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Question Using a non-LFE amp with an LFE subwoofer?


Novice Member
I have a Dynaco Stereo 70 amp. I would like to connect it to a set of Orb Audio speakers w/subwoofer.

The problem is the Orb subwoofer needs an LFE connection and the Dynaco doesn't have one.

I presume there is a magic black box that could remedy this issue?

I have read using the tape loop for the LFE connection but this amp doesn't have a tape loop, the pre-amp does but not the amp.


Active Member
well as you are talking subwoofer then it 99% sure has its own internal amp in which case you feed it from the preamp, not the power amp!

the connection on the subwoofer can be thought of as a combined L&R into one connector as the sub does the bass on L&R channels, so if you have a spare preout then you just need something like this



Distinguished Member
Can you give us the specific model of the Subwoofer? Most Subwoofers have two sets of inputs; one for low level Line Level inputs, and the other for Speaker Level inputs.

I'm assuming the LFE input on the Sub is a RCA-style plug like those shown by Nerox, but the question is does it have ONE of those inputs or TWO?

The next question would be, does your amp have Pre-Amp outputs? I think the Dynaco is a somewhat old amps since I haven't heard of them for years.

Actually, a quick Google search indicate that the Dynaco Stereo 70 is a power amp, that means you must be using something else as a Pre-Amp ... what would that be???

We need to know what outputs you have available on your Pre-Amp, and we need to know the specific Sub you are using and what specific input options it has?

Assuming you have some type of Pre-Amp and assuming that the Subwoofer has two RCA inputs, then you can use a cable similar to that recommended by Nerox to split the signal out of the Pre-amp, and use it to feed both the Subwoofer and the Power Amp.



Novice Member
Thank You for your replies,

Yes, the Dynaco is a very old power amp. I am also using a Dynaco pre-amp. The Dynaco pre-amp has Audio Out and Tape Out (both have left and right RCA connections).

The subwoofer I am hoping to use is Orb Audio (same as the speakers) and it only has a single LFE connector.

The light went off after reading Nerox's post. A Y-connector should work just fine, but I will have to use the Tape Out connectors for the subwoofer. Or use 3 Y-connectors, 2 on the Audio Out, and the third to combine a left and right connection for the subwoofer (yeah, OK, well, probably not).

I was expecting some kind of magic black box that would be connected between the amp and all the speakers, that would then act like a crossover to separate the frequencies and have an LFE connection for the subwoofer as well as the right and left channel speaker connections. This contraption may exist but now seems like so much overkill.


Distinguished Member
You can not connect TWO Outputs to a single input. You need some type of isolating device. You can get Stereo to Mono transformers that will merge the Left/Right signals into a single blended signal.

My advice would be to buy a different, more flexible Sub. One that has both Stereo Line Level inputs and also has Speaker Level inputs.

Also, it is very likely that the TAPE Out on the pre-amp is FIXED level, and by that I mean it does not respond to changes in the Volume Control. So, it is in essence wide open all the time.

The Orb Audio subMini has a single Low Level connection that is meant to work with an amp that has a Sub-Out or with a AV Receiver, which would also have a Sub-Out.

If we are dealing with Line Level signals as we would with a Pre-Amp, there are Stereo to Mono device out there that could blend the channels -

SMC-1 Stereo/mono converter - günstig bei LTT

SMC 1 Audio Converter Stereo Mono Switches | eBay

Split the Left Signal from the Pre-Amp into two using one of the splitter cables. Send one leg to the Stereo to Mono Device, then the other to the Power Amp Channel. Do the same on the other side. Use the Mono output of the Device to drive the Subwoofer.

Remember, you need some type of isolating device like those linked above to blend the Left and Right channels. You can't simply connect them together. Well... you can but we can't guarantee that it will work, or that it will not damage your pre-amp.

That's about the best you can do.


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