# Old school carver or new Crown



## needbass (Mar 7, 2010)

Hey guys,

Have my cerwin vegas at-15's up and running. Had the faulty tweeter protection bypassed and all is good. Looking to upgrade my amp. Have my nad c370 currently hooked up and for 90% of the people out there that would be enough, especially in a 19 by 12 room. But i am part of the remaining 10% of the twisted population that needs extreme spl. Am looking at a Carver tfm-45, 1.5 ect that will pump out 500/channel into 4 ohms OR a new Crown xls 1500 that will also provide 500 into 4ohms. I will use my nadc370 as a pre-amp only. I am looking for raw power, but it has to be CLEAN raw power also. What are your suggestions?
Thanks........


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## jackfish (Dec 27, 2006)

Why not a pair of Crown XLS 1000 Drivecore amps for $600, each bridged for 1100 watts into 4 Ohms?


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## Dale Rasco (Apr 11, 2009)

I use the 3 Crown XLS 1000's bridged to power my Axiom M80's and VP180 and they have all kinds of headroom.


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## needbass (Mar 7, 2010)

jackfish said:


> Why not a pair of Crown XLS 1000 Drivecore amps for $600, each bridged for 1100 watts into 4 Ohms?


...That reminds me of sitting in on a session years ago at the cerwin vega dealer. 1 pair of se-380's hooked up to 2 carver m1 amps bridged mono 1000 watts each, in a room about 30x20.:yikes: Intense bass and spl. I loved it!


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## needbass (Mar 7, 2010)

Dale Rasco said:


> I use the 3 Crown XLS 1000's bridged to power my Axiom M80's and VP180 and they have all kinds of headroom.


...I am wondering how the sound quality of the crown xls 1000-1500 would compare to carver, nad ect?


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## jackfish (Dec 27, 2006)

Marginal differences i would guess, and if you can't A/B them how you gonna know?


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## GranteedEV (Aug 8, 2010)

> What are your suggestions?


:sneeky: Forget the amps and get better speakers!!! :innocent:



jackfish said:


> Why not a pair of Crown XLS 1000 Drivecore amps for $600, each bridged for 1100 watts into 4 Ohms?


would there be any increase in distortion at lower wattages from bridging (where each amp now sees a 2 ohm load)? I'm not too familiar with the consequences so if you can enlighten me i'd appreciate it. I also believe the Crown XLS-1500 has a lower noise floor specified than the XLS-1000.

while I don't particularily look at distortion below clipping at high wattages, I do pay attention to distortion/noise floor at roughly 500mW to 5W, where the amp spends most of its time. Of course the speaker's sensitivity is a big factor in this as well, as less sensitive speakers simply won't reproduce noise floors.



> ...I am wondering how the sound quality of the crown xls 1000-1500 would compare to carver, nad ect?


Being a modern class D amp, the crown should have great performance at low SPLs where some poor Class AB amps can sound gritty and unresolving at low SPLs from the crossover. _Not_ that amps sound particularily different either way. :whistling:

The Crown is 1db down at 20khz so it'll have a slight relaxation in the top octave. Nothing immediately audible, but the biggest difference might be a slightly more natural stereo image with some "hyper-focused imaging" speakers. Then again, this is about the difference from moving your head to the side by a few inches when listening to speakers. In 99% of cases I do NOT subscribe to amp / speaker "synergy" but in this case I can see it slightly taming a more aggressive speaker.

Overall I expect the drivecore crown amps to sound fantastic even if high SPLs aren't needed. And the dynamics will be startling.

...but I'd still get better speakers first :innocent:


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## RTS100x5 (Sep 12, 2009)

Carver was a great amp in its day but is probably not serviceable except by 3rd party = expensive and difficult to repair if at all - they also run hot as hell .... CROWN all the way....


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## RichP714 (Feb 12, 2008)

GranteedEV said:


> :.....would there be any increase in distortion at lower wattages from bridging (where each amp now sees a 2 ohm load)? I'm not too familiar with the consequences so if you can enlighten me i'd appreciate it.


Our site (thecarversite.com) has a section on bridging in the audio terms glossary:

Bridge Tied Load
Using a stereo amplifier to drive a single channel loudspeaker, by strapping the load across the hot terminals of each channel(one channel is inverted in phase with respect to the other). This results in a higher power output from the amplifier, with some caveats.

A standard stereo amplifier is a voltage amplification device, and normally supplies a voltage to two separate 'channels' of amplification. In the illustration below, a stereo amplifier (capable of providing a 45V signal to each channel) will dissipate 250 watts per channel into a nominal 8 ohm load (P=E2/R). Since current is the result of dividing voltage by resistance (I=E/R), the amplifier is able to source 5.5 amps per channel.










When a stereo amplifier is bridged, two things happen. First, one of the channels is inverted with respect to the other (the two channels are now 180 degrees out of phase). Second, the 'hot' terminals of each stereo channel are connected to one loudspeaker (the remaining two output terminals are unused).

The illustration below presents a bridge tied load configuration of a stereo amplifier. The per-channel output voltage remains the same (45V), and the load remains the same (8 ohms). What has changed, is that each stereo channel's 45V output is both out of phase with the other and tied to the same driver. The result is a 90V differential across the load (double the stereo voltage).










Using P=E2/R from the previous example, the power dissipated by the load is now 1012W.

Using I=E/R from the previous example, the current required to sustain 1012W is now 11.25A.

This seems like a very good situation, and can provide more power to a speaker, provided you follow a simple guideline.

The relation I=E/R tells us that as output voltage doubles, so does required current. Also, as driver impedance halves, required current will double.

An ideal current source amplifier (often called load invariant) will be able to source the required doubling of current as the load halves (from 8-4-2-1 ohm). Not all amplifiers are load invariant (few are).

Using the above formulae for a 4 ohm driver would (ideally) provide 500W into a stereo 4 ohm load (requiring 11.25A per channel), and 2025W when bridging the amp (now requiring 22.5A).

The situation becomes harder for the amplifier to tolerate as the load impedance diminishes. At some point, the amplifier can no longer source the current required to provide a doubled voltage level.

This is often experienced sonically as a very loud, but 'flabby' sound (especially in the bass).

For this reason, most stereo amplifiers that are bridgeable are rated into 8 ohm load drivers only.

<pet peeve> It's often repeated that when bridged, each half of the stereo amplifier will 'see' half of the driver load. This is untrue; the load is the load, and hasn't magically sprouted a center tap. What has changed is the current sourcing demand placed on the amplifier due to the doubled output voltage across the load.


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## RichP714 (Feb 12, 2008)

needbass said:


> ...That reminds me of sitting in on a session years ago at the cerwin vega dealer. 1 pair of se-380's hooked up to 2 carver m1 amps bridged mono 1000 watts each, in a room about 30x20.:yikes: Intense bass and spl. I loved it!


Agreed; the M-1.0t is rated at 200W (rumoured to have been uder-rated to match the Conrad Johnson prem 5 amp it is transfer function matched to), but it really will do 360W, and has tighter bass response than the 4.0t.

It's a real sleeper of an amp


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## GranteedEV (Aug 8, 2010)

Thanks for the nice post, Rich.



RichP714 said:


> <pet peeve> It's often repeated that when bridged, each half of the stereo amplifier will 'see' half of the driver load. This is untrue; the load is the load, and hasn't magically sprouted a center tap. What has changed is the current sourcing demand placed on the amplifier due to the doubled output voltage across the load.


hehe. I'm guilty of that one but it's the easiest way to visualize the current demands on the amp :neener:


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## RichP714 (Feb 12, 2008)

GranteedEV said:


> Thanks for the nice post, Rich.
> 
> 
> 
> hehe. I'm guilty of that one but it's the easiest way to visualize the current demands on the amp :neener:


I know it's splitting hairs, it just happens to be a peeve of mine. That and people that talk about speaker 'efficiency' when they mean sensitivity.

also from our site's glossary:

Sensitivity (of a loudspeaker)

Sensitivity is normally defined as the SPL level produced at a distance of 1 meter from the speaker, with 1 Watt of input power. However it is also common to specify an input of 2.83 volts instead of 1 watt of input power. This would be equivalent if the input impedance were 8 Ohms, but it is usually really closer to 6 Ohms. 

<pet peeve> Many people confuse the terms sensitivity and efficiency. An acoustic transducer of any type (low or high sensitivity) is extremely inefficient. The main reason for this is the difficulty of achieving a proper impedance match between the acoustic impedance of the drive unit and that of the air into which it is radiating.

Acoustic transmission lines, waveguides and horns are enclosure designs intended to improve this acoustic impedance match.

Loudspeaker _efficiency_ is defined as the sound power output divided by the electrical power input. e.g. a 92dB/w/m speaker is 1% efficient, a 96dB/w/m speaker is 2.5% efficient and a 101dB/w/m speaker is still only 8% efficient. Here's a link to a loudspeaker sensitivity to efficency calculator.


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