No put a unity gain buffer right after the high pass section to drive the low pass section.
The 100pF capacitor is not just loaded by the 100K resistor it is also loaded by the 5.3K one. So the other option would be to use 2000 pF aka 2 nF or .002 uF.
The 100pF capacitor is not just loaded by the 100K resistor it is also loaded by the 5.3K one. So the other option would be to use 2000 pF aka 2 nF or .002 uF.
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Thanks Ed. I'll try replacing the 100pf cap with a 2000 pf cap.
🙂😱- Those are from Tiffy Teacher.
Cheers,
I've forgotten about the lounge for a while now, it's always fun around here.
In no particular order of things.
Richard, good list for stress relief...also, wasn't that list right after listening to whatever
it was? Just hearing and scanning through that prompted me to counter it...
...Cranking up the old stereo and playing along to two feel good tunes...
Van Morrison, Moondance
ZZ Top, Stockings
Cranked up the Fender Vibrolux Reverb Amp, plugged in and jammed,
with a little red steinberger copy guitar.
Reminded me of many things...
Tube problem with the stereo,
AND
The crappy ceramic capacitors in the old fender amplifers
that had Tremelo (Vibrato) in them and how everyone over
the years has told me not to touch them, they last forever.
That is probably the reason no one uses that part of the circuit
as it "sucks" so badly. In the amps that I've replaced them with
better film caps and some with slightly values....it makes that
circuit work and it sounds great!
Okay, now I've got the jammin' jones again, time to do it again,
this time adding:
Chris Rea...Road to hell: Texas
Al Collins, R. Cray, J Copeland: Showdown
John, Books are in the mail, will get here next week.
The "Cee-Zero-Gee" was the pronunciation that Cyril Bateman
wanted his readers to know about for the caps he specified,
designed, analyzed, used, wrote about, etc.
Daniel, Yes, I've read through Herrn Groner's OpAmp Research.
I lost the information that he used to have on his old website where
he had other circuits, reviews, and other parts to use and what
parts didn't work so well, any one know where that went?
Okay, time to play....
...How do I play?
By feel, I'm a Rhythm guy,
so I find the key they perform
and listen for the changes and
feel the beat, the groove, and go with it.
Cheers,
In no particular order of things.
Richard, good list for stress relief...also, wasn't that list right after listening to whatever
it was? Just hearing and scanning through that prompted me to counter it...
...Cranking up the old stereo and playing along to two feel good tunes...
Van Morrison, Moondance
ZZ Top, Stockings
Cranked up the Fender Vibrolux Reverb Amp, plugged in and jammed,
with a little red steinberger copy guitar.
Reminded me of many things...
Tube problem with the stereo,
AND
The crappy ceramic capacitors in the old fender amplifers
that had Tremelo (Vibrato) in them and how everyone over
the years has told me not to touch them, they last forever.
That is probably the reason no one uses that part of the circuit
as it "sucks" so badly. In the amps that I've replaced them with
better film caps and some with slightly values....it makes that
circuit work and it sounds great!
Okay, now I've got the jammin' jones again, time to do it again,
this time adding:
Chris Rea...Road to hell: Texas
Al Collins, R. Cray, J Copeland: Showdown
John, Books are in the mail, will get here next week.
The "Cee-Zero-Gee" was the pronunciation that Cyril Bateman
wanted his readers to know about for the caps he specified,
designed, analyzed, used, wrote about, etc.
Daniel, Yes, I've read through Herrn Groner's OpAmp Research.
I lost the information that he used to have on his old website where
he had other circuits, reviews, and other parts to use and what
parts didn't work so well, any one know where that went?
Okay, time to play....
...How do I play?
By feel, I'm a Rhythm guy,
so I find the key they perform
and listen for the changes and
feel the beat, the groove, and go with it.
Cheers,
Are you saying that a Sallen-Key LPF (which includes an opamp configured as a +1 gain buffer) can be improved by yanking out the +1 gain buffer stage and replacing it by a cascade of two inverting amplifiers, each with gain -1? Assuming opamp GBW is way way higher than the highest signal frequency of interest, etc, etc
I have not seen a Sallen key filter that did not have a distortion issue from the common mode. Cap upgrades make no difference. Its most severe at F0. I guess you could make one with two cascaded inverters and the feedback to the second stage. There are opamps with less common mode distortion that may help.
what I am looking for are topologies which will have lower harmonics at the output ---- lower than the opamp used --- above -3db of the LP filter. I have some ideas but maybe there are better ones out here/here.
THx-RNMarsh
Seems to me you'll probably have to accept a higher output impedance vs frequency curve, than the bare opamp @ gain = +1 provides. So how high is too high?
whole thread on point for op amp CM distortion: http://www.diyaudio.com/forums/anal...impedance-jfet-input-op-amps.html#post4120385
my posts show a couple of composite op amp options to improve common mode (input impedance modulation) distortion
also indirectly mentioned: http://www.analog.com/media/en/technical-documentation/application-notes/742022599AN232.pdf
Scott mentions Z balancing at +/- inputs, shown in his AD743 ds to reduce the CM distortion
my posts show a couple of composite op amp options to improve common mode (input impedance modulation) distortion
also indirectly mentioned: http://www.analog.com/media/en/technical-documentation/application-notes/742022599AN232.pdf
Scott mentions Z balancing at +/- inputs, shown in his AD743 ds to reduce the CM distortion
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I had to do something, the 743/745 have 50pF input capacitance to the substrate to get the noise (no free lunch).
I've seen the same network in the B. Hofer's presentation "Designing for Ultra-Low THD+N in Analog Circuits".
Now I know the source.
Now I know the source.
I can't find this piece of information on the datasheet! Did ADI omit it, accidentally or purposefully?
Some opamps are good enough to have lower distortion non-inverting. Just use those if you worry about it.
The input impedance spec is there, my memory might be wrong it says 18pF at 15V Vs maybe it was 50pF at 5V. The point is that it was not insignificant and the circuit suggested made a big difference.
the filter question isn't about lowering thd of the opamp.... it is about which LP filter topology (not opamp topology) will give the lowest residual thd at the filter output.
THx-RNMarsh
THx-RNMarsh
I expect R.M. imagines a hybrid active-passive filter in which the opamp's output pin is not the final filter output. Rather, the opamp output pin is the input to a downstream passive filter constructed with Rs Ls and Cs, creating the desired lowpass filter shape AND reducing opamp harmonics too. But output impedance may suffer and it may not be easy to arrange so that all opamps in the filter operate with zero common mode input.
what about the last/output opamp being an integrator or a cascade of integrators... basically, feed-back cap from output to (-) input.
THx-RNMarsh
THx-RNMarsh
inverting mode does virualy eliminate input CM nonlinearity, but at some level any op amp will have other distortion - likely from AB output stage and falling gain at high frequency
there are no perfect op amps - with monlithic at some performance level you simply have to go composite/multiloop/bootstrap and possibly Class A biased output
with composite techniques, using multiple op amps for one gain/function block it is possible to drive audio frequency distortions deep into the noise floor - audio frequency active filters then limited by passive components performance
there are no perfect op amps - with monlithic at some performance level you simply have to go composite/multiloop/bootstrap and possibly Class A biased output
with composite techniques, using multiple op amps for one gain/function block it is possible to drive audio frequency distortions deep into the noise floor - audio frequency active filters then limited by passive components performance
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