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A Modular 2/3/4/n ways Digitally Controlled State Variable Active Crossover
A Modular 2/3/4/n ways Digitally Controlled State Variable Active Crossover
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Old 13th September 2018, 09:25 PM   #11
wintermute is offline wintermute  Australia
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A Modular 2/3/4/n ways Digitally Controlled State Variable Active Crossover
I'm seeing a most of the images in the first post and all of them in the latest one.

Looks like you have done an extremely comprehensive job on this crossover dondo!

Tony.
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Old 13th September 2018, 11:03 PM   #12
dondo is offline dondo
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Thank you Tony!
Actually i have to find the time to continue to fill up the site. There is still a lot to write.
Today I finished to solder all the 6 filter boards and stacked them together.
I tested just the 2 way configuration still and I am very happy with the results.
Stay tuned!
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Old 13th September 2018, 11:28 PM   #13
mkane77g is offline mkane77g  United States
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A Modular 2/3/4/n ways Digitally Controlled State Variable Active Crossover
tuned
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Old 14th September 2018, 01:00 AM   #14
DRONE7 is offline DRONE7  New Zealand
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tuned two too
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Old 14th September 2018, 11:33 AM   #15
AudioH is offline AudioH  United Kingdom
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Tuned three

Very intesting project
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Old 15th September 2018, 11:21 PM   #16
dondo is offline dondo
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Here is the tower of filter boards in test!


Click the image to open in full size.


I tested board by board not-stacked first and then stacked just to be sure.
Till now everything seems to work properly and the sound quality is good to be using just OPA2134s!!!


Click the image to open in full size.

The mistake I've done may be is to tune the last board too low...
(I made confusion about cutting frequency and crossover frequencies when I chose the resistors of the bass boards...).

Fortunately an easy to fix mistake: changing the fixed resistors will help me a lot without changing any capacitor.
with my actual configuration i have a 3 bit choice (8 possibilities) starting from 80Hz to 420Hz. that would be good as cutting frequency but is actually a crossover frequency.
That is not terrible in my case because I will use 15'' or 18'' inches woofers in my configuration.
But I can easy fix that adding a 33k resistor in parallel with every 19k1 fixed resistors (FA, FB.... to FF) to obtain 12k ohm resistors.
that will turn my filter, using 100 nF capacitors, to behave from 131Hz to 469Hz approximately, as crossover points (and not as frequency cut. Those are the kind of stupid problems I have when I can't do a project all at once.)

The result, with the 33k resistors added in parallel to the 19k1 ones, will shift everything 50Hz higher more or less.
there are also series resistors in case you want to change the "curvature".
If the series resistors are just jumpers we have linearity in our frequency options.
Adding them we will have an anti-log behavior.
My question is how to obtain a good logarithmic scale to place our frequency options?
In theory would be enough to have a negative resistor in place of the series resistors...
Is there any simple way to have the frequencies options placed in a "log" way instead of a linear way? may be just with passive components would be awesome. (right now all the frequencies options for every cut are distant almost the same amount of Hz among each other).
would be more convenient to have it in the "log" way!
Cheers!


Testing the "Thing!":
Click the image to open in full size.

Thanks to everybody to get interested on the topic!
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Old 15th September 2018, 11:28 PM   #17
Oneminde is offline Oneminde
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Following. Might be very interesting for my next loudspeaker
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Old 15th September 2018, 11:38 PM   #18
dondo is offline dondo
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Default P.S.

in the SCHEMATICS
you can see the series resistors FA, FB.... to FF (now jumpers in the prototype) as:
R15, R16, R20,R21,R28,R29.
They are on the right side, just coming from the top of every state variable filter, feeding the variable resistors banks.
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Old 15th September 2018, 11:57 PM   #19
dondo is offline dondo
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Here is how I calculated my resistors using the resistor calculator of the site:

Bass board:
Serie Resistor = 0 Ohm
Filter Capacitors = 100 nF
Highest resistors = 33200 Ohm
Fixed Resistors = 12000 Ohm

Mid board:
Serie Resistor = 0 Ohm
Filter Capacitors = 33 nF
Highest resistors = 47500 Ohm
Fixed Resistors = 47500 Ohm

High board:
Serie Resistor = 0 Ohm
Filter Capacitors = 10 nF
Highest resistors = 105000 Ohm
Fixed Resistors = 182000 Ohm

Last edited by dondo; 16th September 2018 at 12:05 AM. Reason: wrong paging from spreadsheet
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Old 16th September 2018, 01:16 AM   #20
dondo is offline dondo
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It took me more then 30 minutes o translate to English.... I'm getting bad!

Here is how I calculated my resistors using the resistor calculator of the site:

Bass board:
Series Resistor = 0 Ohm
Filter Capacitors = 100 nF
Highest resistors = 33200 Ohm
Fixed Resistors = 12000 Ohm

Mid board:
Series Resistor = 0 Ohm
Filter Capacitors = 33 nF
Highest resistors = 47500 Ohm
Fixed Resistors = 47500 Ohm

High board:
Series Resistor = 0 Ohm
Filter Capacitors = 10 nF
Highest resistors = 105000 Ohm
Fixed Resistors = 182000 Ohm


the resistors values at the end of the spreadsheet will be approximated to Vishay/Dale CMF (industrial) or RN (MILITARY) series typical values.
I recommend to use the best resistors having the following properties: a very low noise figure and with a very small tolerance, still having an acceptable impedance.
Translated: Almost the best resistors you can get, not just for price! 0.5%, tolerance would be the best 1% is acceptable.
Notice that sometimes 0,5% is cheaper than 1% in shops!!!


As filter capacitors in the state variable filters should be better a modern technology Polypropylene MKP with minimum 1% tolerance. Matching can improve but is not necessary.
Other option that could result in better quality is a polystyrene set with 1% tolerance, but they are pretty retro, hard to find, expensive, and less durable.


On the Op-Amps power supplies and on the digital side of the filter boards, I recommend X7R ceramic caps in order to have a higher resistance, making with their 100nF capacitance a decent filter.


If anybody want to build this Dream-Machine contact me on the site! (I Know some purists don't like the fact we use Op-Amps. But they are the good way to achieve what we need, and with modern op-amps designs it's hard to beat them!!!)
Just for the people who doesn't believe on CHIPS and Op-Amp: look outside! It is plenty of discrete Op-Amps out there you could try! Just let us know what is your experience with them in a unity gain configuration!


I would like a more precise op-amp then the opa2134 from Burr-Brown. I'm sure there is one for this kind of applications. But till now it is the best I could try in that price range.
I installed them straight on the board without a socket, because there are already to many not-soldered contacts for my standars. This is why I recommend golden contacts on every molex-kk-connectors, and on the headers when possible. Especially the 2 position one giving signal from a board to another. That could be maid of a twisted pair or coaxial cable too.
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