1. NTPC to build India’s biggest solar park in Gujarat
India’s National Thermal Power Corporation Limited (NTPC) plans to set up a 5-gigawatt solar park in the western state of Gujarat, which would be the biggest in the country.
As the top electricity generator shifts toward cleaner energy, which is expected to cost as much as 250 billion rupees ($3.5 billion) and begin operations by 2024.
The plan is part of NTPC's aim to reduce the share of fossil fuels in the energy mix to 70% from around 96% by 2032.
Static/Current Takeaways Important For RRB NTPC/IBPS RRB Mains:
Chairman and Managing Director of NTPC: Gurdeep Singh.
Headquarters of NTPC: New Delhi.
State News
2. Delhi CM Arvind Kejriwal launched ‘champions campaign’ against dengue
Chief Minister Arvind Kejriwal launched “Champions Campaign” to fight dengue and urged citizens to become ‘champions’ and encourage 10 friends to check their homes for mosquito larvae. Earlier, he had also launched 10Hafte 10Baje 10Minute campaign.
He had urged the Delhi residents to give 10 minutes every Sunday to check the surroundings to prevent the breeding of dengue-carrier mosquitoes.
Static/Current Takeaways Important For RRB NTPC/IBPS RRB Mains:
Lt. Governor of Delhi: Anil Baijal.
Appointment
3. IDBI Bank appoints Samuel Joseph as Deputy Managing Director
IDBI Bank's Board of Directors has approved the appointment of Samuel Joseph Jebaraj as Deputy Managing Director (DMD) for a period of 3 years.
He currently serves as Chief General Manager of the Loan Administration and Human Resources Management Groups of the Bank.
The decision has been taken as per the approval received by the Reserve Bank of India (RBI). This is the first major appointment on the Bank’s Board, in which LIC acquired a majority stake of 51 per cent in January 2019.
Static/Current Takeaways Important For IBPS RRB Main 2019:
Chairman of IDBI: M R Kumar.
Headquarters of IDBI: Mumbai; Tagline: Aao Sochein Bada.
Agreements
4. DSCI, MeitY and Google India join hands for 'Digital Payment Abhiyan'
Nasscom's Data Security Council of India (DSCI) collaborated with the electronics and IT ministry (MeitY) and Google India to launch a nationwide awareness campaign 'Digital Payment Abhiyan'.
Communications and Electronics & IT Minister launched the campaign that will educate end-users on the benefits of making digital payments and urge them to adopt security and safety best practices.
The campaign was launched at the Google for India event. To drive the campaign objectives and amplify outreach to users across all states, DSCI has onboarded various digital payments, ecosystem partners.
These partners include representation from banking, card networks as well as a fin-tech segment.
Static/Current Takeaways Important For IBPS RRB Main 2019:
Minister of Communications and Electronics and Information Technology.: Ravi Shankar Prasad.
Chairman of NASSCOM: Keshav Murugesh.
Awards
5. 20th Edition of IIFA Awards 2019
The 20th Edition of NEXA International Indian Film Academy Awards (IIFA Awards) for 2019 was held at Sardar Vallabhbhai Patel Indoor Stadium, Mumbai, Maharashtra.
Here’s the complete list of winers:
S. No.
Category
Winners
1.
Best Film
Raazi
2.
Best Actor in a leading role (Female)
Alia Bhatt (Raazi)
3.
Best Actor in a leading role (Male)
Ranveer Singh (Padmaavat)
Check Complete list of IIFA Awards 2019...Click Here
Sports
6. Bajrang Punia won bronze medal at World Wrestling Championships
Bajrang Punia won a bronze medal at the 2019 World Wrestling Championships in Nur-Sultan, Kazakhstan.
He defeated Mongolia's Tulga Tumur Ochir 8-7 to clinch the medal in the 65 kg weight category.
This is Bajrang's second consecutive World Championship medal after his silver at Budapest 2018. This is also his third medal at the senior World's with his first coming in 2013.
Books and Authors
7. A new book titled “Being Gandhi” by Paro Anand to mark Gandhi's 150th birth anniversary
A new book titled “Being Gandhi” written by award-winning author Paro Anand released. It marks the 150th anniversary of Mahatma Gandhi. The book, published by Harper Collins Children’s Books, explores the life events of Gandhiji.
Obituaries
8. Former Dutch football player Fernando Ricksen passes away
The former Rangers and Netherlands football player Fernando Ricksen passed away at the age of 43. He earned 12 caps for the Netherlands between 2000 and 2003. In six years (2000-2006) with the club of Rangers (Glasgow, Scotland), he also won 2 Scottish Premier League titles, 2 Scottish Cups and 3 Scottish League Cups.
9. Famous filmmaker Shyam Ramsay passes away
Bollywood’s famous horror film producer Shyam Ramsay passed away. He helmed horror movies like Andhera (1975), Saboot (1980), Purana Mandir (1984), Purani Haveli (1989), Dhund: The Fog (2003), Koi Hai (2017). He pioneered the horror genre on Indian television too, giving us the first horror series- The Zee Horror Show which ran from 1993 to 2001.
Important Days
10. International Day of Peace 21 September
Each year the International Day of Peace is observed around the world on 21 September.
The General Assembly has declared this as a day devoted to strengthening the ideals of peace, both within and among all nations and peoples.
The theme for International Day of Peace 2019 is "Climate Action for Peace". The theme draws attention to the importance of combatting climate change as a way to protect and promote peace throughout the world.
Static/Current Takeaways Important For IBPS RRB Main 2019:
Antonio Guterres is the Secretary-General of the United Nations.
The UN Headquarters in New York, United States.
Miscellaneous
11. 16th Session of the Joint Economic Commission between India-BLEU
The 16th Session of the Joint Economic Commission (JEC) between India and Belgium Luxembourg Economic Union (BLEU) was held in New Delhi.
The Joint Economic Commission between India and Belgium Luxembourg Economic Union (India-BLEU) was established in 1997 and is the main vehicle for discussing bilateral economic and commercial issues.
The importance of JEC between India and BLEU was reiterated & both sides negotiate cooperation on a wide range of issues of mutual interest, such as, transportation and logistics, renewable energy, aerospace and satellites, audio and visual industry, agro and food processing industry, life sciences, ICT(Information and communications technology), traditional medicine, Ayurveda and yoga, and tourism.
Static/Current Takeaways Important For RRB NTPC/IBPS RRB Mains:
Google has announced that it will open an artificial intelligence (AI) based research lab "Google Research India".
The lab will be opened in Bengaluru. The Indian AI lab will be led by Dr. Manish Gupta, a renowned computer scientist in the country.
Google has various AI research labs across the world, under its Google Artificial Intelligence arm.
Static/Current Takeaways Important For IBPS RRBClerk Mains:
Chief Executive Officer of Google: Sundar Pichai.
2. India's first central police university to come up in Greater Noida
The country’s first central police university will be set up by the Union home ministry off the Yamuna Expressway in Greater Noida.
The Centre had given in-principle approval for the university and a 100-acre plot has been identified in Sector Techzone.
The government wants to set up an institution to tackle modern-day policing challenges. The national university for policing will help in improving police personnel training, skills, research and also policymaking with regard to policing in India.
Static/Current Takeaways Important For IBPS RRB Main 2019:
3. Union HRD Minister Ramesh Pokhriyal ‘Nishank launches WAWE Summit 2019
Human Resource Development Minister Ramesh Pokhriyal 'Nishank' has launched Waste Management Accelerator for Aspiring Women Entrepreneurs (WAWE) summit.
It will be jointly organized by All India Council for Technical Education (AICTE) and Institute of Waste Management (IIWM) at Jaipur.
This initiative stating that it will empower women and encourage entrepreneurship among youngsters. WAWE Summit 2019 is a great initiative for women who have skills in their hands and it will further empower and motivate them.
4. Telecom body approves Rs 8500 crore for mobile towers & optical fibres
The Digital Communication Commission, the highest decision making body in the Department of Telecom has approved multiple projects worth over Rs 8,500 crore.
The projects aims to set up mobile towers and laying of optical fibre, with an aim to provide improved connectivity. The commission also approved a special scheme to cover upto 12,000 uncovered villages in aspirational districts.
The approved infra projects include laying of BharatNet fibre in Tamil Nadu and Telangana, at an estimated cost of Rs 1,815 crore and Rs 2,065 crore. The projects also includes setting up of 1,917 mobile towers for uncovered villages in the North East.
Appointment
5. RKS Bhadauria is new IAF Chief
The central Government has appointed Vice Chief of the Indian Air Force (IAF) Air Marshal RKS Bhadauria as the next Chief of Air Staff (CAS). He will take over on 30th September.
He will have a two-year tenure. Mr. Bhadauria had played a key role in the negotiations for the deal with France for 36 Rafale jets.
Present IAF Chief and Chairman of the Chiefs of Staff Committee Air Chief Marshal B.S. Dhanoa is set to retire on September 30.
Mr. Bhadauria also served as the Air Officer Commanding-in-Chief of Southern Air Command and, prior to the present appointment, he was the Air Officer Commanding-in-Chief of Training Command.
Important Takeaways for IBPS RRB PO/Clerk Mains 2019:
The Indian Air Force is the air arm of the Indian Armed Forces.
Indian Air Force was founded on 08th October 1932.
Headquarters of IAF is in New Delhi.
Agreements
6. Ola drivers to get healthcare benefits under Ayushman Bharat
Ayushman Bharat Pradhan Mantri Jan Arogya Yojana (AB-PMJAY) has partnered with Ola, a mobility platform, to extend the welfare to its drivers.
The partnership will provide comprehensive health insurance for secondary and tertiary care to tens of thousands of drivers working with the cab aggregator and their families.
The first phase will see Ola and AB-PMJAY conducting a pilot project in NCR, which will subsequently be rolled out at scale to other cities. Eligible drivers as well as Ola employees will be able to avail the benefits of the programme and obtain an Ayushman Bharat card at a minimal cost of Rs 30.
Static/Current Takeaways Important For IBPS RRBPO Mains:
Co-Founder and CEO of Ola: Bhavish Aggarwal.
7. Tata Communications partners with Cisco
Tata Communications has partnered with Cisco to offer enterprises a secure, fully-managed, multi-channel, intelligent and cloud-based Cisco Webex Contact Center solution.
This joint offering is an end-to-end managed solution and gives contact centre users a seamless user experience across up to 150 countries on the back of Tata Communications’ global network.
The solution will allow for simplified licensing; pre-deployed hardware and software with integrations to workforce optimisation.
8. Skill India sign agreement with IBM for Train-the-Trainer programme in AI
The Directorate General of Training (DGT), under the skill development and entrepreneurship ministry, has signed an agreement with IT major IBM to carry out a nationwide Train-the-Trainer programme in basic artificial intelligence.
As part of the programme, ITI trainers will be trained on basic artificial intelligence (AI) skills towards using technology in their day-to-day training activities.
This programme aims at enabling the trainers with the basic approach, workflow and application of artificial intelligence that they can apply in their training modules.
Static/Current Takeaways Important For RRB NTPC/IBPS RRB Mains:
Founder of IBM: Charles Ranlett Flint; Established: June 16, 1911.
Union Minister of Skill Development and Entrepreneurship: Mahendra Nath Pandey.
Banking
9. Public Sector Banks to organise 'loan melas' in 400 districts
Finance Minister Nirmala Sitharaman has announced that Public Sector Banks will organise 'loan melas' or "Shamiana meetings" in 400 districts.
The meetings will be organised to provide loans to NBFCs and retail borrowers, including homebuyers and farmers.
PSBs will focus on giving loans to the 'RAM' category: retail, agriculture and MSMEs. The open house public meetings will be held in two tranches.
The first will be held between October 3 and 7 in 200 districts, while the remaining 200 will be covered October 11 onwards.
She also announced that no MSME stressed loan would be classified as an NPA until March 31, 2020.
10. Airtel Payments Bank launches 'Bharosa' savings account
Airtel Payments Bank launched "Bharosa savings account" services, designed for deepening the financial inclusion in the country. This service enables customers to withdraw cash, check their balance or access a mini statement of their account at over 6,50,000 Aadhaar-enabled payment system (AePS) enabled outlets across India.
Bharosa savings account would offer Rs 5 lakh personal accident insurance on maintaining the balance of Rs 500 along with one debit transaction per month. Customers would also be eligible for cashback, if they decided to receive government subsidies in their Bharosa account or if they made cash deposits in it.
Static/Current Takeaways Important For RRB NTPC/IBPS RRB Mains:
MD & CEO of Airtel Payments Bank: Anubrata Biswas.
Headquarters of Airtel Payments Bank: New Delhi.
11. Wipro Consumer Care and Lighting sets up startup venture fund
Wipro Consumer Care and Lighting has launched "Wipro Consumer Care–Ventures", a startup venture fund to invest in startups in the consumer brands space.
The venture will focus on companies with a differentiated approach where both parties can learn by leveraging their strengths and add value to each other.
Wipro Consumer Care & Lighting is a $1 billion plus arm of Wipro Enterprises, and is among the fastest growing fast moving consumer goods (FMCG) businesses in India.
Awards
12. National Geoscience Awards 2018
Twenty-two scientists across the country were awarded the National Geoscience Awards for the year 2018.
They were awarded for their outstanding contributions in the field of geosciences, mining and allied areas.
The award was conferred by the Minister of Parliamentary Affairs, Coal and Mines, Shri Pralhad Joshi.
Prof. Syed Wajih Ahmad Naqvi, Council of Scientific and Industrial Research (CSIR), received the Award for Excellence for his significant global contributions in the field of aquatic biogeochemical research.
Dr Sohini Ganguly, of Goa University, was conferred with the Young Scientist Award-2018 for her significant work in the fields of petrology, volcanology and geochemistry.
The National Geoscience Awards were given in ten disciplines covering Mineral exploration, Groundwater exploration, Mining technology, Mineral beneficiation, Sustainable mineral development, Basic and applied geosciences, Geo-environmental studies and Natural hazards investigation.
Defence
13. Indian army conducts exercise ‘Chang Thang’ in Eastern Ladakh
The Indian Army conducted a massive rare exercise ‘Chang Thang’ in Eastern Ladakh bordering China.
The exercise involved the use of infantry, mechanised forces, T-72 tanks, with force multipliers such as artillery guns and Unmanned Aerial Vehicles.
The Indian Air Force was also roped in the exercise. This is the first time such kind of exercise has happened in the region.
Static/Current Takeaways Important For IBPS RRBPO Mains:
Chief of the Army Staff: General Bipin Rawat.
Sports
14. Sri Lankan bowler Akila Dananjaya banned from bowling for 1 year
The International Cricket Council has banned Sri Lankan off-spinner Akila Dananjaya from bowling in international matches for 1 year.
The ban was imposed after his bowling action was found to be illegal after. He will be entitled to approach the ICC for a re-assessment of his bowling action after the expiry of this one-year period.
The umpires questioned his bowling action in the first Test against New Zealand at Galle, held in August 2019.
Static/Current Takeaways Important For IBPS RRBClerk Mains:
ICC Chairman: Shashank Manohar; Headquarters: Dubai, United Arab Emirates.
The 13th edition of ICC Cricket World Cup will be held in India from February 9 to March 26, 2023.
15. India Slip to 104th spot in Latest FIFA ranking
The Indian football team slipped a place to 104th position in the latest FIFA rankings released.
Indian Football Team in recent times playing under the leadership of new coach Igor Stimac.
Belgium managed to hold on to the top position, while France has surpassed Brazil to reach the second spot.
Static/Current Takeaways Important For IBPS RRB Main 2019:
President of FIFA: Gianni Infantino; Headquarters of FIFA: Zurich, Switzerland.
Books and Authors
16. The book titled “The Cousins Thackeray: Uddhav, Raj and the Shadow of their Senas” released
The book titled “The Cousins Thackeray: Uddhav, Raj and the Shadow of their Senas” written by the journalist Dhaval Kulkarni was released. It is published by Penguin Random House.
The book depicts the political journey of Shiv Sena president Uddhav Thackeray and Maharashtra Navnirman Sena (MNS) chief Raj Thackeray.
Obituaries
17. Tunisia's former President Zine el-Abidine Ben Ali passes away
Tunisia's former President Zine el-Abidine Ben Ali passed away. He came to power in 1987, ousting Habib Bourguiba to become Tunisia's second-ever president. Ben Ali led the country for 23 years and was credited with delivering stability and some economic prosperity.
Static/Current Takeaways Important For IBPS RRBPO Mains:
Capital of Tunisia: Tunis; Currency of Tunisia: Tunisian Dinar.
Important Days
18. World Bamboo Day : September 18
World Bamboo Day is observed every year on the 18th of September by the World Bamboo Organization to generate awareness about conserving and promoting the bamboo industry.
Bamboo is known as poor man’s timber, bamboo is omnipresent in tribal cultures and community living.
India is the world’s second-largest cultivator of bamboo after China, with 136 species and 23 genera spread over 13.96 million hectares, according to the State of Environment report 2018.
Static/Current Takeaways Important For RRB NTPC/IBPS RRB Mains:
President of World Bamboo Organization: Michel Abadie.
CEO of World Bamboo Organization: Susanne Lucas.
Miscellaneous
19. First Jammu International Film Festival to be held in Jammu
The first ever "Jammu International Film Festival" will be held in Jammu.
37 short films and documentaries from 11 countries will be screened at the inaugural edition of Jammu International Film Festival.
The festival will also present an annual 'Inspiring Icon Award', which will be given to a person, who hails from the region and has made it big in the film industry.
20. Telangana to celebrate 2020 as Year of AI
The Telangana government has decided to declare 2020 as Artificial Intelligence year by organising various activities related to the emerging technology.
A lot of hackathons and meetings will happen and the government agencies will give challenges and make available data sets on which you (companies) can run algorithms.
Static/Current Takeaways Important For RRB NTPC/IBPS RRB Main 2019:
CM of Telangana: K Chandrashekhar Rao; Capital of Telangana: Hyderabad.
Governor of Telangana: Tamilisai Soundararajan.
21. Thaawarchand Gehlot launches MIS portal under Accessible India Campaign
Union Minister for Social Justice and Empowerment Thaawarchand Gehlot launched the (Management Information System) MIS portal in New Delhi.
The MIS has been developed by the Department of Empowerment of Persons with Disabilities (DEPwD) under the Ministry of Social Justice and Empowerment. The portal is made fully accessible for Divyangjans.
The MIS portal will bring all the nodal ministries and States and Union Territories on a single platform for monitoring the progress being made against each target of Accessible India Campaign.
The portal will be useful in maintaining all the function on the digital platform and capture data on a real-time basis.
Throughout the years, Erno Borbely published several project and design articles in Audio Amateur publications (Audio Electronics, Glass Audio, Speaker Builder and audioXpress),
always focusing on the lowest possible noise, best inherent linearity,
and DC coupling. “Of course, all of this should always go hand in hand
with the overall objective in audio: good sound,” as Borbely explained.
The basic circuits on which Erno Borbely based most of his projects are
described in “JFETs: The New Frontiers, Part I and II,” published in Audio Electronics AE 5/99 and 6/99, and “All-FET Line Amp,” published in audioXpress
May 2002. Referring to these articles frequently, the author admits,
these were the “building blocks” on which many - if not all - of his
amplifiers are based. This articles continues his JFETs series and shows
how you can best take advantage of JFET performance.
Figure 12A: Basic differential amplifier with JFETs.
In Part 1 of this article, I discussed the single-stage (or
single-ended) amplifier operating in common-source mode. As these stages
are usually limited in audio to AC signals, the inherent DC drift is of
relatively little importance. You can even use them for DC signals if
you select the working point carefully at zero temperature coefficient.
However, if you remember the formula for zero tempco (VGS = VP + 0.63V), you realize that the condition is different from unit to unit, since VP is different.
A better solution is to use a differential amplifier, where the drifts
of two matched JFETs tend to cancel each other. The configuration is
shown in Fig. 12a. If R0 is large enough, then:
ID1 + ID2 = I0.
Further, if ID1 changes ΔID1, then ID2 also changes by the same amount, but in the opposite direction, i.e.,
ΔID1 = −ΔID2
The differential gain of the stage is:
AV(DD) = (VD1 − VD2)/(VGS1 − VGS2) = RD × gm
which is the same as the gain of a single common-source stage. For R0 to be very large, −VS
must also be very large. This is usually inconvenient, so instead of a
resistor, you use a so-called constant-current source, which delivers I0 independent of −VS (Fig. 12b).
Figure 12B: Improved differential amplifier with constant-current source.
Figure 13: The differential amplifier represented with two symmetrically arranged “half-circuits.”
Due to its symmetrical nature, you can also consider the differential
amplifier as two symmetrically arranged “half-circuits,” each with a
JFET, a load resistor, and half of a current source, providing I0/2.
(1) This is shown in Fig. 13. If the two JFETs are “identical,” then
you can join the two half-circuits together at the sources without
upsetting the DC operation. However, you now have balanced single-ended
amplifiers.(2)
Seen from gate 1, JFET 1 operates as a common-source amplifier, except
that the source is connected to the source of JFET 2, operating it with
source input. Seen from gate 2, the same thing happens - JFET 2 is in
common-source mode, driving JFET 1 in the source. There are a number of
advantages to operating two JFETs in this way, and I will start here
with the common-mode rejection.
Common-Mode Signals
A very important feature of the differential amplifier is its ability to
reject common-mode signals. Common mode means that both gates are
driven with the same polarity and equal amplitude signals. It is easy to
see that if only gate 1 is driven positive, then ID1 increases and ID2 decreases. But if both gates are driven positive, then both ID1 and ID2 must increase, which is impossible because ID1 + ID2 = I0; i.e., I0 is constant. Consequently, the differential amplifier cannot amplify same-polarity or common-mode signals.
Just how good it is in rejecting common-mode signals is expressed with the common-mode gain:
AV(CM) = −RD/2r0
where r0 is the output impedance of the constant-current
source. In order to have low common-mode gain (i.e., good rejection),
the output impedance of the current source must be very large.
The importance of low common-mode gain is closely related to the temperature drift, because changes in ID, VGS, and gm
can be considered common-mode signals if they are the same for both
JFETs. Normally, a common-mode rejection ratio (CMRR) is specified for
the differential amplifier. It is the ratio between the differential
gain and the common-mode gain:
CMRR = AV(DD)/AV(CM) ≈ 2gm × r0.
Obviously the two JFETs must be closely matched to achieve good
common-mode rejection. In fact, these two formulas are valid only if the
two JFETs are perfectly matched. Although it is possible to select
well-matched JFETs, the easier way is to use dual JFETs matched by the
manufacturer, or even better, dual JFETs manufactured on the same
silicon chip, i.e., monolithic duals.
I have been using the NPD 5566 dual N-channel and the AH 5020CJ dual
Pchannel JFETs.3 However, these are not truly complementary types, as I
pointed out in my article.(3) The first complementar y types on the
market were the 2SK240/2SJ74 medium gm and the 2SK146/2SJ73 high gm/low-noise
types. These are closely matched single devices, mounted in a common
aluminum case for good thermal tracking. Unfortunately, these devices
are no longer in production.
Figure 14A: A practical differential amplifier with the 2SK389V dual monolithic JFET.
Figure 14B: The cascode connection reduces the input capacitance.
Dual Monolithic JFETs
Although there are plenty of N-channel dual JFETs on the market,
complementary dual monolithic JFETs are rare. In fact, I know of only
one family, the 2SK389/2SJ109, made by Toshiba. These are still
manufactured and available, so I use them in all my amps with
differential input. Now I’ll describe some practical differential
circuits.
Figure 14a shows a simple differential amplifier with the 2SK389 dual
monolithic JFET from IDSS group V. I hooked it up with ±36V to operate
the JFETs under conditions similar to those of the SE ones. The
constant-current source is a J511 JFET delivering 4.7mA. In order to run
the drains at roughly one-half the supply voltage (about 18V), I chose RD1 = RD2 =10k.
First I tested the amplifier in single ended mode, i.e., gate 2 connected to ground, with the measurements taken at VD2. (VD2 has the same phase as VGS1.)
Although from the operational point of view it is single-ended, I think
this mode is more appropriately called the unbalanced mode. Gain
without local feedback (RS1 = RS2 = 0) is about 64
times, which is 36dB. Frequency response is 175kHz, and the input
capacitance is 330pF. THD, measured at 1kHz, is shown in column 1 of
Table 2.
Next I inserted source resistors RS1 = RS2 = 100R,
and reran the measurements. Due to the local feedback, the gain dropped
to approximately 28 times, and the input capacitance to 160pF. The THD
also decreased by about 6dB.
In order to reduce the input capacitance further, I put 2SK246 cascodes
in the circuit (Fig. 14b). The gain did not change significantly, but
the input capacitance dropped to 50pF! THD also decreased, as shown in
column 2, Table 2.
Figure 15A: Basic JFET source-follower circuits.
Figure 15B: Basic JFET source-follower circuits.
Figure 15C: Basic JFET source-follower circuits.
Balanced Mode
A couple of comments are in order concerning this circuit. According to
the measurements, it is a very decent design, considering that it uses
only a very small amount of local feedback. The gain is still fairly
high, and you can reduce it further by increasing the source resistors,
which in turn further reduces the THD. However, to fully take advantage
of the symmetrical nature of this circuit, you should use it in balanced
mode, which requires applying a balanced signal at the two gates and
taking the balanced signal from the two drains.
I have made some rudimentary THD measurements in balanced mode, shown in
column 3 of Table 2. Unfortunately, my oscillator and THD analyzer
(HP339A) are unbalanced, so I needed to improvise the balanced operation
with op amps, limiting the measurements to the levels shown in the
table (lower levels were masked by noise).
Nevertheless, it clearly indicates that the circuit thrives in balanced
mode, having 10–20dB less THD compared to unbalanced mode. It also
indicates the advantages of this circuit relative to the SE circuits
discussed in Part 1.
The SE purists might naturally say that this is due to the cancellation
of evenorder harmonics in the balanced circuits, which is true. But as
Nelson Pass points out on his homepage, in comparison to the SE stages,
the balanced circuit does not give rise to odd-order distortion. There
is simply not much distortion left in the balanced circuit.
As mentioned in Part 1, the input capacitance is voltage-dependent,
which can cause THD when the amplifier is driven from high source
impedances. I have tested the circuit described in column 2 of Table 2
with 50k, 100k, and 500k sources. There was no measurable change in
distortion up to 100k, but at 500k, I could see a slight increase.
Again, for noise reasons, you should probably keep the source impedance
below 50k, so there is no problem with the capacitance modulation
anyway. I also checked the CMRR by connecting the two gates together and
driving them with a 3V RMS signal. The output, again in balanced mode,
was down 87dB at 1kHz. The CMRR dropped to 70dB at 10kHz and 63.5dB at
20kHz, but even at 100kHz, it was 50dB!
Caption
The Output
I have now described two types of amplifier stages using JFETs, the
common source or single-ended stage, and the differential or balanced
amplifier. You can use either of these to build audio amplifiers,
depending on your preference for balanced or unbalanced operation.
Personally, I prefer the differential circuit, because you can use it
with balanced or unbalanced sources, and it can also feed balanced or
unbalanced power amplifiers. Balanced operation gives a subjective
impression of increased dynamics. It can also be an extremely useful
interfacing consideration in breaking up ground loops.(4)
There are two issues to consider when talking about the SE and balanced
amplifiers. First of all, the output does not sit at 0V DC, but at some
10–20V above ground. If you wish to connect it to, say, a DC-coupled
power amplifier, you must block this DC voltage from reaching the
power-amp input. This is easily done using a capacitor, and this problem
is well known to all SE fans, whether of tube or semiconductor variety.
I will therefore not spend much time on the subject.
A much more important question is whether these circuits can drive the
input impedance of a power amplifier. The output impedance of the amps
examined is basically equal to the drain resistor of the amplifier. If RD
= 10k, then the output impedance is also close to 10k. But if the input
impedance of the power amp is also 10k, then you are certainly in
trouble. First, you lose 6dB of gain by the voltage division between the
10k resistors; second, the 10k input will most likely load the output
and cause a lot of THD. Even with 20k or 50k input impedance, you might
run into problems. It is advisable to put an impedance transformer at
the output to avoid this. Source followers to the rescue!
Figure 16A: These source-follower circuits can drive low-impedance loads with very low THD.
Figure 16B: These source-follower circuits can drive low-impedance loads with very low THD.
JFETs as Followers
Just like tubes and bipolar transistors, JFETs can also be operated as
followers, more specifically source followers. The basic circuit is
shown in Fig. 15a. The drain is AC-grounded, and the output signal is
taken out across the source resistor, which means it operates with 100%
local feedback. The gain of the source follower is:
AV = gm × RS/(1 + gm × RS)
Two things become obvious from the formula: first, the source follower
does not reverse the phase of the signal, and second, if gm × RS
>> 1, then the gain becomes approximately unity. In order to make
RS large, you can use a constant-current source with high output
impedance (Fig. 15b). The linearity is also dependent on RS (see the
1kHz THD measurements in columns 1 and 2 of Table 3).
The circuits in 15a and b have a DC offset voltage at the output—the
gatesource voltage at the given drain current. For the JFETs I used in
the test setup, I measured a 0.2V offset. If you need zero DC output,
you can use the circuit in Fig. 15c. Here the constant-current source is
made with the same type of JFET as the follower.
If the two JFETs are matched and the two source resistors are equal,
then the DC offset will be very small. With two matched K170BLs, I
measured less than 1mV offset. (It would probably be even lower if you
used here a dual monolithic JFET like the K389BL/V.) DC drifts tend to
cancel out as well, because of the matched devices. The circuit also has
very low THD (see column 3 of Table 3).
Figure 17: The all-JFET balanced SE line amp.
Follower Feature
One of the most important features of a follower is its ability to drive
low-impedance loads. I checked all three circuits with 1k and 10k loads
at 3V RMS output. With 1k they measured 1%, 1.7%, and 0.23%,
respectively. Although its output impedance is actually higher than the
circuits in Figs. 15a and b, that in 15c is better in driving
low-impedance loads. With a 10k load, the circuits in 15b and 15c didn’t
have many problems. THD was 0.004 and 0.0022%.
My choices of source followers are shown in Fig. 16. The circuit in 16a
is a JFET version of the tube White cathode follower. (5) Basically,
the circuit is an extension of Fig. 15c, in that the follower is fed
with a constant-current source, but in addition the drain current of the
current source is modulated by the AC signal. When the output signal
goes positive, the tail current decreases, and when it goes negative,
the current increases. The result is a significant reduction of the
output impedance and an apparent increase in drive capability.
Power Dissipation
John Curl used the complementary JFET source follower shown in Fig. 16b
in the JC-2 phono-preamp module. (6) The JFETs work in Class A as long
as the peak load current is less than twice the bias current. After
that, the circuit works in Class AB. I usually let the two matched
devices work at IDSS, to maintain as much Class A headroom as possible.
However, you must watch the power dissipation. If IDSS is such that the
power dissipation is more than the maximum allowed, then you need to
insert a source resistor to reduce the drain current or select a device
with lower IDSS.
I also tested the source followers for THD caused by the
voltage-dependence of the input capacitance. Since the voltage excursion
is much larger at the input because of the unity gain, the circuits are
also more susceptible to the distortion. There is no significant
increase up to a 10k source; however, at 50k the THD is increasing by an
order of magnitude. Normally this is no problem, because the source
impedance is usually very low. However, in certain applications such as
filters, this can cause distortion.
Of course, using any of these sourcefollower buffer circuits with the SE
and differential amplifiers discussed previously solves only one of the
problems stated at the start of this section—the drive-capability
problem. The DC voltage is still there. Given the topology of these
circuits, you must use a capacitor at the output to block the DC
voltage. Naturally, you can also solve this problem by using
level-shifting circuits, but it requires a bit more circuit design. For
now, I’ll look at an all-JFET balanced/SE all-FET line amp, using the
circuits already developed.
The Balanced/SE All-JFET Line Amp
The schematic shown in Fig. 17 consists of the differential amplifier
Q1/Q2, cascoded with Q3/Q4, and the output buffers Q5/Q6 and Q7/Q8. The
differential amplifier uses a dual monolithic K389V JFET. Each JFET
operates at just over 2mA, this current supplied by the J511
constant-current source. The 330R source resistors provide local
feedback and control the gain of the differential amplifier. The trimpot
P1 cancels out small imbalances between the two JFETs, but it is
normally unnecessary with monolithic duals, and you can leave it out.
The Cascode FETs are K246BLs. The output buffers are those I developed
from the tube White Cathode Follower, shown in Fig. 16a (“modestly”
called the “Borbely” source followers here). The supply voltage is ±36V.
Of course, you can make the negative supply much less than 36V; the
constant-current source requires only a couple of volts for proper
operation. I made them both 36V to be able to try other configurations.
The output caps must be of highest quality in order to preserve the
outstand-ing sound quality of this simple circuit. If you are likely to
drive loads down to 1k, then the caps must be a minimum of 10μF. If you
are driving normal 10k or higher loads, you can get away with a 1μF or
2.2μF cap. I tried the Hovland Musicaps, which are rather neutral, but
there are plenty of good caps on the market you can try.
Normal oil caps are not for this circuit; they destroy the excellent
resolution to a “nice” blurred mish-mash. (Don’t get the idea that I
don’t like oil caps; I use them in some of my amps.) I would have liked
to try some silver-foil caps, but, alas, the prices are more ridiculous
than the cable prices, and I refuse to play that game. (If anyone knows
of a reasonably priced silver-foil cap, please let me know.)
You can use the line amp with unbalanced or balanced sources, and you
can feed power amps with balanced or unbalanced inputs. However, you
should really take advantage of its superior performance in balanced
operation, as I mentioned before. Should you use it with unbalanced
sources, then you must short the –INP to ground. And in the unlikely
event that you don’t wish to take advantage of the balanced outputs, you
can leave out the circuit around Q5/Q6, i.e., the negative output. I
recommend a 10k or 20k ladder attenuator as a volume control.
Good luck with the JFETs, the “New Frontiers” in audio amplification.
References
1. Erno Borbely, “New Devices for Audio from National Semiconductor,” Audio Amateur 5/83, p. 7.
2. Nelson Pass, www.passlabs.com.
3. Erno Borbely, “Third Generation MOSFETs: The DC-100,” The Audio Amateur 2/84, p. 13.
4. Walt Jung, private communication.
5. Erno Borbely, “Differential Line Amp with Tubes,” GA 1/97, p. 24.
6. John Curl, “Classic Circuitry,” The Audio Amateur 1977, Issue 3, p. 48.
