• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

How to bypass opamp on PCB

niterida

Member
Joined
Dec 28, 2019
Messages
11
Likes
2
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
 

NTomokawa

Addicted to Fun and Learning
Forum Donor
Joined
Jan 14, 2019
Messages
779
Likes
1,334
Location
Canada
Short the positive input to the output? So short pin 3 to pin 1 on IC401 (1/2) and pin 5 to pin 7 on IC401 (2/2)? Somebody please verify me.
 

LTig

Master Contributor
Forum Donor
Joined
Feb 27, 2019
Messages
5,760
Likes
9,442
Location
Europe
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

Grand Contributor
Central Scrutinizer
Joined
Mar 9, 2016
Messages
13,198
Likes
16,981
Location
Riverview FL
That was quick..

1577501534832.png
 
OP
N

niterida

Member
Joined
Dec 28, 2019
Messages
11
Likes
2
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

Grand Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
20,745
Likes
20,756
Location
Canada
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?
 
OP
N

niterida

Member
Joined
Dec 28, 2019
Messages
11
Likes
2
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.
 
OP
N

niterida

Member
Joined
Dec 28, 2019
Messages
11
Likes
2
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.
 
OP
N

niterida

Member
Joined
Dec 28, 2019
Messages
11
Likes
2
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 ?
 
OP
N

niterida

Member
Joined
Dec 28, 2019
Messages
11
Likes
2
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

Grand Contributor
Joined
Jul 21, 2018
Messages
15,891
Likes
35,912
Location
The Neitherlands
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

Master Contributor
Forum Donor
Joined
Feb 27, 2019
Messages
5,760
Likes
9,442
Location
Europe
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).
 
OP
N

niterida

Member
Joined
Dec 28, 2019
Messages
11
Likes
2
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 :)
 

Doodski

Grand Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
20,745
Likes
20,756
Location
Canada
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 :)
You're welcome. Happy new year >@^_*@<
 
Top Bottom