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pjpoes 26th May 2007 01:02 AM

Pics of parts for new HT amp
Some of you may have noticed my other posts concerning my new Home Theater amp. I bought some Aussie amp modules, the NX150's, which put out between 150 and 180 watts rms depending on rail voltages. I know the design should reject ripple fine, but I always wanted to try a CLC power supply with a solid state Class AB amplifier. I am biasing this amp so that its quiescent current is around 350-400ma, use an 8mh inductor, and over 80mf's of capacitance, with a 600va transformer. Thats per amp, so I would say the power supply is far more than is needed. I got the caps, inductors, and transformers through ApexJR so I didn't pay too much. Now I have to find a way to put all this into a chassis or two, and not miss off the significant other, so far she is less than impressed. Anyway, here is a pic of one channel's worth of parts, not including some of the hardware, the chassis, etc. However in the pic you will see 6 power supply capacitors rated at 22,000uf each and 100v. One 600VA Toroidal rated at 45-0-45, one 8mh inductor rated at 16 amps, and can be wired to 11mh, but I'm not sure the current rating then. There is one NX150 modules, and a bag of .022uf film and foil caps I got off ebay to use as bypass caps and such. 3 dollars for that bag of 50, not too bad.

jleaman 26th May 2007 02:59 AM

That looks to be a great start, keep us posted. What kind of chassis you thinking about building ?

pjpoes 26th May 2007 02:26 PM

More than one chassis, but I'm undecided on how to proceed. I'm going to lay out the parts in different ways and take some measurements. I could build three monoblocks as one option, or a seperate power supply and amp chassis. Thing is, I could easily fit all the power amps into one chassis, keep them nicely isolated from the power supply noise then, that chassis wouldn't weigh much at all. However, then you look at those parts, figure out how big a power supply chassis I would need, and suddenly I have a 100lb power supply thats 19" wide, by 19" deep, and 10" tall. To be honost, I'm not even sure thats big enough, but I believe that gives enough room to mount the transformers upright, which will save some space.

I know they are shielded, but one concern is getting the inductors too close to the amps, I don't want to induce coupling and thus noise. Another concern is how close they get to each other, as the inductive coupling could lower the values. One thought is to mount them on metal "cards" like the expandable HT amps, with the transformer and inductors layed out like this (O8). Then have the capacitors mounted after that. However even this is going to weigh a lot, so I do need to come up with something innovative to make it weigh less.

For anyone curious, this is why linear power supplies have lost out in popularity amongst quite a few designers. When you compare the ripple you get from a switchmode powersupply vs a linear supply, and compare the size of each, its hard to justify the linear supply. I'm actually thinking of buying a switchmode supply at a later date rated for one amp, and then modifying it to get the ripple where I want it. I could be wrong on this, but I believe essentially all switchmode supplies are a regulated design, so a 500 watt design would be like having a regulated 500 watt supply for your amp.

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