RMI-FC100, a single stage audio power amplifier - Page 61

atiq19 · 9th January 2009, 01:31 PM

Hi,

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

Just curious..

Atiq

pooge · 9th January 2009, 06:55 PM

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.

roender · 9th January 2009, 07:09 PM

I have 6ohm speakers, so two paralel 10ohm resistors are close to Self recommandation

pooge · 9th January 2009, 08:40 PM

Sorry. I got the resistor value part. I was wondering about the cap, but realize now it is just scaled up for the lower resistor.

pooge · 10th January 2009, 05:04 AM

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.

AndrewT · 10th January 2009, 11:19 AM

Could we use the spare diode in the output to feed a comparator and give an overheat indication? Maybe a flashing LED?
Thoughts please.

roender · 10th January 2009, 02:08 PM

Quote:

Originally posted by AndrewT
Could we use the spare diode in the output to feed a comparator and give an overheat indication? Maybe a flashing LED?
Thoughts please.

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

roender · 10th January 2009, 02:11 PM

Quote:

Originally posted by pooge
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.

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.

pooge · 10th January 2009, 03:32 PM

Quote:

Originally posted by roender

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

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. ^\^

pooge · 10th January 2009, 03:37 PM

Quote:

Originally posted by roender

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.

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?

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9th January 2009, 06:55 PM	#602
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	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.

9th January 2009, 07:09 PM	#603
roender diyAudio Member Join Date: Sep 2006	I have 6ohm speakers, so two paralel 10ohm resistors are close to Self recommandation

9th January 2009, 08:40 PM	#604
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	Sorry. I got the resistor value part. I was wondering about the cap, but realize now it is just scaled up for the lower resistor.

10th January 2009, 05:04 AM	#605
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	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.

10th January 2009, 11:19 AM	#606
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Could we use the spare diode in the output to feed a comparator and give an overheat indication? Maybe a flashing LED? Thoughts please.