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Mfly 11th December 2010 05:05 PM

Subwoofer Filter PCB with LFE sensing, EQ sections, 12/24 dB LR cutoff
 
4 Attachment(s)
Hello all,

For a subwoofer project for my brother I have designed a PCB for the crossover / filter section. I was wondering if there was any interest in a group buy. The PCB consists of the following components:

-Speaker inputs (speaker to line level conversion)
-RCA inputs
-LFE input
-Adjustable low pass Linkwitz Riley filter (12dB / 24dB selectable)
-3 equalizer sections
-Linkwitz Transform section
-Phase control
-Automatic sensing if a LFE signal is present, resulting in an automatic switch to the LFE input (circuit: Signal Detecting Auto Power-On Unit)
(you can modify the amount of time the circuit relais stays on, and release the relais by a button press)

Block diagram:

Attachment 200442

Schematic:

Attachment 200445

The layout of the potentiometers is for the Bourns PTD90 series and can be mounted on the board. The 2 switches are not meant to be board mounted in the current design.

Bottom PCB:

Attachment 200443

Top PCB:

Attachment 200444

This is my first serious board layout, so any suggestions are welcome. I borrowed some design ideas here and there. There is one jumper from the LFE input to the LFE sensing circuit. Size of the board is 10 x 14 cm.

Depending on desired specifications and amount of boards, the price will probably be somewhere between 12,- (standard board, 20 pieces) to 30,- (golden solder pads, thicker traces, 10 pieces) per board.

klc-audio 6th February 2011 03:58 PM

Did these boards ever came to life. I could use one

Mfly 7th February 2011 08:19 AM

I'm currently improving the layout of the power traces and location of the input caps. My brother wasn't in a hurry to finish this and because nobody showed interest, I wasn't in a hurry to finish the design. But I can speed the process up.

It would be nice to have some more interest. The price per board for 3 boards would come to about 26,- without shipping (1.6mm board, 1 oz copper, silver finish).

Let me know what you think and I'll get the process in gear again.

Cheers Maarten

congo 7th February 2011 08:49 PM

Hello Mfly, i looked almost every where to find schematic and calculation or values of equalizer section and notch filter but whitout success. Can you post them or tell me where to find it. I allready looked at linkwitzlab but there is a little bit different.

Thank you.

highfieldrebel 7th February 2011 09:14 PM

Hi Maarten

I am building a sub-woofer and I need a crossover solution. I've read though that the cone excursion for my sub design is excessive at lower frequencies (<30 Hz) and I should bandpass rather than low-pass the signal to it. Am I right in thinking your board will not do this?
Thanks
Steve

klc-audio 9th February 2011 02:41 PM

I'm interested

Ideas?
http://www.lcaudio.dk/pdfs/subfilter.pdf

parb 13th February 2011 04:40 AM

looks nice. how about changing the eq section to a parametric filter section? seems like a better fit? also a front panel eq bypass switch would make sense?

and you could use a table for choosing components for the lowpass and highpass sections for those who wish to modify them, altough to me it looks straightforward.

finally, maybe considering a polarity shift section on the output?


id also suggest using a led to indicate lfe section active?

par

Mfly 14th February 2011 08:56 AM

Quote:

Originally Posted by highfieldrebel (Post 2460938)
Hi Maarten

I am building a sub-woofer and I need a crossover solution. I've read though that the cone excursion for my sub design is excessive at lower frequencies (<30 Hz) and I should bandpass rather than low-pass the signal to it. Am I right in thinking your board will not do this?
Thanks
Steve

A rumble filter is not implemented in the current design, but can be very easlily. I was contempleting it already and since it seems I will do some redesigning, I will add it.

Quote:

Originally Posted by congo (Post 2460913)
Hello Mfly, i looked almost every where to find schematic and calculation or values of equalizer section and notch filter but whitout success. Can you post them or tell me where to find it. I allready looked at linkwitzlab but there is a little bit different.

Thank you.

These were taken from the design of the active filters of Bob Ellis en Jens Rasmussen (Active Filter Four)(which is a beautiful design by the way). The excel sheet with calculators you can find here: Active Filter Four But Par's suggestion makes sense: to implement a parametric equalizer. It makes the board more versatile. So I'm contemplating changing it to a parametric equalizer, although I'm no fan of all the pots this brings to the design. On the other hand, these can be easily replaced by static components if you would want to.

Quote:

Originally Posted by parb (Post 2466855)
looks nice. how about changing the eq section to a parametric filter section? seems like a better fit? also a front panel eq bypass switch would make sense?

and you could use a table for choosing components for the lowpass and highpass sections for those who wish to modify them, altough to me it looks straightforward.

finally, maybe considering a polarity shift section on the output?


id also suggest using a led to indicate lfe section active?

par

Thank you. As mentioned: not a bad idea to change it to a paramatric equalizer. Do you have suggestions for a good design/schematic?

I'll link to usefull calculators and/or tables when the final design is ready.

Polarity shift I will also do in the redesign.

The LED is present in the LFE sensing circuit. You can put a 2 pole jumper in this position and connect the LED via the jumper.


I'm quite busy this coming period, but I'll try working on this as much as possible.

tangmonster 16th February 2011 05:40 AM

1 Attachment(s)
Hi

I recently designed my own board for an amplifier that is currently running on a strip board. Here are the details just for whatever reason you might find it useful. The circuit is designed to give balanced output since i use it for a bridge application.

It does not support high level or stereo input so the layout is like this.

low level sub input - linkwitz transform - (simple) 2 channel parametric filter - inverting opamp to get balanced output.

The circuit has power supply and a lm555 timer with relay to "mute" outputs on startup and immediately on shutdown.

power supply can run on single 12V ac input or 12 0 12 AC.

linkwitz circuit is based on: Linkwitz Transform Subwoofer Equaliser

paramatric filter is based on: Parametric and Sub-Woofer Equaliser

Haven't built this board yet . but would sure like too to replace the current prototype.

There are connections in the circuit to bypass Linkwitz and parametric filter.

Luke352 16th February 2011 09:11 AM

I would probably take one when you get around to finishing the design though I'm in no hurry so whenever you finish is fine with me.


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