|
Author
|
Topic: Popping GS1200
|
|
|
|
|
David Pannell
Phenomenal Film Handler
Posts: 1072
From: Horsham, West Sussex, UK
Registered: Nov 2004
|
posted June 13, 2008 05:56 AM
Graham,
I am sure that Kev Faulkner can give you the definitive answer to this, if there are any special peculiarities with the GS.
If you get this popping through the internal speakers, you should get the same through any extension speakers connected.
However, there are two rules of thumb with regard to audio amplifiers which should always be borne in mind.
1. NEVER operate an amplifier with the speakers disconnected. The voltage at the output device (output transformers, transistors or ICs) can rise to levels that will damage the output device. The design load of the speaker is matched to the output impedance of the output device to prevent this.
You can, however wire in a resistor of similar resistance and wattage rating instead of the loudspeaker, which will load the output stage of the amplifier correctly. You could even arrange to switch the resistors in automatically whenever the speakers are disconnected.
2. The popping is sometimes caused by a small arc or spark in the on/off switch, and the resultant back e.m.f. producing a spike in the amplifier circuitry. This can often be cured by connecting (soldering) a 0.1uF capacitor across the CONTACTS of the on/off switch. It must be across the contacts, - NOT across the mains supply. The rating of the capacitor should be at least twice the mains voltage.
Best regards,
--------------------
Dave.
Valves and celluloid - a great combination!
Early technology rules OK!
| IP: Logged
|
|
|
|
|
|
|
|
Paul Adsett
Film God
Posts: 5003
From: USA
Registered: Jun 2003
|
posted June 13, 2008 06:59 AM
Several years ago I got fed up with the snap, crackle, and pop of my version 1 GS1200, and disconnected the main speakers. So far this has not caused any problems, and since I always run the machine with the AUX output connected through a 10 band equalizer to my Sony stereo amp, I do not miss the internal speakers at all, and the projector silence is golden! Incidentally, none of my other projectors (all Eumigs) have this 'Rice Krispies' phenomenon, being totally silent when powering up or down. And I have also noted that the GS1200 is supersensitive to switching activity within my house, particularly in the same room.
--------------------
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
|
|
|
|
David Pannell
Phenomenal Film Handler
Posts: 1072
From: Horsham, West Sussex, UK
Registered: Nov 2004
|
posted June 13, 2008 07:55 AM
Thanks for the info input, Kev.
As I said, it was just a rule of thumb; all projectors, audio amps, etc have their idiosyncrasies both in design and components used. Clearly the ones you refer to don't present the usual problems, particularly if the devices already have protection built in. Actually, it all amounts to the same thing - protection is required.
Again, thanks for the clarification.
Best regards,
--------------------
Dave.
Valves and celluloid - a great combination!
Early technology rules OK!
| IP: Logged
|
|
|
|
|
|
Rick Skowronek
Expert Film Handler
Posts: 120
From: Marietta Georgia USA
Registered: May 2005
|
posted June 16, 2008 06:19 PM
Hi Guys,
Been awhile since I've been a responder to the forum but check in regularly. Always enjoy the expertise here in one of my side hobbies, albeit not as much a hobby as I would like to have the time for.
Just thought I'd add a few cents worth to this thread if I may as a long term EE and one who has designed and built audio amps all the way from the old tube days to now.
Everyone is fairly correct but in the case of solid state devices both ICs and transistors there are some sorta misconceptions partially hung over from the "old" days. Yep, I'm older, LOL.
Anyway, in the old tube days it was pretty disastrous to the circuitry if you removed the speaker load. Without getting into the physics, it had to do with the fact these were all transformer coupled devices and the speaker was a reflected load back to the output circuit keeping it in balance. Remove it and this circuit could easily go into a runaway condition. Luckily tubes were pretty hearty so if you didn't let it go too long till it fried the tubes, no harm.
Now, along comes transistors and audio ICs. In the early days any sudden transient could easily cause the output device to cruise past it's max ratings and this would cause an immediate failure. Basically either shorting (nasty) or opening which created no output but less smoke. The difference is, however, that removing the speaker load prevents any over current transient while not bothering the circuitry a whit.
So, in the basic answer to the original question of whether removing the internal speakers from the output would hurt the projector, the answer is an unequivocal no. The output ICs would see a very small current increase on a "pop" but certainly nowhere near what they would see with either the internal speakers (pretty small load) or, more importantly, external higher load speakers. Certainly, per Kev, you should spend some small time cleaning the switches to help prevent the circuit transients especially common with older brass or copper contacts.
Regards to all in the forum.
Rick
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Rick Skowronek
Expert Film Handler
Posts: 120
From: Marietta Georgia USA
Registered: May 2005
|
posted June 18, 2008 06:36 PM
Since it seems like there's a lot of interest in this topic, and there rightly should be with possible damage to irreplacable ICs possible, thought I'd throw a little more "theory" the forum user's way if you're interested.
Everything everyone has said is right on as to impedances and series or paralleling speakers. Just like Ohm's law says, putting impedances or resistance in series adds and putting them in parallel halves it. Current through the speaker and ICs also follows by doubling or halving it. One of the interesting things however are speakers. These really have less resistance than what their rated value says. In fact, any of our esteemed members that have a multimeter with the ability to measure DC resistance should, just for fun, measure a regular speaker that is rated at say 8 ohms. You'll actually find it much less.
In reality, the speaker is what is called an inductive load and it's impedance (resistance) varies by the frequency applied to it. The higher the frequency (treble) the higher the impedance. The lower the frequency (bass) the lower the impedance. Most speakers are basically rated, impedance wise, at 1000 Hz. At that frequency they roughly exhibit the stated impedance like 8 ohms.
That's why amps need to have the reserve power and capacity to handle lower impedances due to heavy and sustained bass notes. Now most amps and devices are based on that premise. If you lower the basic premise by paralleling speakers then a bass note long and heavy can actually take the impedance down to under an ohm. Pretty close to a short in anyone's book.
Certianly will exceed the design parameters. Most newer amps have built in current limiting and safety circuits. Unfortunately, the circuits used in our older but classy projectors we have really didn't have much. Sometimes as basic as a fuse which as a rule could never act faster those little pieces of expensive silicon.
Just a little added piece of theory for anyone interested. That's in case anyone wondered why one of your fuller frequency range films may have put your projector out of commission when it fed a bunch of speakers. Best solution of all is as mentioned by many here. Aux output to an external newer amp is the best of all robust solutions to more volume and sound.
Rick
| IP: Logged
|
|
|
|
|
|
Rob Young.
Phenomenal Film Handler
Posts: 1633
From: Cheshire, U.K.
Registered: Dec 2003
|
posted July 16, 2008 07:56 AM
Just out of interest, on the Beaulieu 708, the level of the aux output to an external amp is controlled by the main volume control, so you have to run the volume at maximum when using an external amp.
Since the built in speaker is still active, the manual advice is to stick a din plug in the external speaker socket which isn't connected to anything!
On my Elmo ST1200HD, I get popping and clicking through the main speaker when using the main switch, but added a speaker switching box from Maplin between the projector and speaker. This lets you turn off the main speaker until the film is running, then you switch it on with no pops at all. This box claims to present a safe load to the amp (?) when in the off mode and certainly hasn't done any harm in all the years I've used it.
As for bangs and pops when using the aux outputs for stereo, I used to have "loads" of problems, ah-hem, no pun intented!, especially as the output from the ST is quite low in this respect (the refridgerator turning on and off would present a massive bang right in the middle of a film!!!)
I found that one of those mains suppressors / clean-up blocks(used to be common for hi-fi gear but are really popular now with modern "home-cinema" gadgets) put this right, although those things aren't cheap!
Seriously though, they genuinely do improve the performance of anything that is plugged into them by effectively isolating them from the rest of the mains in the house.
[ July 16, 2008, 05:36 PM: Message edited by: Rob Young. ]
| IP: Logged
|
|
|
UBBFriend: Email this page to someone!
![[Big Grin]](biggrin.gif)
![[Frown]](frown.gif)
Printer-friendly view of this topic
