His choice of words and phrases may be less than clear in the article. Perhaps one point is the deficiency of current quantification of what "accurate" means to the human ear and brain, and that simple distortion figures are insufficient. Which is why some people now talk about and occasionally quantify the harmonic nature of the distortion. Perhaps for targetting human perception and processing an amp with higher basic distortion figures may actually be not just plesant but more "accurate" where it matters to human hearing. On the other hand, his description of what is "pleasant" might be more relvant to guitar or other instrument amplifiers which are sound generators rather than reproducers.
You're about to be right. Nonetheless these are words of Nelson Pass:
"A very important consideration in attempting to create an amplifier with a natural
characteristic is the selection of the gain devices. A single ended Class A topology is appropriate, and we want a characteristic where the positive amplitude is very, very slightly greater than the negative. For a current gain device, that would mean gain that smoothly increases with current, and for a tube or field effect device a transconductance that smoothly increases with current. Triodes and Mosfets share a useful characteristic: their transconductance tends to increase with current. Bipolar power devices have a slight gain increase until they hit about an amp or so, and then they decline at higher currents."
We can find in many places e.g.
http://www.passlabs.com/pdfs/articles/seclassa.pdf
"A very important consideration in attempting to create an amplifier with a natural
characteristic is the selection of the gain devices. A single ended Class A topology is appropriate, and we want a characteristic where the positive amplitude is very, very slightly greater than the negative. For a current gain device, that would mean gain that smoothly increases with current, and for a tube or field effect device a transconductance that smoothly increases with current. Triodes and Mosfets share a useful characteristic: their transconductance tends to increase with current. Bipolar power devices have a slight gain increase until they hit about an amp or so, and then they decline at higher currents."
We can find in many places e.g.
http://www.passlabs.com/pdfs/articles/seclassa.pdf
F5 blown up
Hi,
someone had the same experience?
today morniung during coffe time one of my f5 did a small pop and my speaker cone went inside,
i switched off immedeatly and found a blown up amp with a self desoldered feedback resistor ( one of the 100R one)
didn´t start to look for the reason
but it was playing radio at moderate levels
my only faulrt could be that the heatsink is on safety earth but circuit gnd is floating and no issues with noise
could the floating ground be the reason because of the high bandwith?
thanks
Hi,
someone had the same experience?
today morniung during coffe time one of my f5 did a small pop and my speaker cone went inside,
i switched off immedeatly and found a blown up amp with a self desoldered feedback resistor ( one of the 100R one)
didn´t start to look for the reason
but it was playing radio at moderate levels
my only faulrt could be that the heatsink is on safety earth but circuit gnd is floating and no issues with noise
could the floating ground be the reason because of the high bandwith?
thanks
Is your speaker still ok?
No idea what caused your problem, but I sure fried a good few $$$ worth of drivers before I started adding speaker protection modules, which sadly won't work for my mini A, as the rail voltages are too low, upc1237 works between 24 and 60V, although I tricked it into running with 70V once...
No idea what caused your problem, but I sure fried a good few $$$ worth of drivers before I started adding speaker protection modules, which sadly won't work for my mini A, as the rail voltages are too low, upc1237 works between 24 and 60V, although I tricked it into running with 70V once...
Then no harm done I guess, I wonder if it was oscillating, I guess with these barebone widerange amps anything is possible. I'd replace the resistor, as it's value probably went south after heating up. Then re-bias and DC check. As with all resistors, don't flush mount, provide some space to radiate heat through all of its surface area.
Have you started testing the fets yet?
Have you started testing the fets yet?
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Similar thing happened to me once when the lead connecting one of the power transistors worked loose. A huge, momentary pop. Later figured that even if one output goes bust and the other is fully conducting, offset is maintained close to zero. The speaker does see close to rail voltage at the instant of the fault, but only for a half second.
results
with resoldering the resistor (i use to 220 style power resistor for feedback, but couldn´t fit it in the pcb holes so i did solder it to -lötnägel- in german no idea if soldering nails is a correct translation so maybe i did some bad solder work and the fault was only the bad contact-because when i turned the amp of the resistor was outside of the amp...)
but the amp was fine. nothing blown so maybe all was my bad craftmanship?
i tested then the current limit circuit and found that it limits the current perfect down to 2 ohms, with 1 ohm it starts to oszillate when cutting of-is this a behavior of the irfp240/9240 or the circuit itself?
an additional result of my testing was that my transformer or the filter choke induces hum to my speakers even when not connected to the speaker itself, these l´s have quite some magnetic pickup in the filter network of the speaker
with resoldering the resistor (i use to 220 style power resistor for feedback, but couldn´t fit it in the pcb holes so i did solder it to -lötnägel- in german no idea if soldering nails is a correct translation so maybe i did some bad solder work and the fault was only the bad contact-because when i turned the amp of the resistor was outside of the amp...)
but the amp was fine. nothing blown so maybe all was my bad craftmanship?
i tested then the current limit circuit and found that it limits the current perfect down to 2 ohms, with 1 ohm it starts to oszillate when cutting of-is this a behavior of the irfp240/9240 or the circuit itself?
an additional result of my testing was that my transformer or the filter choke induces hum to my speakers even when not connected to the speaker itself, these l´s have quite some magnetic pickup in the filter network of the speaker
Easy enough to explore this with the F5. Just adjust P3 to get out of the
2nd harmonic null and take a listen.
Hasn't this been around?
Uhhh, nope.
On the boards I had burned for myself I provisioned using alternative source resistors which effects the same result.
is it worth upgrading Mr Nelson?
i see the different thermistor arrangement and some k2 balancing circuit-maybe only to implement the p3 as a easy fix?
thanks
Hasn't this been around?
i see the different thermistor arrangement and some k2 balancing circuit-maybe only to implement the p3 as a easy fix?
thanks
