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Old 2nd June 2008, 12:19 AM   #91
HKC is offline HKC  Hong Kong
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pcb in 3D:
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File Type: jpg le monstre 3d.jpg (52.8 KB, 1390 views)
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Old 2nd June 2008, 08:45 AM   #92
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HKC- here are some ideas:

* make the tracks that carries heavy currents MUCH wider. As wide as you can make them, ie make copper pours.

* Put the input JFETs so that they "kiss" eachother, so you can later on glue them together

* Move the power resistors to the sides and put the drivers close to the output transistors

* Move the long feedback wire more to the middle of the PCB.

* Move the cascode transistors more to the middle an d closer to the JFETs.

* Maybe a ground plane?

Hirga has a 47u cap on each rail. Did you skip that or did I miss it?

You might want to decouple the cascode resistors with a small cap (say 100n) so that the cascode voltage going in to the small BJTs is low pass filtered. It can give slighly better sonics.


Attached is my layout which has more PS decoupling (incl input section low pass filtering) than the original le Monstre and also an input filter and a feedback capacitor. I also use TO220 power resistors with a heatsink instead of the standard cylindical ones,
and have LEDs power-on indication.
Size is 160x100mm.




Sigurd

Quote:
Originally posted by HKC
Here below is my pcb layout of Le Monstre, comments are welcome:
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Old 2nd June 2008, 09:17 AM   #93
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Sigurd,
it is a beautiful design, excellent sonics and driving capability, indicating genuine sense for audio. The feedback is probably not very harmful here.
Running the FETs at 1mA, instead of 2-3mA, I suspect Hiraga`s intention was to keep the open-loop gain low.
Emitter resistors raise THD, which does not look nice in simulations.
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Old 2nd June 2008, 09:29 AM   #94
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Even better:
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Old 2nd June 2008, 10:07 AM   #95
qwad is offline qwad  Australia
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l'm intrigued by this design, just one question though, can other devices be used ?; i.e: outputs, or the small signal. l ask this as in one schematic l see the use of bc550/ 560 devices besides the j fets......... cheers, live long and prosper
T.C.
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Old 2nd June 2008, 10:08 AM   #96
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Lumba-

Zeners are too noisy in that position - add a cap to filter it out,
or do as I plan to do, and use a blue LED.

The sound of the le Monstre much depends on the power supply as with most power amps,
and also depends on the type of passive components one uses.

As I am running at approx 2.5A idle current, I have skipped the 8 Ohm series resistor in the PS and used a choke instead,
and also used a dual bridge rectifying circuit with plenty decoupling.



Sigurd

Quote:
Originally posted by Lumba Ogir
Even better:
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Old 2nd June 2008, 10:30 AM   #97
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Yes, you can. The design is rather forgiving when it comes to different types of semis.

The output devices can for ex be the very good 0281/0302 from OnSemi or the bigger brother of these.
Some even use the 2N3055 and its complementary...
But I like to use the much faster ones from Onsemi.

The cascode transistors can be 2SC2240/SA970 or smiliar,
and the JFETs can be of other types, too, but you need
to see to that the current is approx correct through them by changing the pot.

You could even use JFETs for the cascode transistors.

The drivers I have not played with as I use the original types.




Sigurd


Quote:
Originally posted by qwad
l'm intrigued by this design, just one question though, can other devices be used ?; i.e: outputs, or the small signal. l ask this as in one schematic l see the use of bc550/ 560 devices besides the j fets......... cheers, live long and prosper
T.C.
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Old 2nd June 2008, 10:50 AM   #98
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Sigurd,
zeners are nasty noise generators causing ugly distortion. They stay on the top of my blacklisted parts toghether with ceramic capacitors and opamps. IC voltages references should be used. LEDs are noisy too, with a zener-like behavior.

Quote:
The sound of the le Monstre much depends on the power supply as with most power amps,
All power amps.
Quote:
I have skipped the 8 Ohm series resistor in the PS and used a choke instead, and also used a dual bridge rectifying circuit with plenty decoupling.
A very wise decision.
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Old 2nd June 2008, 12:04 PM   #99
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qwad,
Hiraga selected the parts with extreme care.
It would be of crucial importance to use some J-FETs from Toshiba.
Quote:
You could even use JFETs for the cascode transistors.
No. Not at all. Those should be bipolars.
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Old 2nd June 2008, 12:43 PM   #100
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Lumba -
Here we disagree. JFETs work fine for cascode work. I have many amp with JFETs for cascodes. Even MOSFETs could be used.

How rock solid the cascode voltages are, can make a difference aswell as how clean they are.

I guess your 5V "Zener" is not a Zener but something else, right?



2Sj74 and 2Sk170 are still widely available in both Europe and the US - get them while the last.



Sigurd

Quote:
Originally posted by Lumba Ogir
qwad,
Hiraga selected the parts with extreme care.
It would be of crucial importance to use some J-FETs from Toshiba.

No. Not at all. Those should be bipolars.
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