Film-Tech Forum ARCHIVE: Epected life of a QSC DCA1644

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Posted by Steven Smith (Member # 8350) on 11-21-2014, 11:41 AM:

Hey guys. I've seting up my new home theater and currently have 3 QSC 2150s for the front stage. I've been eyeballing the crown xls 1500 but stumbled across a used QSC DCA1644 (4 channel amp around 400w @ 4ohms). It has a date code of November 2006, making it 8 years old. It was removed from a cinema.

Is 8 years of steady use (cinema) a lot for this amp Or should I expect years of Home theater usage which is very light usage in comparison? Seems like a lot to me, and the guy want $430 for it and new ones can be found around $750.

Thanks for any recommendations!

Posted by Steve Guttag (Member # 268) on 11-21-2014, 12:16 PM:

We haven't had to retire ANY DCA amps yet so I'd think you'd be safe with it. About all we have had age over the years in them have been the input attenuators.

Posted by Steven Smith (Member # 8350) on 11-21-2014, 12:59 PM:

Thanks Steve!

Posted by Marcel Birgelen (Member # 6801) on 11-21-2014, 01:04 PM:

That's some serious power for a home theater. I pity your neighbors [Wink]

.

What decoder/pre-amp are you using?

Posted by Steven Smith (Member # 8350) on 11-21-2014, 02:55 PM:

I'm building on 3.5 acres and it's sorta wooded..can't even see my neighbors from the house, closest house is 500 ft away... but the 4 18s may still wake them up, I normally listen about 5 db below reference (treated room of course).

This is my second theater and I'll probably just stick with a good AVR. I want a separate amp at least for the mains as I don't want them running out of juice as my AVR will have enough to push. Planning on going ATMOS. I'm planning on going with QSC 8101 all around (except for mains of course) 2 paralled surrounds per side (multi row seating), 2 rears, 4 Atmos speakers. The ceiling is nice and high to accommodate the Atmos..10 feet height on the back row and 11.6 feet for the front. I called and spoke with Sam Hynes at QSC and he gave me a ton of installation advice, baffle wall etc.

If anyone sees anything I'm missing feel free to let me know!

I just thought of something. The amp had data ports for digital processors. Are there any settings that could have been changed by a processor when It was in use that can affect the sound that I can't change back to default?

Posted by Marco Giustini (Member # 4544) on 11-21-2014, 05:26 PM:

Go for it, indestructible.

All settings are via DIP switch, the dataport is just a convenient way to connect the amp.

I've had gain trimmers failures as well, nothing that cannot be sorted by turning it all way up/down a few times.

Posted by Marcel Birgelen (Member # 6801) on 11-21-2014, 05:47 PM:

Maybe someone should rather move this topic to a more appropriate location? It's not really about film [Wink]

.

I don't know too much about the consumer version of Atmos, but the cinema version of Atmos requires far more power for the surrounds than a regular 5.1 or 7.1 setup. Atmos mixes also tend to be a lot heavier on the surrounds, they sometimes pan really loud sound effects across your room.

So, running the three stage channels trough a bunch of oversized dedicated amps and speakers and having the rest of the channels on an AVR sounds a little bit unbalanced. Also, good luck finding an AVR capable of powering a whole array of SR-8101s without running out of headroom rather quickly [Wink]

.

If you can live with "just" 7.1, I would recommend the NuForce AVP-18 and some 5-channel or 7-channel amp that can deliver the required 125W per channel for your surrounds. The primary thing speaking against the AVP-18 is that NuForce is somewhat of an audiophile brand and I'm a bit allergic to certain kind of "audiophiles". But the good thing is, the automatic calibration and EQ makes a whole lot more sense than that Audyssey stuff most AVRs are using. And the best thing is: It comes with a proper RS232 port which you can use to remote control the whole thing, much like professional cinema processors.

Posted by Marco Giustini (Member # 4544) on 11-22-2014, 07:23 AM:

quote: Marcel Birgelen
the required 125W per channel for your surrounds

May I ask where this figure is coming from?

Edit: got it. We're talking about 8101. But those are 125W each and here they're x2, hence the figure we're looking is at least 250W - even though we should consider the room size too: if the power required to reach the max level ends up to be much lower, 250W would not be needed after all.

Posted by Steven Smith (Member # 8350) on 11-24-2014, 01:19 PM:

Sorry if it's in the wrong section, I wasn't sure where to put it.

With the current Atmos AVRs I'll have to supply at least two of the channels power. So I'm choosing to feed that power to the mains and the center as well just so it has the power of the mains.

As for the 8101s, as long as I am feeding them at least 80 watts I can hit peaks of 103db. The farthest 8101 will be the rears when sitting in the front row and to exceed 103 safely it'll need more power. In general I'll be sitting no farther than 8 feet from any 8101 at any time. I listen around -5 below reference so the system should have no issues playing distortion free. And as for the surrounds in parallel the they will drop to a 4 ohm load and give me a 3 db boost.

This is also my second theater with Cinema speakers. I've used the JBL 3677 which was the best most dynamic speaker I've ever heard for home theater. And feeding them power with an external amp greatly improves the mid-bass and dynamics.. So to some it may seem overkill but that's how I like it. I understand on paper the mains shouldn't need that much power but in reality there is a difference at least to my ears. There are several Home theaters using Cinema speakers on AVS and other forums.

Here's a pro reviewers first taste of the JBL 3677 in his theater. skip to 3 minutes to get to the good stuff.

https://www.youtube.com/watch?v=1pvBC0msHUQ

Imax has also began doing Home theater installs using actual cinema speakers as well.

Also I passed on the QSC amp due to age. I just bought 2 new crown XLS 1500 amps for $305 each with free shipping.

Posted by Tony Bandiera Jr (Member # 2365) on 11-24-2014, 02:54 PM:

quote: Steven Smith
....I passed on the QSC amp due to age. I just bought 2 new crown XLS 1500 amps for $305 each with free shipping.

So you spent an extra $200 or so for a pair of inferior amplifiers? [Roll Eyes]

Got it.

QSC's DCA amps are about the best you can get at any price point. They are tough, very reliable and more importantly in a home cinema, have a MUCH quieter noise floor than Crowns. [puke]

There is a thread on here discussing how bad Crown amps really are...along with a few on how much better QSC is, for example my own thread on the DCA line:

Linky

Crown amps also tend to take the speakers with them when they fail, which IMHO is far too often compared to other brands.

I have locations with DCA's over 15 years old still going strong and the failure rate I have experienced has been literally less than 0.02%.

You will ultimately regret getting those shiny new Crowns in time I predict.

Posted by Steven Smith (Member # 8350) on 11-24-2014, 03:25 PM:

Well crap! LOL...I've read lots of good stuff on the Crown (exept the xls1000 which is very noisy) but it's all about them being used in Home theater use which is actually very common. They have a 3 year warranty. I noticed the S/N was a little better but not much ...(on paper). The QSC sold pretty fast as he had another buyer. But yea the age thing is why I hesitated and so many using the crowns..I figured they were both good.

Ohh well. Hopefully I won't have any issues.

Posted by Jarod Reddig (Member # 6363) on 11-24-2014, 03:30 PM:

HT wise Crown amps are great amps. Don't be fooled. QSC are great as well. The XLS models do have some fan noise but I bet anyone designing a no frills HT has there own equipment room in an adjacent room or closet. There are also fan mods for them if they must be placed in the room. Ive used Crown DC300A series II amps for years in my HT with no problems at all and they were over 20 years old when I bought them used. I use 2 to run my stage speakers, JBL 4722n, and just use my AVR to power my JBL 8340a surrounds. My dual subs are active. Cinema gear in an HT is the real deal. Good luck my friend. [thumbsup]

Posted by Steven Smith (Member # 8350) on 11-24-2014, 03:38 PM:

Yea I recognize your name from AVS. On there I'm cdy2179, I have the JBL 3677 have arrived thread.

Anyways I know they're used and held pretty high over there. The guy who sold the QSC actually had several XLS1500 amps in his own theater. If he didn't have another buyer I probably would have went QSC just because my speakers are all QSC. But for $170 more I went for new with a warranty.

Yea my gear will be in the foyer. From what I've read the fans shouldn't run much if at all. The Andrew Robinson Review stated the amps never got worked hard enough to even kick on that he noticed.

Posted by Jarod Reddig (Member # 6363) on 11-24-2014, 03:42 PM:

Oh cool nice to see ya over here man!! Thought your name sounded familiar. Don't blame ya on the warrenty. So many different paths can get us to HT bliss.

Posted by Steven Smith (Member # 8350) on 11-24-2014, 03:47 PM:

Yea I like to lurk here a little too. This forum kinda helped me in my decision to try the QSC 2150s instead of going for the JBL 3677 again in my new theater. I found the QSC 2150s for $400 NIB, couldn't pass it up, especially seeing how highly regarded QSC is around here.

Posted by Jarod Reddig (Member # 6363) on 11-24-2014, 03:54 PM:

Damn great deal on those man! Ya for that price it would have been hard to pass those up.

Ya I have a deep deep passion for Cinema and all the gear related to it. I really love this site as well.

Posted by Tony Bandiera Jr (Member # 2365) on 11-28-2014, 09:19 PM:

quote: Jarod Reddig
HT wise Crown amps are great amps. Don't be fooled.

LOL sorry Jarod, have to disagree 100% on this one. For the reasons I gave in my first post, Crowns are amongst the WORST amps for home theatre use. Two reasons:

quote:
The XLS models do have some fan noise but I bet anyone designing a no frills HT has there own equipment room in an adjacent room or closet. There are also fan mods for them if they must be placed in the room,

I was not referring to the fan noise in my previous post....the noise floor refers to the standby "hiss" in those amps. Crowns are very noisy in that respect...and in one of the other threads on Crowns, a poster there mentioned having to replace and "mix and match" several Crowns to get all of them quiet enough for the application. Unacceptable in a close-quarter screening room. (And for the price of those amps.)

Second:

quote: Jarod Reddig
Ive used Crown DC300A series II amps for years in my HT with no problems at all and they were over 20 years old when I bought them used.

The DCxxx series amps are NOTORIOUS for failing without warning and impressing the FULL DC power supply bus on the speaker terminals at FULL current. You were extremely lucky. BTW, those amps were originally designed for use with "Shaker tables"..they drove linear motors and transducers to provide high-amplitude motion at frequencies from DC to over 40khz. (The same wide range capability, while excellent for audio fidelity, can be and often was fatal to speakers and HF drivers due to lack of protection from DC offset and HF oscillation.)

Crowns are an amplifier that survives on hype and imagined reputation of quality rather than reality. [Wink]

Posted by Sam D. Chavez (Member # 1841) on 11-28-2014, 11:45 PM:

quote: Tony Bandiera Jr
The DCxxx series amps are NOTORIOUS for failing without warning and impressing the FULL DC power supply bus on the speaker terminals

I'd say notorious is too strong a word. This amp had its day in late '70s and early '80's and was the best sounding commercial amps around at that time, partly because the others were so bad. There were high numbers of DC300's that worked flawlessly for 20 years without incident.

BGW's were very good back then but the company was badly run to say the least.

Posted by Jarod Reddig (Member # 6363) on 11-29-2014, 05:03 AM:

Much agreed Sam they have one hell of a track record, even considering its issues.

Tony I guess we can agree to disagree. No harm in that.

Posted by Mark Gulbrandsen (Member # 72) on 11-29-2014, 11:13 AM:

Crown amps suck. Crown has been Harmonized much the same way JBL has been!

The part that fails mostly in the DCA's is the input level pots. They are absolute crap in what otherwise is an excellent amp series. Not sure why QSC chose to use a part that becomes intermittent and some times just completely fails. Sometimes a little Pro Gold fixes them up but they are actually plastic attenuators of the very cheapest variety. Ugh!

Yes... I have driven hundreds of miles because of these DAM pots!

There! That is my one and only RANT about QSC.

Mark

Posted by Jarod Reddig (Member # 6363) on 11-29-2014, 02:19 PM:

Define suck lol.

Ya I had cleaned the pots when I first got them. They were a bit scratchy.

Posted by Steve Guttag (Member # 268) on 11-29-2014, 05:18 PM:

QSC claims it is a particular run of pots that have the issue. I'll admit, I don't have the noisy pot issue on all amps...just a particular generation (I want to say 2007-2009 are the most suspect).

Posted by Mark Gulbrandsen (Member # 72) on 11-30-2014, 09:43 PM:

Also on other models of amps but not on USA or the later DCA. The fan blows the crud right into the pots!!

Mark

Posted by Brad Miller (Member # 2) on 11-30-2014, 10:36 PM:

Very odd. I've not had the issue AT ALL with QSC DCA amps, and I'm quite sure I installed more than enough in the 2007-2009 time frame.

Now the mx series...UGH!!! I'll just leave it at that.

I'm not saying it isn't/wasn't a problem, but I've not personally experienced it. Those amps have been nothing short of awesome for me in every regard.

Posted by Mark Gulbrandsen (Member # 72) on 12-01-2014, 09:18 AM:

If your booths are really dust free you may never experience it. The pots are not sealed so the fan blows crud right into the pot. I've had it happen at a half dozen locations.... and yes! It is dusty around here. A huge waste of time and expense the customer shouldn't have pulling amps out of a rack opening them up to clean a 20 cent pot.

Mark

Posted by Scott Norwood (Member # 30) on 12-01-2014, 09:49 AM:

WRT the MX series...I have had to replace a bunch of pots on MX-1500a units. That seems to be about the only part that goes bad on them, but it is annoying. Is there a better quality replacement than the one that QSC sells?

Posted by Ron Lacheur (Member # 1126) on 12-01-2014, 11:07 AM:

A 10k Bourns or Clarostat pot should do the trick for a sealed replacement. Not sure what the taper is though.

Posted by Marco Giustini (Member # 4544) on 12-01-2014, 02:44 PM:

I haven't seen completely faulty trimpots, but seen 'dead' DCA amps where the problem was fixed by cleaning the pots by rotating them back and forth a few times. Seen it several times unfortunately. But DCA's are still the best out there - IMHO.

Posted by Jim Cassedy (Member # 4115) on 12-01-2014, 04:05 PM:

quote: Mark Gulbrandsen
The pots are not sealed so the fan blows crud right into the pot. I've had it happen at a half dozen locations

No kiddng, Mark! [Frown]

I've had the same problem here with a wholebuncha Ashly amps.

Ashly used the cheapest unsealed pots & mode switches on the input modules of
some of their amplifiers and at least once a year I have to pull the modules
out & douse them with Cramolyn or some similar contact cleaner/lube.

I'll bet they spent less than 50cents each on those pots in the quantities they
were buying them. A couple of even cheap sealed pots & switches wouldn't
have added that much to the overall cost of their amps.

The problem here is not only dust, but the "salt air" since the theatres I've
got the most problems with are located near either the ocean or SF Bay.

I just had to go down & pull all the modules out at one theater due to the
"noisy pot problem" just last week.

Fortunately, the theater owner (and I ) am getting tired of doing this,
so we've begun to swap out the old Ashlys for some new QSC's. thank gawd!

Posted by Steven Smith (Member # 8350) on 01-07-2015, 01:04 PM:

Figured I'd give an update. Well I received and really like the Crown. Plenty of power and sounds great...as long as it's on speakers below 96ish db. I tried it on a 97db and my QSC 2150 @101db sensitivity and there is just too high of a noise floor IMO.

So I ended up buying the same QSC 1644 from the guy who bought it from the guy I almost bought it from.. for a little less $$ too. I got lucky!

You guys were right...the QSC is in another league which is evident with the two just sitting side by side and comparing build quality, of course this is the Crown XLS series, so it's one of the cheaper Crowns. And it's so much quieter. with Crown the noise floor was evident from 8 feet plus with the QSC 2150s, and with the DCA amp it disappears around 2 feet away. It should be perfect for my setup.

I just have to swap the fans as it's kinda noisy but I already have one being shipped and it's no big deal to swap it out, I actually had to unplug the fan so i could quiet the room to test the noise floor, Of course I won't use it without a fan.

Posted by Mark Gulbrandsen (Member # 72) on 01-07-2015, 01:26 PM:

I have never retired ANY QSC amplifier for that matter. Not even a USA Series amp. I just rebuild them to like new again. Cost to rebuild one is about 1/4 the price of a new amplifier. I have had theaters remove them and install newer QSC amplifiers. The old ones eventually find new homes.

At some point even in the DCA you are going to have to replace power supply capacitors. This is true of just about all amplifiers out there. IMHO... if an amplifier hits the 20 year old mark then think about recapping it to maintain best performance. Caps age and they dry out and become leaky and so on. Also, caps age faster in hot running amplifiers, so keep that in mind.

Mark

Posted by Steven Smith (Member # 8350) on 01-07-2015, 02:30 PM:

Thanks for the input. Mine won't get driven very hard at all and I'm even thinking of running a small air supply into the AVR closet to spoil the equipment, but I guess nothing can fight age and like you mentioned caps drying out.

Are there any references on how to troubleshoot these amps? I know basic electronics like testing caps, resistors, diodes, inductors and have the test equipment (LCR meter etc) but usually I know it's highly recommended to take the component out of the system to test it. The only reason I ask is sometimes I see some "not working" DCA amps for sale. Wouldn't mind having another one of these to run some surrounds and rears.

Posted by Bob Healey (Member # 1003) on 01-07-2015, 06:32 PM:

If you do play with forced air ventilation, the QSC amps take in from the rear and exhaust via the front, while the Crowns take in via the front and exhaust via the rear.

I'm not a fan of the new Crown amps myself, but I've never had one of their old Macro-techs fail on me. Just swapped a set of MA-1200s in for a set of failing 20 year old Ashly FTX units. They're on semi-permanent loan until something gets done about the Ashlys. The Crowns survived 20 years of concert/event duty.
A thing to remember with Crown is they were originally signal, not audio amplifiers, so they had none of the protections you would want for speakers, such as DC filters on the outputs. A story I've been told is back in the '80s, the power supply for a mixing console failed. It wanted +/- 15VDC, so the audio crew took a Crown D-150, hooked a D Cell battery to its inputs, bridged it so it made +/- 15V and they ran the show off of that for the night, with minor tweaks to the attenuators as the D cell started to drain.

Posted by Mark Gulbrandsen (Member # 72) on 01-07-2015, 07:02 PM:

Crown amps suck and have always sucked. I have a Macrotech 600 with blown outputs on the bench as I type this. I will post pictures tomorrow and explain why Crown amps suck.

Mark

Posted by Dave Macaulay (Member # 813) on 01-07-2015, 09:12 PM:

Crown amps have been good and bad for me. If they get past the first few weeks without blowing out, they seem to last a good long time.
I have lots of older QSC amps with issues, the early MX series had insufficient airflow (later ones had more powerful fans) and cooked their boards when worked hard for example.
No affordable amp will deliver rated power output indefinitely but the MX and USA series come up seriously short for sustained output power capability (in my opinion): yes, they do deliver rated output but shut down for overtemp within a minute or two at max thermal load. The DCA class D amps are much better at this.
The big problems come when bargain hunting owners install impressive looking amps with a big chassis full of nothing but air - hello Pyramid - that crap out when asked to deliver some reasonable fraction of their "rated" power output. Nice meters, though!

Posted by Mark Gulbrandsen (Member # 72) on 01-08-2015, 01:06 PM:

I also hate using amplifiers that blow their hot air into the rack!! The racks need to stay as cool as possible for long equipment life.

Mark

Posted by Stephan Shelley (Member # 8587) on 01-08-2015, 01:31 PM:

Ashly can repair FET and FXT series 3 no problem and at a reasonable cost. You can remove the amp model for each channel separately. They just plug in. That way you do not have to ship the very heavy amp. Just the much lighter module. FXT series 2 can be much more of a problem. If the PC board is burned it is toast as Ashly does not have any more boards. If it is components they can fix. I have had them rebuild 2 FET modules and recondition an input board for around $180.00 that included return shipping.

I agree with others on here that the QSC DCA amps are rock solid. Older QSC can also be repaired at reasonable cost but they do go out from time to time.