Go Back   Home > Forums > >

Solid State Talk all about solid state amplification.

RK-Auto200W Amplifer
RK-Auto200W Amplifer
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools
Old 11th February 2021, 08:00 AM   #1
RussellKinder is offline RussellKinder  United States
diyAudio Member
 
Join Date: Mar 2015
Location: Austin, TX
Default RK-AutoBias200 Amplifier

Here's a schematic I've been developing for a couple of months, now. I have not laid out the PCB yet, let alone built one.
[The schematic shown in post #92 is the most recent iteration so far.]

The design goal is a 200W amp with distortion below 0.001% up to 20 kHz. VCCP/VEEP looks like they're going to be +/- 63V unregulated. VCC/VEE will be +/- 70V regulated.

Generated rails from the shunt and series-pass regulators will be
VCCP-5V
VEEP+5V
+15V
-15V

I've made an attempt at EF-triple stabilization, with a thread here: Removing MJE1503x in an Output Triple
but I don't think the final answer to that can be found in sims. I have not drawn the feedback yet, nor the final compensation. In IC op amps, a cap from the top of R8 to GND is sufficient, but a T-miller arrangement here will further linearize the output stage.

OL Gain is very high, and the pole from the output stage will between 10 and 20 MHz.

Output transistor biasing will be adapted from William Chater's bias control circuit from 1988. That's what's in the yellow box. I've detailed my adaptation here:
William Chater's "Bias control for power amplifiers," Revisited

Added, 10 Mar 2020:
My plan is to finish this design, documenting my progress and performance on diyaudio. When the design is complete, and the PCBs are laid out, I will make PCBs available. Gerber files, too. Then I will try to stick around to give advice on building and mods.

I still have some expectation that simulated performance, up to 20 kHz can be as low as 0.001%. We will see if my PCB layout skills can get a real circuit to approach that performance.

At this point in my life, I have 35 years experience as a designer of audio circuits, including 12 years where I designed discrete transistor power amplifiers for car audio. After that, I designed class-B and class-D audio amplifier ICs for 10 years. Now, I am a research engineer designing analog to digital converters for 200 GS/s SERDES in silicon processes that are not yet released for production.

I'm hope this design ends up being as good as the best of what's out there, both commercially and DIY.

Outline of the thread, so far:
  1. Addition of cascode below Q5. Discussion of TL431 and replacing with quieter infra-red LEDs--posts #8 - #15
  2. First documentation of performance--posts #15 - #28
  3. Simulated amplifier with clipping. Quasi-sat of KSA1220 driver caused instability exiting clipping. Replaced drivers with 4 each of KSC3503 and KSA1381. This let me increase UGBW to 5 Mhz from 3 Mhz, and increased SR to 94 V/us from 58 V/us. Posts #39 - #45.
  4. Documentation of simulated performance, post revision, Posts #46 - #50.
  5. Discussion with BesPav about my design decisions, Posts #62 - #65.
  6. Addition of SOA limiting, single-slope, dual slope, and eliminating distortion caused by SOA circuit, posts #66 - #78.
  7. Schematic of SOA limit and bias servo offloaded to daughter PCB, post #80.
  8. Replaced LM334 with "ring of two" current source, post #85.
  9. Find sources of distortion and optimize. TPIIC considered. Posts #92 - ...

-----
keywords: power amplifier, design, folded cascode, triple EF, LTspice, low THD, low noise, self bias
.
AutoBias200.PNG
__________________
Best Regards, Russell
RK-Autobias-200W Amplifier

Last edited by RussellKinder; 18th March 2021 at 06:56 PM. Reason: Plans for PCBs added.
  Reply With Quote
Old 11th February 2021, 09:15 AM   #2
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
An imperious doodling indeed - I will need to take a long breath to examine it in detail.
Thank you, Russell.

HD
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com
  Reply With Quote
Old 11th February 2021, 04:14 PM   #3
RussellKinder is offline RussellKinder  United States
diyAudio Member
 
Join Date: Mar 2015
Location: Austin, TX
I noticed a mistake I made in the yellow subcircuit box. The upper VEE15 should read VCC15. I'm sure there are other mistakes in the schematic. Free virtual cookies for each one you find.
__________________
Best Regards, Russell
RK-Autobias-200W Amplifier
  Reply With Quote
Old 11th February 2021, 04:45 PM   #4
BesPav is offline BesPav  Russian Federation
diyAudio Member
 
Join Date: May 2011
Location: Russia, Moscow
Quote:
Originally Posted by AKSA View Post
An imperious doodling indeed
You can use a figure 32 in the AD797 datasheet to simplify things.
Or just see attached pic.IMG_20210211_194343.jpg
  Reply With Quote
Old 11th February 2021, 04:57 PM   #5
RussellKinder is offline RussellKinder  United States
diyAudio Member
 
Join Date: Mar 2015
Location: Austin, TX
In a nutshell, yes BesPav. It's a folded cascode. with an output stage.
__________________
Best Regards, Russell
RK-Autobias-200W Amplifier
  Reply With Quote
Old 11th February 2021, 05:04 PM   #6
RussellKinder is offline RussellKinder  United States
diyAudio Member
 
Join Date: Mar 2015
Location: Austin, TX
I just noticed a pretty glaring mistake in that AD797 figure. gm should not be shown in the transimpedance amplifier.

Transconductance Amp is correct. Iout/Vin = gm. Units are 1/ohms
Transresistance Amp should be Vout/In = 1/(jwC), not gm/(jwC), Units are ohms.

The gain of the two stages multiplies together to give you gm/(jwC). Units are Volts/Volt (well, technically ohms/ohm).
__________________
Best Regards, Russell
RK-Autobias-200W Amplifier
  Reply With Quote
Old 13th February 2021, 02:03 AM   #7
RussellKinder is offline RussellKinder  United States
diyAudio Member
 
Join Date: Mar 2015
Location: Austin, TX
I cleaned up the schematic a bit, moved the supply regulators for the bias servo into the yellow block. Makes it easier to read.
Attached Images
File Type: png AutoBias200.PNG (284.2 KB, 2341 views)
__________________
Best Regards, Russell
RK-Autobias-200W Amplifier
  Reply With Quote
Old 13th February 2021, 08:47 AM   #8
jcarr is online now jcarr  United States
diyAudio Member
 
Join Date: Jul 2002
Location: Tokyo, Japan
Adding a cascode to Q5 would bring its Vce into closer conformity with that of Q8.
It may also be worth connecting the collector of Q12 to the emitter of Q20, and the collector of Q13 to the emitter of Q19.
__________________
http://www.lyraconnoisseur.com/, http://www.lyraaudio.com
  Reply With Quote
Old 13th February 2021, 07:18 PM   #9
RussellKinder is offline RussellKinder  United States
diyAudio Member
 
Join Date: Mar 2015
Location: Austin, TX
Earlier in this design development, I tried a cascode in series with Q5, with its base tied to ground. It actually hurt input offset to do that, which I found odd. Otherwise, it made no difference. In the final PCB, I'll will leave a hole for that cascode. If nothing else it will cut the power dissipation of Q5 in half, balancing its temperature with Q8.

I also tried bootstrapping the collectors of Q12 and Q13 to the Q19 and Q20 emitters. when I first put in the diamond buffer, and that did some very damaging things to the AC stability above 1 MHz. I'll be leaving those collectors tied to the rails.
__________________
Best Regards, Russell
RK-Autobias-200W Amplifier
  Reply With Quote
Old 16th February 2021, 01:09 PM   #10
WatrixReloader is offline WatrixReloader  Germany
diyAudio Member
 
Join Date: Jun 2006
Location: Darmstadt
Super interesting! Thx for sharing.
  Reply With Quote

Reply


RK-Auto200W AmpliferHide this!Advertise here!
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


New To Site? Need Help?

All times are GMT. The time now is 12:24 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 12.50%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki