Kevin Heber

Why isn't my amp loud enough? Connecting consumer audio devices to Crown amps

18 posts in this topic

When connecting a consumer audio device such as a receiver, iPod/mp3 player, or DVD player directly to a pro audio amp, chances are that the output level on these devices will not be high enough to drive the amp to full power. All Crown amplifiers require at least 1.4Vrms (also known as +4dBu) at the input in order to reach full power at the output.

For example, the iPod's headphone jack produces a 1.0Vrms output, which will only allow the amp to produce 50% of its rated power.

Typically, an XLR connector will carry pro audio levels. Most mixing board outputs provide these. The consumer audio standards, on the other hand, are the RCA connector (usually red and white) or the minijack/miniplug (used for portable audio players). The XLR format provides a higher voltage signal as well as two copies of the signal, together called a balanced line. The extra copy of the signal has the added benefit of being used by the amplifier to eliminate noise that gets into the audio link from lights, computers and other nearby equipment.

So the best way to convert an unbalanced, consumer audio output to the Crown's XLR, balanced pro-audio input is with an active converter box -- essentially, a little preamp placed between the unbalanced source and the amp. A simple XLR-to-RCA adapter cable by itself will not provide any boosted or balanced signal conversion, so this usually won't provide satisfactory results.

Converters come in many varieties, but normally you will only need a simple 2-channel version. These should cost less than $100 and can be found at any pro audio retailer. A Google search of "unbalanced to balanced audio converter" will yield several good choices such as the ART CleanBox or Rolls ProMatch.

Unbalanced_to_Balanced_Conversion.pdf

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Hi

I tested with the ART cleanbox and must say I wasn't happy with it. It was to sensitive to outer interference and static charge. When I touch the unit it send nasty spikes through the system.

I would not recommend it.

I am gonna test another unit. The Sonifex Redbox RB-UL1. I will post some result later on.

Thanks

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Hi

I can recommend the Sonifex Redbox. :rolleyes: No problem at all with this unit and works great.

Thanks

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hello, im having the problem mentioned above with my amp i already checked the specs on the mixer i'm using and apparently i would need an active box the one mentioned here. my question is... if i get a crossover would that provide me the extra boost i need going through the crossover or do i still need the active box in the middle of the crappy mixer and crossover?

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You said "All Crown amplifiers require at least 1.4Vrms (also known as +4dBu)", but 4 dBu is equivalent to 1.228 Vrms, I need a mixer with output equivalent to a 6 dBU (1.546 Vrms) to operate this amplifier?

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Dear pegasuspy,

You're correct about your voltage Vs dBu conversions and yes, to get the full power of an amp that needs 1.4Vrms you'll need a 5-6dBu mixer but the difference between the standard 4dBu and 1.4V is negligible so in real life there is no sonic difference.

Avi

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Hello Torres,

Basically, if your equipment has a 'low' (-10dB) output you may want to use a 'preamplifier' (ie. active box) to get the levels to a point where it will drive correctly the amp. And yes, if you used an electronic crossover, such as the dBx 223, you may be able to boost your mixer signal to your preferred listening level. Furthermore, other types of electronic equipment such as eqs, other xovers, may have a selectable -10, +4 dB sensitivity switch for correct input or output voltage conversions.

Alain

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Torres,

The answer to the question if you needed the extra active box between mixer and crossover would be yes, if the downstream equipment (crossover) wasn't equipped with a boost drive or conversion switch. You wouldn't need an active box with the dBx crossover (223) mentionned.

Alain

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Thanks Dakos.

Sorry for the delay, I did not know you answered me.

What mixer brand do you recommend for xls 1500, having 4dBu?

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Hello Torres, Since we are on the 'Crown' [Harman products] forum, I will heartly and energetically recommend 'all' Soundcraft mixers have a nominal +4dBu (balanced, Master L-R outputs).

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FWIW, I've connected several Crown (and other brand) pro amps to consumer gear and never needed a "boost box" to be able to drive rated output (or beyond to clipping). Granted, I have not tried to drive a pro amp directly from an iPod, et al, but from any number of different consumer/home preamps including tube preamp. In these cases I've used RCA > XLR or RCA > TS adapter cables. I also have some home preamps with XLR outputs but didn't count those in my comments (although they work just fine too).

I have several different home amps and several different pro amps. Taking the average of the input sensitivities, the pro amps actually had slightly higher sensitivity (lower voltage needed to drive rated output).

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That's great to hear but unfortunately not always the case. Most of the time to actually know what the max voltage output of the source and if it would suit another type of gear's input sensitivity would require a True RMS DVM and about 5 minutes to measure the voltage values of the data in question. If the values are correct the all you will need are the correct adapters, but if it's not, you'll need "the box" :)

If you don't have the DVM but already have the pro amp, connecting it to verify if it all works together is the correct route.

Avi

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My point wasn't to imply a box is never needed, only that they're usually not needed. For sure there are some situations where they can be quite helpful.

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Well, as a general rule, the more options you have the more broad the potential compatibility.

That said, see previous comments above.

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I hooked up a consumer Arcam Alpha amp pre-out to the Crown XLS 1500 RCA jacks and can verify it's output is well below my usual (XLR) setup.

Gain on the Crown is at the 15:00 position, I will have to crank the volume meter on the Arcam well past 12.00.

However - for easy listening purposes it will suffice, leaving for a sheer unlimited headroom. One might argue this defeats the purpose of such a powerful amp.

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I don't understand the issue here. For one, if you think the system lacks volume, set the amp gain knob at the maximum. Then, why do you think that it's a problem to have the preamp volume past 12:00 ? Hint : it's not!

Consumer home amps usually have too much gain, which is why you are used to set the volume lower on the preamp.

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