1999 Chevrolet Blazer

[hispls 5,000+ posts]

[quote name='gckless']Scope time!

So, went out and scoped my Levi. I was only getting around 160W @ 8ohms on a bridged channel (which is rated at 380W @ 8ohms) where the clipping lights came on, so I needed to investigate. What I found was that I was getting much more power capability after the clipping lights came on, with on caveat: I am seeing harmonic distortion.

So here are two videos I shot. Sorry about the poor lighting. Keep in mind that the clipping lights came on the amp around 36V. This was tested with a 1k 0dB tone, and on a pair of channels bridged.

http://www.youtube.com/watch?v=DW0VFXOGP6E&feature=youtu.be

http://www.youtube.com/watch?v=l24HcfUwDM4&feature=youtu.be

Now I know it's the amp inducing the harmonic distortion. Verified by putting HU on volume 20/62, where there was no distortion at all, and then turning the level up on the amp. I also then turned the HU up to volume 50/62, and turned the amp level down to where distortion went away. Both times distortion started at ~16VAC.

On the plus side the amp has much more power than I thought (based on the clipping indicators), if I don't mind that distortion. I honestly can't hear it, so.....

Couple questions:
- What would make an amp do this? Is it truly a bum amp altogether?
- Why would the clipping indicators be lighting up that early?
- Is this distortion bad? Should I even mind it?
- What are your recommendations?

I'm seriously considering going with a Zapco Z-150.6, and will more than likely swap out shortly.

@TaylorFade ; @keep_hope_alive ; @ciaonzo ; @hispls ; @maylar ; @Anyonewhocanhelp[/QUOTE]

My Zed amps have a bit more go after the clip light comes on. Have you verified it is seeing 8 ohm when you start to push it into distortion? A loudspeaker typically is only at Z-nom at one frequency.

Also have you attempted to reverse phase on the sub to correct your null at the 100hz spot?

 

[gckless 5,000+ posts]

I have this exact problem, very frustrating .
I am well impressed with this setup!!!

As far as the amp inducing those harmonics, best I can guess is it could be something to do with the comparator. Either that or it's simply the limitations of this full range Class D design.

Thanks man! Yeah the reflections are pretty frustrating, but it's bearable I guess for now since I'm not competing or anything.

My immediate reaction was to assume you made up the word comparator. Lol I have no idea what that is. In any event, I don't believe this is normal. However, in the Zed manual it states "Ultra low THD was not our goal but rather an amplifier which sounds the way we want it to." So maybe it could be a nonissue? I just don't know. I have to write an email to Mr. Mantz I think.

My Zed amps have a bit more go after the clip light comes on. Have you verified it is seeing 8 ohm when you start to push it into distortion? A loudspeaker typically is only at Z-nom at one frequency.
Also have you attempted to reverse phase on the sub to correct your null at the 100hz spot?

I did all that scope testing with the speakers disconnected. There's no way my mids could handle what this amp pushes out.

The clipping indicator comes on at ~36V. That's less than half of rated power. I have a feeling it's coming on so early because it's seeing the distortion and picking that up as clipping. I do not think this distortion is normal. Have you ever scoped yours?

I haven't tried switching the phase. My crossover point is at 63Hz, so output should not be seen at 100Hz. I tested it with the subs completely off as well, and it was still there. I'm sure if I bumped my crossover point up it would help that out, but I like the sound crossed this low.

 

[ciaonzo 5,000+ posts]

My immediate reaction was to assume you made up the word comparator.

Like a flux capacitor, lol?
Class D needs a way to derive a duty cycle for the pulse width so it generates a static triangle wave and compares that to the incoming audio signal. This is done by the comparator. The intersecting points of the trianlge wave and the sine wave provide the results, which is then amplified and fitered. I would imagine it's far more complex with a full range Class D design.

 

[gckless 5,000+ posts]

Like a flux capacitor, lol?
Class D needs a way to derive a duty cycle for the pulse width so it generates a static triangle wave and compares that to the incoming audio signal. This is done by the comparator. The intersecting points of the trianlge wave and the sine wave provide the results, which is then amplified and fitered. I would imagine it's far more complex with a full range Class D design.

Ah ok. Makes sense, but on the verge of my education limitations...lol.

I mean really it could be anything though. My last issue was a leaky capacitor. When the amp stepped down from high to low voltage rails, it would shut down the MOSFETs temporarily. I would never think it would be a cap causing that issue, but Mr. Mantz found it //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I'm clearly not the engineer here lol.

 

[hispls 5,000+ posts]

Thanks man! Yeah the reflections are pretty frustrating, but it's bearable I guess for now since I'm not competing or anything.
My immediate reaction was to assume you made up the word comparator. Lol I have no idea what that is. In any event, I don't believe this is normal. However, in the Zed manual it states "Ultra low THD was not our goal but rather an amplifier which sounds the way we want it to." So maybe it could be a nonissue? I just don't know. I have to write an email to Mr. Mantz I think.

I did all that scope testing with the speakers disconnected. There's no way my mids could handle what this amp pushes out.

The clipping indicator comes on at ~36V. That's less than half of rated power. I have a feeling it's coming on so early because it's seeing the distortion and picking that up as clipping. I do not think this distortion is normal. Have you ever scoped yours?

I haven't tried switching the phase. My crossover point is at 63Hz, so output should not be seen at 100Hz. I tested it with the subs completely off as well, and it was still there. I'm sure if I bumped my crossover point up it would help that out, but I like the sound crossed this low.

I'm not sure if measuring voltage without a load on it tells you much of anything. Furthermore, I know for a fact that those amps have a bit more gas after the clipping light comes on. I have not clamped mine. I could really care less, it's plenty enough for my fronts (and even done decent duty on subs when I've experimented with that) and my motto is, if it sounds good, it is good.

A lot of vehicles have a null @ 100hz. Perhaps the best you can hope to do is turn DOWN the frequencies on either side of it to match. If it's an acoustic issue with the vehicle boosting that frequency likely won't help.

 

[gckless 5,000+ posts]

I'm not sure if measuring voltage without a load on it tells you much of anything. Furthermore, I know for a fact that those amps have a bit more gas after the clipping light comes on. I have not clamped mine. I could really care less, it's plenty enough for my fronts (and even done decent duty on subs when I've experimented with that) and my motto is, if it sounds good, it is good.
A lot of vehicles have a null @ 100hz. Perhaps the best you can hope to do is turn DOWN the frequencies on either side of it to match. If it's an acoustic issue with the vehicle boosting that frequency likely won't help.

Yeah I talked to Stephen for a few minutes, we (him really lol, but I agree) said the same thing about a load. But, I did test with a load as well. Got the same readings, but at a lower volume as my mids can't handle that power. One other thing he did mention is that I was testing on a bridged pair of channels. It's a no-no without the proper scope that I don't have. Didn't know. But the clipping light comes on wayyy early. That is a problem. As is the noise I am getting that I mentioned to him. He said to send it back. I might be getting off the Zed wagon. Zap is calling my name.

Yeah, I am going to try to reduce the other frequencies. I want to get my door panels in first though, hopefully they will solve something.

 

[gckless 5,000+ posts]

Well, door panels are going to take a little longer than I hoped:

http://www.caraudio.com/forums/%2Anegative%2A-feedback/594105-gcklesss-panels-04murdalanche.html#post8486054

 

[gckless 5,000+ posts]

So here is my sub amp tested, unloaded:



This kinda baffles me, because I always thought unloaded numbers would be pretty **** close to the same as loaded right? But I just got 6400W @ 1ohm out of my 5k... Leads me to think I am definitely doing something wrong.

Then I simply moved over to the Levi. Didn't change any settings on the oscope except for X and Y axis increments. This one was for a pair of channels bridged (3-, 4+), unloaded:



And accompanying video, showing it's clean up until about 16V:



Now this video was for a single channel (3-, 3+). Same setting everywhere, except Y axis. Again, unloaded:



And a picture I got of that single channel:



I am praying I am doing something wrong, but I kinda don't see how. Probably why I am doing something wrong. What is it???

Edit: I won't be uploading videos to Photobucket anymore -_-

 

[gckless 5,000+ posts]

So, enough of how it measures, how does it SOUND???? Well there Sonny Jim, I'll show ya:

Down in a Hole (Acoustic). This one is more for simply listening.

http://www.youtube.com/watch?v=xvQKysiirA4&feature=youtu.be

Maggie's Farm. Some midbass excursion towards the end.

http://www.youtube.com/watch?v=51lQvCUvgX4&feature=youtu.be

I use a Dayton iMM-6 mic. It's more detailed, but the threshold is lower. It also sounds the best when recording with the mic facing forward, which means the camera is pointed up, so that's why you were looking at the roof for a lot of it.

For the record, I don't like these "SQ" videos. Extremely dependent on mic used, location in vehicle, processing, there's just too many variables for it to be any kind of accurate. I digress.

 

[keep_hope_alive Premium Member]

when using the scope, you cannot land both leads on both amp outputs.

you chassis ground the black lead and test one amplified output at a time.

otherwise the scope is the load.

 

[gckless 5,000+ posts]

Changes are coming. 10 cubes net, tuned at 24Hz. Bracing may change slightly, but this is close to final.

 

[gckless 5,000+ posts]

SHD has been ordered //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Now the waiting game begins //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif

 

[gckless 5,000+ posts]

Went and got the wood for the box. All 4 sheets //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif



I will be taking my time on the box, it's gonna be slow, just warning you guys. I won't have the sub for a while, so I'm just going to leisurely build the box so I have something to do while I wait.

What I am doing now though is build a fiberglass housing for my two new meters. Got the basic wood face down, and some outside supports for the fiberglass:





Will hopefully sit in there just like this when I'm done:



Going to do a fiberglass template over the console tomorrow, and then stretch some fabric over that and see where it goes. My last fiberglass project failed pretty miserably (my what were supposed to be temporary speaker pods), so I'm hopin I can make this better. I'm scared.

For tonight, I'll be drinking some of this and then passing out. Didn't get much sleep with the girl being here the last week.

 

[Sleeklsc 5,000+ posts]

For tonight, I'll be drinking some of this and then passing out. Didn't get much sleep with the girl being here the last week.

 

[gckless 5,000+ posts]

Yep. It's like that //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif