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

[Mfly]

Originally Posted by dentarthur

Just discovered this thread.
Can I join for 3 boards?

Yes of course. See the post above yours for details on the order process (send me PM with info, pay via Paypal).

Cheers, Maarten

[akira]

Hi Marteen,
I got no reply to my PM.
Did you get it ?

[Mfly]

Originally Posted by akira

Hi Marteen,
I got no reply to my PM.
Did you get it ?

Sorry, you have now!

[Mfly]

Hello all,

Here is a LTSpice model for the following filter sections: summing circuit, 4th order Linkwitz Riley filter, 1 EQ section configured as notch filter, Linkwitz Transform section, Allpass section (phase) and an output buffer with volume control.

summing+LR4th+Notch+LTransform+allpass+volbuf.asc

-Simulation from 20-100Hz with 100 sample points/decade

-To change the LR4 filter frequency: adjust R4xx (in my current configuration adjustable from 30k to 130k (~113Hz-26Hz)

-I added values for quite an extreme notch as an example (something like center 50Hz with 3dB points on 48Hz and 52Hz and something like a 20dB cut). Use the sheet provided earlier to calculate values of your own. If you want to 'bypass' the notch, just enter a value of 0.1 (something close to zero) for R500

-The values for the current Linkwitz transform are for an Fsc of 33Hz with an F3 of 28Hz and target Fsc of 20Hz.

-Change PhasePOT from 1 to 100000 to change the phase behaviour. In this frequency range 220nF for C700 is quite ideal. You can test some other values.

-The volume control is just 2 modelled resistors. Change both in unison (keep total value the same) to test different volume settings. The current total is 92kOhm because the Alpha pot I tested has a maximum resistance of 92kOhm.

If you're familiar with LTSpice you know what to do. If not. A quick and easy instruction:

-Download & install LTSpice from the Linear website
-Load the schematic
-Press the 'run' button (small running figure)
-Click with your cursor on the output or any other net to measure the frequency and phase response
-Right clicking on the value of a component lets you change it. Beware: after changing component values you have to press 'run' again.

[Mfly]

Several people have payed their order now. In several cases Paypal charged fees to me so I come up short a few euro's. So I wanted to give an instruction, before I end up being short more than a few euro's:

-If your Paypal payment is done via your creditcard and/or you mark it as 'purchase payment', please add 3,4% + € 0,35 to the total amount.

-If you Paypal payment is done via your bank account or balance already present on you Paypal account AND you mark you payment as 'personal', you don't have to add anything to the total amount.

And the current status of the groupbuy:

Total number of persons that expressed interest on this thread or via PM: 27
Maximum total number of boards current interest: 57
Total number of persons that send me a PM with their address and final board number: 12
Total number of persons that payed their order: 7

I'll give another update after the weekend.

Cheers Maarten

[Ed LaFontaine]

Payment sent

[AndrewT]

Add 2 boards for me.

Can you PM me your paypal address.

I am UK based so Europe postage cost applies.

[Mfly]

I promised an update. So here we go:

Total expressed interest: 62 boards
Ordered and paid for: 32 boards

Next weekend (or maybe coming friday) I will post the updated schematic, BOM and board pictures. After consulting I decided on ground pours for both layers and adding some extra via's. Also after testing the sensing circuit I came to the conclusion this type of circuit needs a high input resistance (gate / base) on the switching transistor to charge the capacitor. So it needs a mosfet and not something like a BC547. These are the changes implemented in the update (and of course the beforementioned separate ground plane for the sensing circuit).

Hopefully many of you are still planning to place a final order, as the board price was based on 50 boards. So a minimum of 18 to go .

[potepuh]

I am interested in 4 board´s

please let me knew

[Mfly]

Hi all,

By now I have received orders and payment for 42 boards. I'll send the 11 people who expressed interest a PM to ask if they are still interested to participate. Hopefully orders get up to 50 pcs. to cover all costs. If they don't respond within a day or 2-3, I'll go ahead and place the order.

Here's the latest (and probably final) schematic and board:

Schematic:
SubFilterMichiel_Schematic_20120408.png

Board top layer:
SubFilterMichiel_Top_201200408.png

Board bottom layer:
SubFilterMichiel_Bottom_20120408.png

And the updated BOM:
SubwooferFilter_BOM_Mouser.zip
The blue grey colored cells are components which you have to calculate or choose according to your personal preference. Please read the remarks carefully.

Here's the LTSpice model again, now including input buffers (input buffers are +6dB for better noise performance):
buffer+summing+LR4th+Notch+LTransform+allpass+volbuf.asc

Update log:
-Ground pours in both layers
-Many ground via's for low impedance coupling of both ground layers
-Separate ground for sensing circuit (ties to ground via jumper or resistor (R911)
-Larger mounting pads (so you can actually fit your screw in there without touching any components)
-Replaced the phase switch with a smaller form factor (is off board anyway and the previous mounting holes were a bit large)
-Replaced all <90 degrees trace connections with ones that are 90 degrees or larger

About grounding:
-The ground of the sensing circuit could possibly induce ground hum issues. First try to jumper R911. If this results in ground hum, you can try to tie the sensing side of R911 to a common power supply or off board star ground. Another option is to put a small valued resistor here (10R).
-Depending on your setup and the equipment you connect the board to, you still can encounter other ground hum problems. This could for example be due to ground connections via both the RCA LFE input and the speaker or L+R RCA inputs (2 ground connections to the same component or a pre-amp connected to the filter and to a power amp, which is in turn again connected to the filter). If you encounter such issues, please post it in this or a separate forum thread. There are always solutions, but these are of course situation specific..

About connecting it to your equipment:
The layout is made for the following 2 combinations:
-LR speaker inputs + LFE RCA input
-LR RCA inputs + LFE RCA input
So do not connect both LR RCA inputs and the LR speaker inputs at the same time!

Errors:
Although I checked and rechecked the schematic and board about a 100 times for errors and modeled the schematic in Spice, I am still just 1 person doing this as a hobby (and I am not an electronics engineer..). If anybody with some experience is willing to recheck my schematic, please do so. I am fairly certain it will work as designed but some extra error checking never hurts.

Oh almost forgot: HAPPY EASTER EVERYBODY!