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Old 13th January 2008, 02:05 AM   #1
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Default mini Zen5 & JBOZ project

After completing the xBosoz a while back I thought it would be right to build some of the power amps too. I have read all the zen articles several times. In an effort to try and understand what is happening I have entered all the schematics into LTSpice, and the only trouble I have experienced is with the Zen 8 and Zen 9 (no good spice model for the LU1014).

Anyway I usually have much more computer-time than workshop-time. So when I got several days in the workshop after christmas eve I was not prepared at all. All I could find was a couple of small heat sinks and some small MOSFET's. Why not try to learn something with a downscaled Zen 5?

A while back I played with the Zen 5 and different front-ends, so I had the schematics stored and downscaling was straight forward.

The power supply is based on one I found in John Linsley Hood - Art of linear electronics. The supply is very small, and based on parts I had available. It has been through an evolution from the first version.

The first version started too quick and the output fets blew right away when started without the variac. With the second version I tried to add some slow start mecanism, which works ok. It takes almost a minute to reach 15V which is the regulated rail voltage. There is quite a hum during startup. The hum goes away after a few minutes when the amp gets a little hotter.

The last improvement was to make it more quiet. Since it consisted of a large number of small caps I added resistors between every cap before the regulator, and one resistor after the regulator.

The amp is biased as much as the heat sinks can take ~100mA per device, giving ~1W in class A.

Sound - it is beyond my expectations to say it mildly.
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Old 13th January 2008, 02:07 AM   #2
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Schematic
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Old 13th January 2008, 02:09 AM   #3
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ps
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Old 14th January 2008, 07:13 PM   #4
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I like it, nice and simple and would make a nice headphone amp.

Whilst playing around with some A class designs operating at higher current than your amp, the benefit of a simple, quiet fail-safe supply soon became apparent! You might find the following thread useful:

Fail Safe Power Supply
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Old 14th January 2008, 08:50 PM   #5
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Thanks for the link Allen. I'll study it thoroughly.
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Old 17th January 2008, 05:33 PM   #6
paulb is offline paulb  Canada
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Nice, I'm thinking battery power for a headphone amp...
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Old 18th January 2008, 07:42 PM   #7
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I think that's a seriously clever version.

I just might have to steal it
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Old 19th January 2008, 07:46 PM   #8
paulb is offline paulb  Canada
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I have some IRFP240 and IRFP9140 I was hoping to use but their input capacitance is about 10x that of the IRF610/9610. Oh well, the 610/9610s are cheap. I think I'll simulate this to check it out.
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