LM3875 Power amp with XLR and phono

[inrank]

hi,

can i make "LM3875" based power amp and a seperate pre-amp that has both phono line in and XLR inputs and outputs.

this is so i can connect a phono line out from a cd/dvd player into the pre amp then a XLR line out from the pre amp into my Tannoy TS8 subwoofer then the XLR high pass output into the power amp then that into my CSS FR125 based bookshelfs.

can this be done ?(easily and on a budget)

could i also have two sets of switchable speaker outputs ( A or B not A+B)

[jimbo1968]

I can answer the last one > Yes; you'll need 2 sets of outputs and a switch.

[inrank]

lol ok, thanks

[jimbo1968]

As for the rest, I haven't got to grips with balanced inputs yet but for the crossover you could put an active crossover in either the pre-amp or in the amp.

if the sub has built in low-pass you only need to build a high pass. Maybe this could be a line level passive filter (?).

What frequency are you going to cross?

I'm about to cross my sealed FR125s at 120Hz (I think) using the active filter board from the current group buy.

[leadbelly]

Originally posted by inrank
can this be done ?(easily and on a budget)

could i also have two sets of switchable speaker outputs ( A or B not A+B)

Very easily done.
Your "preamp" will just be: phono => pot => DRV134 => XLR

Your power amp will just be: XLR => LM3875

And you need a hefty DPDT switch to switch the speaker outputs. Don't get too cheap on this or it will have poor electrical properties.

[leadbelly]

Originally posted by leadbelly
Your "preamp" will just be: phono => pot => DRV134 => XLR

Your power amp will just be: XLR => LM3875

Thought about it some more and this way is better:
phono => DRV134 => XLR
XLR => pot => LM3875

You didn't really say if you want something that will perform well or just want to do it as cheaply as possible. If the latter, you don't need a preamp at all, just make a phono => XLR cable

[inrank]

this is the kind of thing (i think) i need.

at the moment i have a NAD L53 reciever which does not have a line out only a mono sub out.

so making a cheapish pre power for this would be good.


i want to spend as little as possible, so if there is any other way i can connect my sub to my speakers please tell me

[leadbelly]

Originally posted by inrank
at the moment i have a NAD L53 reciever which does not have a line out only a mono sub out.

I am lost now as to what you are trying to achieve. Maybe you should step back and describe what components you have and what you are trying to make your audio chain look like. If that XLR is a mono sub-out from a receiver, you cannot use it as a signal to drive a pair of fullrange speakers.

[inrank]

no...

the pic is what i would want the pre and power amps to look like if i made one using the LM3875 chip.

i currently have a NAD L53 Amplifier/Tuner/DVD all in one system a Tannoy TS8 sub, some Tannoy DC1000's and some FR125 based full rangers that i am making at the moment.

i want to connect either pairs of speakers to the sub so that i can play them loudly and not stress the speakers and fill in for the FR125's when using them.

sorry for the conclusion.

[jimbo1968]

if your receiver has bass management, all you need is the phono to xlr lead.

unless you want to build a chip amp, in which case not having line out is a problem.

what receiver functions are you hoping to retain? source selection, dolby decoding and rear amplification?

edit: just seen your previous post. Maybe all you need is a speaker switch and phono to xlr cable.