QSC Amp and DBX Crossover

[David_NC]

In the quest to find a way to connect my SVS subwoofer to my Luxman receiver, I decided to try an electronic crossover, if I could find one cheap. A guy had a DBX 223XL for sale. At $25, I figured that qualified as cheap. I went by his house on Saturday, and he had a bunch of his stuff which had apparently been sitting unused at his church for sale. The crossover looks like new, so I decided to give it a shot. I had no way of testing it, as all my XLR cables are back in NC, so we'll see how it goes with that.
He also had a couple amps for sale. The one that was in the best condition and that has really good reviews was a QSC USA-900. Other than some masking tape residue, this unit also looks new. I connected to my trusty $5 Goodwill test speakers and a cobbled-together mono adapter - a 1/8" headphone jack to 1/4" plug (with Scotch tape over the R (ring) connector). I got sound and hum, of course, which was to be expected. I made my purchases, and off I went.
Antsy to try out the amp, I used an old stereo RCA cable with the plugs on one end missing. This amp has a screw terminal block, along with the combo TRS / XLR inputs, so this worked. I ended up with more hum than audio until I remembered balanced vs unbalanced + ground thing. After jumpering the ground to the negative terminals, the hum was gone. In fact, this amp is quiet... as quiet as the one in my Luxman receiver.
I listened to a couple albums and an SACD with my R-115 as a preamp (speakers are ADS L780/s). I can't say that there was no sound difference between the receiver's amp and the QSC, but it was really hard to tell which sounded better. The QSC definitely played louder and sounded a bit better at really high levels. I'd not normally listen to anything this loud, but it was quite impressive! I was concerned about cooling fan noise, but it's not an issue with this amp. The fan is only audible with very little ambient noise with my ear a foot or so from the amp. It's a larger 3U chassis with the large, slow-moving fan in the back blowing inwards. The exiting air was fairly warm, but definitely not hot.
The power rating of this amp is impressive, as is typical of DJ / pro amps: 240wpc, 20-20kHz @ .1%THD into 8Ω, 450WPC into 4Ω, and 900WPC into 8Ω bridged at 1%THD. I've read the back and forths about the quality (or lack of) of this type of amp, but I'm really impressed with this one. It seems to run cool. It has a lot of power. The transformer is very heavy. It sounds good. Oh, and QSC is a local company, and this amp is made in the US. What's not to like for $100?

These are definitely not good pics, but here they are (the interior shot is before I blew the dust out)!

 

[drumbum]

I agree with your sentiments about these amplifiers. I have a 1310 in the den system. Zero thump at turn on or off (doesn't matter what sequence), can't say that about my B&K or Altec Lansing amps. Signal/noise@106dba is quiet,...very.

Modded mine with a 12v fan w/PWM speed control. Can't hear it and just blows slightly above room temp out the front.

375w 20-20 @ 8ohm .1%thd and still touts 2db dynamic headroom @ 8ohms.

Whats not to like?

Congrats on your purchase!

 

[Frank Sol]

I have a (QSC) 1310 in the den system...

0.1% thd ...

I'm not saying this applies to 100% everybody

Most folks will not hear the difference , with their Home Speakers , using a properly operating amp be it 0.01% or 0.1% THD

I've been listening , off and on , to a 0.5% THD pro amp since the holidays 2018. I've been surprised just how good the SQ is even with my sensitive Forte speakers

 

[David_NC]

Good to hear others are having similar experiences with their pro amps! I figured the price was right, especially considering the condition of the amp. If I didn't like it, it would seem to be a good candidate for running multiple outdoor speakers as zone 2 or 3 on my HT receiver. As it is now, I'm not really sure where I'll use it. I know I'll initially set it up for a bit with the crossover to see how much adding my sub improves my 2-channel / music system. Hopefully, my XLR cables and adapters will arrive soon so I can get playing with it all!

 

[Frank Sol]

Video is not specifically about this topic but does beat around the bush some

 

[bimasta]

Pro amps have 3 main goals. Accuracy. Play loud when told to. Never fail. How well they achieve these goals varies; price-points have an effect, and age always has effect.

Their downside to 'consumers' is their appearance; balanced or 1/4" ins/outs; and (used to be) their accuracy: they're not 'voiced' to be 'pleasant'. Now that Accuracy is a Holy Grail in highish end audio, I'm curious to see how much Audiophiles really like Accuracy.

You don't mention the DBX xover. Can we look forward to the next installment?

 

[faber12]

My church has that same amplifier, that thing can go loud and still have a rediculous amount of power left over.

 

[grey]

A couple of the biggest names. Everyone wants 1 to 2U, ultra light amps and and DSP in that world now. Good deals and fun experiments to be had. You may find your destination system somewhere in all of the old pro stuff out there.

 

[59volvo]

is this QSC a class D amp? anyone have experience with the QSC vs Crown XLS series of class d amps and which sounds better -- QSC or Crown? tia

 

[David_NC]

I'm also finding QSC MX-1500 amps on Craigslist for about 50% more than I paid for this amp. These are full dual mono construction and are rated at 330wpc stereo and 1000wpc bridged, both into 8ohms, and 500wpc stereo into 4 ohms... all at .1% distortion. Maybe one of these should be added to the mix! Something about the two-channel DBX 31 band EQ's are tempting as well. I need to block Craigslist, I think...

You don't mention the DBX xover. Can we look forward to the next installment?

Absolutely! Balanced cables and adapters should arrive in the next couple days. I'll use a Luxman receiver as a preamp with the crossover splitting the signal to the QSC amp and subwoofer. Speakers are ADS L780/2's and subwoofer is an SVS SB-12NSD. Sources will be a Dual turntable, Sony SACD / DVD player, and iPhone. This should be fun!

is this QSC a class D amp? anyone have experience with the QSC vs Crown XLS series of class d amps and which sounds better -- QSC or Crown? tia

This particular amp has a date code of 10/22/98 inside, weighs something like 34 pounds (most of which is the transformer), and has a large (quiet) two-speed fan. It's also a 3U chassis. All this leads me to believe that it's a standard class A/B amp.

 

[59volvo]

Absolutely! Balanced cables and adapters should arrive in the next couple days. I'll use a Luxman receiver as a preamp with the crossover splitting the signal to the QSC amp and subwoofer. Speakers are ADS L780/2's and subwoofer is an SVS SB-12NSD. Sources will be a Dual turntable, Sony SACD / DVD player, and iPhone. This should be fun!


This particular amp has a date code of 10/22/98 inside, weighs something like 34 pounds (most of which is the transformer), and has a large (quiet) two-speed fan. It's also a 3U chassis. All this leads me to believe that it's a standard class A/B amp.

 

[59volvo]

The founders of QSC sold it off. Then they started another company called Quilter Amps (for live sound)
https://www.quilterlabs.com/index.php/aboutus/about-quilter-labs

 

[twiiii]

My favorite QSC models were in the CX line . They had high pass filters that worked great for HT modes used with subs, or lower HP filters that cut things off below 30 hz. I liked the limiting, it was very similar to Mcintosh power Guard. And I liked the fact they made models that could drive 70.7 volt speaker lines using transformers. They have relatively high damping factors , low distortion and good signal to noise. I never damaged a driver using QSC. I wish I could say that for Hafler, Crown, Quest, BGW, and other commercial amps. Even with Urei limiters Mcintosh 2300 was notorious for destroying loudspeakers. I never had issues with Macs later amps with Power guard. They saved a lot of customers a ton of money over the years protecting drivers from careless DJ's and sound board operators.. Some drivers from JBL, Altec, and EV you could over power by 50 to 100% using Mac amps with Power Guard and never have a failure, QSC with their limiters and filters were just as good if not more flexible and weighed a ton lest and were easier to afford with much lower prices. I liked the CX series with Professional Klipsch and Altec the best. I would have no problem seeing the CX series being used with home stereo or HT systems.

 

[David_NC]

Pro amps have 3 main goals. Accuracy. Play loud when told to. Never fail. How well they achieve these goals varies; price-points have an effect, and age always has effect.

Their downside to 'consumers' is their appearance; balanced or 1/4" ins/outs; and (used to be) their accuracy: they're not 'voiced' to be 'pleasant'. Now that Accuracy is a Holy Grail in highish end audio, I'm curious to see how much Audiophiles really like Accuracy.

You don't mention the DBX xover. Can we look forward to the next installment?

I got it all set up last night temporarily. I'll definitely have to rearrange some things and work on the power switching I used to turn the sub on and off. I started with the crossover set at 45Hz, which obviously didn't have much impact on anything. I eventually settled on around a 57Hz crossover frequency. I turned the bass up until the sub was really obvious and then turned it down a little at a time until it seemed to disappear but the bass was still present. At this point, it sounded like my ADS L780/2's had a bit more low bass. I could increase the volume quite a bit without the woofers overextending themselves. It was pretty revealing when I flipped the power switch off on the sub; the bass suddenly just disappeared. I've always been told that a subwoofer should be detectable only by its absence, and that is the case here.
With the volume control at minimum on the receiver I used as a preamp, the input gains on the QSC amp set about 3:00, I could not detect any hiss or hum from the speakers with my ear inches away from the drivers; both the amp and crossover appear to be very quiet. After a couple hours of fairly loud listening, the fan on the QSC amp did switch to high, and I could hear it from about 18" away from the front grill. It's not an annoying sound whatsoever like some of the smaller fans I've heard. This is a larger, fairly slow turning fan, and what I heard was more of a very quiet motor with a bit of air noise - completely acceptable for any situation, I'd imagine.
After three albums, an SACD EP, and quite a bit of streaming, I'd call this a success.
- an older QSC USA series amp sounds really good, and at 240 watts, it never broke a sweat. At current prices, if in good condition, can be a steal (240 wpc for $100)
- SVS SB12-NSD is a really nice subwoofer that sounds great. I've only used it in my 7.1 system so far, and it's never disappointed. With music, I'm just as impressed. This sub is used with two separate systems - LFE from my Denon HT receiver goes to one input, and the mono sub from the DBX crossover goes to the second input. Otherwise, I could have simply used the internal crossover.
- ADS L780/2 speakers always impress me, especially considering these are over 32 years old. The soundstage is huge. I always enjoy asking people to close their eyes and point to instruments, and then open their eyes and see where they're pointing.
- DBX 223 series crossovers are unobtrusive, easy to use, and don't seem to affect the sound negatively at all
- Luxman R-115 is a great receiver. My biggest gripe about it is that it has two sets of pre outs but no main ins. The phono preamp is very quiet as well.

My listening area is probably 12x15 or so. There was plenty of reserve available, but in a significantly larger area, I'd probably need larger speakers and possibly a second sub. Still, I'll eventually try it in a larger room. All in all, I'd call this mix and match of equipment a success, in terms of sound quality. Other than buying the sub new about a year and a half ago, everything in this setup is used, with the newest pieces being the crossover and amp, which is over 20 years old.

My favorite QSC models were in the CX line . They had high pass filters that worked great for HT modes used with subs, or lower HP filters that cut things off below 30 hz. I liked the limiting, it was very similar to Mcintosh power Guard. And I liked the fact they made models that could drive 70.7 volt speaker lines using transformers. They have relatively high damping factors , low distortion and good signal to noise. I never damaged a driver using QSC. I wish I could say that for Hafler, Crown, Quest, BGW, and other commercial amps. Even with Urei limiters Mcintosh 2300 was notorious for destroying loudspeakers. I never had issues with Macs later amps with Power guard. They saved a lot of customers a ton of money over the years protecting drivers from careless DJ's and sound board operators.. Some drivers from JBL, Altec, and EV you could over power by 50 to 100% using Mac amps with Power Guard and never have a failure, QSC with their limiters and filters were just as good if not more flexible and weighed a ton less and were easier to afford with much lower prices. I liked the CX series with Professional Klipsch and Altec the best. I would have no problem seeing the CX series being used with home stereo or HT systems.

I'm not sure how the USA series or the Model 1200-1400-1700 series compare to the CX series, though I believe these are a good bit older. The top models are huge, with a 'standard' circuit board and a second mounted above facing downwards. All these models have the limiters and dual HP filters, selectable for each channel. The build quality on the 900 seems to be very good - I didn't see any sloppy workmanship inside. The only downside to them is that they are heavy! At least the chassis is shallow! This is definitely a bit of a dinosaur, compared to modern 2U amps, and I suppose that for reliability in situations where one is paid, one might want to replace them with something newer. Still, the ones I'm seeing for sale on Craigslist are in very good to excellent condition. This amp and crossover were from a church for music programs, and I can tell they were rarely used. Other than the very small bit of dust in the amp, their condition is equal to that of most 'open box' specials I've seen.

 

[twiiii]

I was trying to stay positive, so I didn't speak about DBX. My complaint with DBX is they use cheap connectors, switches and controls. If it weren't for that DBX would be a good product. Doesn't matter if you're using consumer or Prof DBX, same story. My DBX's have always been a pain. The ones I installed and the ones installed by others that I serviced needed periodic servicing. After a number of years, we would upgrade the customers when ever possible. Crown processors could be the same way, they just lasted longer.

 

[David_NC]

I was trying to stay positive, so I didn't speak about DBX. My complaint with DBX is they use cheap connectors, switches and controls. If it weren't for that DBX would be a good product. Doesn't matter if you're using consumer or Prof DBX, same story. My DBX's have always been a pain. The ones I installed and the ones installed by others that I serviced needed periodic servicing. After a number of years, we would upgrade the customers when ever possible. Crown processors could be the same way, they just lasted longer.

Luckily, this one looks to have never been used; all controls and switches work fine. Being close to a set and forget device, in my situation, I hope it'll last! When connecting the XLR cables, I did notice a bit of movement / play, likely due to them being mounted on thinner metal and it flexing. There is no such play / flex on the connectors on the amp; that chassis is solid!

 

[David_NC]

My favorite QSC models were in the CX line . They had high pass filters that worked great for HT modes used with subs, or lower HP filters that cut things off below 30 hz. I liked the limiting, it was very similar to Mcintosh power Guard. And I liked the fact they made models that could drive 70.7 volt speaker lines using transformers. They have relatively high damping factors , low distortion and good signal to noise. I never damaged a driver using QSC. I wish I could say that for Hafler, Crown, Quest, BGW, and other commercial amps. Even with Urei limiters Mcintosh 2300 was notorious for destroying loudspeakers. I never had issues with Macs later amps with Power guard. They saved a lot of customers a ton of money over the years protecting drivers from careless DJ's and sound board operators.. Some drivers from JBL, Altec, and EV you could over power by 50 to 100% using Mac amps with Power Guard and never have a failure, QSC with their limiters and filters were just as good if not more flexible and weighed a ton lest and were easier to afford with much lower prices. I liked the CX series with Professional Klipsch and Altec the best. I would have no problem seeing the CX series being used with home stereo or HT systems.

I've been playing with this setup - the dbx crossover and QSC amp - all week and came across this post. I thought I'd responded earlier. Like the CX models, this one has high-pass filters (30 and 50Hz), switchable output limiting when distortion is sensed, thermal monitoring, DC output protection, and input protection, whatever that is. I feel a bit better using this 20 year old amp. With an ear up to the tweeters and the volume on a C31 preamp turned up halfway, I really cannot detect hiss, which is nice. There is zero turn on / turn off sounds from this amp; the only issue I have is that the subwoofer is set to use auto on by sensing inputs, and the dbx crossover causes a thump when it's turned off, as the sub's amp is still on. For now, I'm just leaving it on, unless I'm leaving for the day, going to bed, etc. I'll figure a way around that.
This crossover / amp combination is really good, actually. When one considers the price for this used equipment, it's pretty amazing. I know this is not the end-all amplifier, but it's working for now, and doing it well. It pairs very well with the used McIntosh C31 I picked up over the weekend and the ADS L780's I've had for a while. I can definitely tell a difference when it's in place of the Luxman R-115 feeding the crossover via preamp outputs. Lows seem a bit better defined, and the mids and highs have more clarity. It's fun to point to where I'm hearing individual sounds and seeing that they are above, below, or to the side well beyond the speakers. Hopefully, the longer balanced cables I ordered will arrive so I can get the amp and crossover off the floor. I'm always worried about one of our cats finding something new and feeling the need to mark it...

 

[twiiii]

We basically used the QSC units that could drive 70 volt lines with built in limiters and hi-pass filters and we never had one fail us. We used other models for sound systems but they had the built in limiting and filters too. They didn't fail either. AEI out of Seattle was a big Crown user and we installed systems for them. But the Crowns they used did have issues. They didn't like driving speakers high voltage transformers, be cause most of the time everyone uses cheap transformers, which become so reactive at low frequencies they make the amplifiers put out to much current and with the severe shift make over ly high demands . So they changed to QSC also. This was back in the 80's some where and like I say I don't remember the Amp models. Later on we even used the amps for complex home systems where people didn't want to cough up the money for Mac amps for fill and distributed room, patio and pool speakers. As I can best remember we never had a QSC amp fail. We substituted them in place of B&K amps because they were always giving us fits. I thought for sure QSC sounded better than Yamaha's amps with switching power supplies and the QSC even out performed most of the Marantz amp separates we sold. Some of Haflers amps sounded as good if not better but they just didn't stand up as well. Everyone and their brother were selling Crown it seemed so we were happy. to let them go and be a QSC dealer. In there somewhere we got involved with Crest and BGW, but they didn't perform as well as Crown during the disco days. and the Crowns couldn't touch Mac amps either. So discos had Mac amps, and if they didn't they ended up with them eventually. ,

 

[David_NC]

I thought I should just update this thread instead of starting a new one...
I've been using the C31v / dbx 223XL / QSC USA 900 / ADS L780/2 / SVS combo for a few months now, and it sounds great, and the amp never seems to break a sweat. Yesterday, I swapped some ADS M12's for the L780's, keeping the rest of the system as-is. Wow, these speakers are sure different from the smaller 780's! They sound bigger, definitely play louder, and I'm hearing things in familiar songs that I haven't heard before. That's always been an indicator to me that the piece of equipment is a step up form what I've been using (unless what I'm hearing is not supposed to be there, such as distortion, etc).
The M12's are 4 ohm vs the easy-to-power 8 ohm 780's, and the amp sure let me know... with heat and the fan running on high. Regardless of the level, the air coming out of the front grill of the amp has always been only slightly warmer than ambient, at most, with a faint breeze pushing it out. Driving the M12's to almost painful levels - gotta test this stuff out - I could tell this amp was working a lot harder, though it still sounded great. I could hear the fan running on high only when there was silence; even quiet passages weren't quiet enough to hear it. It wasn't a whine like many small fans make, and it wasn't annoying. With a fan on in the room, AC running, or a HEPA filter on in the next room, the amp's fan was inaudible from my listening position.
I figured this would be good to pass along, in the event someone want's to try a pro amp but is concerned about potential fan noise. Note: lower profile amps with smaller, front mounted fans might not be as quiet. The model I have has a taller, shallow chassis allowing for a larger fan. All that, and these amps are the cheapest 240 / 450 watt (@ 8 / 4 ohm) decent sounding amps I've found.