Would a subwoofer buffer be interesting?

audioengr · « **on:** 9 Mar 2004, 06:19 am »

I have a subwoofer in my HT system, but I do not use it in my 2-channel system for the following reason:

Like most preamps, the recording-loop outputs come from the buffers used for the main outputs, so loading them affects the main outs. Otherwise, I would use the recording-loop outputs. Likewise, I cannot load the preamp main outs without adversly affecting them.

A solution might be a black box with left and right RCA input jacks and two short cables with RCA output plugs on the ends. The main signal would go through this box from preamp to power amp, so volume of the sub would be controlled by the pre. The main signal would not be broken. Instead, a high-impedance connection would be made inside the box to an op-amp that drives subwoofer output jacks. There could also be a left/right mixed output jack. Then this could be inserted between the preamp and power amp without impacting front channel performance and the supwoofer would have a buffered output of its own. The box would have an internal power supply or use a wall-wart. It could even have switching capability to choose between the HT and 2-channel systems for the subwoofer.

What do you think???

ooheadsoo · « **Reply #1 on:** 10 Mar 2004, 02:12 am »

If you routed your signal to your subwoofer through the recording outputs, you wouldn't be able to control its volume through the preamp at all, since that signal is split off before the volume control. The only way to have the preamp control the sub's volume is to use either splitters or if your preamp has a second output.

Another thought...I bet the subwoofer's amp has buffers and oodles of impedance behind its jacks. There's not much difference between putting the impedance in front of or behind the jacks, is there? I have a suspicion your proposal might be redundant.

audioengr · « **Reply #2 on:** 10 Mar 2004, 05:00 pm »

The problem with splitters is that the capacitive loading and dielectric absorption of the sub cable affects the main front signals. The input impedance of the sub is not the problem. It really must be buffered to the sub to not affect the main fronts.

ooheadsoo · « **Reply #3 on:** 10 Mar 2004, 07:43 pm »

How would your sub buffer be connected to the preamp?

audioengr · « **Reply #4 on:** 12 Mar 2004, 02:21 am »

The subwoofer buffer would have short IC's attached to the box that plug into the Preamp outputs. Then the signal would be routed internally to two output RCA plugs. These RCA plugs will connect the Pre to the power amp using your own IC's. Then, internally in the box, I would tap off the two channels with a high-impedance buffer. This would drive the two RCA's which are the subwoofer outputs. This way there would be no loading on the pre outputs.

ooheadsoo · « **Reply #5 on:** 12 Mar 2004, 02:52 am »

I don't know how well the common preamp with two outputs is implemented, but assuming they are "properly" implemented, a preamp with two outputs shouldn't need the subwoofer breakout box. Would the common preamp that has two outputs benefit from your subwoofer box? Also, would your breakout box work well with passive preamps?

audioengr · « **Reply #6 on:** 12 Mar 2004, 04:59 pm »

Quote

Would the common preamp that has two outputs benefit from your subwoofer box? Also, would your breakout box work well with passive preamps?

Even most preamps with two outputs just use the same driver for both, so and answer is "depends on the preamp".

For passive preamps, this would work really well.

ooheadsoo · « **Reply #7 on:** 14 Mar 2004, 02:06 am »

Sorry, I can't think of any more questions to help you flesh out your ideas.

Ok, here's another. Any estimate on the cost?

audioengr · « **Reply #8 on:** 14 Mar 2004, 05:25 pm »

I can only estimate, but would like to keep it between $200 and $300.