F5 - It Works but some problems ...

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Hi Everyone,

I'm a new diyer :)

My First build , The AmpCampAmp and the B1.
Today, I want to build a FirstWatt F5
I've buy on DiyAudioStore the LS 2SK170 & 2J74 for this project.
But problems start at the power on ...

Bias ajustement and Offset, No problem
Two channel are biased at 0.5V, and offset under 10mV DC.
Thermal stability after one hour is OK, under 35°c.

I plugged my old test speaker with no load / RCA cinch disconnected : Loud Hummmm on the two speakers …

::: F5 Configuration :::

PSU = 23,7V / 0 / -23,7V
JFet Linear System 2SK170 & 2SJ74
Mosfet IRFP9240 & 240 Vishay.
176 000uF Capacitor bank filter (CRC)

- Amp board INPUT+ ------------> Isolated from enclosure / RCA ( Hot )
- Amp board INPUT GND -------------> Isolated from enclosure / RCA ( Cold )
- Amp board Speaker GND --------> Isolated from enclosure / Speaker ( Cold / Black )
- Amp board Speaker OUT+ --------> Isolated from enclosure / Speaker ( Hot / Red )
- Amp board 24V+ -----> PSU 23.7V+ Rail
- Amp board 24V- -----> PSU 23.7V- Rail
- Amp board 0V -----> PSU 0V Rail

Inside the F5 >http://rockload.free.fr/Images/photo.JPG

Ground Error ? Bad ground wiring ?... :(
If you're any idea / suggestion for this problem ...

Thank you very much !



  • help.jpg
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yeah , I'm puzzled , too


The 0V Power Supply to 0V Board is currently connected !!
Why add a wire bridge between two main PCBs Grounds ?!


[image]Image:My F5|none[/image]

[image]Image:Input wire shield and Enclosure to earth connection.|none[/image]

1 - One link : Enclosure to Earth.
2 - Two link : Shield of the Input Mogami Cable to Enclosure.

See this link : My F5 wiring > http://rockload.free.fr/Images/CablageF5.jpg
Joined 2002
Paid Member
I've shorted the Input RCA ( Cold & Hot Shunt ) = No Humm, No Buzz on the speakers.

You have a loop between the RCA barrels and the power supply ground. Both are connected to each other on the boards, and you have connected the two barrels externally to each other through the chassis. If you remove all other wiring drawings, you will see the loop quite easily.

Disconnect the RCA sleeves from the chassis and connect the power supply 0V to the chassis instead. You could use a loop breaker but I don't know if that's legal in your country.
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