|
I have uploaded the above as a .ZIP. According
to Bob Pease, the gain at the peak should be close to 34 dB,
independent of the tuned frequency. I don't get either of those
results using version 24.1.8. However, the bandwidth is fairly
constant with frequency, as predicted. I can't believe Bob Pease
reported the performance in error.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Would you please supply the original article, chapter or whatever in which Bob Pease wrote his result? Thank you.
I have uploaded the above as a .ZIP. According
to Bob Pease, the gain at the peak should be close to 34 dB,
independent of the tuned frequency. I don't get either of those
results using version 24.1.8. However, the bandwidth is fairly
constant with frequency, as predicted. I can't believe Bob Pease
reported the performance in error.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
I would have, but I downloaded the article
that triggered my interest it from Electronics Design News some
months ago, and I can't now find it in the EDN articles. In the
article is a reference to page 236 of 'Analog Circuits - World
Class Designs', edited by BP, but this doesn't address varying
R2 over a wide range of tuning. However, it does say that
varying R2 doesn't change the peak frequency gain, and that gain
is R3/2R1.
On 2025-05-11 15:27, Dave Daniel via
groups.io wrote:
Would you please supply the original article,
chapter or whatever in which Bob Pease wrote his result? Thank
you.
I have uploaded the above as a .ZIP.
According to Bob Pease, the gain at the peak should be
close to 34 dB, independent of the tuned frequency. I
don't get either of those results using version
24.1.8. However, the bandwidth is fairly constant with
frequency, as predicted. I can't believe Bob Pease
reported the performance in error.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own
Opinions Only
If something is true: * as far as we know - it's science
*for certain - it's mathematics *unquestionably - it's
religion
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
This circuit is basically an inverter with a bridged-T in the feedback. Since it has only one variable element, the amplitude of the peak and the BW (some say "Q") vary. Its usage is usually reserved for applications where the tuning range is restricted.
|
John,
Your schematic has the net "OUT" connected to the junction of R2 and C2.
Move "OUT" to the output pin of U1.
Mike
|
John,
The article is listed here.
.
NOTE: THE ARTICLE HAS THE TITLE WRONG.
It is a bandpass circuit.
Mike
|
Ah, yes. I have that book and see that circuit. You must be referring to the circuit described starting on page 236 entitled "Multiple Feedback Bandpass Filter". Excellent. Thank you very much.
Thank you.
I would d "have, but I downloaded the article
that triggered my interest it from Electronics Design News some
months ago, and I can't now find it in the EDN articles. In the
article is a reference to page 236 of 'Analog Circuits - World
Class Designs', edited by BP, but this doesn't address varying
R2 over a wide range of tuning. However, it does say that
varying R2 doesn't change the peak frequency gain, and that gain
is R3/2R1.
On 2025-05-11 15:27, Dave Daniel via
wrote:
Would you please supply the original article,
chapter or whatever in which Bob Pease wrote his result? Thank
you.
I have uploaded the above as a .ZIP.
According to Bob Pease, the gain at the peak should be
close to 34 dB, independent of the tuned frequency. I
don't get either of those results using version
24.1.8. However, the bandwidth is fairly constant with
frequency, as predicted. I can't believe Bob Pease
reported the performance in error.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own
Opinions Only
If something is true: * as far as we know - it's science
*for certain - it's mathematics *unquestionably - it's
religion
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Gain being dependent only on the ratio of R3/R1 would depend on having enough gain-bandwidth in the opamp.
|
The bandwidth is constant, so the Q varies
with frequency. I agree that the tuning range is restricted if
R2 isn't varied over a very wide range, because the peak
frequency is proportional to sqrt(R2).
It is interesting to regard it as a bridged-T.
On 2025-05-11 16:24, Jerry Lee Marcel
via groups.io wrote:
This circuit is basically an inverter with a bridged-T in the
feedback. Since it has only one variable element, the amplitude
of the peak and the BW (some say "Q") vary. Its usage is usually
reserved for applications where the tuning range is restricted.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
On Sun, May 11, 2025 at 04:21 PM, John Woodgate wrote:
I have uploaded the above as a .ZIP. According to Bob Pease, the gain at the peak should be close to 34 dB, independent of the tuned frequency.
Then he must hav ereferred to a different circuit, maybe one with two variable elements, as used in the George Massenburg parametric EQ.
I don't get either of those results using version 24.1.8.
Neither do I.
However, the bandwidth is fairly constant with frequency, as predicted.
That's not what I see. I see the BW narrowing a
I can't believe Bob Pease reported the performance in error.
|
DOH! Thanks, Mike.
On 2025-05-11 16:29, Mike Fraser wrote:
John,
Your schematic has the net "OUT" connected to the junction of
R2 and C2.
Move "OUT" to the output pin of U1.
Mike
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Thanks: that's why a search for bandpass'
failed.
On 2025-05-11 16:32, Mike Fraser wrote:
John,
The article is listed here.
.
NOTE: THE ARTICLE HAS THE TITLE WRONG.
It is a bandpass circuit.
Mike
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
On Sun, May 11, 2025 at 06:22 PM, John Woodgate wrote:
The bandwidth is constant, so the Q varies with frequency.
Ok, I understand the misunderstanding. For me BW is always relative (octave or decade)
It is interesting to regard it as a bridged-T.
Now, is really the output where it's on your schemo? I would put it at the opamp's output. There the amplitude is constant.
|
That was the undeliberated mistake.
On 2025-05-11 17:32, Jerry Lee Marcel
via groups.io wrote:
Now, is really the
output where it's on your schemo? I would put it at the opamp's
output. There the amplitude is constant.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
There is another single pot tunable band pass network called Hall’s network.
it can tune over a decade. The commercial worked example is used in the general radio model 1232a tuned amplifier/null detector. It is a different circuit than Pease’s.
Jeff Furman AD6MX
|
You should also note, John, that there are errors in the EDN
article.
The first picture shows the opamp in non-inverting configuration -
this is, of course positive feedback, and sure enough it will latch
to one of the rails.
Further down in the article, variations of the circuit are re-drawn
in the inverting configuration - this is the correct version.
It is a quirk of AC analyses that sometimes an unstable
configuration appears to be stable, when in fact it isn't. Always
check in the time domain!
I presume Bob got it right. He would never have made that mistake.
I'm surprised nobody else pointed that out.
--
Regards,
Tony
On 11/05/2025 16:20, John Woodgate via
groups.io wrote:
toggle quoted message
Show quoted text
I have uploaded the above as a .ZIP. According to
Bob Pease, the gain at the peak should be close to 34 dB,
independent of the tuned frequency. I don't get either of those
results using version 24.1.8. However, the bandwidth is fairly
constant with frequency, as predicted. I can't believe Bob Pease
reported the performance in error.
|
Figure 1 was probably drawn by an EDN person.
Bob's rough sketch is OK. I was taking the output from the wrong
place.
On 2025-05-12 08:40, Tony Casey via
groups.io wrote:
You should also note, John, that there are errors in the EDN
article.
The first picture shows the opamp in non-inverting configuration -
this is, of course positive feedback, and sure enough it will
latch to one of the rails.
Further down in the article, variations of the circuit are
re-drawn in the inverting configuration - this is the correct
version.
It is a quirk of AC analyses that sometimes an unstable
configuration appears to be stable, when in fact it isn't. Always
check in the time domain!
I presume Bob got it right. He would never have made that mistake.
I'm surprised nobody else pointed that out.
--
Regards,
Tony
On 11/05/2025 16:20, John Woodgate
via groups.io wrote:
I have uploaded the above as a .ZIP. According to
Bob Pease, the gain at the peak should be close to 34 dB,
independent of the tuned frequency. I don't get either of
those results using version 24.1.8. However, the bandwidth is
fairly constant with frequency, as predicted. I can't believe
Bob Pease reported the performance in error.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Thank you:Do you have a reference to it?
Google doesn't help, because the name has been re-used. The
Pease circuit will tune over a decade with 100:1 change in R2
value, which is just about practicable, 100 ohms/100k.
On 2025-05-12 00:21, Jeff Furman via
groups.io wrote:
There is another single pot tunable band pass network called
Hall’s network.
it can tune over a decade. The commercial worked example is
used in the general radio model 1232a tuned amplifier/null
detector. It is a different circuit than Pease’s.
Jeff Furman AD6MX
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Yes, I referred to the circuit in the book, which has the op-amp inputs wired "correctly". After reading Tony's post, I looked at the EDN article. It took me a couple minutes to ascertain that circuit topologies in the two drawings were the same (except for the op-amp connections).
The circuit as drawn in the EDN article is confusing, in my opinion.
Figure 1 was probably drawn by an EDN person.
Bob's rough sketch is OK. I was taking the output from the wrong
place.
On 2025-05-12 08:40, Tony Casey via
wrote:
You should also note, John, that there are errors in the EDN
article.
The first picture shows the opamp in non-inverting configuration -
this is, of course positive feedback, and sure enough it will
latch to one of the rails.
Further down in the article, variations of the circuit are
re-drawn in the inverting configuration - this is the correct
version.
It is a quirk of AC analyses that sometimes an unstable
configuration appears to be stable, when in fact it isn't. Always
check in the time domain!
I presume Bob got it right. He would never have made that mistake.
I'm surprised nobody else pointed that out.
--
Regards,
Tony
On 11/05/2025 16:20, John Woodgate
via wrote:
I have uploaded the above as a .ZIP. According to
Bob Pease, the gain at the peak should be close to 34 dB,
independent of the tuned frequency. I don't get either of
those results using version 24.1.8. However, the bandwidth is
fairly constant with frequency, as predicted. I can't believe
Bob Pease reported the performance in error.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
Being lazy, I searched for "another single pot tunable band pass network called Hall’s network"
Thank you:Do you have a reference to it?
Google doesn't help, because the name has been re-used. The
Pease circuit will tune over a decade with 100:1 change in R2
value, which is just about practicable, 100 ohms/100k.
On 2025-05-12 00:21, Jeff Furman via
wrote:
There is another single pot tunable band pass network called
Hall’s network.
it can tune over a decade. The commercial worked example is
used in the general radio model 1232a tuned amplifier/null
detector. It is a different circuit than Pease’s.
Jeff Furman AD6MX
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
|
John Woodgate
Roy McCammon
Tony Casey