5 channels, single transformer

[Moose]

I am planning on building a 5 channel amp for my computer in the case of an dead reciever, recycling as many parts as I can. It will be the standard LM 3875 setup off the data sheet. I want to reuse the transformer, rectifier bridge, and the supply caps (6800 uf each). It produces +/- 29.5 V after rectifying.

My question is how large should the capacitors be for the supply right at each chip. The normal 1000/1500 uf for each rail seems like overkill with the large caps on the rails already, however there will be 5 or 6 inches of wire between the caps and the chips as I am planning it right now. Hopefully I have included enough information..

TIA

[martin88]

I think you should use a transformer per channel realy beccause if you were to hit bass hard on your woofer you could find all of the other channels volume went down where they are not geting enough power and this could be very anoying.

[tlmadsen]

HI Moose

First, you will be fine with just one transformer as long as it is big enough. The +/- 29.5 seems also to be fine.

To answer your question about how big the capacitor at each chip should be, it is not extremly importent. Anything form a couple of hundred uF and up should do the job.
A lot more is actually to be said about thise "on-board" capacitors, but just start out with what you got. No need to go "over board".

Have fun

Thomas

[ir]

Originally posted by martin88
[B]I think you should use a transformer per channel realy.../B]

i'd hate to imagine how heavy an amp with 5 transformers would be...

you could however try putting larger caps on the amps intended for front left/right and just the normal 1000/1500uf on the remaining three. some people would argue that doing that might make a noticable difference in sound but then, so is using smaller speakers for the rears+centre anyway

[Moose]

I'm going to start small with 470 uf per channel, plus the 6800 uf at the rectifier. I will then compare the sound with with my other gainclone which has 1500 uf caps at the chip, and if the bass is lacking go from there. Thanks for your suggestions.

[demogorgon]

i to seriously would consider giving the sub chip it's own components.

teh five rest, you can offcource combine.

good luck on your project
marius

[thomas997]

Originally posted by demogorgon
i to seriously would consider giving the sub chip it's own components.

teh five rest, you can offcource combine.

good luck on your project
marius

5 channel = F/R/C/SR/SL so it sounds like no sub amp.

But you are right, if your going to have a sub amp, make it seperate and put in lots of caps near the chip.

[SheldonD]

Again and again i see references to multi transformers and monobloc etc.

One transformer is the best way to go if we are talking about music. If multi-channel concerns are to drive motrors for example then the following does not apply.

But for music which statistically has a random demand on power,
A single transformer is the best performance for the price.

Just a thought; does your electrical power facility have each house provided with the maximum power simultaeneously by providing lines heavy enough to provide each user the maximum power at the same time from the generating point? Do the power generators get sized to the size that would be needed if every user demanded maximum usage at the same time?

Of course not as it would be overkill and cost far too much and would not in the end provide any benefit.

A single large transformer costs less, regulates better, is more efficient, weighs less, and takes up less space than mult smaller to the same output power.

For the same cost one can get superior power from a simpler power supply.

The same consideration can be applied to the filter capacitors.

The one area which should be considered is the rectifier diode capacities to ensure that mas load is not exeeded.

The one area where monobloc thinking applies is in channel isolation, i suspect that proper decoupling would take care of this as well.

[neutron7]

how about use the current big cap PSU for the "0.1" sub amp make new psus for the other amps.



sub > 3886 or bridged/parralel 3875 using the current psu (depend on woofer)

center >3875 with own PSU 1000/1500 uf

L and R mains > 3875 with own PSU (maybe use carlosfm hi cap + snubbers for those or even regulated to lower voltage)

rears >3875 with own PSU 1000/1500uf

still powered from same trafo but at least they will be a little more isolated from each other.

you could probably share the PSU for rears and center because you dont often get a lot of speech and surround action happening at loud volume at the same time.

all you will need is the boards you will get anyways and a few extra diodes and caps

[jinkuchi]

I make 68w x6 channels.
with one toroid transformer. With Cap. 10000x4
Its very good.