Forums
New posts
Search forums
What's new
New posts
Latest activity
Members
Registered members
Current visitors
Log in
Register
What's new
Search
Search
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
DIY & Tutorials
DIY For Audio
A 1000VA transformer is a scary thing!
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Help Support AVForums:
This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Message
<blockquote data-quote="Ampdog" data-source="post: 430057" data-attributes="member: 144"><p>Jim,</p><p></p><p>One needs to be cautious here. It sounds good to have class A for low output and AB only higher up. But that can cause a discontinuity when going from A to AB, causing high order harmonic products. There is usually an optimum bias current very much lower, about 80 mA to 150 mA depending on the output stage design, where one half of the p.p. stage smoothly crosses over to the other without any 'kink'. ('Knees' in transistor transfer graphs at low current can mutually cancel or augment, whichever way you want to see it. Douglas Self shows this in his book/articles.) </p><p></p><p>One can get as low as 0.02% distortion right across the cross-over region, no need for higher standing current. But to determine this accurately requires either a distortion meter or c.a.d. program e.g. Spice, so it is not easy to determine experimentally otherwise. However, at some 100 mA the chances are good that one will be safe. (These figures are from my own design. I can analise yours for you; unfortunately my Spice program is down at the moment. Hopefully later.)</p></blockquote><p></p>
[QUOTE="Ampdog, post: 430057, member: 144"] Jim, One needs to be cautious here. It sounds good to have class A for low output and AB only higher up. But that can cause a discontinuity when going from A to AB, causing high order harmonic products. There is usually an optimum bias current very much lower, about 80 mA to 150 mA depending on the output stage design, where one half of the p.p. stage smoothly crosses over to the other without any 'kink'. ('Knees' in transistor transfer graphs at low current can mutually cancel or augment, whichever way you want to see it. Douglas Self shows this in his book/articles.) One can get as low as 0.02% distortion right across the cross-over region, no need for higher standing current. But to determine this accurately requires either a distortion meter or c.a.d. program e.g. Spice, so it is not easy to determine experimentally otherwise. However, at some 100 mA the chances are good that one will be safe. (These figures are from my own design. I can analise yours for you; unfortunately my Spice program is down at the moment. Hopefully later.) [/QUOTE]
Insert quotes…
Verification
Post reply
DIY & Tutorials
DIY For Audio
A 1000VA transformer is a scary thing!
Top