my DYI stereo write up is online
The factory sub sound great with the EQ (change the x-over point and increase bass to the sub). Will replace the sub soon with something better.

bananags.netfirms.com

see under stereo

 

BananaGS:

One thing I discovered when looking to upgrade is that coupling capacitors in the stock Pioneer amp are designed to roll off below about 60Hz on the sub output. There are 5 or 6 in the amp and most appear to have 1dB point at 30-45Hz, the net result being a pretty steep cut off below about 60Hz. I increased them all by a factor of about 3 and you definitely now can hear really deep bass. As I think you are using the left and right fronts to get the bass I suspect that these are even more rolled off – the designers did pretty good job in matching the amp to the application and I doubt if driving the 4 inch paper cones called for any input below 100Hz.

I doubt if an equalizer can compensate for this. A big boost at 100 Hz is no substitute for really deep 30Hz bass that you can feel

 

girvan,
" doubt if driving the 4 inch paper cones called for any input below 100Hz" yes, but it will cost more to to block that <100hz out (which does not even do anything to the 4" paper speakers, just add noise) I seriously doubt that the manufacture are willing to pay for that extra cost, may be only the Levington amp.
(if they gonna use the 4" paper cone for speakers, do you think they are willing to go out of the way to block the low freq for the front speakers?, but they are "required" to do that for the sub to make it sound right )

The bass goes very low on my EQ (to 30hz). The stock sub does not do well with real low freq. My x-over point is set at 70 right now. I get solid bass from the sub. (totally different from the stock amp) (btw, I have parametric eq on the Kenwood, I can boost any freq up to 12 dB, currently running no boost, 'cause the rear dash vibrate TOO much, need take it apart to put on some dynamat.)

BTW, I think lexus factory amp sux, not even close to my Honda prelude 97 factory amp with Acoustic Feed back system, couple with the cheap 4" speakers make everything worst.

Also, 100-120hz are mostly noise (engine and road noise), you want to eliminate them, not boost them.

I should have the new sub soon, we'll see how low does it go then

Anh

 

I am not following what you did here...did you modify the capacitors in the amp?

Please share with the group.

Ryan

 

Ryan,

The point is that the stock amp is deliberately designed to act as a high pass filter so don’t expect to get ANY bass lower than about 50Hz regardless of what equalizers you use. You can put in 12db of boost at 30 Hz if you like but 12dBs times nothing is still nothing apart from more noise. This may not matter if you like synthetic bass (harmonics) and a big peak at 100Hz. I like real bass.

This is not a criticism of the left and right amps which appear to be extremely well designed for their intended purpose. It’s also not a matter of cost – larger coupling capacitors cost the same (number of cents). It’s just that the designer matched the roll-off to an application driving small L&R speakers and didn’t seem to want to put too much low frequency bass into the Sub perhaps to avoid warranty claims for rattles.

The fix is not very practical; you need to increase the value of several coupling capacitors. This is not easy to do or document as you need to locate the capacitors by cross referencing the circuit diagram and two layers of printed circuit layouts, then de-solder and replace them while not disturbing some very close surface mount components. Some one experienced in analog circuit design and repairs might be able to help.

 

Ryan,
if you are in austin, come listen in my car, you will see. I am am getting a new sub and a test CD to test this. The x-over cut off point is set at 70, with 0 boost sound extremly good with very solid bass anyway. Get it, the x-over point is set at 70, and I get solid bass, that mean the stock cut off is NOT at 100hz.

If you are saying the designer is so good on the channels, why we don't get solib bass out of the sub, design trade off? if you modify the cap to increase the cut off point, then you are NOT hitting 30hz anyway, you are just getting more range (very likely this is why you get more of the missing bass, since I have not seen the circuit). if adding the cap lower down the cut off, then you need to change your sub too (more vibration complaint anyway), I don't think the designer want to stock sub to run at 30hz. this Does not make any sense. Unless they designed a bandpass filter for the lower range (30-2500) and block everything else, but it is very UNLIKELY to use bandpass fillter for low freq of bass.

man, you make me want to bring the oscillosope from work home to see analyse this signal :eek:

Percy, what you you say in your set up book on this subject?
using the LLC is useless, that is what Girvan is saying.

End of discussion. I was just posting this to show any one who want to improve the sound base on my own set up. Not competition, I would have replace the head unit along time ago with I want extreme sound. (I will wire up the DVD player soon, then, there won't be any factory amp to worry about)

I am not saying that you are wrong, girvan
I am saying that it sounds great with my current set up (way better than stock), and I highly recommend this setup to those that interested.

girvan, are you saying it can sound better? hee hee, will see, one of these day, I will take the amp a part.


Anh