SRPP with FETS, what 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 31st December 2007, 01:08 PM   #11
diyAudio Member
 
Join Date: Nov 2005
The load R25 is attached to the ground rail.

Is there some reasson it should be attached to the positive rail?
  Reply With Quote
Old 31st December 2007, 01:20 PM   #12
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
The load could be connected to either supply rail.

Why did you choose to connect it to the negative rather than the positive?

I would try both alternatives and decide on sound quality which is better.

I think I know which might be better, but I have only ever built one single ended amp, for headphones, and didn't like the result.
__________________
regards Andrew T.
  Reply With Quote
Old 31st December 2007, 02:33 PM   #13
diyAudio Member
 
Join Date: Nov 2005
Hi Andrew,

I choose the ground rail simply because we were always taught in school to connect the load to ground. I will try both and see if it sounds different.

Which one do you think is better? I have seen both ways on different amps. Is there any reason that one may sound better than the other? If the PSRR of an amp is good, I would think the ground rail would be the logical choice if it is wired properly so it is clean. What ever noise or ripple is on the positive line would get sent down the speaker.

Though one should have a clean positive line in this case since the PSRR is very low (don't think there is any rejection).
  Reply With Quote
Old 1st January 2008, 02:09 PM   #14
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi David,
I'll not preempt your experiment for fear of biasing the result.
Nor will I explain why one might potentially offer a superior result until after you tell if either sounds different.
__________________
regards Andrew T.
  Reply With Quote
Old 1st January 2008, 03:13 PM   #15
diyAudio Member
 
Join Date: Nov 2005
Sounds good Andrew. I should hopefully have something built this week that I can respond to.
  Reply With Quote
Old 3rd January 2008, 10:10 PM   #16
diyAudio Member
 
Join Date: Nov 2005
So I built this up with a darlington output transistor (tip120) with a darlington again used in the ccs. I put a 1k resistor from the positive rail to the point were the gate of the top one is connected to the drain of the bottom one, and then a 1k resistor from that point to ground. The point of this was to help drive that point back up to 1/2 Vc when the darlington transistor was connected as well as it brings the gain of the SRPP down a lot.

It sounds good to me. I can't tell any difference between connecting the output capacitor to the positive or ground rail, but my source is a mickey mouse cd player and my speaker is a 8 inch unit from a cheap guitar amp.

So Andrew, now that I have tried it and haven't heard any difference, do you hear a difference when you do it? I would imagine it is more noticeable on a better system than what I was trying it on. What is your preference for where the capacitor is connected?
  Reply With Quote
Old 4th January 2008, 11:27 AM   #17
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
I gave up on my single ended about ten years ago and have not returned to that yet.

The speaker connection to the positive rail gives a true constant current draw on the supply as the signal changes. This can help remove some PSU artifacts from the output and can sound a little different, not necessarily better.

When the speaker is connected to the negative the change in current draw on the supply goes from near zero amps to double the quiescent bias current and causes severe ripple in the supply rails when the signal becomes significant. Do not believe the folk that tell you ClasssA is constant current, they know not what they are talking about. Only a very few ClassA topologies achieve constant current with signal change.

How do you achieve silent power up?
__________________
regards Andrew T.
  Reply With Quote
Old 4th January 2008, 04:43 PM   #18
diyAudio Member
 
Join Date: Nov 2005
My power supply was outputting only 8 volts to get the 1 amp bias that the unit was set up for. This was a different class a stage that I build to run on +-10 volt rails. So the voltage at the output where the cap goes to the speaker is 3.8 volts when I measured it, thus there was not much voltage change there to make a bump. I didn't hear any thump anyways.
  Reply With Quote
Old 4th January 2008, 05:39 PM   #19
diyAudio Member
 
Join Date: Nov 2005
I checked in some sims about the constant current pull on the power supply you were talking about. Its true and seems like a good way of taking the variable load off of the power supply. With the load going to ground, the supplys current is increasing and decreasing with the music which would be constantly changing the supply ripple, while connecting the load to the positive supply causes the load current on it to be constant, thus causing the supply ripple to be constant. Thank you for telling me that information. I think that is a very neat thing to know about class a amps.
  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
CFP diamond buffer output stage with vertical FETs, thermally stable? Russ White Solid State 5 1st January 2008 04:16 AM
srpp input stage nhuwar Tubes / Valves 11 31st July 2007 10:03 PM
6as7 SRPP output stage Molloy Tubes / Valves 4 15th September 2006 05:39 PM
Audio Note DAC4 SRPP output stage problems! bbakota2000 Tubes / Valves 5 12th June 2005 12:25 AM
Biasing output stage FETs PeteMcK Solid State 7 7th February 2002 09:37 PM


New To Site? Need Help?

All times are GMT. The time now is 02:35 AM.


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