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Discussion Starter #1
Hello!

So this newbie to car audio that I am, I turn here to find some advice to settle this last piece in my project setup.
I've read up on basics but I still find it hard to find an answer to this one..

Im trying to choose between the Hertz HDP4 and EP4X which will power 2x HSK165. I will also have 2x Hertz HX250 with the HDP1 if it matters, and want more to the SQ side rather than SPL.

Alltough I know there are probably alot more that comes into play when comparing theese on paper, the differences I've been looking at;

HDP4
Class-D
4x150W RMS
Damping Factor 50 (100hz / 4Ω)

EP4X
Class-AB
4x100W RMS
Damping Factor 130 (1kHz / 4Ω)

More specs at Hertz website which Im apparently not allowed to link since Im new here.

I read somewhere that its more important to have a high damping factor on lower Hz, as its there it will be more noticeable, but how does the HDP's spec for this affect midrange SQ?
What I dont understand is how I can compare the two's damping factor since they are specified at different Hz?
I assume this is one of the things that separate AB to D amps which makes D sound abit flat and cold in comparison.

The HDP4 will be prefered due to its size, but I have room available if necessary for the larger EP4X (it will just mean I need to rethink placing of the crossovers). Pricing is about the same and as you can see my whole setup is going to be Hertz so a different brand is not really on the table at the moment.
Also if anyone has listened to the HDP series playing fullrange I'd appriciate the input as this seems hard to find still even though they've been available for quite some time now.
 

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I think it's been discussed already that damping factor is a meaningless spec. And looking at the ratings above, it's not even an apples to apples comparison. The HDP amplifier was tested in the last issue of Russian internet magazine avtozvuk. It won't be online for a month but a PDF is available (in Russian).
Download

The wattage with 14.4V battery is 25% more than rated. Bridged output is over 600watts. That's crazy power for a small 4-channel amplifier. I could see myself bridging two channels for a subwoofer, and using the other two for midbass or passive components. It measures good overall except that frequency response (0/-1dB) extends only up to 18KHz. They did listening test and thought that the treble still falls short of best of A/B amplifiers. Overall seems like a good amplifier.
 

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Discussion Starter #3
Thanks for the input, seems like a pretty easy choice then beeing superior in most numbers.. :)

My main worry is the SQ abilitys of this class-D amp.
The general discussions about A/B vs D assumes amps on the same price range/age of technology (?) makes it harder to make assumptions in this particular case since HDP is a newly developed amp and EP4X is an "old" A/B

Instead of asking if A class-D can sound as good as A class-A/B, let me put it this way;
Do you think I will notice much difference between THIS class-D and class-A/B?
Disregarding the watt output and the fact that I can crank the volume higher..
 

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I honestly don't know. I actually have an A/B and Class D full-range amplifiers right now, but both are more of budget level amplifiers and I haven't connected my fronts the the Class D amplifier. So I don't know if there will be a difference. Even if there will be, it's hard to say which one will sound better.
 

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The only way for YOU to get an answer to your questions is to have the HERTZ HDP, HERTZ EP4X, and maybe something like the AUDISON VOCE in the same room. Connect them to the same reference system and listen for yourself how full-range class D compares to class A/B...and how a good class A/B amp compares to what is advertised as an even better (or 'High End") class A/B amp in the VOCE. Let YOUR ears answer the question for you...that is the ONLY way.

Having said all that....many are finding that the new crop of full-range class D amps have good sonics, big power, high eficiency, and a small footprint. Many don't see the need to go back to class A/B amps once one factors in the benefits of class D amps in the auto environment.

For what it is worth....there is a debate that the Hertz HDP amps are supposed to be similar in design to the Precision Power Phantom and the Polk D series amps. Look at the pics of the internals: http://www.diymobileaudio.com/forum/member-reviews-product-comparisons/111005-hertz-hdp-amps-5.html

But pics don't tell us everything...Here is a review of the Precision Power P900.4:
PASMAG | PERFORMANCE AUTO AND SOUND - Test Report: Precision Power P900.4 Amplifier
If the HDP is "better" than this amp..then I would say it should suit the needs of many in terms of SQ in a vehicle.You decide for yourself.....

Myself...I'm going with Class A biased class A/B for my tweets and mids...and full-range class D for my midbass and sub....just because I feel this will work best for "ME."
YRMV
 

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khaotic, pasmag.com has a good review of the PPI 900.4, which is a clone of the hdp4. There are a number of good threads on those amps on this site. JPS
 

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The avtozvuk.com review of Hertz HDP and pasmag's test of PPI Phantom have somewhat different test results:

Hertz HDP

RMS wattage, 14.4 volt battery, 1%thd:

4ohm: 196
2ohm: 329

Frequency response (+0,-1dB): 7.9-18500Hz
Signal to noise: 86dB
Channel separation: 63dB (left right)
THD, 1Khz, 4ohm, 0.1Pmax (?) : 0.026
Idle current: 1.7amps
Input sensitivity: 0.4-6.5

If this is some kind of shared design, they probably use different components in their boards.
 

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I've herd both at my local shop and the HDP4 is very clean sounding and has great xovers with plenty of power. If you have the extra cash grab one
 

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Discussion Starter #9
Even though I've not listened to many class-D amps playing full range, and as WLDock says I really would need to sit with a switch between them to really know, Im now convinced that the HDP4 will be a good choice!

Thanks to everyone for the help!
 
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