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How to bypass opamp on PCB

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#1
HI - just joined to see if someone can help me with one question :)

I have an audio amplifier that has an integrated high and low cut filter which I need to bypass. Is this possible and if so can some one outline how to do it ?
I have attached a schematic and itis the 2 IC401 opamps I need to eliminate in the circuit.

Many thanks in advance.
Subwoofer high low cut schematic.jpg
 

LTig

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#3
You'll need IC401 (1/2), its a differential amp, not a low or high pass.

As far as I can see IC401 (2/2) implements a low pass with some gain and IC402 (1/2) a high pass. You could remove C404 to keep the gain without low pass, and use the output of IC401 (2/2) as output; or remove R409 and short cut C405 and C406 to transform the high pass into a simple buffer.
 

RayDunzl

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#5
That was quick..

1577501534832.png
 
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#6
So if I bypass the low pass filter I will still need a crossover to split the amplified signal further to woofer and mid-woofer.
This needs to be a 80 or 100hz crossover - anyone know where I can source a cheap ready made crossover or plans to build to one ?
I need 5 of them and needs to be less than 10USD ??
 

Doodski

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#7
HI - just joined to see if someone can help me with one question :)

I have an audio amplifier that has an integrated high and low cut filter which I need to bypass. Is this possible and if so can some one outline how to do it ?
I have attached a schematic and itis the 2 IC401 opamps I need to eliminate in the circuit.

Many thanks in advance.
View attachment 43872
What model of amplifier is that?
 
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#8
Its an old Pioneer S-W200 subwoofer - I am trying to repurpose it to power my passive speaker as well as the sub drivers - basically make a powered 3-way speaker.
 
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#10
Are you a enthusiast delving into the component level, on a budget or like taking on new challenges?
https://www.pioneerelectronics.com/PUSA/Home/Speakers/S-W200
Service Manual>
https://www.speakermanuals.com/Pioneer/SW200/Download/425290
Neither - just trying to save money by not having to buy more amps :)

I have been doing more research on the crossovers I would need and I think it will be easier and not much more expensive for me to just buy more amps. I can get the amps I need for just $150USD total and at least I know they will work straight up and won't take me any time or risk making mistakes and ruining the existing sub amps or drivers.
 
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#12
You are thinking passive crossovers. Have you considered a active electronic crossover? I've seen some decent and new active crossovers for ~$50 and up.
I need 5 of them so passive is the only viable option.
I will keep looking for a cheap passive crossover or DIY.
Can anybody point me in the right direction for these ?
 
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#14
Yeah been on there but was hoping to find cheaper !!

Plus I think I will need 2 for every amp - a 100hz high pass to send to the speaker and 200hz low pass for the sub ??
 

solderdude

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#15
HI - just joined to see if someone can help me with one question :)

I have an audio amplifier that has an integrated high and low cut filter which I need to bypass. Is this possible and if so can some one outline how to do it ?
I have attached a schematic and itis the 2 IC401 opamps I need to eliminate in the circuit.

Many thanks in advance.
View attachment 43872
IC401/1 is a switchable 1x or -1x gain buffer and is there so you can select the phase of speaker connected to it.

IC401/2 is a buffer with 6.8x gain (+16dB) followed by IC402/1 which is a high-pass filter (low cut).

If you just want to remove the low cut you remove IC402 and jumper a wire from pin-7 of IC1 to pin-7 of IC402.
You may want to lower the gain of the circuit. You can do this by lowering the value of R407.

When you also want to eliminate the volume control and jumper a wire from pin-1 IC401 to pin-7 of IC402. (needs IC401 in there)

When you also want the phase selector gone remove IC401 and 402 and jumper a wire from S401 to pin-7 of IC402
 

LTig

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#16
Its an old Pioneer S-W200 subwoofer - I am trying to repurpose it to power my passive speaker as well as the sub drivers - basically make a powered 3-way speaker.
Do you have two of those subs? If not you'll end up with a mono system despite having two sats (there's one power amp only).
 
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#18
Thanks for everyones help - decided not to do this after all as the amp is not actually powerful enough for what I wanted to do.
Cheers :)
 
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