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Old 6th January 2009, 09:13 PM   #1
jol50 is offline jol50  United States
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Default The distortion difference between amps?

Hopefully I can get some takers on this. I've had this issue many times and could have run a larger amp I suppose, but really curious what could cause this to happen. Amps here I happen to have run recently, and were run on passive front comps in a moderate system for mostly SQ type use. These were both run on a 2v alpine HU with an analog alpine EQ/xover of unknown output (ERE-G190).

Example: amp #1 is an old '80s alpine 3518 that is rated at 2x34 or 40 RMS depending on what I read. Not sure on voltage it was rated at. It is lacking in power a little for my use but sounds nice and clear, I've put a lot of hours on it in various installs. If I set the HP higher it will play louder without distortion, but it breaks up on midbass hits when set lower. Last use I ran this amp on front comps and rear coax at 2 ohms, the manual says nothing about 2 ohms and it is not bridgeable. Had a fan on it, it gets hot at 2 ohms but performs the same maybe little louder than 4 ohms.

Amp #2 is a kicker zx700.5, it is rated 4x70/85 at 14.4. (http://www.sonicelectronix.com/item_...r+ZX700.5.html) It seems to have maybe a little more power overall but not much when run 4ch at 4 ohms. This amp will distort at all frequencies when I get to X number on the HU for a given gain level. I can set the HP up and down, it matters not. Kicker works fine at say 75% and less output, where there may be a SQ difference but it is not much if so.

What happens is the kicker sound gets bad as audible distortion sets in, where with the alpine a breakup on the bass hit lets me know its on the edge but it stays clean otherwise. I'd say the alpine sounds more dynamic too, but would need to swap again to back that up. The alpine will go significantly louder if you cut all the bass out, the kicker does not. As the kicker distorts in the higher ranges, it loses all clarity before it really dies so it does not work well at all near its limits. It acts like it is over driven while the alpine acts like a weak power supply, for lack of a better explanation. I even played a quiet passage in some music, and the kicker indeed will distort at X HU volume there too. I tried various gain levels, and now run it on a Pioneer PRS 880 HU with the same issues.

I have read talk about the 'distortion ratio,' or how fast an amp distorts as output increases is what I think that term means. The alpine manual shows a chart that rises very quickly once maximum output is reached, if it is accurate. I'd guess amps that gradually distort have a less vertical curve, if this even has that much to do with the above differences in these two amps.
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Old 7th January 2009, 12:56 AM   #2
amc32 is offline amc32  United States
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What you are experiening in my opinion has to do with the forward biasing of the predrivers and output transistors.And the comparison between the two is very audible.

Older Alpines work in forgiving but "Classical" Class AB

Were as the piece of chuck from kicker operates barely Class AB and with a little pressure placed on it ,its bias drops and is more like Class B in behaviour and sound.
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Old 7th January 2009, 08:28 AM   #3
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What you hear is not some intrinsic distortion but the amp running out of output level, called clipping. If you would look at the signal on a scope you would see that the max output is reached and that the signal is flattened against the supply voltage.
Clipping is in general a condition to be avoided. Not all designers take the effort to design their amps such that they clip 'gracefully', (and if they do, they charge you more!). So, how an amp sounds when clipping is difficult to predict, it also depends a lot on the speaker load. About the only thing that you can predict is that it sounds horrible!
There's not much you can do except get amps that can deliver higher power.

BTW that 4*70/80W is most probably VERY optimistic. It may be that at max supply (14.4V), only one channel driven, that channel can for a short while deliver 70/80W. But the amp as a whole, all 4 channels, at realistic supply (12V) probably clips at 40W per channel tops.

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Old 7th January 2009, 06:45 PM   #4
jol50 is offline jol50  United States
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LOL, "piece of chuck" I usually use older amps, but thought I would actually buy a 5ch amp because it had a class d sub channel....worked nice for the tight mounting I had available in this car. I read up on it and people seemed to say it was a good budget amp, others told me it was my imagination on another site when I said it was not getting it on IMO. I also read someplace it was 40wrms at 12v x4ch. I'm 90% sure it just isn't a quality amp past 2/3 speed or so but due to not wanting to lay amps on the trunk floor I have not swapped it out yet. And this is one of the larger 5ch, but I do have a V12 alpine 5ch to try rated lower (just to compare ratings) but it can't run my subs.

According to my HU the voltage stays above about 13.8v at full tilt, yes it really loses power with the car off. I have a 5ga wire to it that should be fairly good supply, since I don't care if it is 100% anyway just close. The sub is rated 420rms x1 at the 2 ohms its running...and turning the sub off does not change high side output so I don't see power as an issue. Sub side works well.

Maybe a stupid question, but is there any way to test amps for how they handle this clipping issue aside from auditioning them in a car? I know power cures it, then again I did not have this issue with good older amps when on occasion I wanted to crank it up. My problem has always been that I can't set gains to a max, between sources and even on the same source the max is not the same. Often don't have the room or enough need to run huge amps, though I could try to now.

If I get this PS running I would have 40A of 13.5v to test with, I could test it some.
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Old 8th January 2009, 03:00 AM   #5
amc32 is offline amc32  United States
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Without decifiering the topology of the amp,there's really no way to determine how a amp will sound when driven into clipping.

What's so ironic is that some people actually live for the distortion.
I've had plenty of customers that no matter what upgrade in power from an amplifier they would always prefer the sound at clipping.

Pro-Audio Guitarist make their living on distortion
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Old 8th January 2009, 08:40 AM   #6
jol50 is offline jol50  United States
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I've heard tube amps, they are different and that sound is not nearly as bad to me. IMO a cheap amp distorts in the higher frequency and I might as well have a needle poking me in the ear; I hate it and always have. I don't care if my sub amp distorts, well I care, but it is 99% less annoying if it does happen. Anything around 100Hz and up needs to be clear as a minimum, but yes I've known people like that who like to hear the static mixed in. Its painful, I don't even like bright tweeters give me the soft domes.

Seems like those people equate distortion with the 'sound' of being loud. I want it clear, just loud enough to feel some bump from the subs and not hear anything other than the music. This kicker runs the subs nicely, but there is no way the highs can keep up. In fact if I turn the rears all the way off it is just pitiful. The old alpines seem to be some of the ones that work the best for me, have a couple to try but it is really cold here and have no heat in the garage right now. Unfortunately recognizing amplifier topology detail is not yet a strength of mine. I did consider running a load on an amp, then say a 6x9 with a big resistor for reduced volume. Could try to duplicate the sound known amps make in a car for a baseline and see if I can recognize what other amps do near the point of breaking up. Only problem is a little distortion is so hard to hear, it just makes the music sound bad.
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Old 8th January 2009, 08:59 PM   #7
amc32 is offline amc32  United States
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Good point Jol.
My suggestion also would be to become very familiar with what music actually sounds like.By training the ear with quality home audio (Near-Field) sound.As this will help in decifier the Good,Bad and Ugly of Car Audio. This sort of training will either inspire or disgust with the l compromises that must be made for Car Audio.

Good Luck,and may the Force Be With You,young Jedi
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Old 8th January 2009, 10:20 PM   #8
jol50 is offline jol50  United States
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I used to do that, I would listen to a couple favorite songs in the house and go to the car to tune. Actually headphones I liked even better. Back in the old days before RTAs and all that, it was about the only way to tune in a car and swapping drivers/amps was very common for me as I used few EQs most had noise. Problem now is I don't have time for much of that so my progress is very slow, but do have some amps stacked up here I need to judge for future use. Even a 16 band EQ in a DSP HU can't fix a bad amp, or what I call a bad amp.

Just made a comment about this kicker on an audio site and a guy says they all bench to 4x100w they are underrated. Do people make this stuff up...then again I'm used to mostly 2x50-150rms amps from the late 80s/early 90s. I have two SS rubincon 302s here that I am very sure would do much more than this 4x70 kicker but have not used one on highs yet. I know the D100/200 always worked pretty good. I bet that extra 5w would be significant, or -25w according to that poster. In my experience a good old 2x75 on highs was about the point where I did not get into distortion it was so loud in a car. In fact with old efficient subs a pair of those amps could make a great system. I know it seems to count for about a 1/3 of wattage going 12 to 14.4v, but...ah well power ratings likely never will be fair enough to actually use.

I don't really want this car to sound perfect, because then I will not want to listen to lots of good music that was poorly recorded. That is the classic trap. This amp just sounds so bad when I turn it up, and its not that loud. I am amazed, I've fiddled around with it for a year while people said its a good amp. Its not like I'm a kid anymore and talking about 'really loud' in the car, just listening to music. I can get 20Hz out of my sub setup its great, now the high side is so weak I can't hear them. I'm almost embarrassed, at least I don't put many hours on this car.
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