2ch to 1ch... Stereo to Mono issues.

Once a long time ago I visited one of friends who had Genesis 5 speakers and Sonic Frontiers Power3 amps. One of his amps broke down and was sent for service to Canada. He was feeding his mono-amp from both channels through Y-connector. It seemed that 160W/side wasn't enough to drive even speaker with active(400W?)bass driven system and I'm sure it wasn't his best day even if he wished to demo his speakers. He wondered why from one (only right or left) channel the music comes louder than from both if brought onto one speaker and from two channels might even clip but not fill the room with enough sound.

I recently was running out of two channels preamp out through y-connector to the mono amplifier(certainly I'd prefere a complete music rather than listening from each channel separately). I was facing absolutely the same problem or maybe fact and wondered why I don't have enough gain or enough power and listened almost to the end of preamp's volume controll... Than I tried to feed my mono amp only from one channel right or left and had to turn the volume significantly lower than previousely. Than I played mono record feeding a mono amp from both preamp channels with no compromise to the gain.

I guess that out of phase signal cancellation takes a vast place in transfer of both channels onto one.


What is the best way to bring stereo signal onto mono? Are there more reasons why the signal decreased becides the one I guessed?

Please note that in both cases amps and preamps were unbalanced. Preamps were dual-mono with separate ground for each channel but with one power supply for both.
There are two issues.

One is that there is signal cancellation of anything that is out-of-phase in the two (stereo) channels. There being nothing out-of-phase between the two mono sides, there is no cancellation and the resulting signals are louder.

Another is that the Ycable has the effect of shunting one preamp output with the other. This has the automatic effect of reducing the output voltage seen by the power amp; the amount of reduction dependant on the output impedance of the preamp.

BTW, your friends Power3 (and mine) is a mono amp with 225watts, not a 160wpc stereo amp. Running the two speakers on one requires resetting the amp's output impedance for maximum power transfer.

I should've known the shunting case!

I should've recalled Bryston preamps that have MUTE switch that basically switches the preamp to MONO thus reducing an output signal by 20dB simply by shunting whattafool!

I guess I should use transformer to transfer signals onto mono or...

I'd biamp with two monoblocks from the different channels onto one speaker or...

I'd connect signal speaker binding posts through the ON/OFF or A/B switch to have flexibility(I know I thus reduce impedance but amps can handle it) simply because...

...of my personal likes to mono v.s. stereo.

Any better ways?

Thanks for the insight!
My SF Line3 has a mono switch which maintains 6dB of channel separation to minimize phase cancellation and puts the mono(!) output on both channels. Works well.
Don't tell me you wanna sell me your line3... ain't no budget for now for this "mono solution" even used!:-)

Assume you've got a hell of a rig that you never introduced except SF-3 components here!

Best of luck

One way to do this is to use a "passive resistive network". Normally used after the power amp (not after the pre) -- in other words, put both stereo channels from your amp into one of these, then feed the speaker from that. The guys who setup expensive "whole house" systems sell these, under $100 (I realize that's not zero, though). This is not a transformer, it's a passive device.