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I have an Altec Lansing ATP3 2.1 audio system PCB which I reverse-engineered, and I would like to bypass the JFET compressor that's on it. Its active components are a JFET and four op-amps. I will connect the input to the output so it gets forwarded to the next stage.

My question is: should I disconnect the input and output from the compressor (in that case should I remove power supply as well, which would be very annoying), or can I leave it connected but short-circuited?

The block I want to short-circuit is the pink one on the left.

ATP3 circuit diagram

I realize the image is very small. The sound comes in on the right, in the green box. In the middle yellow box there's some trebble/volume/bass control. The small green box on its left merges the left and right channels to forward it to the subwoofer section, which is the complete left half of this diagram (except the red box on the left, which is just power). Signal then goes through a low-pass, a small equalizer and a compressor (the big purple box). It finally gets amplified in the brown power amp.

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    \$\begingroup\$ You reverse engineered the circuit, so how about sharing the circuit so we know what you are typing about? \$\endgroup\$ – jippie Feb 22 '14 at 17:39
  • \$\begingroup\$ sure, but two things first: it's an illustrator document (did that by hand) and isn't this kind of information typically non-open source? I mean: it's an altec lansing atp3 2.1 speaker system, so I guess they wouldn't be happy about me sharing it here no? \$\endgroup\$ – yannick Feb 22 '14 at 17:52
  • \$\begingroup\$ The document type is not an issue, you can convert that. I don't know about the intellectual property issue, that should be a question for meta. I don't think you will get much feedback without a circuit diagram, can you make a block diagram from it, showing only the parts that actually matter? \$\endgroup\$ – jippie Feb 22 '14 at 17:56
  • \$\begingroup\$ meta.electronics.stackexchange.com/questions/3366/… \$\endgroup\$ – jippie Feb 22 '14 at 18:01
  • \$\begingroup\$ i can do that. let's wait for meta though, might save me some work. I can also put it on my website and link to it here, what about that? \$\endgroup\$ – yannick Feb 22 '14 at 18:04
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I would probably do couple things:

  1. Detach 'Equalize basses' output and ensure the level is similar to input 'Bass amplifier';
  2. When levels are similar (either directly, or through a attenuator or simple amplifier stage) disconnect the 'Equalize basses' from 'Compressor' and connect it to 'Bass amplifier'. Notice that there is a small low pass filter in the input stage of the 'Compressor' block that probably belongs in the 'Equalize basses' block.
  3. Connect the 'Compressor' input to ground (leave the 1uF cap in place) so it is effectively silenced. You could consider removing power from that block or removing the opamps in it.
  4. Leave the 'compressor' output detached from the 'Bass amplifier'
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  • \$\begingroup\$ fantastic! two questions: regarding 1., can I do that with just a multimeter while sound is playing? Or do I need an oscilloscope or similar. Regarding 2., I am guessing you refer to the portion before the 1uF capacitor? Will try to improve the circuit then. \$\endgroup\$ – yannick Feb 23 '14 at 9:58
  • \$\begingroup\$ @yannick There is a coupling cap between the blocks so DC is not an issue. Best to check the signal amplitudes with a scope otherwise just connect the stages and see how it sounds. A multimeter is really only useful if you can insert a sine wave of a given frequency, and one that your meter actually responds to. \$\endgroup\$ – jippie Feb 23 '14 at 14:39
  • \$\begingroup\$ got stuck at stage 2 :( Otherwise thanks for the idea of connecting it to the ground through a cap. By the way if I use a polarized capacitor, which way would you put it? + towards ground? \$\endgroup\$ – yannick Feb 23 '14 at 18:25
  • \$\begingroup\$ @yannick check with a voltmeter in DC-voltage mode. But Why don't you use the cap that is already in the circuit? You only need one coupling cap per signal line. The coupling cap is essential. \$\endgroup\$ – jippie Feb 23 '14 at 18:46
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    \$\begingroup\$ Check with the voltmeter in DC-voltage mode and make sure the cap obeys the polarity. \$\endgroup\$ – jippie Feb 23 '14 at 19:41

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