I have a suspicion your KLH amp might have a big boost at just the right spot for your dual 12" sub and/or maybe the sub is sitting in a room null around 25Hz. Yes, you might have to play with it/location etc a bit to come to an understanding of exactly what's going on with that sub/amp combo.your post has convinced me to pull mine back out and play again. it could be just the stack up of my component and no way to shape the sound that gave me more poor experience. will you be posting any pics of that finished sub?
I believe what his pics show is shorting those two big blue caps from the back side of the PCB... its also what he stated he's done. My guess is that shorting the caps bypasses those resistors. I ordered the 0805-SMD resistors offa eBay (from RadioShack really) and am going to attempt the resistor mod just for giggles. I've never replaced such tiny components before but I read up on it and have seen a couple YouTubes now on how to do it properly plus I've got a steady hand and good close-up vision so... wish me luck. My sub driver/box combination benefits from the boost so I'm keeping it, I'm just seeking a slightly lower -3dB in-room and since its basically for my wife's system I'm sure the driver will never get overdriven... well that's the plan anyway.its hard for me to see, but it looks like you shorted the tabs from the back side but left the resistors in place?
No, THANK YOU for all your knowledge and help in this thread. Thanks to you I successfully changed the response of my Yung 500-6 ...I've never done a surface mount anything before, it was the smallest soldering by far that I've ever attempted (and without the aid of a magnifying glass nor tweezers) but I did it, didn't take long either. Unfortunately when selecting values for the HPF I got too carried away and used values for an Fc=11Hz (and a 2nd order slope I believe) that really jacked up the low end response beyond what Audyssey could deal with... there is just too much output below 30Hz down to about 18Hz where I believe the driver finally rolls off. I can't even dial the receiver volume to previous levels for fear of bottoming the sub driver on the really loud and low scenes, however even at lower volumes the vibration throughout the room is quite visceral. So I've ordered resistor values for an Fc=18Hz and WinISD Pro is showing me a predicted response that's overall a bit more reasonable and balanced for my particular sub combination. So bgarcia, a big thanks, so far I've learned much from this little exercise. :T...Thanks for reading, and please ask any questions here if you need more info.
Okay I have a question... I notice that in the above quote R23 is twice the value of R8 and in fact no matter what Fc is used (according to all the HPF calculators I could find online using Butterworth) this two to one relationship holds. So how is it that the original R8 (10K) and R23 (57.6K) are no where near this two to one ratio? Also I did experience a huge increase in output (like on the order of 8-9dB) after I replaced those two resistors with values obtained from a Sallen-Key Active high pass filter calculator. Are you sure those are the correct two resistors used in the HPF? I would think their original values should have also been approximately 2 to 1 instead of almost 6 to 1R8 = 42.6K, R23 = 85.2K. This nets response which is down only 0.3dB at 20Hz, and down 3dB at 12Hz.
OR, as you asked...
R8 = 34.1K, R23 = 68.1K. This nets response which is down 1.2dB at 20Hz, and down 3dB at 15Hz.
Both filters have a Q of 0.7, which means there is no boost along the way anywhere.
The closer to 2:1 ratio yields a flatter Q. When I play with the the calculators, I do find that to be the case. A 2:1 ratio always gives a Q of 0.7. The actual resistor and cap values then determine the Fc. Remember, the stock HPF has a Q of 1.2, so their ratio is much different. I am certain that these are the two resistors in the HPF circuit.Okay I have a question... I notice that in the above quote R23 is twice the value of R8 and in fact no matter what Fc is used (according to all the HPF calculators I could find online using Butterworth) this two to one relationship holds. So how is it that the original R8 (10K) and R23 (57.6K) are no where near this two to one ratio? Also I did experience a huge increase in output (like on the order of 8-9dB) after I replaced those two resistors with values obtained from a Sallen-Key Active high pass filter calculator. Are you sure those are the correct two resistors used in the HPF? I would think their original values should have also been approximately 2 to 1 instead of almost 6 to 1
Nope... its a sealed design and I wanted a decent amount of extension in a fairly open room so I was pretty sure (looking at my driver/box/EQ response model in WinISD Pro) that I needed to hang on to the boost. Don't get me wrong, the response is pretty flat (+/-4dB) down to about somewhere between 20-16Hz (can't get any more precise because I'm using stepped tones!) but be aware that's with Audessey's help. Since my driver's Fs=25Hz which happens to be exactly where the boost peak is my guess is I could probably stand to lose about 2 maybe 3dB of that boost and be good but I obviously don't know how to do that....Did you defeat the bass boost circuit by shorting out the caps? ...
What kit did you get? It seems to me useful values would be between 10k and 200k.I ordered a kit on EBay with 117 values, so I'm set to modify quite a bit.
Thanks for the thanks, and I'm glad you were able to mod your amp. We also need to thank this site and the greatness of REW. REW enabled me to track the frequency response along the way, checking each individual op-amp to see what it was doing to the signal. Long live the mighty REW!
Okay, I just found the equation for determining Q-factor on an active multiple feedback band pass circuit and it works here as well. I have essentially no background in electronics (just a basic course taken like 40+ years ago) and so its taking me a bit of research to try and get a handle on all this HPF stuff. Since Q determines selectivity on a band pass filter it must determine slope of the cut-off on a 2nd order HPF and I'm thinking ripples are a non-issue if they are contained in the cut-off band (Type II circuit) which I'm assuming this must be since it originally had a Q of 1.2, so I'll wait to get my 18K SMD in from eBay and then shoot for a Q of .97 and an Fc somewhere around 16Hz (R8=18K and R23=68K). Thanks, I'm learning a lot here. I probably should have just ordered that kit for $14 (had I known about it before) as I've already given RadioShack almost $9 now for 8 different strips of 0805's.The closer to 2:1 ratio yields a flatter Q...