Stereo to mono

[karatestu]

I would greatly appreciate some advice on this and please excuse my limited understanding.

I was thinking about having only one speaker (omni directional) and listening in mono, well actually both right and left channels summed into one speaker.

I can only think of two ways to do this and don't know what the best way is regarding safety and sq. Bridging two monobloc amplifiers was the first option I came up with (diy NVA jobbies with passive pre). The other is to join the channels (somewhere) before the power amplifiers using isolation resistors in both signal lines of approx 1K ohms.

My speakers are diy NVA inspired three way things with doped drivers and only a single cap on the multiple tweeters. I will be tri amping so bass, mid bass and tweeters each get their own dedicated amp. The load on each amplifier is likely to be between eight and 30 ohms depending on how I wire up the multiple drivers up, so bridging the power amps could be possible.

I would like to explore the possibility of trying this without blowing anything up, degrading the sound quality or having any impedance issues between stages (I use passive volume control with no active preamp stages or buffers).

Would anybody be kind enough to advise me on the best way to proceed ?

Many thanks, Stu

[Nick]

Best/simplest way is to join them in the preamp. You don’t say how your preamp is wired.

[karatestu]

Hi Nick. Thanks for replying.

My preamp (at the moment) is just a couple of resistors wired up as a potential divider in shunt configuration with 10k in series with signal and 680R to ground. It will eventually be a 10K shunt stepped attenuator (same thing essentially) or volume pot as per nva preamplifiers. There will be a source selector as well ofc but that is probably not of any importance. That is it.

[karatestu]

Just had a thought.

Could I not just use the 10K resistors I already have in series with the signal and join the two channels after those ? I assume the variable resistance to ground after this junction just does it's potential dividing job and controls volume as usual ?

If i can do it like this then I don't need any more parts and the number of stepped attenuator gangs, power amps and speakers I require is halved

I won't ask about the disadvantages of mono .....just yet

[Nick]

Yes, just connect the top of the two 680R together.

[ed]

I won't ask about the disadvantages of mono .....just yet

in the land of mono the one eared man is king(or woman, queen)

[karatestu]

Thanks Nick.

I will connect the two channels after the 10K series resistors at the junction with the 680R to ground. Do I actually need two of the 680R to ground ?

If i disconnect one of the 680R will it change the volume ?

[Nick]

Do I actually need two of the 680R to ground

You don't need them. You never needed them, only if you wanted the volume to be lower than 10k into the power amp input resistance would give.

If i disconnect one of the 680R will it change the volume

Yes, however the volume of two summed signals is more complex than you may think. It depends on the two signals. If (for example by extreme) you had two 1kHz sine waves in each channel out of phase, then you would have got two signals out of the loudspeakers so the volume the room would be high, with a null between the speakers. if you join these two signals with your sum to mono the result will be zero signal and nothing from the speakers.

So the simple answer is "it depends"

[karatestu]

I won't ask about the disadvantages of mono .....just yet

in the land of mono the one eared man is king(or woman, queen)

[karatestu]

Do I actually need two of the 680R to ground

You don't need them. You never needed them, only if you wanted the volume to be lower than 10k into the power amp input resistance would give.

If i disconnect one of the 680R will it change the volume

Yes, however the volume of two summed signals is more complex than you may think. It depends on the two signals. If (for example by extreme) you had two 1kHz sine waves in each channel out of phase, then you would have got two signals out of the loudspeakers so the volume the room would be high, with a null between the speakers. if you join these two signals with your sum to mono the result will be zero signal and nothing from the speakers.

So the simple answer is "it depends"

Sounds more complex than i thought, however I will give it a go

[karatestu]

Listening to it now. Nothing got hot and smoked so good so far Overall volume seems about the same.

It is interesting . Not sure what to make of it yet although my speaker is not in the right place. It sounds like all the sounds are still there but it is more obvious where they are coming from with how I have it set up at present. Going to move the speaker more central along the wall I have it on.

Seems to be less bass volume but maybe I am imagining that Speaker sounds brighter - cymbals stand out more.

[karatestu]

Giving up on this now as I have heard enough and it is giving me a headache. Not sure why. The frequency response has shifted. Going back to stereo asap. At least I have tried it.The prospect of fewer amps and speakers was very appealing but alas not to be.

[vinylnvalves]

You maybe need to add some electronics to make it sound good... Something like “airsound” from orbit sound https://www.orbitsound.com/en-gb/. I am skeptical of these technologies though as if great as they claim they would be mainstream.I have a few quadrophonic LP’s which I have never had the opportunity to play on a quadrophonic system, another fad in audio.

[Nick]

another fad in audio

But it did prompt a lot of work on stylus profiles so not a complete waste.

[vinylnvalves]

Oh yes that’s why we have the Shibata stylus. Listening to one as I type. I would like to listen to my first pressing of Machine Head in its full glory..