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Old 25th October 2008, 11:33 AM   #1
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Default Subwoofer pre-amp

Hi,

I am trying to design subwoofer pre-amp. I don't have a lot of experience (read: no experience ) with analog / audio designs and I would like your opinion on the design I made.

The requirements for this project are:
- stereo balanced line ins
- unbalanced line out
- high quality (quality over cost)
- variable cut-off frequency (~150 ... ~350Hz)
- VU-meters for both input signals and the output signal

Things I'd like know:
- are there any (big) mistakes in the design ?
- are there resistors / caps / etc. missing ?
- is the combination of opamps possible ?
- does anyone have tips on the designing the pcb ? for example should I use SMT ?

Thank you in advance.
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File Type: zip vestzaksubdriver.zip (83.6 KB, 126 views)
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Old 25th October 2008, 12:16 PM   #2
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I think there is something wrong with your zip file, I can see anything when I unpack and open it.
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Old 26th October 2008, 07:57 AM   #3
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I am able to open the PDF file inside.
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Old 26th October 2008, 08:05 PM   #4
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mmm strange... here it is again!
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Old 26th October 2008, 08:20 PM   #5
AndrewT is offline AndrewT  Scotland
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go to doug Self's site and to ESP's site and read up on balanced signals and balanced inputs.
Then read the expert, Walt Jung.

Your schematic has unbalanced impedances, 10k & 20k on the hot and cold inputs.
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Old 2nd November 2008, 02:27 PM   #6
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@AndrewT, thanks you for your response. The 'hints' you gave were very useful.

I updated the schematic so that the impedances on hot and cold pins are the same.

Do you, or anyone else, have additional comments on this circuit ?

Regards,
Niels Bergsma
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File Type: zip vestzaksubdriver2.zip (94.6 KB, 50 views)
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Old 2nd November 2008, 03:08 PM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by nbergsma
I updated the schematic so that the impedances on hot and cold pins are the same.
where?
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Old 2nd November 2008, 10:20 PM   #8
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I added two op-amps (one for Audio IN L, one for Audio IN R). They are located on the left side of the schematic, horizontal mirrored (next time I'll resolve the component numbering)

I used the circuit from Doug self's site, figure 12 (
'Superbal'-configuration)
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