RMI-FC100, a single stage audio power amplifier

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atiq19

Member
Joined 2007
Hi,

Is it worthwhile adding some kind of mods like technics ouput scheme to make output transistors free from switching?

Just curious..

Atiq
 

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pooge

Member
Joined 2003
Mihai,

I am curious about how you arived at the particular component values for your Zobel network. Not critizing, because I am not an expert here.

I ask because in Self's treatment of the matter he indicated that the resistor is usually selected to be about the same as the speaker load, with the capacitor at 100nf, and concluded that it simply worked that way. Although he tried different resistor values to no gain, he didn't mention any experiments to change the 100nf cap.
 
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pooge

Member
Joined 2003
Mihai,

What kind of package is D1 1n4148? Can't see it between the transistors in your photos. Is it a DO-35 package? I ask because I assume the diode is stood up with the leads bent over at the top, and I see that the resistor in series with it has an insulated lead, yet there is no reason the resistor and diode can't touch, since they are connected together anyway.
 
roender

roender

Member
Joined 2006
pooge said:
Mihai,

What kind of package is D1 1n4148? Can't see it between the transistors in your photos. Is it a DO-35 package? I ask because I assume the diode is stood up with the leads bent over at the top, and I see that the resistor in series with it has an insulated lead, yet there is no reason the resistor and diode can't touch, since they are connected together anyway.
Click to expand...

The 1N4148 diode has 1W glass package. I don't know the code name of the capsule...
The diode leg is isolated in order to not dissipate heat into cascode voltage reference 10Kohm resitor.
We want that diode to closely track the thermal variance of the cascode devices.
 
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pooge

Member
Joined 2003
roender said:


Yes Andrew, good idea.
I was thinking to cut the power when heat sink temperature is over 85C
Click to expand...


I was thinking the same thing. Of course, with the present board layout, those leads would be hard to access if the transistor leads are not soldered the board, unless some traces are cut and jumpered elsewhere. Perhaps in MK1.2a boards. ^\^
 
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pooge

Member
Joined 2003
roender said:


The 1N4148 diode has 1W glass package. I don't know the code name of the capsule...
The diode leg is isolated in order to not dissipate heat into cascode voltage reference 10Kohm resitor.
We want that diode to closely track the thermal variance of the cascode devices.
Click to expand...


Is it one like this, stood up with the top lead bent over?


DO35 diode

So should both the diode lead and the resistor lead be insulated?
 
roender

roender

Member
Joined 2006
pooge said:
Again. What about the wattage of the 36v zener in the front end power supply? Anything I find availabe in 1W comes in a DO41 package with .8mm dia leads that won't fit in the holes on the circuit board.
Click to expand...

I put in the BOM what I had in my parts box and used in my PSU.
If you do the math you'll see that at Vr 1mA that diode will dissipate 36mW, so 500mW glass case will be more than enough
 
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pooge

Member
Joined 2003
Mica insulators

About a year and a half ago there was a thread about thermal pads for TO264 packages like the ThermalTraks, and how no one new a source for any. It looks like after another year and a half, not much has changed.

I did find a mica one from Aavid that would appear to work, but I can't find any suppliers for small quantities. It is model number Aavid Mica Insulator #56-02-101

If anyone can find a source for it, a group buy may be in order. Any other suggestions?
 
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