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Subwoofer Filter PCB with LFE sensing, EQ sections, 12/24 dB LR cutoff

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#21
Mfly said:
Finally got some time to work on the board... Sorry for you people who have been waiting.

I've added a rumble filter and a phase switch. I also moved the power input to the top of the board. I have decided to keep the equalizer sections as they are, because they have more flexibility for adjustment compared to a parametric equalizer and take a lot less space on the control side. A subwoofer will probably be in the same room for a long period of time so there shouldn't be any need for continuous adjustment.

I am now almost finished with the board, have to find a solution for 1 trace and do some error checking.

I'll upload the new schematics and board in the coming weeks (before the end of the year, I promise!). I will also collect all calculation tools for the equalizer, linkwitz transform, etc.

For people still waiting, thank you for your patience!
Click to expand...

Thank you! :up:
 
#22
All right, still a few hours left till new years...

Here we go:

The new schematic. Changes:

-full phase switch (for > 180 degrees control)
-rumble filter

Subfilter Schematic.jpg

New top layer:

Subfilter Top.jpg

New bottom layer:

Subfilter Bottom.jpg

Calculating tools:

View attachment Calculating Tools.zip

There are 2 spreadsheets in the zipfile, one is called 'Linkwitz Transform Calculator', this is a handy little tool I found to calculate the possibilities for the Linkwitz Transform section. This includes effect of the rumble filter, needed power, Xmax, and so on (credit to Mr. Linkwitz and mr. John L. Murphy).
The other is called 'Active Filter Four'. The sheet 'Notch and boost EQ' contain 2 different tools for calculating the equalizer sections (credit to mr. Bob Ellis).

Then there is the LFE sensing circuit. This is a design by mr. Rod Elliot, for a full explanation of the circuit, including values for timing:

Signal Detecting Auto Power-On Unit

Any other changes you would like to implement (range of the low pass section or range of the phase section), there are several tools easily found on the internet. I maybe have a LTspice model somewhere for the phase section. Let me know if I need to look it up.

I am still thinking about a solution to do the power supply lines all from the top part of the board, but haven't thought of something satisfying yet. If I think of something soon I'll let you know. Otherwise I'll go with this design (if any of you don't find any errors..)

Happy new year everbody!
 
#24
Well, if nobody finds any serious issues with the design. I think this will be the final version.

Changes:

-Better power supply lines (shorter and all from the top)
-Option for larger output capacitor (Wima MKS type (larger just wasn't an option on this board))
-Made it possible to use both types of EVOX capacitors for C700 (10mm base and 15mm base)
-Options for both Bourns 90 series, as well as 91 series for the phase and volume control (and many others if you put them off board of course)(the Bourns 904 for the filter frequency is still the only ready available 4-gang pot I have found so far)
-Removed the via and found an on board solution

The Top:

SubFilterMichiel_Top_20120308.png

The Bottom:

SubFilterMichiel_Bottom_20120308.png

I have a BOM with Mouser part numbers. I'll clean it up and upload it.

And I'll PM people who have shown interest, see who's still interested and get a quote for production. Everybody else interested: feel free to show your interest here or via a PM.

By the way: no matter what the volume, I will order this board 😀.
 
#37
Nice to see there's plenty of interest in the PCB. This should make the price per board bearable.

Here's a preliminary BOM file:
View attachment SubwooferFilter_BOM_Mouser.zip

Remarks:

  • The total pricing of components excluding RCA connectors, speaker connectors, power supply and AC inlet (so basically the components to populate the board, including the switches) is about 70 euro's.
  • Use a bipolar power supply +/- 12V - 15V and transformer, with a current capability of a least 200mA. The op-amps use ~11mA/piece I think, the relay something similar at 15V, then there's the LED with about ~20mA, the relay driver and some miscellaneous current draw. I'll probably be using the TPA LCBPS with a 0,3A - 0,5A transformer.
  • Populating the board can be cheaper if you use cheaper components (especially cheaper switches)....
  • No components are selected in the BOM for equalizer, Linkwitz transform and rumble filter sections. Calculate these for your own situation with the tools provided in the earlier post. If you want to order a selection of components for multiple situations, have a look at the calculating tools to calculate some value ranges.
  • I will test the LFE sensing on breadboard to determine the base signal voltage and see if a transistor or mosfet driver is preferable (anyone experience with this / recommendation for this situation?)
  • If you want to use other components and have questions about lead spacing and component size, please send me a PM.

I will come up with preliminary pricing for the boards somewhere this week.

Cheers, Maarten
 
#39
I have looked into fabrication and quoting. Seems that several people have a fine experience with PCBCart. There is currently a minimum interest for 24 boards and a maximum for 33 boards. So we'll probably end up with an order for 30 - 40 boards.

This results in the following pricing:

For green soldermask, FR-4, 2mm board thickness, 70um tracing, 100x140mm, gold immersion boards:

30 boards: ~9,50 euro's/board (including import taxes and customs handling (if they use the correct codes etc.), excluding shipping to you guys)
40 boards: ~8,- euro's/board

If we want another color soldermask it adds another 0,5 - 1 euro per board.

Shipping from the Netherlands (indication, depends on final weight/board):

Countries in Europe:
1 board: € 2,55
2-3 boards: € 3,40
4-6 boards: € 6,80

Other countries:
1 board: € 2,85
2-3 boards: € 5,70
4-6 boards: € 10,45

I sent a PM to all members who expressed interest a while ago. I will wait a few days for their responses. After this I will ask everybody to make their final interest known and give you the details for ordering.

In the meantime I will clean up the component placing some more and probably add the possibility to use on board Alpha pots as well (901 series is currently out of stock at Mouser and won't be available till May).

I will also order the BOM from Mouser this week and will start breadboarding the LFE sensing. I would like to wrap up testing that before I order the boards.

Is everybody ok with standard green soldermask?
 
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