According to my sim at .57 and .47 I get 2nd at -65db and 3rd at -81db (1W peak 8 ohms 1 khz sine)). With .51 and .47 I get 2nd at -72 db and 3rd at -81 db (1W peak 8 ohms 1 khz sine), 1st harmonic at +5 db for both. So reduction of 7db in 2nd harmonic, no change in 3rd.
The closer the two source resistors are in value, the less second harmonic.
That's assuming closely matched output devices. Otherwise, the 2nd might go up or down.
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If the transconductance of the outputs is matched, and the source resistors are the same value,
the 2nd should be much lower than the 3rd. Look for the First Watt NP talk showing a pot across
each F6 source resistor, allowing variable 2nd.
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Not on the stock pcb circuit. You need to reroute the cap leads for this to work.
Although I purchased matched IRFP240s because they were offered in an advert on DIY Audio
It's not really required
Attachments
Pots locations have screened images with little tangs on one side. Easy to read.
Why no R13 If planning on fitting the LED?
F6 Bias
Hi Guys and Girls,
Question about amount of bias.
I started out at .50 across the .47 ohm R2 source resistor. Moved up to .60, then .63v. After hours of being on, the amp heat sinks (HS) are very warm, but not hot. Can keep my hand on the heat sink indefinitely.
Any point in going higher with the bias?
When measuring the mosfets temp, do you take the temp from the plastic body or the metal tab? I would think the metal tab approach would be dangerous, if used at all.
I have a DDM temp probe and laser thermometer. I believe the laser thermometer would be less accurate, but helpful from a safety stand point.
I read here that a laser probe doesn't work well on shine objects, so might not help with the metal tab temp.
BTW- I used a thin-film type isolator. It's very much like the pink stuff in the store, just not as spongy. It's probably not as efficient as the pink stuff, but I doubt it's the reason for the low HS temp.
The pic shows the rectifiers using the amber thin-film isolators and the HS are anodized black.
The power supply voltage is dead nuts on.
Any thoughts?
Thanks,
Vince
Hi Guys and Girls,
Question about amount of bias.
I started out at .50 across the .47 ohm R2 source resistor. Moved up to .60, then .63v. After hours of being on, the amp heat sinks (HS) are very warm, but not hot. Can keep my hand on the heat sink indefinitely.
Any point in going higher with the bias?
When measuring the mosfets temp, do you take the temp from the plastic body or the metal tab? I would think the metal tab approach would be dangerous, if used at all.
I have a DDM temp probe and laser thermometer. I believe the laser thermometer would be less accurate, but helpful from a safety stand point.
I read here that a laser probe doesn't work well on shine objects, so might not help with the metal tab temp.
BTW- I used a thin-film type isolator. It's very much like the pink stuff in the store, just not as spongy. It's probably not as efficient as the pink stuff, but I doubt it's the reason for the low HS temp.
The pic shows the rectifiers using the amber thin-film isolators and the HS are anodized black.
The power supply voltage is dead nuts on.
Any thoughts?
Thanks,
Vince
