What needs improving?
It could be fancier. But simplicity is a virtue.
It could be more efficient. As designed it does 25% at best; true push-pull class A can approach 50%, or half the idle heat, half the heatsink, half the power transformer. Does it run too hot for you?
The documentation is not clear on HOW a beginner would select and adjust the idle current. There is mention of "880mA" but not how to figure that for other supply voltages, and there is no in-line resistor (or amp-meter tap) where current may be measured. An unwise idle current setting could smoke the output transistors quick.
Functionally I have no objection. The DC stability (after turn-on thump) seems excellent. Unity DC NFB will force the output DC to a few mV very reliably; I don't see need for an output cap. I do also like the idea of single-supply with output cap, because it is safer in the hands of experimenters (not only beginners), but many DC-coupled power amps have run fine.
You could split the bootstrapped VA load dufferentky.. e. g. instead of 1k5 to 1k5, make it 470R to 3k3. Migjt need to increase the bootstrap cap.... It will increase OL Gain, and lower the THD.
Yeh, I would make it PushPull, instead of SE. Isolate the power supply for the inputstaage and VA stage from the output stage. Decrease the input series resistance.
Lately I have been experimenting with switxhing the VA stage for a folded cascode. That will lower the OL gain, but make it faster... that would become a entirely different...
Yeh, I would make it PushPull, instead of SE. Isolate the power supply for the inputstaage and VA stage from the output stage. Decrease the input series resistance.
Lately I have been experimenting with switxhing the VA stage for a folded cascode. That will lower the OL gain, but make it faster... that would become a entirely different...
Too low for what??
If you are running from a 1959 vacuum-tube preamp, yes, it is shockingly low.
If you come from modern preamps, DACs, or cellphones with <100r output impedance, 4.7K is too high to worry about.
I am not understanding the random suggestions to re-split the bootstrap or change over to JFETs or take key parts out. He "likes it a lot", why make it into something else?
He was asking for ideas. My suggestions improve the amp objectively, without increaing parts count. But they are just suggestions.. Especially respitting the VA load is low hanging fruit.
How about you, did you like it? I have built many Pass amps and other amps with equal power and simplicity and when I built this one, I thought it was not even close as the others.
IRFP240 is much lower capacitance than IRFP150 and should be better?
As i remember i made it mono amp and did not listen to a stereo version.As i listened in mono i remember i liked it.And maybe Nico built it with IRFP150 because it is more powerful than IRFP240.And i remember when it is built with IRFP150 it was giving more bass than IRFP240(maybe because of higher input capacitance)
Did you built RAS10? Did you like it? How is it compared to Pass amps at similar power?
Its weird variation of JLH amplifier with LTP input. Well from 60-70-s at best. Due to lower transconductance at the output it's, most likely, inferior to the all-BJT kin. Symmetry per say is nowhere to be seen. One may change input stage to full symmetrical/complimentary one. The same can be done to VAS and output stage. However it will be completely another story. BTW I you see Radical in description of something ordinary, and such word does not come from Master Joda, run, as Luc Skywalker did.
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