my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Bad amp?

Author Topic: Bad amp? Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 06-10-2004 03:06 AM                     I was curious to know what happens when an amp goes bad. Does it just completely stop working or can it just start to cause distorted sound? If an amp starts going bad but still works, what kind of distortion would it cause?  |  IP: Logged Robert L. Fischer Expert Film Handler Posts: 145 From: Montreal, Quebec Registered: May 2004 posted 06-10-2004 03:12 AM                    From my experiences, it almost sounds like a static problem -- only much worse. It's sort of a loud buzzing noise, like if you turned a guitar amp up really loud. If an amp is bad, you'll know it, and so will customers.  |  IP: Logged John Anastasio Master Film Handler Posts: 325 From: Trenton, NJ, USA Registered: Sep 2000 posted 06-10-2004 06:30 AM                        It all depends upong which section of the amplifier has gone bad and whether or not it's a tube amp or solid state. A bad power supply, for instance, can manifest itself as either 1.)a loud hum or 2.) total non-functioning amp. A bad phase inverter on a push-pull amp will just make the amp sound very distorted. A bad power amp stage has yet another set of symptoms...so you can't just say "bad amp"...it's like going to the doctor and just saying "Something's not right".  |  IP: Logged Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 06-10-2004 11:58 AM                     Well the problem I am having is distortion in the sound. I checked the A chain which turned out fine. The sound is sort of scratchy(loud speaking parts) and it seems to be pulsing(like during a scene with an applauding crowd the clapping seems to fade in and out). The sound seems to also have too much trebble. I also checked the EQ which also seemed ok. I am using a CP50 with a reverse scan Kelmar reader. Right now I only have one speaker behind the screen with the other speakers coming soon. So, I am running the CP50 in Dolby stereo with no surround mode so that the noise reduction cards are utilized(CAT280 SR cards). I tried replacing the CAT117 output card but the problem is still there. Any help would be appreciated. I think I will try another amp today (using Smart amps). Thanks.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 06-10-2004 12:04 PM                        The "pulsing" comment makes me wonder if you are playing a Dolby A print in Dolby SR. Are you? Also, if you are using cat. 280 (not 280T) cards, they need to be modified for use in the CP50. Otherwise, they go into "encode" mode by default instead of "decode" mode. Amp failures can be especially fun when you start hearing loud popping noises and find out later than a horn diaphragm has blown. I haven't seen the SMART amps, but I think that most people here would recommend that you check out the QSC USA/MX/DCA product lines instead.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 06-10-2004 12:22 PM                     If you are playing in Stereo Mode with only a centre channel then you will be hearing all sorts of the gain riding artifacts of the matrix as it is steering portions of the audio the left and right speakers that are not there. Remember that matrix sound relies to a large extent on psycoacuostic masking effect Smart Amplifiers are usually either a Hafler circuit or made by AB International and seem to stand up well  |  IP: Logged Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 06-10-2004 12:41 PM                     The SR cards have been modified for playback only. I will be installing the left and right speakers tonight and I will see if the problem stops. Thanks.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 06-10-2004 07:04 PM                     It can be from completely dead to maximum smoke. Everything in between is possible.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 06-15-2004 11:06 PM                     You should also be sure your CP50 has the newer Power supply Module (Cat 114C I believe) as the older power supply can't handle the draw from the CAT 280T's. (Or the later Cat 150's)  |  IP: Logged Oscar Neundorfer Master Film Handler Posts: 275 From: Senoia, GA Registered: May 2000 posted 06-16-2004 05:50 AM                        Tom, Please tell me what model SMART amps you are using.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 06-16-2004 07:44 AM                     I've yet to have a problem with the Cat. 280s affecting CP-50 performance. The Cat. 280s draw from the +24 supply and not the +/-12 volt supply. However, adding cards with LEDs on them will suck down a CP-50 supply in a hurry. The Cat. 150C or later, the Cat 517 and the Cat 560 will surely draw the supply down to below +/- 10VDC and a hum will develop. Also the Cat. 113C with its power supply LEDs will also suck some juice. Steve  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 06-16-2004 02:44 PM                     Maybe the original poster has added the other channels and could report back soon  |  IP: Logged Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 06-16-2004 05:42 PM                     The other channels were added so now the CP50 is in dolby stereo with no surround mode.(L,C,R channels) The sound quality is much better but there still seems to be a pulsing problem where the sound seems to fade in and out slightly when there is a scene with applauding or with any other type of "continuous sound".(hopefully that makes sense) The only test I did not perform for the LED alignment is with illumination test film. Could this be causing the problem. I am using Smart TA240 amps.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 06-16-2004 06:53 PM                     It might as uneven illumination will cause a compressor effect did you set the dolby level with the processor in mono?  |  IP: Logged Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 06-16-2004 09:34 PM                     Yes, I did set Dolby tone with the processor in mono. Today I checked the illumination of the LED and only had to make a very slight adjustment. The "fading" problem in the sound is still present. Could this have anything to do with the fact that the surround channel is not being used? The surround speakers are going to be put up soon and I can see if the problem stops. [ 06-17-2004, 02:17 PM: Message edited by: Tom Wienholt ]  |  IP: Logged

All times are Central (GMT -6:00)

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.