LM329 doesn't need 2mA.
He was saying 2mA through feed resistor to meet minimum data sheet requirements of 0.6mA.
Anything between 5k and 7k would certainly be ok for lm329.
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Ok, I see, thanks. I was thinking he meant through the zener because it was in the same sentence as the lm329. Data sheet does say from 0.6ma to 15ma.
Thanks to the people that commented on this.
Special thanks to Mr 6l6.
I now understand both sides of the discussion.
Better still I can see what I want to do. 🙂
Special thanks to Mr 6l6.
I now understand both sides of the discussion.
Better still I can see what I want to do. 🙂
Update
Zenners changed to LM329 DZ with 3k6 resistors.
Biased up fine and at first impression does seem more stable / easy to get settings balanced.
Just a comment, It's a rotten job to do on already built boards simple for a new build.
also pay attention to the pin out on the LM329DZ!
Pin 1 does nothing.
Thanks to all the previous commentators and Mr 6L6 for the build instructions.
Zenners changed to LM329 DZ with 3k6 resistors.
Biased up fine and at first impression does seem more stable / easy to get settings balanced.
Just a comment, It's a rotten job to do on already built boards simple for a new build.
also pay attention to the pin out on the LM329DZ!
Pin 1 does nothing.
Thanks to all the previous commentators and Mr 6L6 for the build instructions.
It seems like the left channel in my F6 has gotten slightly louder than the right. Any thoughts as to why this might be? I have confirmed it is not the source.
Thanks Colin, that was it, one of the channels had drifted from 600mV to 500mV. Odd, such a large drift over time...
Edit: the reduction in volume in one channel was actually due to a different issue - looks like one of my woofers is slightly damaged. Glad I caught the F6 bias drift anyhow...
Edit: the reduction in volume in one channel was actually due to a different issue - looks like one of my woofers is slightly damaged. Glad I caught the F6 bias drift anyhow...
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Edit 2: It was the offset which had drifted by 10V(!), this was pulling the cone inwards and reducing the output significantly in the right channel. Problem solved...
Might I suggest fixed but not solved, why did it drift?
What voltage zenners are you running (and what value resistors?)
It would be useful to others to get to the bottom of the problem.
yes that's the way it should be looked at, fixed for now.
built as per the guide with 2 mods: 1) the output degeneration version, and 2) 6.2v zeners and 3.3K resistors (as per ZM suggestion) to further stabilize the bias. the left channel did not drift at all. i will continue to monitor the values over the coming weeks.
built as per the guide with 2 mods: 1) the output degeneration version, and 2) 6.2v zeners and 3.3K resistors (as per ZM suggestion) to further stabilize the bias. the left channel did not drift at all. i will continue to monitor the values over the coming weeks.
OK thanks, Mine has the ZM mod.
Checking today it is rock steady where I last set it on both channels.
Checking today it is rock steady where I last set it on both channels.
what differences has the output degeneration version ?
Tanks
ps :i am gonna build my F6 too ;-)
Sorry missed your post. Glad you found the info. It is confusing and I didn't really get to the bottom of the difference between the two versions. What I believe the difference is that the no-degeneration version is the production schematic where Nelson tweaks 2nd harmonic with hand matching mosfets based on their transconductance. Since we DIYers are typically using very closely matched mosfets the degeneration version allows us to tweak transconductance of the mosfets (and hence 2nd harmonic) via the resistors, which I believe is the way to go for the DIY community.
If that is way off I would appreciate if someone could set me straight. 😉
Looks like there is now a serious problem with one of the channels in my F6. A few posts ago a described a drift in DC offset I had in the problematic channel which was then fixed via adjusting DC offset pot. Last night I noticed the woofer in the same channel was pulled in again, and on measuring the DC offset I measured -24V.
I then noticed a smell, and found that R2 (0.47ohm 3W) was extremely hot (too hot to touch). I used CPF3R47000JNB14 which I believe is the recommended part. On the other channel it stays cool to the touch.
Any thoughts as to what may have gone wrong? I have had the bias set at 600mV (=1.28A).
Looks like my F6 is out of action for a while 🙁. Any help is appreciated.
I then noticed a smell, and found that R2 (0.47ohm 3W) was extremely hot (too hot to touch). I used CPF3R47000JNB14 which I believe is the recommended part. On the other channel it stays cool to the touch.
Any thoughts as to what may have gone wrong? I have had the bias set at 600mV (=1.28A).
Looks like my F6 is out of action for a while 🙁. Any help is appreciated.
Attachments
besides electrical/part culprit , sure that mosfets are flawlessly mounted ( torque, no burrs and flack on heatsink ? )
I just double checked, the mosfets look flushly mounted with adequate torque. This amp has been running flawlessly since Oct 2015, almost a year now with practically daily use.