Solid state Class-A question

[neazoi]

Hello, I try to find a simple to build Class-A solid state preamplifier.
All the schematics I have found use symmetric PSU +V-V
I was wondering why it always have to be symmetric?

Are there any schematics for preamplifier or even power amplifiers non symmetric Class-A


Thanks

[Kinnja]

Here is one for a power amplifier:

http://diyaudioprojects.com/Solid/ZCA/ZCA.htm

[woody]

You might look at the ZEN amplifiers and the Son of Zen preamp
at passdiy.com

[neazoi]

Yes, that is a nice example.
Are there any other designs of class-A solid state preamplifiers or amplifiers using single PSU?
Maybe some direct coupled circuits?
I think that would be of much interest in this thread.

[Lumba Ogir]

neazoi,
no direct coupling.

[AndrewT]

Hi,
is the original JLH a single polarity pre?

[AndrewT]

You will not find any direct coupled single polarity PSU pre-amps.
The input must be biased to get the input into it's operating range and the output will try to mimic that input bias voltage. This appears as an output offset and must be blocked before feeding into the next stage.

[neazoi]

see this
http://www.headwize.com/projects/sho...e1_add_prj.htm
This headphone preamplifier could be used as a preamplifier to that one?
http://diyaudioprojects.com/Solid/ZCA/ZCA.htm

this would create a cheap class-A system