Pass A40 versus ZEN-4

[Nelson Pass]

I don't usually bother with mounting the bias devices on the
output stage - I always run the whole thing hot anyway.
Stability is provded by high bias, large sinks, big output stages,
and large Source resistors. The amplifier typically has a slight
positive tempco, but one it heats up, its quite stable.

The bias circuit on the A40 was an effort to eliminate all
adjustments on the part of the builder, and it seems to have
worked quite well. You can do as well or better with a Vbe
multiplier and a pot and some time.

For replacement parts, you can use decent generic parts - there
was nothing special about any of the front end parts, and the
Darlington output devices were unusual only in the small value
of the driver emitter resistance. You can replace them with
the Motorolas or TIPs easily enough, or make them discrete.

[jacco vermeulen]

Originally posted by Nelson Pass
I always run the whole thing hot anyway.

Aren't you the one who invented Hot End ?

I am about to finish Jam's Mosfet version of the A-40.
Can you pinpoint the reason for the A-40 still being a cherished design ?

[MikeW]

That is a good sounding amp. Let me know what you think.
I may have to order some boards.
Nelson has you elbow healed up?

[mpmarino]

I may have to order some boards.

more?!

[Skorpio]

Originally posted by Nelson Pass
I don't usually bother with mounting the bias devices on the
output stage - I always run the whole thing hot anyway.
Stability is provded by high bias, large sinks, big output stages,
and large Source resistors. The amplifier typically has a slight
positive tempco, but one it heats up, its quite stable.

The bias circuit on the A40 was an effort to eliminate all
adjustments on the part of the builder, and it seems to have
worked quite well. You can do as well or better with a Vbe
multiplier and a pot and some time.

For replacement parts, you can use decent generic parts - there
was nothing special about any of the front end parts, and the
Darlington output devices were unusual only in the small value
of the driver emitter resistance. You can replace them with
the Motorolas or TIPs easily enough, or make them discrete.

I guess you say that therminal runaway are caused by small heatsinking in class A/B.....and will be no problem when using heatsinking designed for A?

[jacco vermeulen]

Originally posted by MikeW
Jam's?

That's what he said about your boards :
http://www.diyaudio.com/forums/showt...046#post627046

Am i barking up the wrong tree, Mike ?

[MikeW]

Originally posted by jacco vermeulen


That's what he said about your boards :
http://www.diyaudio.com/forums/showt...046#post627046

Am i barking up the wrong tree, Mike ?

Jam is the design man. He just has a hard time building amps and going to the post office. He is an excellent cook though. Not a very good driver. Happy Thanksgiving Jam.

[mpmarino]

Oh my god, Martha, it's a giant amplifier.

LOL...

my mother has a poster in her house that reads " Martha Stewart would die if she saw this house, let's invite her over"

Oh..sorry, that's off topic.

[hqcabl]

Hello, please tell us what pre-amp can be done to amp The Zen Variations - Part 4.
Thank you very much for your reply, I am new in electronics.