look like the opposite, at last for pwamp
Originally posted by Nelson Pass
Most customers want total silence from the amplifier, including
mechanical noise. If there is not complete matching between the
secondary coils and only 1 rectifier bridge, any net DC imbalance
between the current of the + supply and the - will tend to
saturate the core of the transformer and create noise. This is
seen for quite low current differences and can also show up with
low frequency output. Using two bridges eliminates the problem
Originally posted by Nelson Pass
Most customers want total silence from the amplifier, including
mechanical noise. If there is not complete matching between the
secondary coils and only 1 rectifier bridge, any net DC imbalance
between the current of the + supply and the - will tend to
saturate the core of the transformer and create noise. This is
seen for quite low current differences and can also show up with
low frequency output. Using two bridges eliminates the problem
I hate to display my ignorance and even tho' I do use 1 bridge per winding, I've never quite understood this thing about uneven secondary windings and 1 or 2 bridges, - perhaps someone could enlighten me ....For example, if a trannie has 1 sec winding of 15 volts and the 2nd one of, say, 16v - so different secondary winding properties (resistances, inductance, capacitance, etc) for the same flux density via the single primary winding - okay, so far.For the single bridge system - we have one 1/2 waveform at about 20v at 1/100 sec (50Hz power here) and the 2nd 1/2 wave at about 21v out of the bridge ... .... and so we have the same combination of 20 and 21 volts going into both +ve and -ve ripple caps, and this would balance out to equal rail voltages and have no dc component at all, yes?Now, if we use 1 bridge per winding, the 15 volt ac winding ends up going to the just the +ve rail (assuming ....) at about 20 volt dc and the 16volt ac winding will end up at the -ve rail of about 21 volts, and we end up just the situation we're trying to avoid, no? (with different voltages & currents thru the 2 windings and hence a saturation situation?) So, on the surface, it appears that 2 bridges are less desirable, even tho most of us prefer doing things this way.So, what am I mussing?The shunt reg does a really good job of controlling LOAD variations of voltage, current, etc, and can quite easily adjusted to provide different rail voltage and it supplies different currents for each rail on demand with no problems, but still needs to draw the same current and voltage from each side of the bridge(s), hence the emphasis on setting same CCS current in the Regs and also building a good primary supply before we get to Salas' extremely good shunt regs.
Things seemed a little quiet here...I finally built another v2 which I intend to power my DAC.
One thing I noticed though is that the MOSFET 2 heats up very quickly and I can hear a high pitch "whinning" sound from the first V2 built when power up. It went quiet again after about two minutes and play well in my system. No such problem with the second v2 noted.
Is the noise due to some failed components?
Rgds
One thing I noticed though is that the MOSFET 2 heats up very quickly and I can hear a high pitch "whinning" sound from the first V2 built when power up. It went quiet again after about two minutes and play well in my system. No such problem with the second v2 noted.
Is the noise due to some failed components?
Rgds
Tham said:
Oh, that sounds to me like it was oscillating. At this point remember, v2 is like F1 racing; tiny difference in components and layout will increase or decrease the output impedance. The Idss of the 2sk170, the hfe of the bipolars, all these together can result in high enough gain and result in oscillation. Some experimenting may be needed to get a stable configuration. One thing that can help if the regulator oscillates and you don't want to try different jfets or bipolars is to use small (20-200pF range) caps on the B-C pins of the NPN (for the positive version).
The negative version will be more likely to oscillate, in my experience. Also, it will naturally have a lower output impedance.
What current is the second shunt mosfet passing? The one that was getting hot.
Voltages seem ok. 260mA is not too much for this regulator. I hate to leave you like this, but I'm leaving for a few days trip with no access to the internet. I've had one regulator once that no matter what I did to it, it oscillated (it was not v2, but another variation on v1). In the end I just built another one that worked right away and used the parts of the one that oscillated for other projects. Since you already have one v2 that works fine, you know it can be done. Good luck! I'll check on you when I get back.
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