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

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John is on the right way now, and I think that it won't take long until he posts: "Simply beautiful sound".

Best regards - Rudi

P.S.: I love your pictures!
 

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The other side

Hi After sorting out one side with Rudi s guidance i started on the other side.
No problems works perfectly 36mv with 5 active tt diodes.:)

The problem i had with r28 smoke stopped when i changed the input short from 2 wires to ground(alum plate) to using a croco clip as in pic .:confused:. next music

regards john
 

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Hi After sorting out one side with Rudi s guidance i started on the other side.
No problems works perfectly 36mv with 5 active tt diodes.:)

The problem i had with r28 smoke stopped when i changed the input short from 2 wires to ground(alum plate) to using a croco clip as in pic .:confused:. next music

regards john

You don't want a DC connection between circuit common and earth/heatsink. It should be connected AC only, via a cap. Something around 1uf will do.

Sheldon
 
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Hi Rudi, follow up Post #610.
I wish I could say the New Year started on a happy note, but I'm starting to think this amp only works in Germany ( joking of course).
I measured the Vf's as best I could. The "hot" channel values varied from 430-450mV with the bypass on a 447mV one. The bias is steady at 36-38 mV, the DC offset is low at 1 mV but and the heat sink is hot at 60+C.
However the "cool" channel values were higher (470-490mV) with the bypass on a 470mV one BUT one diode measured low at 386mV. So I bypassed it since I don't know what I'm doing and now the bias on this channel starts at 25-30 and just keeps increasing 35-40-45-50 no sign of leveling off even while tuning back the trim pot, so power off. If I don't bypass that one but another, all is okay bias at 38 mV offset <3 mV and heat sink stays cooler at 45C!!!
This amp seems very touchy. Any ideas?
Happy New Year to all.
Jean
 
It work Jean , it work very well, even at Quebec City.....i have two of them.

so i solve my temp tracking problems by changing the NPN output and all goes well. There really a production problem with some of this transistors and it fall on me.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
It work Jean , it work very well, even at Quebec City.....i have two of them.

so i solve my temp tracking problems by changing the NPN output and all goes well. There really a production problem with some of this transistors and it fall on me.

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


Pictures not opening.
 
Rudi, I know I have to bypass the highest Vf, I was just trying to bypass the "odd" NJL to see if I could resolve the heat differences. Since nothing measurable seems to explain the differences in heat sink temperatures, I guess I will have to line with one side at 45-50C and the other side at 60-65C until something gives! It this okay???
I will look for more NJL's and try to match them like Denis seems to suggest.
2013 is here.
Jean
 
Rudi, I know I have to bypass the highest Vf, I was just trying to bypass the "odd" NJL to see if I could resolve the heat differences. Since nothing measurable seems to explain the differences in heat sink temperatures, I guess I will have to line with one side at 45-50C and the other side at 60-65C until something gives! It this okay???
I will look for more NJL's and try to match them like Denis seems to suggest.
2013 is here.
Jean

Theres many things that can cause this problem.

1- check the current in each branch of the output for be sure that each transistor sink the same current.

2- If not equal, be sure that ALL transistors (output and drivers) are tight on the heatsink, a loose transistor will overheat and will affect the compensation of all others too.

3- Dependly of the heatsink used and the physical location of output transistors on it, you MUST short a thermal track diode at the SAME side of heatsink.
Ex. if you decide to keep 2 diodes on the upper side of the heatsink, you will have a NPN shorted on one side and a PNP shorted on the other side. This is CRITICAL to have the channels compensation working the same on each side because the upper of heatsink is hotter than the base.
 
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