Roender's FC-100 prototype and builder's thread

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passive420

passive420

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Joined 2013
wineds said:
Update :
Most of the 2SA1360Y have Hfe about 155. A few about 170. Same lot number
Most of the 2SC3423Y have a Hfe of about 184. A few close to 200. Once again all from the same lot number.
How close a match do I need for the 2SA/2SC pair?
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surely 170 for 2SA and 184 for 2SC - Or do you need the higher value 2SC for the other pair?

Can I ask how many you have gone through?
 
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AndrewT

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Joined 2004
Sheldon said:
If there is a better solution than the one I used, then fine, I'm willing to adopt it. As to the chance of mains power contacting a circuit component, the chance is not zero, but not much more likely than the mains contacting the output of a double isolated build with no separate earth.

Sheldon
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double insulated is Class11
That is designed and built and tested and guaranteed to NOT allow mains to electrocute the user.

And it is a condition of that DESIGN and BUILD, that it must NOT have an Earth.
 
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AndrewT

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Joined 2004
Sheldon said:
If there is a better solution than the one I used, then fine, I'm willing to adopt it. ...........
Click to expand...
Here is the ambiguous statement that could lead to a VERY DANGEROUS construction if implemented by a Beginner that did not realise what he/she was incorporating.
The common is DC referenced via the input common to the preamp.
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The least you can do is expand on what you said to make the "SAFETY" part appropriately important.
Or.
simply remove the potentially fatal advice.
 
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pooge

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Joined 2003
PeterLeest said:
This is how I handle the external bias compensation diode (I used MBR0520L), first, use a wire and wound around the diode, then, soldered the body on a wire connection ring and mount on top of the transistor. The heat dissipated from the transistor will transfer to the diode effectively thru the mounting screw.

I have tested this method and it is very effective, I saw the bias start to raise but quickly corrected. It is able to maintain a constant bias current without thermal runway nor over compensated.
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Seems like it would be easier to find a diode of the proper characteristics in a TO220 package and mount it on the back of the power transistors using the same screw along with some thermal paste in between. The diode would help clamp the power transistor evenly to the heat sink, and the leads would be much easier to solder. I would opt for putting one on every output transistor, though, even if not used, to maintain an equal thermal environment for each transistor.

Alternatively, glue a SMD packaged diode on the collector lead of each transistor. The collector lead is connected to the heat plate of the transistor, so heat should conduct to the collector lead a diode very quickly.
 
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pooge

Member
Joined 2003
wineds said:
What is the best option for the input DC blocking cap? It should be 3.3 to 3.9uF according to Andrew? I haven't been able to find any quality polypropylene caps that would fit 15mm lead spacing on Rudi's board.
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If your preamp output is capacitor coupled or otherwise DC output protected, you shouldn't need a cap here. I have lived without an input cap for almost 40 years without losing a moment of sleep.
 
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AndrewT

R.I.P.
Joined 2004
OK, now I see.
The time constant around 85ms to 100ms suits me. But it must also suit the abilities of the amplifier.

That was the point I was making.

Stating capacitance alone without the resistance value tells us nothing. It's a filter and both parts of the filter require specification.
 
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atupi

Member
Joined 2010
Solved bias issue by exchanging all the 0281/0302's. I was complaining last year about my bias was rising slowly with temperature and becoming suddenly unstable.

I have discovered that my transistors has some diode problems also quite high Vfe. The old ones has Vfe diode around 0.520V and the new working ones are very close to 0.500V.

It seems that Onsemi has some problem in the past with thermaltrack diodes.
 
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wineds

Member
Joined 2006
andreasw said:
@atupi
On the picture you can see how it works.
I took 2 Conrad heatsinks (350x150x60mm), 8 Aluminum angles and a plate of 3mm Aluminum.
The plate doesen´t reach the heatsinks there is a 10mm slut.
With the holes in the top plate there is enough air circulation.

At first the amp has to play some hours.
Later I will write something about the sound in comparsion to an Aleph J and Symasym (at this moment ...).

Regards
Andreas
Click to expand...

Andreas, can you please tell me where you bought the Aluminum angles?
 
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