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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?
 

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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 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.

I could take a pic or two of my sub to post here but it would just be basically a featureless ('cause its downfiring and the amp faces a wall) box 17" square and 25" tall covered with vinyl (maple) veneer. Its standing on black isolation cone spikes and both driver and amp are "recessed" if that's the right terminology... its got some good internal bracing for its size. I'm no great woodworker and only have basic cheap tools and a small garage to work in so I just didn't think to take pics of the build even though I am kinda proud of it now (my design)... anyway there are far more impressive build threads already in this forum, (didn't want anyone laughing at mine). The sub's stashed into a corner in between a bookshelf and one of the mains (I discovered after locating a previous sub there that, in terms of reduced nulls from the listening positions, that was the best location for a single sub in the room... once Audyssey shaves off the peaks the bass response is relatively flat considering it actually needs to be a compromise across all 4 seating positions).
 

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Just to wrap things up...it is possible to easily defeat the boost circuit. Just need to jumper them two suspicious caps (short across their connections). The circuit adds this boost stage with the HPF stage to then feed the phase and low pass sections, so no harm done. We do lose a little bit of signal level, but nothing to worry about. Here is the response of my SD200-6 after defeating the boost. I compared components to my CSS 500W, and I concluded that boost/no boost is done by changing resistor values for this circuit. But trust me, it's not easy to replace these resistors, so shorting the caps is better advised.



I can provide pics of the jumpers if anyone is interested.

So in conclusion....these Yung plate amps are tweakable, and not as difficult as I first thought. The HPF is easy to access/mod since the resistors are located near the edge of the pcb by the led. Then the boost can be defeated if desired by shorting out two capacitors.
 

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Here are a couple of pics. This one shows the two resistors used to modify the HPF.



This the back side of the pcb, with the jumpers installed to defeat the bass boost circuit.



Remember, this will void your warranty.
 

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I took the liberty of enlarging the area of interest:

enlargement.jpg
 

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its hard for me to see, but it looks like you shorted the tabs from the back side but left the resistors in place?
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.
 

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Actually, let me apologize for not being clearer. I should have ended with a short review. So here it is.

These amps actually have a HPF (subsonic, rumble, whatever you want to call it) and a SEPERATE bass boost circuit. The resistors are the components you'd change to modify the HPF, and the bass boost circuit is defeated completely by shorting out (bypassing) the two capacitors with the jumpers. These two circuits are summed to give the overall response curve.

Earlier in this thread, I showed the response before/after modifying the HPF of my 200-6 amp. The bass boost circuit was still clearly there, although modifying the HPF did extend the low end response a bit. I also posted the response curve after I had defeated the bass boost circuit, and you can see the big difference in response after doing so.

Also earlier in the thread, we learned directly from Yung that all of these amps have the HPF set to around 30Hz, with a little bit of boost above that (even if the bass boost circuit is completely defeated). We have visually verified that the 200-6, 300-6 and 500-6 (from PE) have the exact same HPF, but different boost circuits as spec'd. I verified that the CSS has a different HPF, but I couldn't measure its bass boost circuit seperately (yet), to see if it actually has one. And I have a 300 non-boost on order for evaluation as well. I suspect the non-boost models are as described, and have a bass-boost circuit that is configured to actually have no boost (through use of different component values).

Thanks for reading, and please ask any questions here if you need more info.
 

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...Thanks for reading, and please ask any questions here if you need more info.
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

BTW, those SMD's on eBay come on a strip in a quantity of 20! ...don't know what to do with the other 19 but at $1.05 and free shipping it doesn't really matter much I guess.
 

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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!
 

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R8 = 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.
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
 

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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
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.

And that's what added to the 'mystery' of these amps. At first it seemed like the boost was coming from this high Q HPF, when in fact it was only part of the boost.

What was the frequency range in which your gain was obtained?
 

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I did notice in the calculators that selecting Chebyshev gave a slightly higher ratio which results in a steeper roll-off however it supposedly adds some rippling (I read this stuff offa Wikipedia) also I'm assuming a Chebyshev Type II where the rippling is in the cut-band... and so after looking at your posted graphs (200-6) of the pre- post- mods the thought did cross my mind that perhaps lowering the ratio might have been the cause in your change in slope... but then yesterday after playing around with the sub some more I realized that Audyssey hadn't turn the sub level down enough... it only dropped it by 2dB after the mod and so when I measured it manually (holding the SPL meter nearfield and accounting for the meter's irregularities at low freq measurements) it appears to need an additional drop of 7dB's more to bring it in line. At first I lowered it 5dBs in the reciever's calibration level but it ended up at -12dBs so I eventually dialed the gain down on the amp from 11o'clock to 8o'clock and that got me to a 0dB level at the reciever. I still haven't gotten REW loaded into my wife's (new) laptop so I'm currently using a handheld RS digital meter and taking readings using step tones. After the mod it appears the lower freqs was much extended and the SPL boosted at the bottom end more than near cross-over... and when listening to programmed material it sounds exactly like that's indeed what's happened to the response since the mod. To tell the truth, after dialing down the sub to what's now a more appropriate level I'm quite pleased with the sound and balance and may not change the resistor values (even though I have ordered them already)... btw, I did intentionally change the ratio slightly to 2.15 to 1 (R8=43K and R23=91K) and had thought about even going to 3:1 (R8=27 and 23=82K) as I already had the resistors.
 

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If you can get the sound right, and you're not in trouble of abusing the sub (with the Fc so low), you should just keep it as is. Did you defeat the bass boost circuit by shorting out the caps? I'm guessing you did.
 

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...Did you defeat the bass boost circuit by shorting out the caps? ...
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.

EDIT: Okay I've decided to go with R8=27K and R23=68K , that should give me an Fc=16Hz and with a ratio of 2.5:1 for a little steeper roll-off. Hopefully these changes will not impact the sub's current performance and yet provide a little bit of safety for the driver just in case.
 

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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!
What kit did you get? It seems to me useful values would be between 10k and 200k.
 

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I just bought the 1% values (63.4k & 127k) from Mouser to set mine to 8Hz. For my SPA1000 I bought all the values needed to set it between 10Hz and 20Hz at 1Hz increments.
 

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The closer to 2:1 ratio yields a flatter Q...
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.
 
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