RMI-FC100, a single stage audio power amplifier

[Rudi_Ratlos]

Marc, I myself have used the ISC - VAS transistors and am happy with them.
Finding a suitable, matched 2SK170BL transistor - quad is the bigger challenge.

Regards - Rudi_Ratlos

 

[bandol83]

Thanks Rudi, I will buy them, I have seen that Reichelt carry them at a very reasonable price 🙂

Best regards
Marc

 

[zdr]

Can someone clarify these blue and red voltages for me? What are these, at which points are they actually measured?

I could use some help with troubleshooting of the front stage. Both channels are behaving the same way:

1) all components mounted, 34v power switched off, 39v switched on and stable, one diode bypassed.
2) all leds lit happily
3) voltage drop across diode string is 1,5v, too low to turn on power stage. Voltage drop across trim pot 0,7v.
4) If I turn on power stage voltage, diode string drops even less voltage, around 1,2v, and none of the njls turn on at all.

 

[zdr]

Both channels up and running🙂

 

[lordoff]

Excellent!!! Bravo! 🙂
So, you allready have a gift fo Christmas!!! Good Santa Klaus!
btw, what was a problem with diode string. If you have a time, can you describe?

 

[zdr]

I have no idea. All transistors around diode string were off and I couldn’t figure out why. There were no mistakes to be found. While I was poking around, suddenly everything turned on and string was biased. It seems like a bad solder joint somewhere which I poked at some point.

My output transistors seem to be badly matched, as I have variations from 16 to 22 mV at output resistors. Need to repeat that exercise with different approach.

 

[zdr]

This is the latest version of the compact board I used. It allows for vertical mounting to distribute heat more evenly. Power transistor positions are exactly the same as in original layout.

 

[zdr]

Up and running on both channels😉

 

[zdr]

If someone is interested, I have extra boards available for sale.

 

[ernesternest]

How much are they?

 

[zdr]

5eur each.

 

[ernesternest]

OK, would like to get a pair. Pm you later.

Cheers, Ernst

 

[zdr]

I have made a compilation of all useful tips and comments from this thread in one doc, to make the build of this wonderful app easier. If you feel anything else should be added, please let me know.

Fc100 - Google Docs

 

[lordoff]

Whohooo, excellent initiative! 🙂 Good work, zdr!

To be honest, I started to write the same doc (for personal use) year before, but finally I think is not fully finished.
Later I will look in my doc, what other info can be added.

 

[rotundu]

PCB

If someone is interested, I have extra boards available for sale. View attachment 730739

I would like to buy them.
How many do you have?

 

[zdr]

I would like to buy them.
How many do you have?

They are all gone now.

 

[rotundu]

They are all gone now.

:crying
What a pitty.
In case there will be a group buy, or anybody have them, Please let me know.
Thank you.

 

[zdr]

:crying
What a pitty.
In case there will be a group buy, or anybody have them, Please let me know.
Thank you.

I ordered some more, you can reserve them with PM 🙂

 

[rotundu]

I ordered some more, you can reserve them with PM 🙂

Sorry for maybe stupid question - what is PM? 🙂
I woul like to buy 4 pcb.
Thanks!

 

[zdr]

🙂 pm - private message, but this is fine too 🙂