Using Joachim Gerhard Filter Buffers as balanced crossover - Page 2 - diyAudio
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Old 10th January 2013, 02:20 PM   #11
EUVL is offline EUVL  Europe
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The Sallen Keys as you have drawn already have buffered outputs.
So no extra buffer required.


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Old 10th January 2013, 03:00 PM   #12
APK is offline APK  United Kingdom
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Like this?
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Old 11th January 2013, 08:50 AM   #13
APK is offline APK  United Kingdom
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Having thought about it Like this
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Old 11th January 2013, 11:36 AM   #14
Calvin is offline Calvin  Germany
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Hi,

basically You could do it as in #12, but itd be complicated to achieve the desired 4th order steepness and Q. One can generate 3th order by adding a RC-network ahead of the 2nd order SallenKey stage, but for 4th order cascade two unity-gain Sallenkey stages.
Design is then easy using LTSpice and/or TexasInstruments FilterPro software.

jauu
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Old 11th January 2013, 01:54 PM   #15
APK is offline APK  United Kingdom
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Thanks
I have been having a session with Texas Instruments FilterPro software, getting there slowly
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Old 11th January 2013, 02:02 PM   #16
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APK,

You need to consider if you are targeting a specific electrical response or acoustic response. The roll off of the drivers, enclosure (baffle step) etc will contribute to the acoustic response. Targeting an electrical response might not be the best way to develop a crossover design.


Otherwise as a fellow builder of JG filter-buffer ... neat idea and application of these boards!! I will follow with interest and have no specific advice to offer other than the general waffle above

Chris
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Old 12th January 2013, 01:54 PM   #17
Calvin is offline Calvin  Germany
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Hi,

Yep, I assist that suggestion ;-)
With passive speakers, no one would expect good results from a Xover after the textbooks. With active Xovers though its seems rather common to design after textbook. In better designs one may find additional EQs to correct for driver anomalies. Unfortunately such designs tend to be OPamp graveyards. The sonic results of suchalike leave alot to wish for.
Theres basically no reason not to design active filters similar to passive technology with the drivers transfer function in mind, hence to perfom filter and equalizer-function at the same. Typically such filters place a lower number of parts and active devices into the signal path and sound much more musical/authentic.

jauu
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Old 13th January 2013, 10:40 AM   #18
APK is offline APK  United Kingdom
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Hi Calvin & Hochopper
I understand what you are saying however with very limited knowledge I'm finding even this daunting, first looks simple however like everything else scratch the surface and all sorts of complications arise.
I think the initial plan is to follow the specific electrical response route and once I have achieved that and hopefully learning along the way,tackle what I am assuming is the more complicated path of the acoustic response.
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Old 13th January 2013, 12:12 PM   #19
APK is offline APK  United Kingdom
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From most the circuit's I have seen each stage is followed by a unity buffer which would mean using twice the number of JG Filter buffers (which isn't a problem) as indicated by Calvin in post #14. EUVL would seem to suggest in post #11 that this in not needed? the only circuits I found that don't have a buffer after each stage have some amplification as below.
As I have already said I'm fine with the practical side but c##p at theory
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Old 14th January 2013, 07:10 AM   #20
Calvin is offline Calvin  Germany
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Hi,

See #8, 2nd sentence! Each 2nd order SK filter stage has its Buffer. Since the Buffer is a low impedance output node, no additional Buffering towards the output node is required. Hence, a 4th order SK requires 2 Buffers. A 3rd buffer is not needed. Of course should the buffer circuit be capable to drive the attached filter components and output load. In case of the simple cascoded JFET buffer here, load impedance should not drop much below ~10kOhms. If more drive capability is needed, then use a beefier Buffer as for example shown in #5.

jauu
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