New Lineup IDEA - Power Follower/Output stage - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 4th November 2012, 02:26 PM   #11
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Quote:
Originally Posted by Fast Eddie D View Post
Kudos. I like this implementation with the local feedback in the output stage.

Is this buffer linear enough to operate out of the global feedback loop? It does have local feedback. Because if you build it as a two stage amplifier, you will have less distortion fed back to the op amp. Do you think this is worth a try?
It is very precise with MOSFET output devices. Not much distortion.
My guess it is like THD 0.002%
So it can be used outside feedback loop. I will test to see the figures.

Another thing which Bonsai mentioned in post up here is the DC Offset on output. It can be an issue in real circuit. But I think we can find a way to balance output close to zero.
Another redical solution to DC Offset is to use output cap. This is something we never should be afraid of. Many old amplifiers performed very well usning big output caps.
__________________
lineup
  Reply With Quote
Old 4th November 2012, 02:49 PM   #12
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Fast Eddie D.
Here are my testings for Power Buffer.
I put signal at buffer input. No feedback. I did test with FFT on output.
8 Ohm.
04 Vp = 01 Watt THD 0.00020%
08 Vp = 04 Watt THD 0.00042%
12 Vp = 09 Watt THD 0.00067%
16 Vp = 16 Watt THD 0.00093%

We can see the buffer performs very well. Better than 0.001% is very good. So in real circuit the distortion will be very low. My guess is better than THD 0.005%. This is better than most power buffers I know about.
__________________
lineup
  Reply With Quote
Old 4th November 2012, 03:15 PM   #13
diyAudio Member
 
Join Date: May 2010
Location: Skokie Il
Quote:
Originally Posted by lineup View Post
It is very precise with MOSFET output devices. Not much distortion.
My guess it is like THD 0.002%
So it can be used outside feedback loop. I will test to see the figures.
Good. You do realise the practical advantages to a two stage power amp, right? It can reduce speaker interaction with the amplifier. There are discussions of this in another thread here.

When back emf is fed back into a unity gain feedback network, it is not amplified. When it is fed all of the way back to the input voltage gain stage, it is amplified!
  Reply With Quote
Old 4th November 2012, 03:20 PM   #14
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Yes. I know about this. The speaker has a coil and can transmit pulses into global feedback loop.
This is where a circuit like my power buffer can do a duty.
One voltage amplifier with local FB. And one buffer to follow. And no back emf to the voltage amplifier.
__________________
lineup
  Reply With Quote
Old 4th November 2012, 04:04 PM   #15
diyAudio Member
 
Join Date: May 2010
Location: Skokie Il
Quote:
Originally Posted by lineup View Post
Yes. I know about this. The speaker has a coil and can transmit pulses into global feedback loop.
This is where a circuit like my power buffer can do a duty.
One voltage amplifier with local FB. And one buffer to follow. And no back emf to the voltage amplifier.
That's it. My old Nakamicha TA4A reciever works that way. It is very well behaved and very powerful in an "old school" way. It uses a traditional diamond buffer with current sources. It's my favorite solid state amp. It can drive any single pair of speakers "6 ohms nominal" or higher quite well.
  Reply With Quote
Old 5th November 2012, 09:57 AM   #16
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Nakamichi has done a lot of good things. I have own a Nachamichi taperecorder. It was the best
__________________
lineup
  Reply With Quote
Old 5th November 2012, 10:10 AM   #17
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Here is the next part in development of this circuit.

I have added 'real' current sources.
I have added 2 compensation caps. This makes the circuit have good stability. I think it slows down the MOSFETs.

Now is only half the distortion att full output (30 Watt into 8 Ohm).
The input impedance is >11k. THis makes the buffer an easy lood for the frontend.

I now use OPA604 for voltage amp. It has max +/-25 VDC supply.
And so it can put out +/-22 Vpeak.

The diagram shows circuit at full +/-22 Vpeak output.
THD is 0.00067% at 30.25 Watt output.
Where OPA604 contributes 0.00028% and the buffer 0.00039%

These are good figures. It points to we can build a very good amplifier which is not too complicated.
THe MOSFETs run in 217mA idle.
Attached Images
File Type: jpg powerfollower6.jpg (93.1 KB, 459 views)
__________________
lineup
  Reply With Quote
Old 5th November 2012, 11:51 AM   #18
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Nice idea Lineup, one can construct a pure class-A preamp section also using your topology, as it nicely fits in some of the places of interest.
  Reply With Quote
Old 5th November 2012, 12:03 PM   #19
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Yes.
With a discrete Class A preamp we can put out more Watt.
Chip opamps are restricted to lower voltage. (Max 30 Watt)
I have now adjusted the needed capacitance across GATE-DRAIN for MOSFETs.
One cap 1.5nF across seems to be pefect for AC values.
The input impedance is set by those two resistors to ground.
__________________
lineup

Last edited by lineup; 5th November 2012 at 12:08 PM.
  Reply With Quote
Old 5th November 2012, 12:15 PM   #20
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Here is the AC Analysis with those 2 caps across MOSFETs.
And the current working circuit.
1. OPA604 as voltage amplifier +/-22Vpeak.
2. The Power buffer
Total THD 0.00067% for both parts.
Attached Images
File Type: jpg powerfollower7.jpg (96.0 KB, 419 views)
File Type: jpg powerfollower8.jpg (108.7 KB, 411 views)
__________________
lineup
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
four transistor emitter follower (diamond buffer) as power output stage? capslock Solid State 113 12th August 2013 06:16 PM
mosfet source follower output stage. Printer2 Tubes / Valves 21 18th January 2013 04:43 AM
LINEUP Input-VAS, idea lineup Solid State 57 14th March 2011 11:33 PM
Do we always need an emitter follower to drive a LATFET output stage??? Leolabs Solid State 37 9th January 2011 04:16 PM
Cathode follower Class A output stage? Circlotron Tubes / Valves 14 15th May 2003 11:11 PM


New To Site? Need Help?

All times are GMT. The time now is 06:55 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2