Active crossover & buffer stage for a 5 channel amp

[sunil]

I'm building a 5 channel GC based amp with a buffer input. I'm confused over a few things.

a) Where should the buffer be placed, before or after the active filter ?

b) Am I right in assuming there will be individual buffers for each of the 5 channels, since the source will be hooked up directly to the GC ?

c) If option b is right do I still require a preamp stage, other than to switch more than one source ?

Thankyou,
sunil

[AndrewT]

Hi,
you may require buffers both before and after the filter stages.
It depends on how you match the output and input impedances.
Medium length lines, say upto 5m, will need an output impedance of less than 600ohms but longer lines eg around a room will be better at less than 200ohms. Input impedance is usually recommended at more than 10 times the output impedance feeding it.
good researching & regards Andrew T.

[richie00boy]

Do the searching, the information is out there. My advice would be to forget the buffer infront of the chipamp. Just have a buffer before your crossover to make sure the filters work properly, then feed the output from the filters directly to the chipamps.

[Optical]

Originally posted by richie00boy
Do the searching, the information is out there. My advice would be to forget the buffer infront of the chipamp. Just have a buffer before your crossover to make sure the filters work properly, then feed the output from the filters directly to the chipamps.

i do it this way and have had no problems..
(buffer first)

[sunil]

Thanks for the replies. If I put the buffers just before the filter can I get away with the PS & GC cases which are 2 metres apart, yes that's 200 cm. It's a 8 channel amp & the tranny is BIG. The PS output will be regulated (all channels) but the distance to the GC...........

Thanks,
sunil

[richie00boy]

2 metres between PSU and amp is not good. The inductance of the wiring may well cause instability and/or not reaching sonic potential.

[sunil]

Yeah, thats what I thought. Guess I have to figure out something.

Thanks for all the help.
sunil

[joensd]

HI Sunil,
which active-XO are you using?
Have you made a PCB layout for it?

Cheers

[Markje]

Originally posted by sunil
Yeah, thats what I thought. Guess I have to figure out something.

Thanks for all the help.
sunil

Place it near the amp, as close as you can. Even a separate housing in the same model on top of the amps enclosure can be a good option (the lenght of your cables will then be only 1 or 2 feet). If you cant place your PSU closer, try twisting your cables, but only as a last alternative. If you can fit it all in one enclosure, you could make a seperate section for you PSU by placing a piece of aluminium between PSU and the rest.

Greetz Mark

[sunil]

Hi Joensd,

I've made some boards with a buffer & BS included. Each board is a 2nd order. The buffer & BS board is separate for more flexibility. To get a 4th order I cascade 2 boards.

Hi Mark,

Thanks for the advise. I realize now, to get the best possible sound I have to keep the PS & amp close to each other. I'm thinking of one chassis. Quite complicated, since the 2 cases have already been made, separately.

cheers,
sunil