Krell KSA5

Zen Mod said:

More/better pictures.

There are only 4 MOx power resisors between the heatsinks.
The SCG devices are not mounted on both sides of the heatsinks, like regulator devices in some of Krell's pre-amp models.
Between the capacitor bank and the heatsinks : a parallel TO92 VAS pair, a silvermica cap, again a pair of TO92 drivers in parallel.
There's no bipolar cap visible for DC-blocking in the NFB path, no DIP8 opamp.
There are too many small signal devices in the front end for the TO-5 to be the input stage, a metal can LF411 is the first to come to mind.
That also explains the small green foil cap adjacent to the TO-5 critter.
No zeners visible in the front end, the device count suggests a front end a la KSA with all-bjt semi shunt voltage regulators and CCS's.

Complementary differential input + parallel VAS pair + parallel driver pair=> 300i
Could be the reason why the KSA-5 doesn't live up to expection, as the very first real sota Class A SS headphone amp you'd expect it to be a benchmark.
Sounds pretty good through a high efficiency large loudspeaker system. heard the KSA-5V on bigga bucka Alfred Rudolph horns.
 
Official Court Jester
Joined 2003
Paid Member
kamis said:
Zen Mod,I am interested in older high end solid state preamps and power supply topologies and how to incorporate good designs ideas in my own projects. Also, i like to compare them to more modern approaches.BTW term "semi shunt" is unknown to me.


well , maybe I'm not so well informed , but I can't see much differences between modern and old good preamps ;

differences in topology between various manufacturer are obvious, but I can't place them in time frame ;

anyway - that's not really issue ;)

like you - I'm always interested to see new (to me ) schematic ; I resume that's more passion than anything else .

"semi shunt" ......... Jacco is always playin' with words ............ dunno what is that......

most interesting shunt reg I saw lately on DiyA is certainly reg for driver stage in this thread

hehe :devilr: , not counting Shunty ........ from obvious reasons - it is fave to me :clown:
 
Member
Joined 2002
Paid Member
Ksa 5

I am out of the office but will post in the next day or two.
FYI the To-5 is a dual FET and the op-27 is used as a servo.
This is from about 1991 - 1994. It was done by Todd Eichenbaum if I guess correctly. He is now head of engineering at Krell. A fine engineer and a helluva a nice guy.

I reverse engineered it off of a unit I repaired. Cat hair and pee will screw up a servos operation.
 
Member
Joined 2002
Paid Member
KSA 5 Schematic

Here is the schematic. This is most of it. Not shown is bias or servo circuit.
Power supply is an R core in an external box OP27 a reference and pass transistors. + - 22 Volts
 

Attachments

  • KRELL_HEADPHONE.pdf
    31.4 KB · Views: 1,610