Subwoofer pre-amp

nbergsma · 25th October 2008, 12:33 PM

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.

MJL21193 · 25th October 2008, 01:16 PM

I think there is something wrong with your zip file, I can see anything when I unpack and open it.

454Casull · 26th October 2008, 08:57 AM

I am able to open the PDF file inside.

nbergsma · 26th October 2008, 09:05 PM

mmm strange... here it is again!

AndrewT · 26th October 2008, 09:20 PM

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.

nbergsma · 2nd November 2008, 03:27 PM

@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

AndrewT · 2nd November 2008, 04:08 PM

Quote:

Originally posted by nbergsma
I updated the schematic so that the impedances on hot and cold pins are the same.

where?

nbergsma · 2nd November 2008, 11:20 PM

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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25th October 2008, 01:16 PM	#2
MJL21193 Account disabled at member's request Join Date: Mar 2007	I think there is something wrong with your zip file, I can see anything when I unpack and open it.

26th October 2008, 08:57 AM	#3
454Casull diyAudio Member Join Date: Jan 2004 Location: Toronto, ON, Canada	I am able to open the PDF file inside.

26th October 2008, 09:20 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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.

2nd November 2008, 11:20 PM	#8
nbergsma diyAudio Member Join Date: Aug 2008	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)