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Active filter board GB

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#104
Bob,

i`ve just paid via paypal but same here as in capslock`s case. The money has to be transferred to my paypal account first before it will be credited to your account. The bank transfer has been authorized and it usually takes two business days.

illusionxx
 
#106
Comments about component selection:

For those who need a better understanding of

"Sallen-Key"

filters, a search is helpful. That is how I found the following suggestions in this link:

http://www.elecdesign.com/Articles/Index.cfm?ArticleID=7486&pg=1


Until now, the choosing of resistor and capacitor values has been left without mention. Theoretically, any values of R and C that satisfy the equations may be used. But practical considerations call for certain guidelines to be followed. Given a specific corner frequency, the values of C and R are inversely proportional to one another. By making C larger, R becomes smaller and vice versa.

In the case of the low-pass Sallen-Key filter, the ratio between the output impedance of the amplifier and the value of filter component R sets the transfer functions seen at frequencies well above cutoff. The larger the resistor's value, the lower the transmission of signals at high frequency. Making R too large may result in C becoming so small that the parasitic capacitors, including the input capacitance of the amplifier, cause errors. The best choice of component values depends on the particulars of your circuit and the tradeoffs you're willing to make.

Here are some general recommendations for capacitors and resistors: You should avoid capacitors with values less than 100 pF. If at all possible, use an NPO type. X7R is okay in a pinch, but avoid Z5U and other low-quality dielectrics. In critical applications, even higher-quality dielectrics, like polyester, polycarbonate, Mylar, etc., may be required. As for resistors, values in the range of a few hundred to a few thousand ohms are the best bet. You also should choose metal-film resistors that possess low temperature coefficients. Finally, use 1%-tolerance capacitors and resistors, preferably those of the surface-mount variety.
 
#107
Jens--

The board rendering looks cool!! But I have a question...

What are P1 and P2 (the black rectangles) on the board? I don't see them on the schematic.

Can you post a final schematic?

Thanks again for your work in putting this together.

--Greg
 
#110
The schematic linked to in my last post is NOT the final version , but it is close to give you an idea of what it looks like. Component designations and the connection to make a bandpass have changed.

We'll get the final version posted shortly.
 
#113
Ed,

The problem with NP0/C0G is that you have to go for the bigger SMT types e.g. 1206/1210 to get above about 2nF...

This means bigger resistor values to get til same filter response.... and resistors should be below 10-15kOhm in order to get the noise down. As with everything it is a trade off.... IMHO through hole caps is the better solution.

You end up spending more space on the PCB + there must be room for VIAs also... all in all I think it is better to use through hole film caps for this type of project.

You will be able to fit 1uF types on the board in the filter sections.

\Jens
 
#114
I will be placing the order this morning when Advanced wakes up.

So far 288 boards of 356 requested are paid for, counting those who promised to send money orders.

Although I understand they responded to the email notification effort, I have not heard from:

Harryeng
vgeorge
t3447ml
saml

Are you guys still interested?

Bob
 
#118
ORDER PLACED - 4 Week Delivery

I ordered enough for everyone who signed up here or contacted me directly, plus a few extras. So if you are still interested, let me know. I'm holding some of the extras to make sure that everyone who paid receives theirs. I'll release them and any unpaid orders later.
 
#120
OpAmp GB

I am happy to run a European group buy if that is wanted/beneficial, eg if whoever volunteers to run the main GB would prefer it that way.

As long as the orders reach 250 we don't lose much discount by splitting the order.

When I looked at digikey UK the LM6172 quantity discount was hardly worth bothering with, so I am mostly interested in OPA2134 (although there is always that nagging question > why not build both and see if I can I hear the difference?)


PS. Do we want sockets as well or is soldering straight to the board preferred?
 
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