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Amplifier gain control, etc., questions ->>


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9 replies to this topic

#1 of 10 Zach M

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Posted February 28 2001 - 08:19 AM

I finally got my amplifier and hooked it up, but it is really quiet! Posted Image I have to turn the gain controls all of the way up and turn the sub level to +10 on my receiver just to get a moderate volume. What is going on? Posted Image I split the receiver's sub output, used RCA -> 1/4" unbalanced connectors. The speaker cables are hooked up with bananas (Not a very 'tight' fit[?]) They play but just not loud at all. I turned off all of the hz filters on the amp, set the clip control to 'on'. What am I missing? Please help I want my bass!
Thanks

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#2 of 10 Patrick Sun

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Posted February 28 2001 - 08:58 AM

More details, please. Like, what's kind of make/model of amp are you using? Is it a pro-gear amp which may require a "hotter" input level than a home-gear amp?

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#3 of 10 Zach M

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Posted February 28 2001 - 09:07 AM

Thanks for replying Patrick. It is a QSC RMX 1450 amp (pro style, 450 watts per channel 4 ohm). What do you mean by hotter input level? How would I acheive that? It is powering my dual Tempests and gets its signal from my Kenwood receiver. Any other ideas?

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#4 of 10 Patrick Sun

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Posted February 28 2001 - 12:29 PM

Well, you've got a pro amp, and it expects to see a certain input level (sometimes you can get away with it) like +4dbu for pro gear, but the home gear puts out -10dbv and there's a level mismatch. I think the home gear is lower in output, so it would sound lower in volume. But it could be your Kenwood might not be putting out enough voltage to drive your amp's input. Do you have access to another receiver?

Here's the only thread I could find that talks about this input voltage level "gap" by mixing pro and home gear. I've read others, but they must have fallen off the server by now. Vince Maskeeper knows about this stuff, so perhaps you could message/email him for more ideas.

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#5 of 10 Zach M

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Posted February 28 2001 - 01:39 PM

Thanks again P@. Do you think it would be alright to run the amp at 85% full gain and my receiver's sub level at +5 all the time? Also, when I turn it up really loud, the amp's red 'clip' lights flash. I don't want this right???? Have I depleted the amp's 450 watt headroom? When I saw those lights, I turned it down immediatley, which is what I should have done, right (or is is ok to have them flash a little with clip protection on?)?
Thanks

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#6 of 10 Patrick Sun

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Posted March 01 2001 - 12:37 AM

Do you have a SPL meter? You need to record the SPLs when the amp's red lights are flashing.

Normally, you should turn up the amp 100%, and then then the receiver's LFE/sub adjustment (pad) to control how much juice it sent to the sub.


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#7 of 10 Vince Maskeeper

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Posted March 01 2001 - 02:23 AM

Quote:
Thanks again P@. Do you think it would be alright to run the amp at 85% full gain and my receiver's sub level at +5 all the time? Also, when I turn it up really loud, the amp's red 'clip' lights flash. I don't want this right???? Have I depleted the amp's 450 watt headroom? When I saw those lights, I turned it down immediatley, which is what I should have done, right (or is is ok to have them flash a little with clip protection on?)?

1) Run the amplifier's gain knobs at 100%. These are not volume knobs, these are input attenuation knobs, they control how much voltage is allowed to enter the input stage of the amplifier. All the way up allows the voltage to pass from the receiver to the amp fully without being trimmed. Use them all the way open and control the level using your Receiver's sub output volume control, and only reduce the amp's knobs if you have to (i.e. the output is too loud, even at -10 on the receiver, to calibrate - and in your case it sounds like you won't need to reduce them).

2) Turn off the clip eliminator. The QSC one isn't that good anyway, and it will just mess you up for the calibration stage. You can turn it back on when everything is done. Just make sure to keep an eye on the amp as your calibrating to make sure you don't clip.

3) Reduce the sub speaker output on the Kenwood to -10, or as low as it goes. Make sure the LFE pad is in the proper position (the louder of the vailable settings).

4) Using VE and your RS SPL meter calibrate all you speakers (L,R,C,RS,LS) and make sure they're all 75db dead on. Then calibrate the sub to 75 as well.

5) Can you get the sub to 75 Db SPL without going to +10 output on the Kenwood? Watch the QSC carefully and make sure it doesn't clip with test tones (it shouldn't). If it starts to clip while playing the VE test tones, reduce the sub level immedaitely (although it really shouldn't clip with the tones).

If you cannot get the receiver output high enough to get a 75 db measured spl (you get to +10 and it still isn't metering 75db), then your Kenwood probably isn't passing enough voltage. This can be corrected with any number of convertors you can order online or buy at a music store).

If you can get enough to calibrate to 75 db or can get the amp to clip, then it is passing enough voltage.

If you get it calibrated, pop in a bass heavy DVD and watch the QSC closely. Does the clip light come on? If yes, then there isn't enough amp there for your room. If you have to clip the amp to get ref level then it simply is not enough amp for you.

If that is the case, you could try running it bridged, but I assume you have to rewire everything (if these drivers are dual VC) in order to make it work.

But if you can get the amp to clip with the eliminator off, then your Kenwood is supplying enough voltage! If the amp clips when calibrated to ref level, then there isn't enough amp.

-vince

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#8 of 10 Zach M

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Posted March 01 2001 - 08:44 AM

Vince,
Thanks to your help I have gotten the subs in perfect working condition! I had trouble finding the time to write this because I've been listening to the subs with a silly grin on my face, replaying most DVDs for the "first time." Anyway, I turned the gains all of the way up and I think that made a huge difference. With Avia, the sub registered at 75 on the dot at -10 on the Kenwood. So its working! The clip light never came on except when I watched that scene from The Haunting really loud. My hair was trying to jump off of my head! I am completely satisfied.

Thanks for all of your help and going above and beyond for a fellow enthusiast. You too, Patrick. There is no way I could have done any of this without your webpages and personal help. I think I speak for all HTF members when I say you guys are some of the most valuable assets to the forum.

One more question: I should have the clip limiter off all of the time?

-Zach

P.S. pics up soon!

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#9 of 10 Vince Maskeeper

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Posted March 01 2001 - 09:13 AM

Quote:
One more question: I should have the clip limiter off all of the time?

Nah, you can go ahead and turn it back on. All it is is a simple limiter circuit that will keep you from actually generating hard square waves when the amp clips. I just figured for calibration it's best to bypass any unnecessary processing or filtering.

If you aren't clipping unless it's REALLY loud, it shouldn't matter if it's on or off, but you may as well ahve it on as a JUST IN CASE measure. I personally could hear the clip elimination on the RMX stuff pretty clearly, and it seems to kick in slightly before clip. I prefer the Carver clip eliminator, much smoother.

But again, it shouldn't hurt anything to have it on, especially if you are never approaching clip. Turn it on and have it as a just in case.

-Vince

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#10 of 10 Patrick Sun

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Posted March 01 2001 - 10:28 AM

Zach, glad things are working out for you. That grin is tough to shake once it's engaged. Posted Image

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