KLH Bassbite II Subwoofer works, satellite speaker channels do not

[Mrx3750]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

At the very least it will rule it out, but I think it's bad for the following reasons:

The sub woofer works fine. This tells me that the other IC I saw on the power board probably controls the subwoofer only.

The power supply/subwoofer board shows no signs of burned components

The IC is in the same circuit as at least one of the failed 22uf capacitors. Judging from the pinout, the failed 22uf was on the trace that feeds power to the IC.

I've replaced every component in the burned area except the diodes which seem to be fine, and the IC.

And finally the IC has obviously seen some heat as some of the lettering was burned off, and it took holding it up to the light to read the part number.

I'm starting to think that whoever owned this sub last blew his satellite speakers. This caused the glue to cook on the parts of the board and likely killed the amplifier IC.

[Mrx3750]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

Okay. I got the replacement IC's today. I put one in, and no change.

I have started probing for voltages, something I guess I should have done from the beginning, and discovered that the IC is getting power, around 12 volts which is in its operating range. I tested a few film capacitors and discovered something interesting. On one spot on the board is a socket for a polarized electrolytic capacitor. However the component in that spot is a big 1uf film capacitor which I'm pretty sure is not polarized.

Looking at the pinout of the amplifier IC, would it be possible for me to solder an audio input to the input pins, and solder the output pins to speakers?

[budm]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

That LM324 Quad OP-AMP IC is proably used as low level signal amplifier, not for driving the speakers. There are power amps for driving the speakers on the other board.
Can I see more picture of this whole unit. The pot on that board in the picture seems to be for controlling the signals feeding the LM324.
Pictures of the out side of this box also.
Is this the one, the subwoofer?
http://www.amazon.com/KLH-BB-II-Powe...pr_product_top

[Mrx3750]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

Yeah that's the subwoofer.

Okay I've been working on this thing all day. You are right in that there's another amplifier. It's a SK 18751 or SI 18751 It's taken me hours to find info on this IC, but I believe it's a 25 watt audio amplifier.

I will provide pictures tomorrow, but I can tell you that I have either tested or replaced almost every component on the speaker terminal board.

Can I test this SK 18751 IC? I can't find a datasheet, can't tell if it's bad or not.


Another question is now I have four of these LM324 IC's, with no plans for them. Could I build a headphone amplifier out of one of them?

[budm]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

This unit is just the sub woofer that is made be connected to the stereo amplifier, the speaker output of the amplifier is fed into the input speaker terminal, then the speakers is connected to the speaker output terminal, it basically rout the speaker output of the amplifier through this sub woofer box, part of that signals from the stereo is mixed into mono signal to feed that IC to drive the sub woofer speaker. That is one way of getting the signal (High speaker level) to feed the sub woofer, another way is to use the RCA LOW Level signal input jack instead of the speaker terminal to get the signal to the sub woofer, you just connect the RCA jack to the line level out put of the stereo and the leave the stereo speakers connected to the speaker outputs of the stereo.
It does not have THREE amplifer to drive the two speakers and the one sub woofer.
Your sub woofer is typical just like MY JBL PB10 and PB12 that I have. I use RCA line level from my receiver sub woofer out to feed my JBL.

[Mrx3750]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

Something doesn't make sense with your explanation. When I found this thing, the subwoofer worked, but the speaker terminals did not, and while yes the terminals can be connected that way, the circuitry layout suggests that they can also be powered via the low level input.

Then again I could not find even a user guide for this damn thing so I've been running on a lot of assumptions. I don't have much experience repairing subwoofers.

So is what you are saying is how this thing normally works is it takes input from the stereo speakers and attenuates it for use in the sub, or it uses the low level input and amplifies it, but only for the sub?

[budm]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

"So is what you are saying is how this thing normally works is it takes input from the stereo speakers and attenuates it for use in the sub, or it uses the low level input and amplifies it, but only for the sub?" Yes, that is. The reason they give you the speaker in and out terminal is for easy wiring nad if you do not have lowe level sub woofer out like most newer stereo does, the sub woofer become the junction box for the two speakers, two pair of wires from the stereo speaker output to the sub woofer speaker input terminal, and then it is routed out to the speakers that were hooked up directly to the stereo before having the sub woofer, just as shown in the JBL manual.

[Mrx3750]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

Thank you budm! I got it working on both low and high level inputs! Seriously if it hadn't been for you I would have probably given up on it as I was convinced those were outputs. (I only had experience with computer subwoofers, which power both the speakers as well as the sub.)

I learned a lot from this, and have a few regrets, one being that I purchased all those LM 324 IC's... Could I use one of those for a headphone amplifier?

Oh say, uh you wouldn't be able to help with my HK 690i's tuner issue, could you?

[momaka]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

one being that I purchased all those LM 324 IC's... Could I use one of those for a headphone amplifier?

Most likely.
I never tried it myself, but I'm guessing with the op-amp driving an output stage, you can probably make a pretty decent headphone amplifier. A single transistor simple class-A emitter follower amp should be sufficient. I made a full class-A headphone amp with just 6 transistors, and it worked great.

[Mrx3750]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

My plan is to rig one of those IC's up to a 12 volt power source, wire the inputs to a headphone plug, and the outputs to a headphone jack.

Wondering if it'll be that simple.

[momaka]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

No, not really.
At the very least you will need several resistors to adjust the gain of the amplifier (running at maximum gain will give you terrible results) and some small caps for input/output coupling + supply bypassing.

[Mrx3750]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

Hm, then not really sure how to go about it.

Well there's a few DIY tutorials out there. I might give it a shot.

Thanks all. Glad I got the sub working and might be able to do something with these IC's

[momaka]

Re: KLH Bassbite II Subwoofer works, satellite speaker channels do not

Just to let you know, I tried using a 358 op-amp to drive my 2-transistor class A amplifier, and it didn't sound that great. Of course the 358 op-amp is just a regular cheap general purpose op-amp, so that could be the reason why. IIRC, the LM324 is much better. But if you try to run headphones straight from its output, you'll probably be limited to a few mW (and that's with average 30 Ohm headphones), so your headphones won't be able to go too loud. If you don't listen to loud music, then it shouldn't be a problem (I do, so this will be no good for me). However, a simple output stage can easily change that.