!)

NEXT: Cable Management!

Posted by Mathew James (Member # 4581) on October 02, 2016, 05:00 PM:

Steve said above:"To solve this I'll give a twin track machine one stereo input and one monaural input and use the individual level controls to choose which. –no swapping cables, just flexibility."

Can you explain this part for me further please Steve. I am on this myself currently, and is how i stumbled on this informative thread.

Basically, I am noticing that the built-in speaker sound on my ST1200HD is starting to get to me, me being the one to sit next to the projector all the time, as operator,although on the right side(facing projection) and speaker is on left, i am finding it is just too loud and tingy sounding overtime...
I thought yesterday to try some computer speakers i have, ones with its own amp, it it was much better, but like you, I found only sound in one speaker,Left.
my question: I have a preamp in a box somewhere i can probably find and use...and i will keep my eye out for a mixer for better control, but in the meanwhile, is there any other way, with what i have to get sound to both speakers, even if mono being duplicated and fed to the right channel, for now?

On another point regarding stereo. To me, true stereo is when you record 2 separate sound files simultaneously at different positions...for example, if you put a small microphone under each ear, it would record 2 separate sound files since you will hear sound differently in each ear,Stereo. You then would put both of those sound tracks onto your media, ie Super 8 would have 2 mag strips, one for what each 'ear' would hear, that you would then split into 2 speakers (L R) ultimately.
Since my films are only 1 track(mono), I am only looking to duplicate that one track, but into 2(or maybe more) speakers. Hope this makes sense to what i am trying to achieve!

Posted by Steve Klare (Member # 12) on October 02, 2016, 05:56 PM:

Basically it comes down to this: you can think of a monaural film and/or a monaural projector as being stereo channel "left" only.

The monaural sound winds up on the tip (mono) of 1/4" or 1/8" audio plugs and the sleeve (ground).

Stereo sound is tip (left) ring (right) and sleeve (ground).

-so if you plug a monaural projector into a stereo system or play a monaural film on a stereo projector you will wind up with just "left" since "mono" and "left" both use the same jack contacts.

What the mixer lets me do for twin track machines is have a monaural channel that gets sent equally to both stereo amplifier channels PLUS an independent stereo connection, and the ability to choose between them.

This way when I go back and forth between monaural and stereo films I just twist some knobs instead of fumbling with plugs, cables and jacks in the dark.

Monaural machines just get a single channel that gets sent to right and left equally.

Since I wrote all this I've reached the conclusion that Super-8 stereo is pretty underwhelming(1), and just for simplicity I run blended monaural even with stereo films. Here and there I get the other cables out and go all out, but it's not exactly on par with switching over to cinemascope!

(1)Once I hooked up Doug Meltzer's GS through my stereo amp at CineSea. We may or may not have gotten "right" and "left" swapped, but it was hard to tell one way or the other!

Posted by Janice Glesser (Member # 2758) on October 02, 2016, 08:46 PM:

I just daisy-chain a couple of small guitar amps. Same mono channel on each amp...but the sound is remarkably better than from the projector speaker.

Posted by Mathew James (Member # 4581) on October 02, 2016, 09:16 PM:

Thanx for explaining that Steve, I understand now. I think a mixer is a good idea ultimately.
Until then however, i am going to try what Janice does! I didn't think to try this and i just happen to have 2 guitar amps. I hardly amp my taylor guitar anymore...too lazy and i don't play live anymore. I have a Roland Ac-100(100W) and I also just got a smaller peavey 40W for my son, so i try with it. Fantastic!
Can't wait. Thanx very much for the advice folks!

Posted by Steve Klare (Member # 12) on October 02, 2016, 09:32 PM:

What you run into is the signal is a lot better than the internal speaker in the projector. As soon as you plug in something nicer you have all sorts of bass and treble you never even imagined!

The other shoe that often drops is better speakers often bring up the nasties too: hiss and hum in particular.

-but we'll cross that bridge when we get to it!

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