help powering 41hz amp3 and an active crossover on the same supply

[Nemophyle]

hello

i post this here as i don't really know in which section it belongs. I'm in the process of building small high quality monitors for listening and mixing music while travelling. I have 2 41hz amp3 lying around and planned to use one for each monitors, using one channel for the woofer and the other for the tweeter, by using an active crossover in each speaker. I already have the crossover boards, wich are classic 12db linkwitz riley, normally working on a symmetric +-12v supply. My problem is that the amp3 uses +12v single supply, and i would like to find a cheap and elegant solution for powering both with a single transformer, if it is possible.

i have thought of making the op amps work in single supply, although i don't really know if this is possible, or making a simple split supply circuit like described here :http://sound.westhost.com/project43.htm

but i'm not sure that the "heavy" load of the amplifer on the + rail would not screw it up

so i'm in desperate need of help on this one, if someone can shed light on my problem, thanks !

[Buckapound]

I'd sure like to find a solutio to this as well.

I know there are dc-dc converters which can provide a dual supply, such as the C&D Technologies HPR410c ( Mouser). Not cheal at $17 each, but it solves the problem. Other voltages are available. Actually, cheaper versions available from same supplier at about half that price, 1 watt.

Anybody know if you can just hook up one of these and go, or if it requires building a circuit around them?

--Buckapound

[FastEddy]

" ... I already have the crossover boards, wich are classic 12db linkwitz riley, normally working on a symmetric +-12v supply. ..."

What kind of op-amp is on the crossover boards? Often even high quality op-amps will work just fine from a +/- 6 VDC source, thus you may be able to "split" your main +12 VDC supply. Of course you will have to have some sort of DC blocking cap in the circuit between the crossover board(s) and your main amp(s).

Check out this: http://www.national.com/pf/LM/LMH6624.html ... works fine from +/- 6 VDC and has very good power supply noise rejection and it is intended for low pass, high pass, band pass filters =

Your op-amp may do the same without swapping it out ...

[Pano]

That TI op amp looks like a good choice as long as it's stable at low gain. Sure is a good choice for low voltage.

I've done some opamp stuff inside the little T-Amps but the trouble is always the single low voltage rail and all the switching noise on the power. You can only filter out so much.

On the other hand, even a seperate preamp and active crossover will see some of the RF power noise because it comes out the inputs of the T-AMP!

If you're clever you can use the same DC blocking cap for the input of the Triapth chip and the output of your opamp.

[Nemophyle]

thanks for your usefull replies !

so what i'm getting is that if i get an opamp able to work on low voltage i could use the split supply circuit provided by rod elliot, along with a dc blocking cap, and then the only thing i'd have to worry about would be noise of the amp.

Also, my electronics are basics but if i understood it right, the filter and the amp would have separate grounds, the ground for the filter being some kind of virtual ground, am i right ?

I planned to put the amp3 in a separate aluminium case which would be the heatsink, along with providing some shielding, i don't know if that helps.

Also, i can put any op amp in my circuit as i mounted , i don't know how you call them in english, but sort of "threads" for the ics. For the moment,they are tl082, but i planned to get a bunch of OPA2134. I can't get the amp you refered to easily, but i get from the opa datasheet that it would be reliable for such an application , no ?

i found some ics that provides symmetrical output from single input voltage and that i could get (not cheap) but they're all limited to around 10ma of output current , and i fear that it wont be enough to power even a single 2 way 12db filter

here they are

http://datasheets.maxim-ic.com/en/ds/MAX680-MAX681.pdf

http://www.linear.com/pc/downloadDoc...14,P1233,D2572

Also , i don't know where should i put the dc blocking cap in the circuit so if you can please enlighten me !

[Pano]

The OPA2134 is a nice opamp, it sounds good and is easy to use. Works better at higher voltages, but does OK with low voltages too.

A "socket" is what the opamp goes into.

For single rail supply the DC blocking caps go on the inputs and outputs. The virtual ground is supposed to eliminate those, but I have not had good luck with it in a T-Amp.

You are putting the amp in a seperate case? Then why use the same power supply? Mieux faut une alime separee, je pense.

[Nemophyle]

thanks panomaniac !

well about the enclosure, everything is going to be fixed on the rear of the monitor, but i have some spare little enclosures in aluminium, so i thought i could use them as heatsinks for the amps, aswell as providing some additionnal shielding. everything is then gonna be enclosed in wood.

i don't want to do a second PS, because i thought there could be a cheaper way of doing it. Adding a second transformer + rectifier + filtering caps would raise the price of about 30 euros, and althought that's not much, it's not cheap either. I'm gonna try it this way as it doesn't seem very difficult to do and it would cost me almost nothing.

what kind of caps do i need as dc blocking cap ?

thanks much !

[Pano]

OK, give it a try. It won't sound awful. The little Lepai amp uses a dual opamp as an input buffer run right from the 12V supply. It sounds OK.

Use whatever good film caps you would normally use. I assume the volume control is before the crossovers? Do you have your filter topology worked out yet?

[Foxx510]

What about this simple low power switching supply. It uses one ic($5AUD) and a few external components. I'm about to build one for a linkwitz transform circuit in my car.

http://sound.westhost.com/project69.htm

[FastEddy]

p: " ... if you're clever you can use the same DC blocking cap for the input of the Triapth chip and the output of your opamp. ..."

N: " ... so what i'm getting is that if i get an opamp able to work on low voltage i could use the split supply circuit provided by rod elliot, along with a dc blocking cap, and then the only thing i'd have to worry about would be noise of the amp. ..."

p: " ... the TI [LM6624] op amp looks like a good choice as long as it's stable at low gain ..."

N: " ... The OPA2134 is a nice opamp, it sounds good and is easy to use. Works better at higher voltages, but does OK with low voltages too. ..."

Yes, by all means use the [IMOP, better] OPA2134 ... can run from as low as +/- 3 VDC, and has excellent features & specs at +/- 6 VDC ( http://focus.ti.com/lit/ds/symlink/opa2134.pdf ... page 5 graphs indicate that extra filtering may be in order, like a fat plastic MKT cap right across pins 4 and 8 ... )