Power jfet SRPP amplifier - Page 1
Forum section: electronics / projects

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: March 26, 2023, 09:42:31 am
content: A member asked me on PM to design an SRPP amp using power Jfet. So I am posting it here may be other members give him extra advice.The lower jfet adjusts the quiescent output voltage, the upper, the bias current. The P jfet keeps the voltage of R1 +R2 constant, by this it modulates the upper jfet current inversely to that of the lower. All values are to be considered as demo.

author: jonpaul
author_rank: Super Contributor
timestamp: March 26, 2023, 12:46:58 pm
content: SRPP ?

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: March 26, 2023, 01:34:34 pm
content: SRPP=Shunt regulated push pull. The upper part is a shunt regulated to act in push pull.https://en.wikipedia.org/wiki/Shunt_regulated_push-pull_amplifier

author: TimFox
author_rank: Super Contributor
timestamp: March 26, 2023, 04:13:23 pm
content: For the vacuum-tube "SRPP", including a short history of its development and nomenclature, I recommend M Blencowe,Designing High-Fidelity Tube Preamps, M Blencowe 2016, pp 293-304.His detailed discussion includes the important difference between having a high-impedance load and a load that requires current.This book goes into great detail about all the reasonable circuits using two triodes, which are popular since dual triodes are readily available.Under "Totem-Pole Gain Stages" (two triodes in series), he discusses in detailThe half-mu stageThe SRPPThe mu-followerThe cascodebefore discussing the cathode-coupled stage.

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: March 26, 2023, 08:58:54 pm
content: The jfet UJ3.... cannot work with this circuit. It has -10V Vgs cutoff voltage with very high transconductance, that makes biasing without feedback impossible. If I wrote distortion numbers on the circuit, it means I simulated it on Tina. The simulated model is not exact, The bias source resistance is never the same in real world.

author: ampedup_electronics
author_rank: Contributor
timestamp: March 26, 2023, 09:40:40 pm
content: Quote from: Kokoriantz on March 26, 2023, 08:58:54 pmOk, Thank you for the advice. I am looking for circuit design ideas that I can simulate and build on my bench that use SiC uj3n065080k3s.

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: March 26, 2023, 11:33:09 pm
content: The manufacturer gives the spice model but it doesn't work with Tina. It looks to be made for LTspice.

author: shakalnokturn
author_rank: Super Contributor
timestamp: March 26, 2023, 11:55:09 pm
content: There's been some discussion about this on DIYaudio.If they're of any interest to you IXYS make a few models of N channel power depletion MOSFET devices.

author: ampedup_electronics
author_rank: Contributor
timestamp: March 27, 2023, 10:36:43 pm
content: Quote from: Kokoriantz on March 26, 2023, 09:42:31 amOk, I will work with this circuit next. Do you know what the expected power output and THD is into 8 OHM?

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: March 28, 2023, 03:08:48 am
content: TO220 even rated 175w cannot be used reliably more than 25W continuous dissipation, especially intended for switching. Maybe pushing to 28W, you will get 25W rms output max.

author: Circlotron
author_rank: Super Contributor
timestamp: March 28, 2023, 03:16:17 am
content: Quote from: shakalnokturn on March 26, 2023, 11:55:09 pmDefinitely THE place to look.=1&o=relevance

author: ampedup_electronics
author_rank: Contributor
timestamp: April 02, 2023, 02:20:43 pm
content: Quote from: Kokoriantz on March 26, 2023, 09:42:31 amThere is current source near 20vDC supply? Is it just for the software or do I need to provide a current source. What do you recommend for this part?

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: April 02, 2023, 08:18:49 pm
content: Ordinary CCS. Two transistors and two resistors.

author: ampedup_electronics
author_rank: Contributor
timestamp: April 05, 2023, 03:07:45 pm
content: Quote from: Kokoriantz on March 26, 2023, 11:33:09 pmI got the model working in Multisim and setup your circuit. I have attached you the model to try in TINA.

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: April 06, 2023, 03:29:54 am
content: Tina doesn't accept the model. Use 2sj74 for the P jfet and current bias adj.

author: ampedup_electronics
author_rank: Contributor
timestamp: April 09, 2023, 02:50:25 pm
content: Quote from: Kokoriantz on April 06, 2023, 03:29:54 amI don't quite understand how to implement these changes. Can you update your original drawing?

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: April 10, 2023, 03:33:04 am
content: adjust P1 for bias current 1.2A-1.5A. adjust R5 to get VCC/2 on the output.

author: ampedup_electronics
author_rank: Contributor
timestamp: April 13, 2023, 11:17:45 am
content: Is there a current production substitute for 2SJ74 you recommend? OK to use J176 or J175?

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: April 13, 2023, 12:43:40 pm
content: Alternate sources are ok.

author: ampedup_electronics
author_rank: Contributor
timestamp: April 15, 2023, 01:01:44 am
content: I finished schematic capture and simulation of your CCS version of this circuit but I am requesting further help as we cannot get the correct results:https://forums.ni.com/t5/Multisim-and-Ultiboard/Multisim-Error-when-importing-JFET-model/m-p/4298566/highlight/true#M24562I can offer you a copy of the educational software if needed.

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: April 15, 2023, 05:53:12 am
content: use only 2sj74 of other source than Toshiba. J174-j175 have gate cutoff voltage too high, it must be less than 1v. 2sj74 is less than 0.5v.

author: ampedup_electronics
author_rank: Contributor
timestamp: April 15, 2023, 03:18:51 pm
content: My friend wanted me to ask you what the voltages are supposed to be at the gates of the FETS?He says: As per the basic drawing:We increased R1, R2 to 6 ohms. It was possible to achieve half the voltage and a current of 1.2 Amperes with independent sources of constant voltage. Can you find out from Kokorian what voltages are on the gates in his real circuit?

author: ampedup_electronics
author_rank: Contributor
timestamp: April 25, 2023, 08:27:40 pm
content: Quote from: Kokoriantz on April 15, 2023, 05:53:12 amI re-stimulate using your latest schematic and Linear Systems LSJ74D but the circuit still has some problems. I have put it to the sidewalk: