Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

Bob Cordell's Power amplifier book
Bob Cordell's Power amplifier book
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 Search this Thread
Old 15th April 2019, 12:39 AM   #9211
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Thanks Bob for such a detailed answer.
__________________
David.
  Reply With Quote
Old 15th April 2019, 08:48 AM   #9212
stuartmp is offline stuartmp  Australia
diyAudio Member
 
Join Date: May 2016
Location: Gold Coast
I second that. Thanks for such a detailed answers Bob I appreciate your time in responding with such insightful information.

I like the Idea of a specific chassis star ground point not on the PSU or Amplifier boards. I can connect my speaker protection board ground to that point too.

I was also wondering where do you run your signal ground and safety ground too.

Do you run your signal ground back to the Amplifier star ground point were the speaker return ground, the power supply ground and the chassis star ground is connected?

Then connect the safety ground to the chassis star ground point. I guess that this point could be insulated from the chassis so if a ground lift circuit is used you can create a difference in potential between the chassis star ground point and the safety ground which of course is connected directly to the chassis.

Last edited by stuartmp; 15th April 2019 at 08:55 AM.
  Reply With Quote
Old 17th April 2019, 02:42 AM   #9213
Fred Soop is offline Fred Soop  United States
diyAudio Member
 
Join Date: Jun 2013
Comment on ground. I have been working on a preamp design (part of a vintage receiver restoration/modernization project) using LM4562 op amps. They have no actual ground connection, just the 15 V supply. Bypass ground was run separately from signal ground back to a common ground bus. This thing was oscillating in the MHz region. After much investigation and reworking, I was finally able to duplicate the problem with a single stage on a breadboard. It would only oscillate with the op amp connected in the inverting configuration. The usual small capacitors connected in various locations at the op amp did not help. If I short the bypass ground to the signal ground at the amplifier (they are connected to exactly the same point about 6 inches away), the oscillation stops. The bypass ground appears clean, so I eventually connected the signal ground to the bypass ground at the preamp boards with a 4.7 Ω resistor. The complete preamp section is now installed, wired, and seems to be ok. But, this goes against everything we have been told about keeping the grounds separate back to a central ground point.
  Reply With Quote
Old 17th April 2019, 03:56 AM   #9214
davada is offline davada  Canada
diyAudio Member
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Scott Wurcer said to me once "If you have to do 7 board layout with different grounding so be it.".


Whatever works.
__________________
David.
  Reply With Quote
Old Yesterday, 02:24 AM   #9215
Fred Soop is offline Fred Soop  United States
diyAudio Member
 
Join Date: Jun 2013
Quote:
Originally Posted by davada View Post
Scott Wurcer said to me once "If you have to do 7 board layout with different grounding so be it.".


Whatever works.
I kept remembering the quote from Thomas Edison: "I have not failed. I have only found 10,000 things that don't work."
  Reply With Quote
Old Yesterday, 08:41 PM   #9216
Bob Cordell is offline Bob Cordell  United States
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by Fred Soop View Post
Comment on ground. I have been working on a preamp design (part of a vintage receiver restoration/modernization project) using LM4562 op amps. They have no actual ground connection, just the 15 V supply. Bypass ground was run separately from signal ground back to a common ground bus. This thing was oscillating in the MHz region. After much investigation and reworking, I was finally able to duplicate the problem with a single stage on a breadboard. It would only oscillate with the op amp connected in the inverting configuration. The usual small capacitors connected in various locations at the op amp did not help. If I short the bypass ground to the signal ground at the amplifier (they are connected to exactly the same point about 6 inches away), the oscillation stops. The bypass ground appears clean, so I eventually connected the signal ground to the bypass ground at the preamp boards with a 4.7 Ω resistor. The complete preamp section is now installed, wired, and seems to be ok. But, this goes against everything we have been told about keeping the grounds separate back to a central ground point.
Hi Fred,

In your last sentence, I think you are referring to star grounding. I do not blindly follow the star grounding strategy. I follow it where it makes sense. What I do usually could be called star-on-star grounding with some tree grounding towards the input end of an amplifier. What really counts is where the currents are flowing and what impedances they create and what voltage drops may occur. Follow the currents. I also try to keep circuit routes tight. I also do not blindly follow entirely separate signal ground vs power ground philosophy, but I always want signal ground where it counts to be quiet and not have any garbage currents flowing through it. I almost never use a ground plane for audio circuits. Note that if you stick everything on a big ground plane, you no longer really have control over where and how currents flow. Ground planes are great for RF, but it is also not unreasonable at times to just connect the ground plane at a single point. It is also not unreasonable to emply ground islands.

One needs to be pragmatic and intentional with grounding. It is a bit of an art form, and a one-size-fits-all approach like star grounding does not always work best.

Finally, be especially watchful of grounding when testing an amplifier, where you may have multiple pieces of test equipment, with their own safety grounds, involved.

Cheers,
Bob
  Reply With Quote
Old Yesterday, 09:35 PM   #9217
Fred Soop is offline Fred Soop  United States
diyAudio Member
 
Join Date: Jun 2013
Thanks Bob.

Yes, I definitely see additional issues with test equipment connected. Even tried an isloation transformer on the scope. I'm not using ground planes. My circuit boards are actually perf boards with component leads folded over and connected. This is more rugged than pc board foil and allows for major changes without producing a new board. In fact, the boards pictured below have now been rebuilt twice since the pictures were taken.

During the analysis, I looked at the layout of my Harman Kardon Citation 21 preamp and it appears to use the star-on-star grounding as you mention and is quiet. That's what I ended up doing with this design.

Now working on the power amp section. The receiver is a Fisher 600-T which used 4 transistors in series to handle the voltage. So the physical layout is ideal for parallel output transistors in a modern design. I am deviating from one of your preferences, using EF2 rather than EF3. The output transistors have beta of around 60 and the drivers are over 200. Power is 38 V no load and I'm looking at about 50 watts into 8 Ω. Driver standing current is about 50 mA and VAS about 10 mA. Maybe not perfect, but certainly better than the 1962 RCA transistor manual, germanium PNP, original design.

Have spent MUCH time reading your first edition book (along with material from Self, Leach, Andrew Russell, and others) and looking forward to your new edition.

Images of top and bottom of one of the preamp boards .....

1827
Click the image to open in full size.
1828
Click the image to open in full size.

Fred

Last edited by Fred Soop; Yesterday at 09:47 PM.
  Reply With Quote
Old Yesterday, 11:04 PM   #9218
Mark Whitney is offline Mark Whitney  Netherlands
diyAudio Member
 
Mark Whitney's Avatar
 
Join Date: Feb 2013
Location: Netherlands
This is what I try to achieve. A-B PSU, the rest is the amp board.
Attached Images
File Type: png Grounding.png (9.7 KB, 79 views)
__________________
Regards Mark.
  Reply With Quote
Old Today, 12:14 AM   #9219
Grendel321 is offline Grendel321  Congo-Brazzaville
diyAudio Member
 
Join Date: Jan 2019
Location: DRC
Quote:
Originally Posted by Mark Whitney View Post
This is what I try to achieve. A-B PSU, the rest is the amp board.
I follow a similar layout, except i dispense with the 1ohm resistor as it induces a output error voltage (albeit small) when referenced to the input voltage. In order to minimize ground loop area, i prefer to join the supply earth and the chassis earth at the input signal ground.
This leads to a dead silent amplifier, no hiss or hum.
  Reply With Quote
Old Today, 12:48 AM   #9220
Mark Whitney is offline Mark Whitney  Netherlands
diyAudio Member
 
Mark Whitney's Avatar
 
Join Date: Feb 2013
Location: Netherlands
I want the route from the transformer to chassis to be capable of passing high current in the case of a transformer failure. I should have drawn the PE that also connects to the chassis. This layout also works well when using multiple channels or as a pre-amp.
__________________
Regards Mark.
  Reply With Quote

Reply


Bob Cordell's Power amplifier bookHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Another realization of Bob Cordell's THD Analyzer giulianodes Equipment & Tools 164 22nd February 2019 08:56 PM
Audio Power Amplifier by Douglas Self mikee12345 Solid State 147 21st February 2019 10:35 PM
Project 11.1 from Slone "High-Power Amplifier" Book Karl71 Solid State 47 12th April 2018 02:47 AM
best audio amplifier book?? Bouvett Everything Else 30 13th August 2012 02:43 AM
Amplifier Design Book pixie Everything Else 27 11th June 2010 08:36 PM


New To Site? Need Help?

All times are GMT. The time now is 12:32 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki