RMI-FC100, a single stage audio power amplifier

[DRZ1]

' noisy corner ' i like that Roender

Read you while listening Dire Straits on my FC-100.......

[AndrewT]

It's the variation on voltage that is more of a problem when current is very low. Hard to predict final regulated voltage.
I'm not disputing the Zener action.

[AndriyOL]

Shall I buy 43V zeners to have 42-43VDC on outputs?

[roender]

Originally Posted by AndrewT

It's the variation on voltage that is more of a problem when current is very low. Hard to predict final regulated voltage.
I'm not disputing the Zener action.

For 36V zener there is no significant voltage variation between 0.2 to 10mA Ir if this diode is thermally compensated by a series direct conducting junction.

[zdr]

Originally Posted by roender

For 36V zener there is no significant voltage variation between 0.2 to 10mA Ir if this diode is thermally compensated by a series direct conducting junction.

Mihai, do you have any recommendations for DC filtering of mains AC that would not impact the sound quality of FC100?

[Sheldon]

Originally Posted by roender

Too bad that ONsemi f..ked up some production lots of NJLs. I'm convinced that they put by mistake other type of diode inside which requires other compensation current in order to correct track the transistor Vbe over temperature.
I do not recommend to bypass all the diodes string with the pot. Just use what Andrew recommend, one resistor over the diode with way out Vf than the others.

Seems odd that they would mistake the diode type, but I also have experienced some problems. In my instance, it seems more a case of variable behavior.

One of the two amps I built would suddenly bias high, then lower. I chased the problem down to one diode that was apparently unstable. It would measure slightly different than the others with the diode setting on the multi meter, but would show about 50% higher voltage drop under load. I had originally bypassed another diode, and when I opened that connection that one read over 1V!! on the MM. However, when I ran current through that one, it dropped back to the normal reading, and was normal with the FC current load.

The take home lesson: Measure all your diodes with the expected operating current (about 2mA). Measure each one a couple of times. I would then mount them on the heat sink and short one with a clip lead. Adjust bias, then check bias with each one shorted before you button things up. If you do not shut the amp off when you move the clip lead, you should short the next one in line before you remove the clip on the prior one - or your bias will be way too high.

Sheldon

[Rudi_Ratlos]

Sheldon, I have bought 175 of each NJL0281DG and NJL0302DG for the German FC-100 group-buy from VERICAL some weeks ago.
A DIY-friend of mine matched them and also measured the Vf of the integrated TT-diodes at a current of approx. 2.5mA. (12V / 4K7).
He did all the measurements twice.

The Vf of the NJL0281 - TT-diodes is in the range of 509 - 518mV; the Vf of the NJL0302 - TT - diodes is in the of 519 - 529mV.

Some of the Germans have already built the FC-100.
Their builds work with 5 active TT-diodes, and I have not heard about any adjustment / TEMPCO problems.

I therefore think that if you buy the NJLs from the current production, you won't have any problems with the internal TT-diodes.

Best regards - Rudi

[Sheldon]

Originally Posted by Rudi_Ratlos

I therefore think that if you buy the NJLs from the current production, you won't have any problems with the internal TT-diodes.

Thanks Rudi. My comments were more directed to any users who might have Thermaltraks already on hand. I think I have solved my issues by just checking each diode under actual operating conditions, and selecting the best one to bypass. Had I known that there might be some variability, I'd have checked more carefully before I installed them. Both my amps (four channels) are fine with 5 diodes in the string.

Sheldon