Under
https://glass-ware.stores.yahoo.net/nostmfbcr.html
I read follow:
The multiple-feedback filter is based on the inverting amplifier topology, whereas the Sallen-Key is based on the non-inverting topology. This makes a big difference, as the assumption behind the Sallen-Key topology is that the buffer's output actually realizes absolute unity-gain; no buffers do. In contrast, the multiple-feedback filter relies on there being phase inversion of the input signal, which there always is. In addition, the MFB's initial RC filter are outside the feedback loop, so this pre-filter is essentially passive, therefore incapable of overload.
Usual both commercial and diy active crossover network units are in general wired according the best known Sallen-Key topology - here is present the great benefit of variable XO frequency with help of simple pots.
Maybe this is an important reason of the very low popularity of active XO in MFB topology.
Mostly the ask of the best op amp I note often - e. g.
https://www.diyaudio.com/community/threads/which-opamp-for-active-crossover.187095/
https://www.diyaudio.com/community/threads/op-amps-for-active-crossover.88513/
https://www.diyaudio.com/community/threads/op-amps-for-active-xover-and-line-drivers.249499/
https://www.diyaudio.com/community/...r-active-crossover-design-for-speaker.383631/
https://www.diyaudio.com/community/threads/active-crossover-parts-selection.378555/
But nobody ask about differences concerning the topology. Therefore the question:
Who have heard both versions especially in the high frequency rail e. g. with JBL or BMS drivers or any AMT driver ? - like those under
https://www.diyaudio.com/community/threads/amt-ess-1-vs-stage-accompany-sa8535-sa-8535.164153/
https://www.diyaudio.com/community/...401-sa8535-ess-amt-or-beymas-tpl-150h.267960/
Thanks for comments and URL's.
https://glass-ware.stores.yahoo.net/nostmfbcr.html
I read follow:
The multiple-feedback filter is based on the inverting amplifier topology, whereas the Sallen-Key is based on the non-inverting topology. This makes a big difference, as the assumption behind the Sallen-Key topology is that the buffer's output actually realizes absolute unity-gain; no buffers do. In contrast, the multiple-feedback filter relies on there being phase inversion of the input signal, which there always is. In addition, the MFB's initial RC filter are outside the feedback loop, so this pre-filter is essentially passive, therefore incapable of overload.
Usual both commercial and diy active crossover network units are in general wired according the best known Sallen-Key topology - here is present the great benefit of variable XO frequency with help of simple pots.
Maybe this is an important reason of the very low popularity of active XO in MFB topology.
Mostly the ask of the best op amp I note often - e. g.
https://www.diyaudio.com/community/threads/which-opamp-for-active-crossover.187095/
https://www.diyaudio.com/community/threads/op-amps-for-active-crossover.88513/
https://www.diyaudio.com/community/threads/op-amps-for-active-xover-and-line-drivers.249499/
https://www.diyaudio.com/community/...r-active-crossover-design-for-speaker.383631/
https://www.diyaudio.com/community/threads/active-crossover-parts-selection.378555/
But nobody ask about differences concerning the topology. Therefore the question:
Who have heard both versions especially in the high frequency rail e. g. with JBL or BMS drivers or any AMT driver ? - like those under
https://www.diyaudio.com/community/threads/amt-ess-1-vs-stage-accompany-sa8535-sa-8535.164153/
https://www.diyaudio.com/community/...401-sa8535-ess-amt-or-beymas-tpl-150h.267960/
Thanks for comments and URL's.
MFB stages are usually designed for an infinite inverting gain, which there never is.
If you are into extremely low distortion levels, the large common-mode signal at the Sallen & Key op-amp inputs is a clear disadvantage.
If a MFB or Sallen-key filter is configured as a LPF (and no post-filters are added to further shape the response), you are likely to find that above the frequency region targeted by the filter, amplitude increases rather than decreasing.
The effect can be seen in both MFB and Sallen-Key, but is more pronounced with the latter.
Not exactly desirable behavior in an active crossover.
sloa049b by Texas Instruments covers this topic, starting from page 11.
https://www.ti.com/lit/an/sloa049b/sloa049b.pdf?ts=1650516126900
hth, jonathan
The effect can be seen in both MFB and Sallen-Key, but is more pronounced with the latter.
Not exactly desirable behavior in an active crossover.
sloa049b by Texas Instruments covers this topic, starting from page 11.
https://www.ti.com/lit/an/sloa049b/sloa049b.pdf?ts=1650516126900
hth, jonathan
great advice - thank you very much.
Concerning reproduction the upper frequency range I am not a good friend of active crossover networks because on the use of high quality drivers like BMS horn drivers or AMT versions - unfortunately each additional active gain stage is audible due it's own distortion signature.
Unfortunately even best available integrated op-amps change it's distortion behaviour more or less dependent of the topology (MFB/Sallen-Key) and filter characteristic (CH-LR-BU-BE) - go to
https://www.elektormagazine.com/magazine/elektor-200507/18078
my favorite approach is the use of mixed filter, i. e. partly passive and partly active structure as show under
https://www.diyaudio.com/community/...-op-amp-for-ultimate-sounding-phl1230.154703/
without additional transistor or OP-amp stages.
Even with best op amp an extra MFB high pass stage, which was used in front of the tweeter power amp, provide an audible loss of sound quality.
In the moment there was the same issue by an other user and I want to reduce additional parts in the signal pad - go to post #28 under
https://www.diyaudio.com/community/...ditional-transistors-or-op-amps.379379/page-2
for details.
some more URL's MFB vs. Sallen-Key
https://trp.org.in/wp-content/uploads/2017/05/AJES-Vol.6-No.1-January-June-2017-pp.23-28.pdf
https://www.sciencedirect.com/topics/engineering/sallen-key
https://www.iasj.net/iasj/download/ceca8bad4ee05e7c
https://www.changpuak.ch/electronics/downloads/sloa088.pdf
https://www.analog.com/media/en/tra...ks/Op-Amp-Applications/Sections5-5-to-5-8.pdf
https://www.diyaudio.com/community/threads/analogue-active-filter-mfb-or-sallen-key.223961/
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An op-amp with as much loop-gain as possible (e.g. LM4562 has 70dB at 20kHz) would keep the transfer function predictable, while also reducing distortion. The MFB is generally considered better than the Sallen-key filter. However, any ceramic capacitors (if applicable) need to be NP0/C0G for best possible filtering.