The crossover distortion is “fixed” by negative feedback. The local negative feedback on the VAS causes the output stage to generate less crossover distortion than it otherwise would. EF (1,2, or 3) crossover distortion is a STRONG function of driving-point (source) impedance. Lower is better, period - and that local NFB lowers it. And supposedly good for TIM distortion as well but the jury is still out on that one. It’s NOT on the effect on crossover distortion - the jury HAS come back with a not guilty verdict.
I was referring to global feedback. Leach promoted the idea of starting with a reasonably linear amplifier and applying only modest amounts of global feedback (<25dB) without introducing a pole in the audio band. That still produces a good amplifier even though modern designs use much more feedback and have a dominant pole <<20KHz.
Ed
Ed
Edgr..thanks for pinching in.. no there's no connection between top and bottom.
I measured the resistance of each pair of secondarys, using Kelvin probes and my old hp,
I think theire pretty close, 712-716 miliohm 712-740 miliohm.
Same ac on primary give theese numbers on secondarys.
3.6815 - 3.6800 volt from center .. rail to rail 7.356 volt.
3.6436 - 3.6450 volt from center.. rail to rail 7.2850 volt. All unloaded.
Yes the leach is a special amp, its actually what got my interest in audio, this and the old bulb loaded zen.
I measured the resistance of each pair of secondarys, using Kelvin probes and my old hp,
I think theire pretty close, 712-716 miliohm 712-740 miliohm.
Same ac on primary give theese numbers on secondarys.
3.6815 - 3.6800 volt from center .. rail to rail 7.356 volt.
3.6436 - 3.6450 volt from center.. rail to rail 7.2850 volt. All unloaded.
Yes the leach is a special amp, its actually what got my interest in audio, this and the old bulb loaded zen.
Yes, mine do that (extra stages at the INPUT side to get the loop gain back) .The VAS has local feedback (modest gain) and as such there’s almost no crossover distortion left to correct. And it doesn’t need some fragile Uber low capacitance EOL unobtainium device. Another side benefit is the high damping factor when clipping. With a higher source impedance, the EF output stage‘s Zout increases when clipping (loss of global feedback). If this doesn’t happen you maintain control of your woofers when the amp is overdriven. You cannot underestimate the importance of this at a music festival, rave or anywhere the system is driven into the red. It sounds like a MUCH bigger rig than it actually is.
Okay, so we both kept the VAS gain modest by loading it as Leach did. It is true that EF3 has low (0.2%) distortion when optimally biased and driven by low impedance. I realized that a long time ago but quantified the distortion only recently.
Ed
Ed
Hi again, I did the dual bridge as can be seen on photo, but something is not as it should be, it consumes 30 watt ideling, and buzzes, but lower. transformer with nothing connected iddles at 10w roughly.
It really bugs me, I did not care for phase as it shouldn't matter, I did put some 100nf across secondarys, did not do anything, this arrangement is powered through my vario, could it interact somehow??
I watched the capacitor banks voltages, they are close within one volt, discharge time seems also close, so assume no bad capacitors?
It really bugs me, I did not care for phase as it shouldn't matter, I did put some 100nf across secondarys, did not do anything, this arrangement is powered through my vario, could it interact somehow??
I watched the capacitor banks voltages, they are close within one volt, discharge time seems also close, so assume no bad capacitors?
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Did you make a back-of-the-envelope-calculation on how much power all those big resistors visible in the background eat up?
20W is a lot, which should produce some heat, which could be located using your nose, fingers, or a thermal imaging camera, for instance.
20W is a lot, which should produce some heat, which could be located using your nose, fingers, or a thermal imaging camera, for instance.
This whole psu is getting on my nerves, I spend way to many hours and money, yes 20 watts is definitely to much, but can we agree that the phase doesn't matter?
What is the logic step next? Try with rectifiers only? If it's okay put in shunt resistors between rectifier and capacitor?
Certainly. Start low and watch the ammeter.
One more thought: how does the power draw share between the two banks, i.e. just connect one at a time, and maybe swap the transformer windings to check every possible combination.
One more thought: how does the power draw share between the two banks, i.e. just connect one at a time, and maybe swap the transformer windings to check every possible combination.
I'm not sure about that, that's why I suggested putting in shunt resistors.
I thank you for valuable inputs, some times I get lost, can't see the forest for trees.
Will clean up, make fresh coffee, and try those things and report back.
I thank you for valuable inputs, some times I get lost, can't see the forest for trees.
Will clean up, make fresh coffee, and try those things and report back.
its just frustrating that a simple linear power supply can cause grey hair.
ive build dozens over the years, always worked fine
ive build dozens over the years, always worked fine
How do you measure the power consumption? An unloaded ps has a horrible power factor. Not all power measuring devices handle that well...
Put a dim bulb limiter on it both ways - trafo by itself and with caps. It will draw a little more with the caps - just a dull orange glow. The poor power factor will cause additional losses in the transformer and caps do have a few mA leakage. With the power factor THAT poor you can’t tell unless you’re measuring real power consumption. The bulb may be only zero decimal place accuracy but does respond only to real power draw. Maybe you‘ve got a cap in there that’s bad or needs reforming. Or maybe everything is as it should be.
And how much capacitance do you HAVE? The proper amount is 20,000uF per rail. That will make an amplifier put out full power down to 20 Hz with a 4 ohm load. R, C and F scale in the usual way, if your goals are different. Any less and power supply ripple will cause you to lose maximum capability at low frequency. Any MORE just results in additional heating in the transformer, and buys nothing if you are not using it. Of course if you WANT full power at 10 Hz, you would want to double it. If 40 Hz or 8 ohms only, you get away with half.
If youre sitting there with 200,000 uF hanging on the supply I wouldn’t be surprised at all to see excessive idle consumption. It ain’t needed and causes additional power loss.
If youre sitting there with 200,000 uF hanging on the supply I wouldn’t be surprised at all to see excessive idle consumption. It ain’t needed and causes additional power loss.