Does the Crown D-150A-II need to be looked at?

[Steve K]

Hi everyone,

I just purchased an used Crown D-150A Series II amp to drive a pair of 4313.

Question: Is it normal for the volume knobs on the D-150 to be turned all the way to the right, where '0' is indicated?

Symptom: I'm using a Mac C46 pre-amp to feed the source signals to the D-150 from its second output connectors. Compared to the volume gain I get from the first output which goes to a Levinson No.23.5 driving L300s, the loudness level I get with the same pre-amp volume knob setting is much lower with the Crown/4313 combination, even with the gain on the D-150 set to maximum. The sound itself seems fine - no distortion, no noise or hum coming out, except the highs are a little weak but not by that much.

I'm aware that the absolute power levels of the two amps are significantly different (75W/ch vs. 200W/ch into 8ohms), and the 4313 has a lower efficiency rating (89db vs. 93db), but I'm not all that convinced that that these are the reasons for the big difference in the sound volumes attained.

Your comments, insights, advice are appreciated.
Thanks,

Steve K

[BMWCCA]

First, they're not volume knobs but input attenuators. Does the Levinson have knobs? Have you tried swapping the Mac outputs to the different amps to see if it makes a difference?

Here's what Crown has to say about how to use those "volume controls": http://www.crownaudio.com/pdf/amps/137467.pdf

And read the last two posts in this thread: http://audioheritage.org/vbulletin/showthread.php?p=209737


The knobs are the input attenuators. The idea is to set them so that your normal listening level takes advantage of the correct level from your pre-amp based on your amp's input sensitivity. I usually set mine so that wherever I listen the pre-amp volume pot is set at mid-way or slightly higher. If I could measure output voltage I could match it to the amp's input sensitivity but this is a best-guess scenario that has even gained approval from the Crown factory guys on their forum. So if your HK is designed to work with less pre-amp voltage then it might be louder at the same pre-amp volume setting, no denying that. Both amps will reach their maximum output if the gain is high enough, and the more powerful one should actually be "louder" at full-output than a smaller one. I'm no engineer but that makes sense to me. I never run any of my (eight) Crowns with the input attenuators at full-right because even at 3/4 pre-amp volume the animals would complain and I'd soon be deaf.
All this means is that the HK amp has a higher sensitivity. Many "consumer" amps are rated for -10dBV on the inputs, while "pro" amps are usually rated for +4dBV. This means that most pro amps require a much stronger input signal to reach rated output.

The only meaningful way to compare your two amps is to run a test into clipping, (prefereably, using test equipment ;) ). The generalizations you're making between the two amps have no basis in objectivity - they're just subjective observations that really tell nothing about the actual capabilities of the two amps.

[Steve K]

Thanks for the insight, member BMWCCa!

I think I understand what you're saying, but excuse me if I'm wrong here. The Mac pre-amp's specs state the following:

Rated Output Voltage:
2.5Vrms Unbalanced (Main and Outputs 1 and 2)
5Vrms Balanced (Main and Outputs 1 and 2)

Maximum Voltage Output:
10Vrms Unbalanced (Main and Outputs 1 and 2)
20Vrms Balanced (Main and Outputs 1 and 2)

Output Impedance:
240 ohms Unbalanced
480 ohms Balanced

I'm using balanced connectors for the Levinson, and obviously the unbalanced for the Crown. As seen from the specs shown above, the Crown amp gets less input voltage (gain) than the Levinson, which translates in the difference in the 'loudness' obtained from the same setting at the pre-amp's volume pot. Is that right?

Steve K

[BMWCCA]

Steve,

To me, that would certainly seem to be the case. I see the Levinson has no attenuators so if balancing the apparent output is important to your using your system you might have to look for another solution. Unless you have the specific connectors your amp requires to run it in unbalanced for a comparison.

Crown states the input sensitivity for the D150A-II at 1.19V ± 2% for full rated output at 8-ohms, but then the specs says there's an "optional sensitivity" of 0.775V. You might contact Crown to see if this is a user-made change or what it involves. I can't seem to find anything on the Levinson's sensitivity for comparison, nor am I knowledgeable enough to even understand the correlation between input voltage spec'd by Crown and output voltage you're quoting from McIntosh.

Of course there's always the problem of mismatch between the speaker systems you're trying to compare. The L300 lists a sensitivity of 94dB and the 4313 is 89dB. That's a whopping differential you're asking your least powerful amp to make up for you. Okay all you EEs out there. How much more power does it take to make up 5dB differential in sensitivity? :)

Swap the speakers between the two amps and see what that does for the levels. Or try a Crown PS-400 instead of the Levinson and sell the Levinson for gas money! ;)

[Steve K]

Thanks again, BMWCCA. Your analysis makes a lot of sense.
Yeah, I guess I'll try looking for the XLR->RCA cable. If I remember right, there was a store carrying that item.
Hey, I'm definitely not selling the Levinson!!! ;) It's the best amp I've had to date, and it sure brings out the best in the L300s, deep bass and all.
Since you brought up the matter of gas prices, in Tokyo where I am now, a gallon costs $7.20 at today's exchange, and they say prices will go up again in August. So selling the Levinson won't buy me a lot of it here.:biting:

Steve K

[subwoof]

The D150's have had at least 8 versions and only the very last of the series II has the ability to change the sensitivity to .775V It can be between 1.15 and 1.4 depending on version.

If you remove the rear cover, and the circuit board has lettering on it for components, you will see 2 open jumper positions. Simply short both and the change will occur - you will need to solder.

There is also a LARGE sensitivity difference between the L300 and 4313. You are after all comparing a 3" coil 10 cone system to a 4" coil 15 system with a horn. 4db AND bandwidth will make is sound a lot louder.

sub

[Steve K]

Subwoof, thanks for your input!
I confirmed the sensitivity change feature on the downloadable manual at Crown's website, so I may try it as a last resort, granted that my 150A II has that option available.

I brought out an old Sansui AU7700 integrated amp from storage and hooked it to the Mac. This integrated has a switch on the back panel to separate the amp from the pre section to work as a stand alone 50w/ch power amp. I don't have the specs for the input sensitivity for this amp, but the result is more than satisfactory decibel levels from the 4313s. Plus I'm reminded of how good this old Sansui amp sounds. Anyway, so it seems the Crown is unusually low in input gain (I don't know what the exact terms to use, but you know what I mean, right?). Or, perhaps, the amp has some problems.