This is a 30 watt sub-woofer, plate amplifier from the early nineties, by Kenwood. I have put a new driver into the sub-woofer box and tuned the port and box volume, but it still sounds terrible. My worry is that there is an undesirable bass boost circuit built into the chip. I am wondering is if any one can take a look at it and tell if there is a bass boost circuit on the board, and also how I might bypass it by making some simple soldering edits.
The first image here is of the amp board.
The second image is of the back of the amp-board.
The third image is of the front of the switch-board, as I am calling it, that has the LED light, the power switch, and the RCA jacks on it.
The last image is of the face plate itself, showing the volume pot, LED, and RCA jacks.
Any Ideas?
Thanks for any advice or information.
The first image here is of the amp board.
The second image is of the back of the amp-board.
The third image is of the front of the switch-board, as I am calling it, that has the LED light, the power switch, and the RCA jacks on it.
The last image is of the face plate itself, showing the volume pot, LED, and RCA jacks.
Any Ideas?
Thanks for any advice or information.
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Can you tell me if this circuit is too simple to have a bass boost circuit be a part of it?
From what I can tell bass boost circuits can be quite complex.
For some reason this sub-woofer is just too loud in the 30-50 Hz range, and every sound even up 100 Hz seems to produce a rumbling note in this range.
Could it be a ill tempered bass boost circuit!?!
Maybe I should add a few more soda bottles full of water in the box to see if the volume is still off ;-) Also, I might invest in couple dozen tennis balls for this reason.
Thoughts, Please,
From what I can tell bass boost circuits can be quite complex.
For some reason this sub-woofer is just too loud in the 30-50 Hz range, and every sound even up 100 Hz seems to produce a rumbling note in this range.
Could it be a ill tempered bass boost circuit!?!
Maybe I should add a few more soda bottles full of water in the box to see if the volume is still off ;-) Also, I might invest in couple dozen tennis balls for this reason.
Thoughts, Please,
hi , the only thing you can do is to follow the 'maze' and figure it out by yourself !😛
The 'amp' board contains also the PSU (without the transformer ) and the output protection . What you call 'the switch board' is indeed the suspect .
After the RCA plugs there are 4 ICs deputed to : mix the l and R channels ,make a 4th order 😕 lowpass , give a special targeted slope and equalization which basically may also cover the old driver's deficiencies .
So you may skip the 'special EQ' or 'ill tempered bass eQ' 🙂 stage .
The 'amp' board contains also the PSU (without the transformer ) and the output protection . What you call 'the switch board' is indeed the suspect .
After the RCA plugs there are 4 ICs deputed to : mix the l and R channels ,make a 4th order 😕 lowpass , give a special targeted slope and equalization which basically may also cover the old driver's deficiencies .
So you may skip the 'special EQ' or 'ill tempered bass eQ' 🙂 stage .
picowallspeaker - Thank you.
This is very hopeful. I know that there is a low-pass filter set to about 100Hz. The slope on that seems pretty sharp... I would want to keep this. As far as mapping things out to discover a "special EQ", I am at a loss.
Based on this information, however, I have done the only thing that I really can do and taken better pictures of the "switch-board".
Here is a composite image of the front and back.
Every little bit helps guy's, thanks.
In the mean time, I will do my best to sketch a circuit diagram...
This is very hopeful. I know that there is a low-pass filter set to about 100Hz. The slope on that seems pretty sharp... I would want to keep this. As far as mapping things out to discover a "special EQ", I am at a loss.
Based on this information, however, I have done the only thing that I really can do and taken better pictures of the "switch-board".
Here is a composite image of the front and back.
Every little bit helps guy's, thanks.
In the mean time, I will do my best to sketch a circuit diagram...
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you're welcome . hhhmmm ( not very skilled ,sorry)
At the right of the RCA input plugs : mixing ,lowpass ,buffer ; the output from the buffer goes to amp input AND to all the circuitry located at the left of the RCA plugs , which rectifies the signal and send it to a comparator that changes the status from standby to on, indicated by the 2 colors LED .
I would firstly change the two capacitors at the input, to better non polarized types .
Then....ugh !!
At the right of the RCA input plugs : mixing ,lowpass ,buffer ; the output from the buffer goes to amp input AND to all the circuitry located at the left of the RCA plugs , which rectifies the signal and send it to a comparator that changes the status from standby to on, indicated by the 2 colors LED .
I would firstly change the two capacitors at the input, to better non polarized types .
Then....ugh !!
If you have a model number, we can hunt on the interweb for a schematic - much easier than drawing it from a picture of the circuit board. 😉
Well, here is my best effort to sketch the circuit diagram, so don't laugh. I tried to color code some things to make it easier to look at.
I believe that the blue, red, and orange lines are for power.
I think that the circuit which contains chip #3 and #4, as I have them indicated in the diagram, might be my special EQ. I am thinking that it might be possible to bypass it by shorting out the board almost all the way from the volume pot to the output #3 (pink). I will need plenty of advise how to do this, if that is correct.
I was looking at the amp-board again, and I think that the big square thing is an inductor, and that this may comprise the low-pass filter all by itself. Is this reasonable?
Thanks,
I believe that the blue, red, and orange lines are for power.
I think that the circuit which contains chip #3 and #4, as I have them indicated in the diagram, might be my special EQ. I am thinking that it might be possible to bypass it by shorting out the board almost all the way from the volume pot to the output #3 (pink). I will need plenty of advise how to do this, if that is correct.
I was looking at the amp-board again, and I think that the big square thing is an inductor, and that this may comprise the low-pass filter all by itself. Is this reasonable?
Thanks,
I went ahead and tried to bypass the circuit that contains chips three and four by shorting out the connections shown here on my previous diagram. It didn't work, but it's okay because I put everything back.
Here is a picture of the wire that I used to short the board itself. I just used what I had...
Now I am thinking about trying this again but in a different spot.
Really I'm not even sure which way the signal is running through the pot!?!
Here is a picture of the wire that I used to short the board itself. I just used what I had...
Now I am thinking about trying this again but in a different spot.
Really I'm not even sure which way the signal is running through the pot!?!
Birdyfoot, as Ingenieus suggested its better if you tell us the model of the amplifier, so we could look for a schematic on net.
I have looked without any luck, but here it is anyway.
Kenwood Sub-woofer model: SW-30
Part Number on the back of the Plate-Amp: WF-30K
Thanks,
Ok, I got a digital copy of the manual, and it is much better than the one that I drew up, but I have to say, I was pretty impressed with myself with how that one turned out.
Here is the real deal: https://docs.google.com/open?id=0B1FbYI288Q-nYXlSRmVBdUZSTi1iWkdBbnBQVnZuZw
Sorry, you must download it to see it at 100% size.
Thus, what is your opinion please? Is there a special EQ, or a Bass Boost circuit present? How and where should I bypass it if there is one?
This is really cool :-D
Here is the real deal: https://docs.google.com/open?id=0B1FbYI288Q-nYXlSRmVBdUZSTi1iWkdBbnBQVnZuZw
Sorry, you must download it to see it at 100% size.
Thus, what is your opinion please? Is there a special EQ, or a Bass Boost circuit present? How and where should I bypass it if there is one?
This is really cool :-D
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I cant see any bass bost circuit here just a subsonic filter (IC502 2/2) and low pass crossover (IC 503 1/2). To pass them both you should unsolder C509, also unsolder that pin of R537 which goes to pin 1 of IC 503, then you can implement an low pass filter according to your needs connected between the pin 1 of IC 502 to unsoldered pin of R537.
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This is extremely exciting!
If I am right the "Sub-Sonic filter" is some kind of bass-boost and I can bypass it by shorting out the circuit from C510 to R522!?!
If I am right the "Sub-Sonic filter" is some kind of bass-boost and I can bypass it by shorting out the circuit from C510 to R522!?!
To skip the subsonic you should unsolder C509 and that pin of R522 connected to IC502 pin 7 and R520, then connect pin 1 of IC 502 1/2 and free pin of R 522 through a capacitor of 10 mf.
Oh, we must have both posted at almost the same time.
I think I would like to keep the low-pass filter, but I would like for there to be no other special filters, like a bass boost , or something that corrected for deficiencies in the original driver.
Would you say that to remove the "Sub-Sonic filter", if it is what I think it is, I should unsolder C509 (one pin or both sides?) and also unsolder R522 (one pin or both sides???) and then connect them, via the unsoldered pins, or remove them completely? If I am completely removing them, I suppose I could use the available holes in the PCB board to connect a wire.
You can unsolder the C522 on both sides, but only one side of R522 (the one which goes to IC502 pin 7 and R520, then through a capacitor connect the pin 1 of IC502 1/2 and the unsoldered pin of R522
One more thing, please;
How do you suggest I "connect" pin 1 of IC 502 1/2. Should I leave it in place in the PCB board or try to free it from the board? Should I try to solder a piece of wire to the bottom of the board where there is already an existing solder, adding to it without removing pin 1 from the board?
Please advise.
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