Mono Subwoofer

[croccodillo]

Hi all,

I have a mono subwoofer and I want to drive it from my car radio pre-out (of course with the help of a mono amplifier).
So, I need a simple, active circuit that converts (sums?) the two stereo channels into a single, mono one, togheter with a crossover (low-pass filter) network. Perhaps using some op-amps.
I'm lazy, so my question is: is there an already done circuit or do I have to draw it from scratch?

Thanks in advance,
Giovanni

An externally hosted image should be here but it was not working when we last tested it.

 

[sagarverma]

So, I need a simple, active circuit that converts (sums?) the two stereo channels into a single, mono one

y active for summing?????

use two simple resistances,10kohm.metal films preferred.
join two resistances end to end at one end,join one out to one end,and other out to other end,u get summed output at other the conjoined end.its so simple!

for lpf::::go to www.download.com
,download filterpro.design simple active filter of your use.🙂

 

[richie00boy]

Active summing is better 🙂 And seeing as you will be using an op-amp for the filter, use a dual device and one half can perform the summing.

 

[sr20dem0n]

Or you could just buy a mono amp that sums the two inputs together (90% of them do) and has a built in lowpass filter (99% of them do)

 

[croccodillo]

Thanks for your answers...

I already have sub and amplifier, the amp (an old Sony XM-4520) does not have a sub input, so I have to provide a summing/filtering stage before to feed it with the signal.

I downloaded the FilterPro software (thanks sagarverma), and I'm trying to design a simple filter.

Thanks a lot,
Giovanni

 

[sr20dem0n]

what kind of input does it have?
or do you mean it only has a single rca input?

edit: That's a 2ch amp isn't it? Do you have it bridged? Because the act of bridging sums the two channels together, exactly like you would be doing with this circuit. You'd still need a lowpass filter though.

 

[richie00boy]

The act of bridging per se doesn't sum channels, but the way that car amps tend to implement bridge does.

 

[sagarverma]

Because the act of bridging sums the two channels together, exactly like you would be doing with this circuit.

no

 

[sr20dem0n]

no

with car amps, yes

 

[sagarverma]

with car amps, yes

how?car amps r no special.

 

[richie00boy]

If you need to connect both left and right to make the bridge (like every car amp I've ever seen) then it sums them.

 

[sagarverma]

If you need to connect both left and right to make the bridge (like every car amp I've ever seen) then it sums them.

its not sum exactly.the power increases by a factor of 4 bec of bridging(theoritical).but due to losses etc(real world conditions),the power out is only double or even less but definately >than individual out power.

 

[richie00boy]

That wasn't my point. My point is left+right is the output. The fact that the PSU are generally not up to the job and losses are present wasn't really under debate 🙂

 

[croccodillo]

Well, this is my first car amplifier, so I do not know how they usually work.
Now I'm a little bit confused.
The amp has four screw connectors for the output:
1. Left +
2. Left -
3. Right+
4. Right -

The input is composed by two RCA connectors, left and right; over the left one there is also a "mono input" label.
I'm at work now, I will take some picture tonight and post them tomorrow morning.

Ciao,
Giovanni

 

[Crazy-Stereo]

The input is composed by two RCA connectors, left and right; over the left one there is also a "mono input" label.

You just connect the pre-out into the mono input.

originally posted by sagarverma
use two simple resistances,10kohm.metal films preferred.

You still need this to sum the input before bridging the output, croccodillo.

 

[richie00boy]

He won't need any summing resistors or op-amps if the amp bridges like most car amps do.

Look on the speaker terminals and it probably says something like

left + (bridge +)
left -
right +
right - (bridge -)

If this is the case just connect both left and right phono leads and one speaker across the bridge terminals and that's it. Unless the amp has a switch specifically for stereo/bridge mode then you just need to connect one phono lead to the mono input, and summing will be required. I've never seen this before on a car amp though.

If bridging is not mentioned then it maybe a cheap chip-based car amp that is already internally bridged on each channel so cannot be bridged further.

 

[sagarverma]

He won't need any summing resistors or op-amps if the amp bridges like most car amps do.

rightly said.or how the hell will they get huge power demanded by people for their car.

I've never seen this before on a car amp though.

i have seen🙂

If bridging is not mentioned then it maybe a cheap chip-based car amp that is already internally bridged on each channel so cannot be bridged further.

he must be careful with that.lest everything goes up in smoke.

 

[sr20dem0n]

If bridging is not mentioned then it maybe a cheap chip-based car amp that is already internally bridged on each channel so cannot be bridged further.

I haven't been able to find much on the amp, but I have found bridged power ratings.