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Stereo to Passive Sub


Standard Member
I want to use my system for 5:1 movies and for CD Stereo music.

I have a Denon AVR-3802
Using the Pre-Out Sub Woofer I want to connect this to a
Technics SA-GX100L which I want to use as the amp to drive a passive woofer rated 3 OHMs. (what kind of cable connections do I need?)
A or B speaker outputs on the Technics are rated at 4-16 OHMs per speaker.
Two More Questions:
1. Can I run the 3 OHMs woofer connected to the speaker outputs without damage to the Technics?
2. How do I combine the Stereo Left and Right channels so that they can drive the mono woofer which has just a pair of spring clips connections +/-, Any helpful wiring diagrams and advice would be much appreciated.


Established Member
I think your Technics will struggle to drive a 3 ohm load. That's very low!

You could connect the Sub out from your Denon into any input on your Technics amp and use one channel to drive a passive sub. For example, plug from subwoofer out on Denon to left CD in on your Technics and then use the main left speaker out on the Technics to drive a passive sub. But like I say 3 ohm may well be too low.

You can't really combine the left and right to drive a sub. There is such a way, called "bridging", but your amp would have to be suitable for that and it requires driving the left channel out of phase with the right channel. Probably a non starter.


Standard Member
Hi again folks.

In an attempt to get both stereo channels feeding my passive sub I've connected both positive speaker outputs on the Technics SA-GX100L one to the subs positive and one to the subs negative connections. The negative speaker outputs on Technics are not connected to anything.

Whilst it seems to work I have a couple of questions:

1. Am I actually getting the full feed from both stereo channels reproduced by my sub?

2. By connecting in this way am I courting trouble in the form of an amp or speaker mealtdown?

Does anyone know if this amp can be bridged?

Many thanks for your help.


Standard Member
1. Am I actually getting the full feed from both stereo channels reproduced by my sub?

No. Imagine playing a mono signal. The signal is the same on left and right channels, so your sub sees no signal at all. (you might hear something anyway - thats distortion, not signal)

TrophyJem is right that you probably need to use one channel of the amp.

It should be easy to get both channels of your pre-out driving one channel of your sub amp if you are up for some simple soldering. Replace that straight-through rca cable with one which uses a resistor network to mix stereo to mono. A quick google led me to this stereo to mono summing box.

In practice I dont think I would bother. There is very little stereo separation in low frequency content, so using any one source channel is nearly as good as using both.

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