Subwoofer circuit: Going from speaker level to line level

[champ04]

Greetings,
Most modern sub-woofers have both speaker level (high) and line level (low) inputs.

My sub does not have the speaker level inputs. This was not a problem while I was using a pre-amp in my system. But now that I've gone direct from the source, I need a way to include my sub in the system.

I was thinking about creating a circuit that would allow my sub to get it's signal from the main amp.

But before I go any further I am wondering, what's the opinion here on how complicated this might be and degree of difficultly to implement.

All I need is a circuit that takes me from the output level of my amp back to a workable line level that my sub amp can a handle.
Seems simple enough.
Any ideas?

Thanks!!

[frasco]

I'm by no means an expert but wouldn't it be more logical to take the signal from the amp input instead of the output?

[champ04]

Originally Posted by frasco

I'm by no means an expert but wouldn't it be more logical to take the signal from the amp input instead of the output?

Perhaps.
I am using a shunt attenuator connected at the back of the amp.
So in order for it to work, the signal would have to branch off between the shunt circuit and the amp.

I'm not certain how this would effect the various impedances.

As it is, my source output impedance is 5ohm. The amp input impedance is 100Kohm. And the shunt circuit has a 2kohm for it's series resister. (technically, 1k per balanced leg.)
I haven't looked yet to see what the input impedance of the sub amp would be.

I'm just assuming that the input impedance of the sub amp would be a lot more benign parallel to the speaker load. It also keeps as much out of the primary signal circuit as possible. (though I may be naive in this thinking.)

[frasco]

I have no idea TBH, let's wait for the experts to answer.

[ODougbo]

Sounds like you want to build one, however there are a lot of different models for sale.

e.g. Amazon.com: XANTECH SLLC1 Speaker Level To Line Converter: Electronics

I've used them here and there, they seem to work okay/fine.

[champ04]

Originally Posted by ODougbo

Sounds like you want to build one, however there are a lot of different models for sale.

e.g. Amazon.com: XANTECH SLLC1 Speaker Level To Line Converter: Electronics

I've used them here and there, they seem to work okay/fine.

I would prefer the experience gained in building one. But it is nice to see that there is something to fall back on. Didn't even cross my mind that such a product already existed.

Thanks!!!

[vacuphile]

If your amp is not bridged (so that black=ground) you just need two resistors in series over the speaker output, with the output to the sub taken from the middle. This will divide the voltage from speaker level down to line level when the two resistors are choosen right. What is right, is not critical when your sub has a volume control, so a ball park figure to start off with could be 10KOhm and 1KOhm, with the large value connected to speaker + and the small one to speaker ground. This will give you 20dB attenuation. If you can't get your sub to play loud enough, move from 1KOhm to 2KOhm.

Take 1 Watt resistors, that would keep you safe unless your amp delivers more than 1750 Watts ,

vac

[rabbitz]

This may help.... comes from Linkwitz.

[UV101]

But how does this effect the speaker that is still connected to the amp?
Are you intending to drive you main speakers and this circuit at the same time?

[vacuphile]

Originally Posted by UV101

But how does this effect the speaker that is still connected to the amp?
Are you intending to drive you main speakers and this circuit at the same time?

This does not affect the speaker still connected to the amp, because the speaker has a much lower resistance than the voltage dividing network. Therefore, the resistance of the resistors in this network should not be choosen too low. Linkwitz I feel is on the low side with his 1000/50 Ohms.

vac