Need help with QSC Amp Setup

[Youthman]

I have a pair of Klipsch CF-2's driven by a HK AVR55. I've never used an external amp but know that my HK has the ability. I brought home a QSC RMX1450 to try out on my system. The QSC is 280 w/ch @ 8ohm. I hooked everything up but I get no sound out of the main speakers.

Here is what I did.

Amp is hooked up via my HK. I unplugged the jumpers on the back of the HK and went into the "Main Preout" with an audio cable that has RCA on one end and RCA on the other end attached to a RCA to 1/4" converter. The 1/4" is connected to the input of the amp.

I have tried both analog cd in stereo and a Dolby Digital DVD via my digital coax. When watching a movie, the center channel is heard, but nothing from the mains. On the amp, the power light is on but the sig light is not. From my troubleshooting, I have come to the conclusion that the signal is not getting from the HK to the QSC. The fan on the amp is running.

I tried turning off the speaker button on the HK thinking that might tell the preouts to send the signal. It just shut off the center channel and still no sound from the mains.

I know the amp works because I use it in my youth building (I'm a youth pastor).
I know the rca to 1/4" cable works because we use it to connect our CD player to a mixer in my youth building.

Is there anything I need to do on the HK to tell it to send the signal via the preouts?

This is the first time I've ever tried to use an external amp with my HT. I really want to compare the difference between my 45 watts internal HK amp and a 280 w/ch external amp. [] So any help would be greatly appreciative. The links above have the owners manuals for both the HK and the QSC.

[Youthman]

Ok, I got the amp to work. Problem was I was chicken. I didn't want to blow the speakers so I had everything turned down so low I could not hear it. [:$] I had the gains on the amp at 1/4 volume and the HK at 30 and wasn't hearing any sound. I slowly turned the gain on the amp up to 1/2 then to 3/4. I then began to turn up the HK from 30 up to 65. My normal listening volume on the HK without an amp is 45.

I hear absolutely no difference from the QSC than I do the HK but how can this be? Quality isn't any different and the volume isn't any different. I would think with the QSC gains at 3/4 and my HK at 30, it should be pretty loud and it is not.

I have tried turning the "speaker" button on the HK on and have tried it with it turned off and there isn't any difference.

On the back of the QSC, I have it set to stereo and bridge mono set to off (don't want to pump 800 watts to my CF-2's)

I am using banana plugs to the CF-2's and the back of the QSC.

I am using Monster Cable speaker wire but not sure the gauge ( maybe 16 or 12 gauge).

Here are some screenshots:

My QSC settings:
Clip Limiter is set to On
LF set to 30HZ
Stereo is set to On
Bridge Mono is set to OFF
LF Filter is set to ON
LF set to 30HZ
Clip Limiter is set to On

I am coming out of the HK Preout (#27) using a monster cable RCA to a 1/4" adapter into the 1/4" inputs (#5) on the QSC and using speaker outputs (#8) on the back of the QSC going to the CF-2's.

[michael hurd]

I checked the specifications of the reciever in the link to the manual, but it does not state the ouput voltage of the pre-out jacks. The QSC RMX 1450 requires an input of 1.15 volts for rated power at maximum gain.

I would increase the drive level in your reciver by manually going into the menu and bump the channel levels up of the left front and right front. I would begin by setting them about 3/4 of full output. ( if maximum was like + 12db in menu, then set at + 8 or so )

Turn the gain controls up on the RMX more, it would be near maximum position, when driven by consumer level equipment. You should have no problem then.

With a voltage gain of 40x, 1 volt in results in 40 volts output. ( with gain controls up to max ) 40 volts into an 8 ohm load = 200 watts. If you have the gains less than that, and / or have weak signal into the amp ( in terms of millivolts ) you will not be able to produce anywhere near full power. With the amplifier ( RMX ) gains turned all the way down, you would need 10 volts at the inputs to produce rated power, this is why you had zero sound.

When you turn your H/K up, you should see the signal lights on the amp come on, this is at a low drive level. As long as the clipping lights are not coming on, you are not overdriving the amp.

Hope this helps.

[Youthman]

Michael, thank you so much for the reply. I totally understood what you were talking about (well...at least it made sense). The channel levels on my HK were set at +3 so I bumped it up to +10 since it goes up to +15. I turned the QSC up to 30 with 32 being max. No clipping ever occurred, 45 on the HK sounded perfect. I demoed both 2 channel audio and 3 channel movie (I don't have rear surrounds at the present) and left my sub turned off. I am impressed! Before, my CF-2's didn't have much bottom end to them without the QSC. With the amp, they have a lot of bottom end even at low to mid volume. Although my wife is at a conference tonight, I didn't get a chance to really crank it since my kids are in bed. Ah but tomorrow is a new day. []

I can truly understand the benefit of an external amp. I guess the best way to describe it would be to compare my HK to a scrawny built guy and the QSC to a body builder. The scrawny guy would struggle to bench 100 lbs but the bodybuilder could bench 200 lbs without a sweat.

When I listen to the HK without the amp, around volume 50 - 55, the sound starts sounding strained. With the QSC, it handles the same volume effortlessly and still sounds crystal clear. This is definitely what I wanted to find out for myself. Now I just have to save up for a B&K 200.5 amp. That would be sweet, especially paired with the RF-83 package!

[michael hurd]

If most people knew how bad their amplifiers were "clipping" and producing nasty distortion products, they would quit debating that X speaker has .05 % less distortion at x output. []

Music is dynamic in nature. ( at least most all except the popular pop / rock music today with 0 dynamics ) In the pro audio world, it has been said that a 20 db dynamic range is the norm. Even though Klipsch speakers are efficient, and can produce lots of ouput with lower voltage ( wattage ) than others.... it still does not change the fact that amps can still "run out of gas".

At a one watt average level ( still pretty loud ), a 21 db transient ( momentary signal ) will require 128 watts to reproduce the transient faithfully. Couple that with the fact that some of the newer designs from Klipsch are less than 4 ohms in the bass section, they require an amplifier with more horsepower in the tank.

[Islander]

In most case where you have two volume or level controls in the signal chain, one should be turned up all the way and the other control used to adjust the volume. Most power amps don't even have a level control.

In my system, I'm using a 500Wpc power amp, controlled from the pre outs on my receiver. The higher power and higher quality of the power amp gives the music greater presence and clarity and I'm happy with it.

The speakers are rated at 100 watts, but I've probably never put more than 2 or 3 watts of continuous power into them. As Michael pointed out, the high power comes into play during musical transients. It takes a surprising amount of power to make a drumbeat or rimshot sound realistic.

Where I have to be very cautious is when switching inputs. The volume can be as high as -15dB when listening to the turntable (record cartridges usually have fairly low output), while -30 is pretty loud for a CD, so I turn down the volume whenever I switch inputs. Also, I make sure to turn the volume very low, to -72 or so, when I turn off the system. That way I won't get any nasty surprises the next time I power it up.

Happy listening!

[michael hurd]

"In most case where you have two volume or level controls in the signal
chain, one should be turned up all the way and the other control used
to adjust the volume. Most power amps don't even have a level control."

In most cases, pre-amps will clip before they get to the maximum level indicated... as there is no more "headroom" left. Some are better than others in this regard. Professional power amps have gain controls to allow system matching..... they adjust how much INPUT voltage is required to put out full power. They do not control how much power the amp puts out.

Giving a pro amp a weak input will result in dismal performance, with the possibility of added noise. Different amplifiers, even those in the same amp line require different input voltages to reach maximum power. If a preamp voltage is known, then the actual output voltage of the amplifier can be calculated, knowing the voltage gain of the amplifier.

This can then be calculated into "watts" into a load. Amps don't put out more "watts" into a 4 ohm load, vs an 8 ohm load, but they do put out more current. For instance, 40 volts into an 8 ohm load is 200 "watts". ( 40 x 40 / 8 = 200 ) The same 40 volts into a 4 ohm load is 400 watts. ( 40 x 40 / 4 = 400 )

[michael hurd]

Islander: "The speakers are rated at 100 watts, but I've probably never put more
than 2 or 3 watts of continuous power into them. As Michael pointed
out, the high power comes into play during musical transients. It
takes a surprising amount of power to make a drumbeat or rimshot sound
realistic."

So true!

[germerikan]

Where I have to be very cautious is when switching inputs. The volume can be as high as -15dB when listening to the turntable (record cartridges usually have fairly low output), while -30 is pretty loud for a CD, so I turn down the volume whenever I switch inputs. Also, I make sure to turn the volume very low, to -72 or so, when I turn off the system. That way I won't get any nasty surprises the next time I power it up.

Happy listening!

This is a sound piece of advice, I once turned on my amp and found out that my wife was listening to Shakira and ear bleeding levels when I was not there, scared the bejesus out of me. I then set my amp to power up at -55 volume so I don´t fry the speakers when I turn it on.

Ran

[Youthman]

Oh it's a sad day. Today, I had a chance to sit down and listen to a variety of music and movies. Transformers sounded amazing! So much detail and clarity. Sarah McLachlan's "In the Arms of an Angel" sounded absolutely fabulous. Very smoothe, refreshing and sensual. I even went old school 90's rap and was enjoying a blast from the past. [] I have to return the QSC to it's home tonight so we can use it tomorrow. [:'(] I have enjoyed our brief time together.

Thanks so much Michael for the help with getting the amp setup. I would have never turned the amp up that loud nor turned the receiver inputs up that high either. Thanks for the explanation that the gain on an amp is not a "volume" knob but more like a valve to let signal in. I guess it's kind of like a faucet. The valve doesn't push water in, it merely opens the gate for it to flow. Maybe that's not totally accurate but that's my understanding of it from what you have said.

I do have a question. Why am I only able to adjust the front levels on the receiver when it is in Dolby Digital and not in stereo? The volume was lower in stereo so I had to turn up the volume to achieve the same loudness as it was in Dolby Digital.

[DrWho]

For what it's worth, the individual channel volume controls are all done digitally...as is the master volume control (on most receivers anyway). Boosting the individual channel gains is no different than turning the master volume up. The only time it matters is when trying to match the output to other channels (like the center and surrounds for movies).

What I would suggest is cranking the gain on the amp up all the way and setting the FL and FR channels to 0. Then cut back on the center channel and surrounds so that the volume lines up...this will keep things the same volume when you switch over to stereo. Basically, in stereo mode the receiver knows you don't need to balance the sound with the other channels so just lets you control the volume with the master control. It's possible this was done if there was ever a case where you wanted an analog bypass through the system.

[Youthman]

Thx for the input Mike. I've been a HT hobbyist for many years but have a lot to learn on the technical side of things.

[DrWho]

Would you happen to have a voltmeter readily available?

One
thing you could do is put a 1kHz sine wave on a CD and crank your
receiver up to 100% (with no speakers attached of course) and see what
kind of voltage you get at the preamp outputs. Combined with the input
sensitivity of the proamp, we can figure out the peak power output
you'll be seeing with your configuration. My guess is that you actually
have less available watts with the proamp hooked up right now. In other
words, my gut feeling is that your preamp is running outta steam before
the amplifier.

Nevertheless, that's not to say that you don't get
better sound from the pro amp....the increase in damping is gonna give
you way more control over the woofers.

[billybob]

Whoa! That was it! Sounded good!

[Youthman]

Yes, it sounded good enough to when I have our home built with dedicated theater room, it will definitely have separate amps.

[jacksonbart]

Top Notch!

[Youthman]

Well, I couldnt' resist. I went and borrowed the QSC to try out on my RF-83's. Once again, it really opened up the speaker dynamics. More bottom end, crystal clear. FYI, the fan is pretty loud on the QSC. If someone bought it, you would probably want to replace the fan on it or have it in another room. Watching Transformers, my KV-3 couldn't keep up with the RF-83's. They really tried, but they are just no match for the 83's hooked up to an external amp. []

I just wanted to say that anyone that has a receiver, even without going to full separates, would benefit greatly from a good external amp. I'm not even sure QSC is a "good clean amp" but it sounds amazing to me.

One thing that is interesting is that the woofers do not move very much, even at high volume. I saw a youtube video of a guy that played a Peter Gabriel song and the excursion on his RF-83's were pushing out like crazy. I had mine pretty loud and the woofers weren't even coming close to moving that far.

[michael hurd]

"I saw a youtube video of a guy that played a Peter Gabriel song and the
excursion on his RF-83's were pushing out like crazy. I had mine
pretty loud and the woofers weren't even coming close to moving that
far. "

Depends on the frequencies in the song. Some songs have extreme LF content. One example is " I love you" from Sarah Mclachlan off the Surfacing CD. Strong LF content, more than most CD's.

[Youthman]

That's true because I remember putting in a Test CD that I downloaded from the internet and there were some inaudible frequencies that made the speakers jump big time.

[Youthman]

I found the

. I was remembering them having more excursion than in that video.