Film-Tech Forum ARCHIVE: Low frequency cuts out

This is topic Low frequency cuts out in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=010761

Posted by Tim OBrien (Member # 5605) on 12-29-2010, 09:55 AM:

Help! I'm running a CP650 through biamped Ashly FTX-2001 amps. Sporadically, my low-frequency drops out on the center channel. When I switch the i/o to a different amp(s) I usually end up with no low-frequency on the right and/or left channels. If I tap on the installed crossover or the front of the amp while running pink noise the low end will kick in for a moment and then drop out again.

When I power up the next day everything is fine for days or weeks until a customer tells me that the sound is whacked again. My service tech thinks I'm crazy as the problem can't be duplicated when I try. I'm inclined to blame the crossovers, but it seems strange that this would affect two amps simultaneously.

Your ideas are greatly appreciated.

Posted by Sam D. Chavez (Member # 1841) on 12-29-2010, 10:43 AM:

The crossovers are inside the amp?

When you say i/o, do you mean both the input audio cables and the speaker wiring?

Posted by Randy Stankey (Member # 64) on 12-29-2010, 11:10 AM:

Use logic.

First, be sure the CP-650 is working as it should. Use your booth monitor to be sure. If you don't have a booth monitor that can listen to both "processor" and "amplifier" signals, use an inductive amplifier like this one.

http://www.newark.com/jsp/search/productdetail.jsp?SKU=06C5591&CMP=AFC-GB100000001

My old boss used to call it a "banjo."

You don't have to disconnect anything to use a banjo. Just gently touch the tip to the wire you want to test. You should be able to hear the signal through the small speaker.

Just touch the banjo to the INPUT of the amp then to the OUTPUT.

If you hear the correct sound at the output but not the input, you know it's the processor that's faulty.

If you hear sound at the input but not the output, you know it's something inside the amplifier that's faulty.

If you hear sound at both the input and the output but still don't have sound, you know it's something farther down the line, either the speaker(s) or the wiring.

You can spend hours and hours fooling around trying to figure out where the problem is but using that little "banjo" can help you pin the problem down to a specific area of interest in less than a minute if you use your head.

Posted by Tim OBrien (Member # 5605) on 12-29-2010, 12:07 PM:

In this case, I'm using the Ashly crossovers which are installed into the amp, and by i/o I'm referring to the XLR input and the speaker cables (essentially just swapping amps).

I like the idea of the "banjo" if only because I can make an instant determination of the situation when it's in fail mode.

Posted by Tony Bandiera Jr (Member # 2365) on 12-29-2010, 02:56 PM:

Not to rain on Randy's idea for the "banjo" (the set with tone generator and inductive pickup are sometimes known as "Fox and Hound") there is no need to overthink this.

The problem is in the crossover, amp or the connector for the crossover, here's the proof:

quote: Tim OBrien
If I tap on the installed crossover or the front of the amp while running pink noise the low end will kick in for a moment and then drop out again.

Could be bad solder joint, loose connection, or component failure.

Get the amp/crossover fixed.

Meantime, swap with the left or right amp, the center is far more important, and let the left/right do without low end if need be, it would be far less distracting than having the center go in and out.

Posted by Randy Stankey (Member # 64) on 12-29-2010, 03:37 PM:

You're right, Tony. I also think the crossover is suspect.

The point about the inductive amplifier was meant to be as instructive as it was a solution. (Give a man a fish... )

Posted by Steve Guttag (Member # 268) on 12-29-2010, 05:08 PM:

I don't just think it...I have had so many of these turds crap out like this. Change the crossover module...the problem is gone. Better yet, throw the crossover out with the amp...they are god-awful unstable pieces of crap that don't sound good either. <there...I feel better>

But honestly, it is the crossovers...I've seen it happen MANY times...the suck.

-Steve

Posted by Louis Bornwasser (Member # 3063) on 12-29-2010, 06:36 PM:

Steve & I have a major disagreement; the Ashly just might be the best thx or any other amp ever made. The crossover, however, is another matter.

Too many switches and pots. Contact me, we make a replacement crossover for inside that amplifier or we can repair the existing module.

fyi: In the UK, all or nearly all mixing and review rooms are Ashly equipped. (They are stable, too.) Louis

Posted by Steve Guttag (Member # 268) on 12-29-2010, 07:42 PM:

Yeah, I figured I would offend you...I know you like the Ashley. However, I can not express my dislike of them enough...not just from a reliability standpoint but I truly find that they sound BAD. They are also the source of many recones for us as they have been known to go DC on a driver and cook the voice coil.

You can have them as I have nothing but bad things to say about them.

However, it is good to hear that you have a solution for the crappy crossovers.

-Steve

Posted by Tim OBrien (Member # 5605) on 12-29-2010, 09:07 PM:

The amps and crossovers were pulled today for repair or replacement. We moved my sub amps and installed some different Ashly crossovers and the sound is way off, but at least has full dynamic range.

Thanks, everyone for your response and expertise! Will contact Louis offsite.