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Active filter board GB

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#721
Here are a few pictures of my active filter.I used an old technics tuner cabinet to mount the components.The transformer is a 30VA/18 volt type.
The current drawn by one board varies between 56 and 80 mA.

Kees
 

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#728
Hi,
the regulated DC voltage can usually match the Vac from the transformer.
i.e. 15Vac gives 15Vdc after regulation. But you might need 16Vac or even 17Vac if you draw a large current.

Lower voltages need more ac volts and higher output voltages may manage with a little less. A large low regulation transformer produces less opencircuit voltage than a small transformer of equal voltage rating.
 
#731
Add up the current draw, multiply by the rail to rail voltage then use a transformer rated at least double the result.

Figure 10 mA per opamp on the filter boards.

Quick and dirty answer - the price difference between 30VA and 50VA is a couple dollars.
 
#732
I've found 2 boards so I can get started!!!🙂

http://www.twistedpearaudio.com/lcps/lcps.aspx

I've two of these together with 2 30Va trafo's as power supply, Opamps will be the LM4562..

The filter will be a relatively simple 24db/oct 2way, inputbuffer with bafflstep, a notch for the alu seas woofer, outputbuffer for the low channels with extra gain and volumecontrol...

Right now I'm reading a lot and try to understand everything that concerns correct implementation of the boards...

Any tips for reading material?

(already found the manual😉 )
 
#734
I saw on Bob's page that on the Power Supply , we can make it at 15V or adjustable depending on the resistor values we choose for R11 and R13.

Quote: "Note that if you want 15V nominal output and are not going to use the trim-pot option, you must substitute a 2K ohm resistor for R11 and R13. Using the 3K3 shown on the schematic will give you 13V nominal output. With a 10K trim pot and 3K3 resistor in R11 and R13 you will be able to adjust the voltage from 14V up to 3-5V less than your raw DC depending on current draw"

I suppose that I have an advantage to select the option with the trimpot.....but with our active filter, is it also true and why?What voltage should I use? Excuse my newby question.
 
#735
Most chips are perfectly fine with 15V +/- a bit, but for those obsesses with perfection you could trim it to exactly the same voltage according to your DMM and theoretically reduce offset.

Some chips want other voltages, like SMD parts tend to want 12V or less, but those superfast types aren't recommended here. Just check the voltage rating of the chip you are using and stay below it.
 
#736
You know, it's a super big shame that these boards and the PSU kit aren't available any more. Are there any plans to make another run of these these boards? I really feel like this is such a great offering to the community that it's a terrible shame for them not to be more regularly available.

Also, how are everyone's projects coming? I'd love to see some results from these boards!
 
#738
It would be nice if someone could step up and organize another buy. I get emails pretty regularly asking for boards, so there should be interest to make it worthwhile.

I just plain don't have time to run another group buy, though. My soldering iron has only been warm once in the last six months, and that was only to fix a friend's sleep apnea machine :bawling:
 
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