pioneer a09 clone zero feedback output buffer

[kevin gilmore]

Saw some talk about this and decided to make a new version. 

use either the tube unbal/bal to bal board, or the solid state version

result is about 125 watts rms into 8 ohms at thd of .005% 

will definitely drive 4 ohms with suitably large power supplies.

transistors are standard pinout, so pick your favorite output transistors.

the to220 transistors are mje15034/mje15035

perfect for so many things, including esl boost transformers.

pioneera09.pdf

[jokerman777]

Curious what's the purpose of Q1/Q24 pair? The configuration seems to improve thd noticeably.

[kevin gilmore]

clever huh?   first time i have seen this.  what it really is, is some local feedback around the current mirror.  the lower impedance load forces  the current source to supply more current to the drive of the output transistors. all those output transistors in parallel really form an extremely stiff drive current without global feedback.

in single ended form, perfect for low impedance ribbons.   and 30v/10a switchers are cheap.  lot of heat however, 1.5 amp bias current. (total) i have a single ended gain stage to go with it.  basically half of the balanced version with a cfa capable input section.

input section can have local feedback as shown. or remove that resistor. updated to current version

 

 

pioneera09pre.pdf

Edited December 15, 2025 by kevin gilmore

[kevin gilmore]

amp board for single ended. you can run this as low as +/-24v  and as high as +/-40v

 

pioneera09amp - CADCAM.ZIP

pioneera09pre2gain - CADCAM.ZIP

Edited December 18, 2025 by kevin gilmore

[Michelag]

And merry Christmas!

 

Can we call this cfa full class A?

[kevin gilmore]

you can certainly set the bias at 2 amps, then into 8 ohms its 32 watts class A and the rest is class B or bridged 4x 

[jokerman777]

Don't know if I'm doing it right but I found in sim somehow this output stage doesn't like the high output impedance of the I/V converter gain stage. Adding another buffer in between helps. Partly the reason why you did a local feedback version of the preamp in the single ended version?