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.

32 output devices ffor 60W  in Luxman M800A
32 output devices ffor 60W  in Luxman M800A
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
Thread Tools Search this Thread
Old 4th October 2012, 01:27 AM   #21
Struth is offline Struth  Canada
Join Date: Aug 2012
Location: books at londonpower.com
Hi Guys

Where Cordell tended to add BJT pairs with identical Re and idle current through each new pair to keep the overall situation stable, Leach suggested that the optimal idle current could be shared among additional paths. I can't recall what Self said about it if he even did. His way might have followed Leach in this regard.

Everyone seems to concur that there is an optimal idle point for lowest THD in a class-B output stage, with most defining class-B as being idled at the low-THD point. Over or under this point THD is higher. Without a THD meter, you can't set class-B idle precisely and you end up with a class-AB compromise. However, if there is enough feedback and/or openloop bandwidth, then THD should be low anyway, especially up to 1kHz or so.

Overbias to an extreme gives you a broad class-A region where crossover distortion is abated but there are still transition artifacts when the signal goes out of the class-A region. Self made a point that the gm-doubling in class-B amps itself is not so bad an effect as when the transconductance drops when the other side of the circuit stop conducting. Were gm constant, then crossover artifacts and class transition artifacts would be greatly diminished. This suggests that a local loop to maintain high-gm, like the error correction circuit in Cordell's amp, could be of benefit to every type of output stage.

In the example of the poster above, gm for each paralleled output will be reduced by conducting a part of the current. The overall gm will be the same as with a single device. Paralleling devices broadens the gain wobble near crossover and reduces its amplitude, so overall THD will be lower even driving the same load and with shared idle current instead of multiplied idle.

Biasing for a larger class-A region pushes the class transition away from where most listening is done, so this can be a good thing.

The point here is to add the output pairs for THD reduction NOT for extra power or current handling. Self showed that this works as hoped and is a reliable improvement. Cordell showed this as well and Leach concurs in his low-TIM amp evolution.

Have fun
Kevin O'Connor

Last edited by Struth; 4th October 2012 at 01:30 AM.
  Reply With Quote


32 output devices ffor 60W  in Luxman M800AHide 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
6N11+TDA7293 60W+60W Amplifiers fn9mm Chip Amps 5 28th August 2011 01:37 PM
Tube output stage for Buffalo Saber 32-bit DAC? Curly Woods Tubes / Valves 0 23rd July 2009 03:18 PM
Output Devices ! cloud Pass Labs 11 11th November 2008 12:37 AM
Output devices? Mr Evil Class D 42 12th January 2005 03:18 PM

New To Site? Need Help?

All times are GMT. The time now is 02:15 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio