12v single supply subwoofer preamp - diyAudio
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Old 6th August 2014, 11:47 AM   #1
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Default 12v single supply subwoofer preamp

Hello Friends. I am new here. My friend and myself made this sub woofer preamp. Please check it for perfection and give your valuable advises.
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Old 6th August 2014, 05:07 PM   #2
AndrewT is offline AndrewT  Scotland
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starting on the left.
The two inputs through C/Ra and C2/R2 allow the first opamp to sum the input.
The VR when set to 47k gives an output that is L signal PLUS R signal.
When set to zero the output is zero.

The R3 sets the output offset. This should be equal to the parallel combination of E1||R2 ||VR .
It's MAXIMUM value should be ~ 15.7k.
You could set it a bit lower for less noise, if you measure the VR setting at your typical listening level and calculate the parallel combination. It could be anywhere from 1k to 12k.

The second opamp is some kind of filter that I don't understand. It is not S&K, nor MFB.
R6 seems far too high same reasons as previous.
I can't help any further.

The 3rd opamp looks like a unity gain buffer, but with both inputs connected to the same output I don't understand it. R11 is far too high. Same reason.

Th 4th opamp looks like 3rd: buffer, with both inputs connected to the previous output.R12 is far too high. same reason.

Output DC blocker is OK.

I/2 rail voltage divider is OK.
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Old 7th August 2014, 03:37 AM   #3
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Thank you sir for your kind advice and suggestions. Sir can this be modified for better results?? If any please advice. Thank you once again.
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Old 7th August 2014, 03:42 AM   #4
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Hope this helps
Warm regards
Andrew
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Old 7th August 2014, 06:07 AM   #5
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thank u andrewlebon sir. but we r using is preamp before 12v single supply power amplifier. actually this amplifier had a passive tone control previously but we are trying to make it as a mini sub-woofer with 12v linear supply. please give any nessessary changes to my schematics. thank u once again.
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Old 7th August 2014, 09:00 AM   #6
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For trail we build the attached sch on a prototype PCB. Every thing connected but no sound coming from woofer, but the power amplifier ic is heating up. when we removed the preamp and connected signal directly the amp works nicely. please somebody give some advise or find some faults if any from the circuit.
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Old 7th August 2014, 09:28 AM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by patnaik_kottakki View Post
............... please give any nessessary changes to my schematics. ..........
is this your design? or is it a copy of someone else's design?

Are the 2nd, 3rd and 4th opamps supposed to be S&K filters?
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Old 7th August 2014, 09:30 AM   #8
AndrewT is offline AndrewT  Scotland
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post6 uses dual polarity opamps layout but with a single polarity supply. That won't work.

Either adopt dual polarity supply and dual polarity opamp layout
or
adopt single polarity supply and single polarity opamp layout with the 1/2Vcc taken to the input of every opamp.
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Old 7th August 2014, 09:55 AM   #9
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Quote:
Originally Posted by AndrewT View Post
is this your design? or is it a copy of someone else's design?

Are the 2nd, 3rd and 4th opamps supposed to be S&K filters?
This schematic (first one) was drawn by seeing noname company subwoofer pcb. It was a gifted to one of my friends from their relatives.
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Old 7th August 2014, 10:01 AM   #10
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Quote:
Originally Posted by AndrewT View Post
post6 uses dual polarity opamps layout but with a single polarity supply. That won't work.

Either adopt dual polarity supply and dual polarity opamp layout
or
adopt single polarity supply and single polarity opamp layout with the 1/2Vcc taken to the input of every opamp.
this sch was copied from 320v.com site. it was actually used with tda7375 ic subwoofer system. but my prototype didn't worked.
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