First DIY-input appreciated

[jrgoswick]

This will be the 'FIRST' DIY I've done. It's going to be based on an M-501 Onkyo(will post scats when I get them, I don't know all the terminology but it looks like a long tailored pair to me). Unlike the original, I'm using ALL the devices in the final stage in parallel(the original has a pair per channel, I've got two amplifiers, giving a total of four pairs per channel). Papa Pass has been kind enough to offer his assistance(or opinion, either way I thought was HELLA COOL) with power supply design. I'd also like input from you guys. I'm using a pair on modded Monitor 12 Polks(pretty much all the mods MINUS the driver rings-ON THE LIST).

An FYI-this 'thing' is using MOST of the parts from the originals in a dual monoblock configuration.

POWER SUPPLY-The heart of the whole thing.
1)-Transformer(s)-I've been eye balling a 1.5kVA Plitron toridal for this project. Would I be better off using one per channel? What about using the factory transformers? That would cut costs and free up coin for other parts. INPUT PLEASE-this is the one that's gonna hurt the build.
2)-Rectification-I'm thinking two bridges per channel. Any and ALL input is welcome with this one. My train of thought is this-use a high(35A) bridge for each rail. This will cut down on rectifier stress at power up, each rail has it's own rather than both rails sharing.
3)-Filtering-Go HUGE with it. Bigger isn't always better, I know this. I'm wanting about 400WPC@8ohms. How much is too much? I was going with about 40kuF per rail(MINUS RC filters and such) What about using a bunch of smaller values to get what I need VERSUS using beer can caps? Smaller ones will drop the ESR, dump better, and charge faster. Bigguns just look cool? Any thoughts? Another thing I/we(my father is my co-pilot, mentor, and mathematician) are considering is stacking a cap at each device(size to yet be determined). This will be after final main filtering of course.
Another thought(and NOT COST EFFECTIVE AT ALL) is using lead-acid batteries in series/parallel INSTEAD of caps. DC IS BEST RIGHT? Has ANYONE thought about ditching caps for inductors in the power supply. My father keeps bringing this up, BUT the math is so overwhelming to both of us.
4)-WIRING-Should this be done point to point or on etched boards? I'm saying there's a 50/50 mix here.

All comments, either positive or negative are welcome. This is my learning curve and a whole community can't be wrong!

JRG

[AndrewT]

Hi,
Power supply.
For a 400W 8ohm amplifier you need between 400VA and 800VA for good value for money. Too small and the performance drops too much. Too high and the extra costs give only tiny improvements in performance.
If you are using 8ohm speakers then I beleive you can use +-20mF on the supply rails for good bass. Others recommend much less than this. eg. +-4700uF or +-10mF
Using one rectifier on a centre tapped transformer for monoblock amplifier has no downsides that I can hear or measure.
Using two rectifiers on a dual secondary does not reduce the stresses on the rectifier. It increases the voltage losses through the rectifiers.
However, on a multichannel amplifier, I believe dual rectifiers offer more flexibility in attenuating mains hum and buzz from the amplifiers' outputs.

Amplifier.
400W into 8ohms requires outputs of +-80Vpk (160Vpp, 56.6Vac) and 10Apk into 8r0 resistor load. The maximum current capability of this amp should be aimed at 30Apk while still retaining the ability to maintain output voltage at near (75 to 80%) the 80Vpk.

This will demand supply rails of ~+-90Vdc. This in turn demands smoothing capacitors rated to 100Vdc or more.
This is expensive and potentially dangerous.
I recommend a smaller first build and use that experience to attempt this big build.