Film-Tech Cinema Systems
Film-Tech Forum


Post New Topic  Post A Reply
my profile | my password | register | search | faq & rules | forum home
  next oldest topic   next newest topic
» Film-Tech Forum   » Operations   » Film Handlers' Forum   » Kelmar 150+ --- Sound is Not Good

   
Author Topic: Kelmar 150+ --- Sound is Not Good
Cody Martin
Expert Film Handler

Posts: 214
From: Edinburgh, IN, USA
Registered: Jun 2004


 - posted 07-01-2006 02:16 PM      Profile for Cody Martin   Author's Homepage   Email Cody Martin   Send New Private Message       Edit/Delete Post 
Hello again,

Just ordered a screen today, so in preparation I was cleaning up the booth and doing a little wiring and such. The only change I made was I ran some wires through a wall, so I'm pretty sure the wiring is fine.

I'm set up with 4 Kelmar 150+ amps(L, C, R, S) plus one backup, all ran with a CP50. I ran a test loop(trailer) through the projector today and noticed my L channel sound like crap. I switched the amp out and it sounded fine then... so the problem is with the amp. It sounds the way speakers do when you over drive them. I turned all the levels down so that I could make sure it wasn't over driving anything and when I did that it still sounds bad...just at a lower volume. I checked the fuses also and the speaker.

I was wondering if there is something inside the amp that may be proned to go bad or something I should be looking for. I haven't had a chance to pull the amp yet, but i will soon.

Hopefully someone may have a suggestion.

Thank you for all your help,
Cody

 |  IP: Logged

Cody Martin
Expert Film Handler

Posts: 214
From: Edinburgh, IN, USA
Registered: Jun 2004


 - posted 07-03-2006 10:26 AM      Profile for Cody Martin   Author's Homepage   Email Cody Martin   Send New Private Message       Edit/Delete Post 
Any ideas on this? I'm not very electronics smart, so I'm at a total loss right now.

Thank you,

Cody

 |  IP: Logged

Robert Minichino
Master Film Handler

Posts: 350
From: Haskell, NJ, USA
Registered: Dec 2005


 - posted 07-03-2006 12:00 PM      Profile for Robert Minichino   Author's Homepage   Email Robert Minichino   Send New Private Message       Edit/Delete Post 
Could be that one of the power supply rails bit the dust which, depending on the exact design of the amp, could give you heavily distorted (half-wave rectified) output or no output at all. It also could be that some of the output transistors are bad; they usually fail shorted, however, and that usually results in taking out the rest of the output transistors and/or getting DC on the output. If some failed open then that might also result in getting half-wave rectified output (only half of the signal, either above or below 0V). Also could just be very badly underbiased, meaning that there's a gap around 0V where there's no output.

These scenarios are all very easy to detect with a voltmeter and an oscilloscpe. Open up the amp, power it on, and (VERY CAREFULLY) check the +/- DC rails from the power supply to make sure they're both powered and at similar levels from ground. Then check the outputs with a voltmeter set to DC volts with no input; they should be very close to 0V. Then run a sine wave into the amp and check the outputs with an oscilloscope. If you see a flat spot around the zero-crossing, then you need to rebias or the bias circuit is borked. If there's a flat on the top and the bottom there might be an issue in the input section of the amp. If half the waveform is missing, then there's probably an issue with the output transistors.

See, it's very simple. [Wink]

 |  IP: Logged

Cody Martin
Expert Film Handler

Posts: 214
From: Edinburgh, IN, USA
Registered: Jun 2004


 - posted 07-04-2006 12:27 AM      Profile for Cody Martin   Author's Homepage   Email Cody Martin   Send New Private Message       Edit/Delete Post 
Sounds like this will be a little out of my league. may be sending this to someone to check out and repair if possible/feasible.

Thank you for your help, it is greatly appreciated.

thank you,
Cody

 |  IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16273
From: Bountiful, Utah
Registered: Jun 99


 - posted 07-04-2006 07:31 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
They are older amps and will need re-capping. This is also common on the AS-7200 series of Kelmar amps. Usually its the input cap that fails and the result is alot of distortion. A set of caps shouldn't set you back more than 25.00 per amp. If you can find them surplus then they will cost less. Call Kelmar and get a schematic then make a list of all the electrolytics and replace them.....

Mark

 |  IP: Logged

Gordon McLeod
Film God

Posts: 9470
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 07-04-2006 08:09 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
With the low cost of some of the china amps I would ditch the Kelmars as I never found them that good sounding at best
for small screening rooms I have used the PRZ1000
http://www.pyleaudio.com/itemdetail.asp?brand=PylePro&cat1=Pro%20Audio&cat2=Power%20Amplifiers&model=PZR1000

 |  IP: Logged

Phil Hill
I love my cootie bug

Posts: 7595
From: Hollywood, CA USA
Registered: Mar 2000


 - posted 07-04-2006 08:16 PM      Profile for Phil Hill   Email Phil Hill       Edit/Delete Post 
Cody, all these "experts" are guessing at what is wrong. If you want, email me for my address and if you send it to me, I'll look at it for free and see if I can help you out.

I have found those amps to be an economical theatre sound solution.

 |  IP: Logged

Richard Fowler
Film God

Posts: 2389
From: Ft. Lauderdale, FL, USA
Registered: Jun 2001


 - posted 07-05-2006 11:40 AM      Profile for Richard Fowler   Email Richard Fowler   Send New Private Message       Edit/Delete Post 
The slide in amplifier boxes which where popular in the 1980's most are very basic construction and easy and cheap to fix.
Gorden, that Chinese amplifier is pretty wimpy for the price: a few dollars more get Chinese amplifier product from Crown or QSC [Razz]

 |  IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16273
From: Bountiful, Utah
Registered: Jun 99


 - posted 07-05-2006 07:15 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
Well, they may be economical but I will certainly side with Richard on this. Thay never did sould that good and they have a class B output stage... old stuff. If the Philster is going to fix it free thats a nice gesture and I would send it off to him, the parts shouldn't cost you that much.

I couldn't agree more with Richard on the cheap Chineese amps! Gord, We got in a couple models of the Pyramyd amps that you reccomended to me and that you had installed a bunch of. Had you bench tested them before hand I doubt that you would have installed them... pretty awful performance and he is correct that for about 50.00 more the Chinese built Crown or QSC is alot better deal. To my ears the Crown amps also sound the best of the "Cheap" amps, very dynamic and with a warm midrange that is wonderful. We ended up giving both the Pyramyds to an employee for his home system.

Mark

 |  IP: Logged

Cody Martin
Expert Film Handler

Posts: 214
From: Edinburgh, IN, USA
Registered: Jun 2004


 - posted 07-05-2006 09:13 PM      Profile for Cody Martin   Author's Homepage   Email Cody Martin   Send New Private Message       Edit/Delete Post 
Hello guys,

Thanks for all your replies. I'm going to go ahead and send the unit til Phil Hill and hope it's fixable. I would just purchase a newer amp, but I just purchased a screen and automation controller so funds are limited as usual.

Thank you for the amp advise though. I had though about the pyramid ones, but will stay away from those now.

Thank you,
Cody

 |  IP: Logged

Gordon McLeod
Film God

Posts: 9470
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 07-05-2006 09:36 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
well Mark at last count we have about 200 of the pyramid pa1000 in service in 150 seat screens with A5 speakers and have had one fail they are capable of sustained 120watts RMS per channel and with an efficient speaker like the A5 that is all that is needed in many smaller rooms
they Pyle has a few extra features like a balanced input and less space and we have wuiet a few of those in service

I will never use a crown product on an installation as I have had just too much overall grief from their products

Larger rooms I use QSC

 |  IP: Logged

Louis Bornwasser
Film God

Posts: 4435
From: prospect ky usa
Registered: Mar 2005


 - posted 07-06-2006 09:09 AM      Profile for Louis Bornwasser   Author's Homepage   Email Louis Bornwasser   Send New Private Message       Edit/Delete Post 
Ashly FTX-2001 amplifiers in all theatres regardless of size including my living room. Louis

 |  IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16273
From: Bountiful, Utah
Registered: Jun 99


 - posted 07-06-2006 02:14 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
Gord,

I think in the long run you will find that they will not last anywhere near as long as the Chinese QSC or Crown amps will. Also they spec out really raunchy with an awful looking harmonic content, especially at the high end of the response.

Over the years I only had a little trouble with Crowns... Nothing that was a big deal and no more really that I've had with QSC. We are starting to see alot of older QSC's start to drop and requiring rebuild kits put in them. Grented these are well over 20 years old.

Louis,

Ashleys are good amps and have a MOSFET output stage that is more likely to generate even harmonic distortion which is not nearly as fatiguing as odd order distortion is. The transconductance of a properly biased MOSFET is also much higher than a similar sized bi-polor deivce and there are many other important advantages to MOSFETS. We have basically zero problems with the FET 2000's out here... a fan now and then is about it and they are built to at least an adaquate quality level. The FTX 2001 has been retired.

Mark

 |  IP: Logged

Louis Bornwasser
Film God

Posts: 4435
From: prospect ky usa
Registered: Mar 2005


 - posted 07-06-2006 08:27 PM      Profile for Louis Bornwasser   Author's Homepage   Email Louis Bornwasser   Send New Private Message       Edit/Delete Post 
Retired? officially, yes. They are still made for us when we order in quantity. Currently dealing with the "lead free" in Europe. Louis

 |  IP: Logged

Mark Gulbrandsen
Resident Trollmaster

Posts: 16273
From: Bountiful, Utah
Registered: Jun 99


 - posted 07-06-2006 11:07 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
I build alot of high end audio clones and I use alot of the new ROhS parts and have had zero problems with them. Here is the DATA on the maxlmum levels allowed just in case no one is interested.

Mark

 |  IP: Logged



All times are Central (GMT -6:00)  
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:



Powered by Infopop Corporation
UBB.classicTM 6.3.1.2

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.

© 1999-2018 Film-Tech Cinema Systems, LLC. All rights reserved.