Hallo jd, unfortunately this is the follow article from:
http://anacon-tech.com/IPdocs/JLH_LINIAC.pdf
found by:
"Liniac" by John LinsLey Hood esq.-
at last post
but the term "Super Pair" was the right keyword (thank you very much) - by the second post about weblink
Adding currents; PCM1794A in mono
was follow mentioned:
"I wonder about using Baxandall Super Pair. That's discussed in an 1988 paper by Hawksford:"
http://www.essex.ac.uk/csee/research/audio_lab/malcolmspubdocs/J10 Enhanced cascode.pdf
I. e., in this pdf article
"Reduction of Transistor Slope Impedance Dependent
Distortion in Large-Signal Amplifiers"
the term "Baxandall Super Pair" was mentioned (but I must still be found the right place)
By the way, I no longer hunt for the ideal voltage gain stage circuits for power amplifier, because for me I've already found my favorit. But I want to create a schematic overview of all the known topologies, together with the simulation results.
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High gain circuits are sometimes unstable.
I always use a none darlington transistor for the VAS stage.
The mroe gain you use the more capacitance you need to slow down the amp to stop it oscilating.
An amplifier is basically a servo system and so often has very similar problems getting the critical damping just right.
What happens is the output of the amp gets ahead of the LTP and so the output voltage overshoots with too much gain.
I always use a none darlington transistor for the VAS stage.
The mroe gain you use the more capacitance you need to slow down the amp to stop it oscilating.
An amplifier is basically a servo system and so often has very similar problems getting the critical damping just right.
What happens is the output of the amp gets ahead of the LTP and so the output voltage overshoots with too much gain.
exactly - even by perform of the simulation this overshoots in the frequency response are clearly to observe and even not easily eliminated; additional the wiring and layout so as GND management is more critical the higher the VAS voltage gain is. Therefore I prefer high open loop gain VAS stages only for power amps, that drive sub woofer loudspeaker. In this case the high values of compensating capacitances haven't audible influence by upper frequency range above 500Hz
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I don't understand the last 2 posts
the improvement in input, output impedance, gain and linearity with cascodes, buffer or super pair VAS shouldn't change Cdom for a given diff pair gm value - excepting where you’ve used inappropriate high Cob VAS Q such it was a substantial part of Cdom
likewise amplifier closed loop dynamics should be essentially unchanged, I believe the instability we’ve discussed is a local RF phenomena and can be cured without noticeable effects at typical Audio power amplifier global loop gain intercepts of < a few MHz
the higher VAS gain is only easily observed as higher low frequency open loop gain/lower intercept frequency with the Cdom curve - and possibly reduced distortion at high audio frequencies from lower open loop VAS nonlinearity
the improvement in input, output impedance, gain and linearity with cascodes, buffer or super pair VAS shouldn't change Cdom for a given diff pair gm value - excepting where you’ve used inappropriate high Cob VAS Q such it was a substantial part of Cdom
likewise amplifier closed loop dynamics should be essentially unchanged, I believe the instability we’ve discussed is a local RF phenomena and can be cured without noticeable effects at typical Audio power amplifier global loop gain intercepts of < a few MHz
the higher VAS gain is only easily observed as higher low frequency open loop gain/lower intercept frequency with the Cdom curve - and possibly reduced distortion at high audio frequencies from lower open loop VAS nonlinearity
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Boxall, Larson, Baxandall-Swallow, and Thompson Constant Current Circuits
Some Further References Related to the Boxall, Larson, Baxandall-Swallow, and Thompson Constant Current Circuits:
Earlier posts to this “Baxandall Super Pair” thread offered a chronological annotated list of references. It will be seen that this thread name actually applies to the Baxandall-Swallow constant current source (#5, below). The updated reference list below expands on this theme, with several key historical items added. As previously, some comments on the first few of the references follow. When carefully read, the comments should help in understanding this most clever circuit and the many variations.
Before any discussion, it is worthwhile noting the pros and cons of these bipolar transistor circuit developments, either as it might apply to an amplifying stage, or to a constant current source (CCS). On the pro side, there are improvements seen in the distortion of an amplifying stage, as well as an increase in the output impedance, particularly with regard to frequency. On the con side, these circuits do not address circuit linearity and/or output impedance, as they might be limited by the Early effect.
In #1 and 2, Frank S. Boxall describes a form of feedback using a compound PNP transistor connection which, upon some analysis, can be seen to have improvement properties similar to the Baxandall-Swallow circuit of 1966. Boxall's "Base Current Feedback" can also be described as a re-circulation of the transistor base current back to the emitter. It should be understood that Boxall's feedback is not a form of global feedback around an amplifier, the latter as introduced by Harold Black of Bell Labs.
Boxall's work predated Baxandall-Swallow by nearly a decade, and the context is actually more concerned with reducing distortion of low quality PNP output drivers in communications applications. In the patent document (#1), it does present some challenges to complete interpretation of the intended biasing (Fig. 5). The document includes expressions for distortion reduction and output impedance increase, as resulting from the feedback. In #2, Boxall further clarifies the biasing issues, showing AC-coupled feedback in Fig. 8, and in Fig. 9, presents a DC-coupled circuit which is functionally equivalent to that of the Baxandall-Swallow circuit (albeit of a NPN/PNP format).
The Roger Webster article, #3 within a Texas Instruments Communications handbook, summarizes Boxall's base current feedback methods, and reiterates the expressions for distortion reduction and output impedance increase. Webster references a work by Aldridge, which also addresses distortion reduction techniques.
In #4, Lester L. Larson provides an analysis of a composite PNP/NPN complementary pair as a functional high-gain NPN, with two such pairs operated differentially, or push-pull. The impedance characteristic of the output stage composite device is seen to be improved by a factor of β, the gain of the driving transistor. Larson's work was independent of Baxandall-Swallow, and was part of the development of a push-pull driver for CRT displays.
In #5, Peter J. Baxandall and E. W. Swallow discuss a single current source stage of the PNP/NPN type, having improvements similar to that of Boxall and Larson with regard to output impedance. This is in fact the seminal paper that led to this “Baxandall Super Pair” thread. In a follow-on letter, #6, Baxandall describes a key point of the Baxandall-Swallow current source: "The effect of collector-base capacitance in Trl, which shunts the output in the Fig. B circuit, is degenerated in the Fig. C circuit, and output capacitance values of well under 1 pF are obtained." This point is what allows this type of stage (Boxall, Larson, or Baxandall-Swallow) to extend the effective bandwidth of a current source. Simply stated, the output capacitance of the transistor used is effectively reduced, as seen at the collector or output node.
In #7, Jim Thompson describes an op amp with a Figure 6 NPN/PNP current source, designed to overcome the PNP IC transistor β limitations. This NPN/PNP configuration is a functional complement akin to 1/2 the Larson and to the Baxandall-Swallow setups. It was to be used many times over in other Motorola ICs of the period, in addition to discrete circuit examples within applications.
In #8, Jim Solomon offers a detailed analysis on the use of a composite complementary NPN/PNP pair ala Thompson (above), as a functional high-gain PNP pair, within the front end of what became the MC1556 IC op amp.
In #9, Tom Frederiksen describes use of the Figure 6 Thompson composite complementary pair within a high powered voltage regulator IC.
In #10 the Thompson composite complementary pair is used in Figures 9 and 10 as a current mirror employing 2N3904/3906 discrete transistors. In #11 the Thompson composite complementary pair is used in Figures 3 and 4 as a current mirror employing 2N3904/3906 discrete transistors.
In #12, Maurice Free describes the MC1595 multiplier design, which uses externally the Thompson current source scheme, within an output stage current mirror (Figs. 3 and 4).
Credits: For this July 2012 update, I am indebted to several DIYAudio friends for bringing my attention to the Boxall references. Brad Wood, Dmitri Danyuk, and Samuel Groner were all most helpful here. Brad, writing as bcarso, delineated a lot of background on tracking down the Boxall and Larson references (see also http://www.diyaudio.com/forums/solid-state/166306-origins-baxandall-super-pair.html. As per John Addis, Larson's Tektronix co-worker, Brad reports that the Larson output stage connection was internally known as the "super-alpha".
Earlier, my thanks went also to Jim Thompson for help with his MSEE thesis (#7), and to Maurice Free for help with his MSEE thesis (#12). Thanks also to an anonymous friend for providing the Larson reference, and to Ben Duncan and Morgan Jones, who also provided several references and other background information. Bob Pease has also related his independent development of this type of circuit, in #19 and 21.
Walt Jung
(Editor's note: My apologies here, but see the attachment for best formatting)
Home
Rev N6 7/4/2012
1. F. S. Boxall, “Feedback Amplifier Circuit”, US Patent 2,960,660, filed June 7, 1957, issued Nov 15, 1960.
2. F. S. Boxall, "Base Current Feedback and Feedback Compound Transistor", Semiconductor Products, Vol. 1, no. 5, pp. 17-24, September-October, 1958.
3. Roger Webster, "Transistors in Wide-band Low-Distortion Amplifiers", within Communications Handbook Part II, 1965, by Engineering Staff of Texas Instruments Incorporated; John R. Miller, Editor. Further reading: E. E. Aldridge, "Engineering Treatment of Transistor Distortion", IRE Trans. On Circuit Theory, vol. CT-9, p. 183, June, 1962.
4. L. L. Larson, “Differential Amplifier Having Common Base Output Stage of Very High Impedance”, US Patent 3,394,316, filed Jan 29, 1965, issued July 23, 1968.
5. P. J. Baxandall, E.W. Swallow, “Constant Current Source With Unusually High Internal Resistance And Good Temperature Stability,” Electronic Letters, Sept. 1966, Vol. 2, No. 9, pp. 351-352.
6. P. J. Baxandall, “Constant-Current Circuits,” Wireless World (Letters), Dec. 1966, pp.
609.
7. James Elbert Thompson, “A High Performance Operational Amplifier Utilizing Field Effect Input Devices Compatible With Integrated Circuit Fabrication Techniques”, MSEE Thesis, Arizona State University, June, 1968. See also
http://analog-innovations.com/MS_Thesis_JE_Thompson_1968.pdf
8. J. E. Solomon, “Lateral PNP-NPN Composite Monolithic Differential
Amplifier”, US Patent 3,538,449, filed Nov 22, 1968, issued Nov 3, 1970.
9. Thomas M. Frederiksen, “A Monolithic High-Power Series Voltage
Regulator,” IEEE Journal of Solid-State Circuits, Dec 1968, Vol. 3, #4, pp.
380–387.
10. Ed Renschler, “Analysis and Basic Operation of the MC1595,” Motorola
Semiconductor Products, Multiplier Series Part I, Application Note AN489,
September 1969.
11. Brent Welling and Loren Kinsey, “Using the MC1495 Multiplier in Arithmetic Operations,” Motorola Semiconductor Products, Multiplier Series Part II, Application Note AN490, September 1969.
12. Maurice George Free, “An Integrated Linear-Transconductance Analog
Multiplier”, MSEE Thesis, University of Arizona, 1970. See also “An Integrated Linear-Transconductance Analog Multiplier”, Simulation, Vol. 13, #5, November 1969, pp. 243-251.
13. “MC1594L/MC1494L Data Sheet, Figure 17,” Motorola Semiconductor
Products, October 1970.
14. Allan Grebene, section 4-5, pp. 133-136, 143-144, within Analog IC Circuit Design, Van Nostrand Reinhold, 1972, ISBN 0-442-22827-9.
15. Hans R. Camenzind, ‘Voltage-to-Current Converter’ section, pp. 266-269, within Chapter 16 ‘Linear Elements, Circuits, and Subsystems’ of Electronic Integrated Systems Design, Van Nostrand Reinhold, 1972.
16. R.C. Jaeger, “A High Output Resistance Current Source,” IEEE Journal of Solid-State Circuits, Aug 1974, Vol. 9, # 4, pp. 192–194.
17. B. Hart, “Homage To Baxandall,” Electronics World (Letters), Jan. 2003, pp. 41.
18. N. Terzopoulos, K. Hayatleh, B. Hart, F. J. Lidgey and C. McLeod, “A Novel Bipolar-Drive Circuit for Medical Applications,” Physiological Measurement Journal, Issue 5, N21-N27, October 2005.
19. Bob Pease, “What's All This PNP Stuff, Anyhow?,” Electronic Design, Sept. 11, 2008, pp. 80. See also http://electronicdesign.com/article/analog-and-mixed-signal/what-s-all-this-pnp-stuff-anyhow-19605
20. Dimitri Danyuk, “On the Optimization of Enhanced Cascode,” Preprint #7571, Presented at the 125th AES Convention, October 2–5, 2008 San Francisco, CA, USA.
21. Bob Pease, “Mailbag; letters from Walt Jung and James E. Thompson”,
Electronic Design, October 23, 2008, pp. 72. See also http://electronicdesign.com/article/power/bob-s-mailbox19868
Some Further References Related to the Boxall, Larson, Baxandall-Swallow, and Thompson Constant Current Circuits:
Earlier posts to this “Baxandall Super Pair” thread offered a chronological annotated list of references. It will be seen that this thread name actually applies to the Baxandall-Swallow constant current source (#5, below). The updated reference list below expands on this theme, with several key historical items added. As previously, some comments on the first few of the references follow. When carefully read, the comments should help in understanding this most clever circuit and the many variations.
Before any discussion, it is worthwhile noting the pros and cons of these bipolar transistor circuit developments, either as it might apply to an amplifying stage, or to a constant current source (CCS). On the pro side, there are improvements seen in the distortion of an amplifying stage, as well as an increase in the output impedance, particularly with regard to frequency. On the con side, these circuits do not address circuit linearity and/or output impedance, as they might be limited by the Early effect.
In #1 and 2, Frank S. Boxall describes a form of feedback using a compound PNP transistor connection which, upon some analysis, can be seen to have improvement properties similar to the Baxandall-Swallow circuit of 1966. Boxall's "Base Current Feedback" can also be described as a re-circulation of the transistor base current back to the emitter. It should be understood that Boxall's feedback is not a form of global feedback around an amplifier, the latter as introduced by Harold Black of Bell Labs.
Boxall's work predated Baxandall-Swallow by nearly a decade, and the context is actually more concerned with reducing distortion of low quality PNP output drivers in communications applications. In the patent document (#1), it does present some challenges to complete interpretation of the intended biasing (Fig. 5). The document includes expressions for distortion reduction and output impedance increase, as resulting from the feedback. In #2, Boxall further clarifies the biasing issues, showing AC-coupled feedback in Fig. 8, and in Fig. 9, presents a DC-coupled circuit which is functionally equivalent to that of the Baxandall-Swallow circuit (albeit of a NPN/PNP format).
The Roger Webster article, #3 within a Texas Instruments Communications handbook, summarizes Boxall's base current feedback methods, and reiterates the expressions for distortion reduction and output impedance increase. Webster references a work by Aldridge, which also addresses distortion reduction techniques.
In #4, Lester L. Larson provides an analysis of a composite PNP/NPN complementary pair as a functional high-gain NPN, with two such pairs operated differentially, or push-pull. The impedance characteristic of the output stage composite device is seen to be improved by a factor of β, the gain of the driving transistor. Larson's work was independent of Baxandall-Swallow, and was part of the development of a push-pull driver for CRT displays.
In #5, Peter J. Baxandall and E. W. Swallow discuss a single current source stage of the PNP/NPN type, having improvements similar to that of Boxall and Larson with regard to output impedance. This is in fact the seminal paper that led to this “Baxandall Super Pair” thread. In a follow-on letter, #6, Baxandall describes a key point of the Baxandall-Swallow current source: "The effect of collector-base capacitance in Trl, which shunts the output in the Fig. B circuit, is degenerated in the Fig. C circuit, and output capacitance values of well under 1 pF are obtained." This point is what allows this type of stage (Boxall, Larson, or Baxandall-Swallow) to extend the effective bandwidth of a current source. Simply stated, the output capacitance of the transistor used is effectively reduced, as seen at the collector or output node.
In #7, Jim Thompson describes an op amp with a Figure 6 NPN/PNP current source, designed to overcome the PNP IC transistor β limitations. This NPN/PNP configuration is a functional complement akin to 1/2 the Larson and to the Baxandall-Swallow setups. It was to be used many times over in other Motorola ICs of the period, in addition to discrete circuit examples within applications.
In #8, Jim Solomon offers a detailed analysis on the use of a composite complementary NPN/PNP pair ala Thompson (above), as a functional high-gain PNP pair, within the front end of what became the MC1556 IC op amp.
In #9, Tom Frederiksen describes use of the Figure 6 Thompson composite complementary pair within a high powered voltage regulator IC.
In #10 the Thompson composite complementary pair is used in Figures 9 and 10 as a current mirror employing 2N3904/3906 discrete transistors. In #11 the Thompson composite complementary pair is used in Figures 3 and 4 as a current mirror employing 2N3904/3906 discrete transistors.
In #12, Maurice Free describes the MC1595 multiplier design, which uses externally the Thompson current source scheme, within an output stage current mirror (Figs. 3 and 4).
Credits: For this July 2012 update, I am indebted to several DIYAudio friends for bringing my attention to the Boxall references. Brad Wood, Dmitri Danyuk, and Samuel Groner were all most helpful here. Brad, writing as bcarso, delineated a lot of background on tracking down the Boxall and Larson references (see also http://www.diyaudio.com/forums/solid-state/166306-origins-baxandall-super-pair.html. As per John Addis, Larson's Tektronix co-worker, Brad reports that the Larson output stage connection was internally known as the "super-alpha".
Earlier, my thanks went also to Jim Thompson for help with his MSEE thesis (#7), and to Maurice Free for help with his MSEE thesis (#12). Thanks also to an anonymous friend for providing the Larson reference, and to Ben Duncan and Morgan Jones, who also provided several references and other background information. Bob Pease has also related his independent development of this type of circuit, in #19 and 21.
Walt Jung
(Editor's note: My apologies here, but see the attachment for best formatting)
Home
Rev N6 7/4/2012
1. F. S. Boxall, “Feedback Amplifier Circuit”, US Patent 2,960,660, filed June 7, 1957, issued Nov 15, 1960.
2. F. S. Boxall, "Base Current Feedback and Feedback Compound Transistor", Semiconductor Products, Vol. 1, no. 5, pp. 17-24, September-October, 1958.
3. Roger Webster, "Transistors in Wide-band Low-Distortion Amplifiers", within Communications Handbook Part II, 1965, by Engineering Staff of Texas Instruments Incorporated; John R. Miller, Editor. Further reading: E. E. Aldridge, "Engineering Treatment of Transistor Distortion", IRE Trans. On Circuit Theory, vol. CT-9, p. 183, June, 1962.
4. L. L. Larson, “Differential Amplifier Having Common Base Output Stage of Very High Impedance”, US Patent 3,394,316, filed Jan 29, 1965, issued July 23, 1968.
5. P. J. Baxandall, E.W. Swallow, “Constant Current Source With Unusually High Internal Resistance And Good Temperature Stability,” Electronic Letters, Sept. 1966, Vol. 2, No. 9, pp. 351-352.
6. P. J. Baxandall, “Constant-Current Circuits,” Wireless World (Letters), Dec. 1966, pp.
609.
7. James Elbert Thompson, “A High Performance Operational Amplifier Utilizing Field Effect Input Devices Compatible With Integrated Circuit Fabrication Techniques”, MSEE Thesis, Arizona State University, June, 1968. See also
http://analog-innovations.com/MS_Thesis_JE_Thompson_1968.pdf
8. J. E. Solomon, “Lateral PNP-NPN Composite Monolithic Differential
Amplifier”, US Patent 3,538,449, filed Nov 22, 1968, issued Nov 3, 1970.
9. Thomas M. Frederiksen, “A Monolithic High-Power Series Voltage
Regulator,” IEEE Journal of Solid-State Circuits, Dec 1968, Vol. 3, #4, pp.
380–387.
10. Ed Renschler, “Analysis and Basic Operation of the MC1595,” Motorola
Semiconductor Products, Multiplier Series Part I, Application Note AN489,
September 1969.
11. Brent Welling and Loren Kinsey, “Using the MC1495 Multiplier in Arithmetic Operations,” Motorola Semiconductor Products, Multiplier Series Part II, Application Note AN490, September 1969.
12. Maurice George Free, “An Integrated Linear-Transconductance Analog
Multiplier”, MSEE Thesis, University of Arizona, 1970. See also “An Integrated Linear-Transconductance Analog Multiplier”, Simulation, Vol. 13, #5, November 1969, pp. 243-251.
13. “MC1594L/MC1494L Data Sheet, Figure 17,” Motorola Semiconductor
Products, October 1970.
14. Allan Grebene, section 4-5, pp. 133-136, 143-144, within Analog IC Circuit Design, Van Nostrand Reinhold, 1972, ISBN 0-442-22827-9.
15. Hans R. Camenzind, ‘Voltage-to-Current Converter’ section, pp. 266-269, within Chapter 16 ‘Linear Elements, Circuits, and Subsystems’ of Electronic Integrated Systems Design, Van Nostrand Reinhold, 1972.
16. R.C. Jaeger, “A High Output Resistance Current Source,” IEEE Journal of Solid-State Circuits, Aug 1974, Vol. 9, # 4, pp. 192–194.
17. B. Hart, “Homage To Baxandall,” Electronics World (Letters), Jan. 2003, pp. 41.
18. N. Terzopoulos, K. Hayatleh, B. Hart, F. J. Lidgey and C. McLeod, “A Novel Bipolar-Drive Circuit for Medical Applications,” Physiological Measurement Journal, Issue 5, N21-N27, October 2005.
19. Bob Pease, “What's All This PNP Stuff, Anyhow?,” Electronic Design, Sept. 11, 2008, pp. 80. See also http://electronicdesign.com/article/analog-and-mixed-signal/what-s-all-this-pnp-stuff-anyhow-19605
20. Dimitri Danyuk, “On the Optimization of Enhanced Cascode,” Preprint #7571, Presented at the 125th AES Convention, October 2–5, 2008 San Francisco, CA, USA.
21. Bob Pease, “Mailbag; letters from Walt Jung and James E. Thompson”,
Electronic Design, October 23, 2008, pp. 72. See also http://electronicdesign.com/article/power/bob-s-mailbox19868
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Walt, wow what a comprehensive post! I really must say thanks for the renewed effort you seem to be putting in around the forum lately! Its content and interaction like this that makes this forum so rich. I wish I could compose something more meaningful, but its 3.20am here at the moment and i'm off to bed. I couldnt help but comment.
thankyou!
just read the references, thank you all! bcarso in particular, i'll bury myself in the content over the next weeks,
thankyou!
just read the references, thank you all! bcarso in particular, i'll bury myself in the content over the next weeks,
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That's kind of you Bob, but I had some great help.
Beyond this, there is an even more promising topic, and, I hope in time, another topic and thread. Right now, a break.
Best regards,
Walt
and a well deserved one at that! too right its enough to immerse myself in, such an incredible amount of well focused and topical references; broad enough to show wide/differed application and opinion, but focused enough to not be overwhelming or muddied.WaltJ said:
where to start... at the beginning I guess.. thanks again!
More than a mere 2c, I'd say, Edmond! Will take some study to digest, for sure.
I took a real quick look, and may come back later with some questions. But it surely looks like you are mining the fruits of Baxandall-Swallow.
Walt
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Edmond, see in particular the WJ-provided Dimitri Danyuk reference along these lines. Yes, Boxall et al. works particularly well when sourced from a relatively high-Z source.
Brad
Hi Walt,
If time permits, you also might have a look at my website for more information about the 'Super TIS'.
Cheers,
Edmond.
Hi Brad,
I did read his article on this subject (it's also listed on my website) and he advices me with his broad experience in the development of my new amp.
Thanks for the hint anyhow.
Cheers,
Edmond.
The website article is nice. Have you built any of this yet?
What is that simulator by the way? Is there an option to make the connection dots larger, or of a more distinctive shade? Although I have full color vision I fear that red-green colorblind people will have a rather difficult time.
Cheers,
Brad
Thank you Brad.
Not yet. I'm busy with the translation of the simulation schematic to a PCB schematic and package definitions. When this is finished I'm finally ready for the PCB artwork itself.
MicroCap
I can't make them larger without enlarging the whole schematic, though I can give them another color. Next time I'll make them black, or, even better, using two point connections, as shown below.
Cheers,
E.
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