Two amp questions

[bcampbell]

Back with more questions.

My current setup consists of:
2 T39 20" with 3012lf (retrofit...not too bad, but haven't put it to the test thoroughly yet)
2 OT12s
DBX PX+
Carvin DCM 1000 one side powering the subs, the other the OT12. The Carvin is heavier than I want and has some minor noise, good for a backup, but its time to upgrade.

I've set up the limiter for both the OT12s and T39s and dialed things with the DBX the best I could.

So my two questions:
1. I've been looking at the crown xls 1500 and other comparable amps. Do I need more than that? I'd rather have a content amp running comfortably, than running things to the limit and hoping it doesn't crap out on me.
2. With the DBX taking care of the crossovers, limits, DSP stuff, I'd like to have an amp similar in functionality to my current amp....plug in the inputs, set the limiter with the DBX, and be done with it. So when given a choice, I'd obviously go with the nonDSP version, but I've read about people having troubles working around some amps limiters, etc. Any models to stay away from? Not too keen on paying for features that I'm not going to use.

Always appreciate the advice.
Brian

[Bruce Weldy]

The 1500 will not run tops and subs on one amp....not to their potential anyway. The 3012lfs can take more than that amp can deliver on one side. You can bridge it and run two off it (that's what I do - I have two 1500s running my 4 T39s with 3012s). Then run the tops off something else.

Or, get a bigger amp - like an xti 2002, if you want to do it all on one amp.

[whines]

The 1500 will not run tops and subs on one amp....not to their potential anyway. The 3012lfs can take more than that amp can deliver on one side. You can bridge it and run two off it (that's what I do - I have two 1500s running my 4 T39s with 3012s). Then run the tops off something else.

I'm running two t39's off a 1500XLS, but one channel per sub. What's the benefit of bridging...fewer cables?

[Bill Fitzmaurice]

What's the benefit of bridging...fewer cables?

http://billfitzmaurice.info/forum/viewt ... =6&t=19292

[Bruce Weldy]

The 1500 will not run tops and subs on one amp....not to their potential anyway. The 3012lfs can take more than that amp can deliver on one side. You can bridge it and run two off it (that's what I do - I have two 1500s running my 4 T39s with 3012s). Then run the tops off something else.

I'm running two t39's off a 1500XLS, but one channel per sub. What's the benefit of bridging...fewer cables?

The XLS1500 only does 300 watts/channel at 8ohms....even less when you consider horn-loading ups it to 10ohms.

You can't get to the limit of the 3012LF with that amp running one per side - I bridge it to get about 1100 watts and run two off of it.....leaving some headroom. It's worked fine like that for two years. If you can afford a bigger amp to run one per side, then do it. I had the 1500, so I went the bridge route, then bought a second one when I added the additional T-39s. That was the only way to get enough voltage to run them to their appropriate limit with that amp.

[whines]

If you've measured it, what kind of voltage does the 1500XLS put out bridged into that 5ohm load? That's the bottom line, right, getting the 50 volts that the driver can take?

I'm fuzzy on how the resistance of a load affects voltage, but it's reassuring to hear that the XLS1500 is good at running the speakers in parallel if need be.

[bcampbell]

I was under the impression that voltage doesn't care if it is 4, 5, 8, 10ohms. 50V is 50V. I hope so, because I'm not resetting my limited if I change the number of cabinets. My DCM1000 can do 50V, but just barely.

I'm wondering if there is benefit to having an amp that can do 65V but I can still limit it to 50V, so the amp is less likely to overheat, fail, etc. I think this is what is referred to as "headroom", but I'm not sure.

As nice as the Crown XTi 2002 is, it has features that I won't need and weighs similar to the amp I've got now. If I didn't have the driverack and it would play nicely with a Mac, then I would be there.

[Grant Bunter]

I was under the impression that voltage doesn't care if it is 4, 5, 8, 10ohms. 50V is 50V. I hope so, because I'm not resetting my limited if I change the number of cabinets. My DCM1000 can do 50V, but just barely.

I'm wondering if there is benefit to having an amp that can do 65V but I can still limit it to 50V, so the amp is less likely to overheat, fail, etc. I think this is what is referred to as "headroom", but I'm not sure.

As nice as the Crown XTi 2002 is, it has features that I won't need and weighs similar to the amp I've got now. If I didn't have the driverack and it would play nicely with a Mac, then I would be there.

Perhaps you don't want to go into the theory, but you have to know enough of it to make some sense of using your gear.

A "perfect" amplifier would be linear in output. It would put out X voltage regardless of load.
Even getting near to being perfectly linear amps are hard to find though, and cost a lot of money.
If you look at most amps specs (that are affordable at least) you will notice that the output in voltage at 8 ohms is higher than the output in voltage at 4 ohms.
Energy cannot be created nor destroyed, so, when you drop the overall impedance, the amp works harder (because the output current increases), and the "loss" in voltage is attributed to either a power supply that can't keep up and/or losses due to heat.
You can calculate your voltages with:
http://www.rapidtables.com/calc/electri ... ulator.htm
It's very easy to use.

Since you have DSP with your DBX, you don't need an amp that has it as well. As you say, you're paying for something you don't need.

As far as headroom goes, headroom in an amplifier is perhaps best described as the output left available that is over and above the level you are currently using, at any given point in time.
So, if you are running an amp at 100% then you have no headroom. Similarly, if you're running your amp at 50% you have 50% headroom etc.

It's a curious concept, but I have always contended that if you limit an amp to deliver a maximum of, say, 50V, then you only have headroom if you are using less than 50V in output. It is irrelevant that the amp may be able to put out more than 50V, other than, as you say (when you're looking at a 65V capable amp), you're not running the amp as hard as it can be run (which is better for the amp).

As per the link, Bill suggests not to bridge, unless that is the only way to achieve the required voltage swing.
I can see why Bruce bridges his XLS 1500 Drivecores.

It happens that the XLS 2000 Drivecore does 51V at 4 ohms, or 650W a channel. And 54V at 8 ohms. So about 1dB of limiting for the sub channel would give you not quite 50V and prevent transients.

If your Otops are premium loaded, then you can limit them to 40V on the other channel. A rough estimate of 7-10dB limiting would be a good starting point, and adjust from there.

You might think that running an amp to within 1dB of it's capability is a bit to close for comfort. The same old adage applies, if you're running a pair of sub cabs that hard, you probably need more cabs...

[escapemcp]

The same old adage applies, if you're running a pair of sub cabs that hard, you probably need more cabs...

2 more subs is a LARGE proposition though. It is a nice idea (and the correct way to go), but it's not always practical due to packspace/finances/etc. I'd love an 8 sub rig, but it just isn't going to happen quite yet, so I run my 4 close to the limit. Even with 8, I am pretty sure that for the free parties that I do, they will still be run at 49.999V

[miked]

Being that you already own the Carvin, I'd buy another amp, like the XLS1500 (excellent amp...it runs my electric bass rig) and run your subs off one and the tops off the other. Both amps will run cool and clean. Problem solved. Another amp only adds 2U of rack space and not even 20 pounds. That is a very fair trade, IMO vs. trying to run everything off 1 amp.

Want to run it all off one amp? Pony up the big bucks. This will do anything you want it to. Stable down to 2 ohms per side. http://www.musiciansfriend.com/pro-audi ... -amplifier

Or this one...also a great amp (better features but irrelevant if you're using a DSP, which you are) but not quite as powerful as the PLX3602. http://www.musiciansfriend.com/pro-audi ... ier?pfm=sp

Those two amps bridge the gap b/t "prosumer" and "big name touring amps" such as Labgruppen and the others made of unobtanium.

[DJPhatman]

Answer 1: If you want the Crown, go with the XLS2000. If/When you add more cabs, you will need to add an amp, anyways, and this will drive 4-6 T39s to 50V without bridging.

Answer 2: I am surprised nobody suggested the Behringer iNUKE3000 non-DSP. Forum member "escapemcp" uses one with his T30s and likes it.

Whatever amp you choose, for it to fit your budget, pack-space and weight requirements, needs to be at least 4 Ohm stable (2 Ohm preferred) and capable of at least 625 watts@4 Ohm, or 50V. Once you set your limiter, you should never exceed this setting.

[byacey]

As far as headroom goes, headroom in an amplifier is perhaps best described as the output left available that is over and above the level you are currently using, at any given point in time.
So, if you are running an amp at 100% then you have no headroom. Similarly, if you're running your amp at 50% you have 50% headroom etc.

It's a curious concept, but I have always contended that if you limit an amp to deliver a maximum of, say, 50V, then you only have headroom if you are using less than 50V in output. It is irrelevant that the amp may be able to put out more than 50V, other than, as you say (when you're looking at a 65V capable amp), you're not running the amp as hard as it can be run (which is better for the amp).

It happens that the XLS 2000 Drivecore does 51V at 4 ohms, or 650W a channel. And 54V at 8 ohms. So about 1dB of limiting for the sub channel would give you not quite 50V and prevent transients.


You might think that running an amp to within 1dB of it's capability is a bit to close for comfort. The same old adage applies, if you're running a pair of sub cabs that hard, you probably need more cabs...

This is all good information that Grant has provided here. Having that headroom available is a good thing, even if you are hard limiting and it's never used, because this means that the amp isn't running as hard as it was designed to, which means less heat and stress on the amp.

In the XLS2000 example, 1db of limiting below clip is balancing a fine line. With a conventional power supply type amplifier, this may be even more of a problem as you may easily lose the 1db of headroom due to line voltage fluctuations or sag which will cause the amp to clip prior to the limiter clamping down. I would make an effort to find an amp that has at least 20% reserve voltage above the limiter voltage target.
As an example, if you want to limit your subs at 50V, look for an amp that is capable of driving 60V into the load.

[jswingchun]

Answer 1: If you want the Crown, go with the XLS2000. If/When you add more cabs, you will need to add an amp, anyways, and this will drive 4-6 T39s to 50V without bridging.

Are you driving 3 T39s per side of a xls2000?

Why didn't I think of that? I am running two per side of my xTi2000 now and somehow got it in my head that I would need to add another amp to add two more T39s.

[DJPhatman]

Answer 1: If you want the Crown, go with the XLS2000. If/When you add more cabs, you will need to add an amp, anyways, and this will drive 4-6 T39s to 50V without bridging.

Are you driving 3 T39s per side of a xls2000?

Why didn't I think of that? I am running two per side of my xTi2000 now and somehow got it in my head that I would need to add another amp to add two more T39s.

No, I have 2 dual HL10C loaded T39s, that I drive with XTis. If you have 10 Ohm nominal cabinets, 3 in parallel = 3.34 Ohm nominal load. Should be fine on an XLS2000, and the amp can provide voltage swing above 50V. Your XTi2000 can handle 3 per side, no problem.

[jswingchun]

No, I have 2 dual HL10C loaded T39s, that I drive with XTis. If you have 10 Ohm nominal cabinets, 3 in parallel = 3.34 Ohm nominal load. Should be fine on an XLS2000, and the amp can provide voltage swing above 50V. Your XTi2000 can handle 3 per side, no problem.

Thanks for the info. I think I'm going to build some more T39s this coming summer since I can add them to the pile without having to add another amp. Going to build some at the minimum width for the 3012lf.