Do you have some pros and cons on these two interesting construction?
My speakers are Snell E3 and I don't expect high sound pressure, rather high quality (jazz, blues, etc.). Vocals are important.
My own list:
A40 Pros: Reputation, output power, BJTs
A40 Cons: Old, power transistors hard to get
Z4 Pros: Reputation, simplicity
Z4 Cons: Output power, MOS-FETs
My speakers are Snell E3 and I don't expect high sound pressure, rather high quality (jazz, blues, etc.). Vocals are important.
My own list:
A40 Pros: Reputation, output power, BJTs
A40 Cons: Old, power transistors hard to get
Z4 Pros: Reputation, simplicity
Z4 Cons: Output power, MOS-FETs
Pass DIY Addict
Joined 2000
Paid Member
Eric nice website.
MOSFET A-40
http://www.diyaudio.com/forums/showthread.php?postid=581527#post581527
MOSFET A-40
http://www.diyaudio.com/forums/showthread.php?postid=581527#post581527
Pass DIY Addict
Joined 2000
Paid Member
Nelson Pass said:
If you want to operate the amp Class AB, or for that matter if
you want to bias it to other than the default value, I suggest
an ordinary Vbe multiplier like you see everywhere else.
I guess this will require some terminal feedback from the main heat sink to the VBE transistor? Is this also relevant in the original design?
Is it possilbe to make it switchable, A/B in normal mode and A with feed-back i special mode? And can this switch be operated in listening mode?
Also I thinking on changing the original in-package darlington power transistors to a discrete variant:
Two set of MJ15003/4 on the main heatsink with 0.68ohm emitter resistors.
On the PCB board with heatsinks, drivers for the output, BD139/140 as emitterfollowers, with 100ohm between emitters.
Will this work ok?
Do I need resistance between BD139/140 and bases on output transistors?
Two set of MJ15003/4 on the main heatsink with 0.68ohm emitter resistors.
On the PCB board with heatsinks, drivers for the output, BD139/140 as emitterfollowers, with 100ohm between emitters.
Will this work ok?
Do I need resistance between BD139/140 and bases on output transistors?
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.
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.
Nelson Pass said: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?
Jam's?
That's what he said about your boards :
http://www.diyaudio.com/forums/showthread.php?postid=627046#post627046
Am i barking up the wrong tree, Mike ?
MikeW said:
That's what he said about your boards :
http://www.diyaudio.com/forums/showthread.php?postid=627046#post627046
Am i barking up the wrong tree, Mike ?
Re: Jam's?
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.
jacco vermeulen said:
That's what he said about your boards :
http://www.diyaudio.com/forums/showthread.php?postid=627046#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.
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