I run an external mixer, myself. It is also good for external wavetable/MIDI devices if you have or plan on integrating those in the future.

Either you run your output of one to the input of the other, or you use an audio switch like they use to test speakers in stores, or you run it to a mixer. Mixer is most flexible setup. Something like the Rolls Mini-Mix II stereo would be perfect for the purpose--it's just inputs and separate volume knobs. Make sure you get something that supports line level signals. Mic level signals are not what you want here and eBay often sells "mic/line" mixers that are not line level mixers.

It's possible to go with a mixer that is more expensive and has two audio buses. You can often pan an input to one or the other bus (in other words left or right channel) as well as equalize it. It's an expensive fix to the flipped channels in the SBPro 2.0. 😉

Check eBay, it's full of these little mixers and what you want can probably be had for under $60 in the US outside. YMMV.

Multiple options, in general order of sound quality (depends a little on component quality):
1. Hook your speakers/headphones to whatever card you need for that session, or get an external switch. (Won't mix concurrent sources like separate MIDI and digital sound.)
2. Get an external mixer or possibly speakers or receiver with multiple inputs.
3. Run the line out from one card to the other's line in to output both.

Assuming both sound cards output stereo, another simple and very cheap dumb analog solution is just a 2x3.5mm to a single 3.5mm adapter. You will get garbage if both output at the same time, but that's probably not something you will do.

Using a home made passive mixer (basically just a little piece of perfboard and a few resistors) to connect two sound cards to the same receiver. Very convenient, no switches needed.

dr_st wrote:

Assuming both sound cards output stereo, another simple and very cheap dumb analog solution is just a 2x3.5mm to a single 3.5mm adapter. You will get garbage if both output at the same time, but that's probably not something you will do.

I'd be very reluctant to connect two active sources together without any impedance in between. It might work, but you're definitely taking a risk.

dr_st wrote:

Assuming both sound cards output stereo, another simple and very cheap dumb analog solution is just a 2x3.5mm to a single 3.5mm adapter. You will get garbage if both output at the same time, but that's probably not something you will do.

Actually, if the output would be garbage, it would be garbage even if only one of them is outputing anything, because the other one is actively outputing steady state level.

And connecting two outputs together is never a good idea, sound cards may have speaker outputs driven by speaker amplifier that runs from 12 volts, so they would be fighting hard against each other. Line outputs that are driven by simple operational amplifiers might work but it's really better not to do that either, as sometimes you can't tell if the only output on the sound card is speaker or line level output. The speaker output connected to line output might even blow up the line output.

Basically same thing as connecting two amplifiers at the same time to one speaker, I would advise against connecting two outputs together, unless I know what kind of output stages the connectors have.

Jepael wrote:

And connecting two outputs together is never a good idea, sound cards may have speaker outputs driven by speaker amplifier that runs from 12 volts, so they would be fighting hard against each other. Line outputs that are driven by simple operational amplifiers might work but it's really better not to do that either, as sometimes you can't tell if the only output on the sound card is speaker or line level output. The speaker output connected to line output might even blow up the line output.

Basically same thing as connecting two amplifiers at the same time to one speaker, I would advise against connecting two outputs together, unless I know what kind of output stages the connectors have.

Running two amps in parallel is almost never done, but bridge mode with two amps in series is very common. Of course, proper isolation of the outputs is a concern, but not a big problem.

As for parallel amplification or sources, yes! You're depending on the impedance of the output stages and cabling to limit any current being sourced from one output and sunk into another. Potentially even jitter will result in significant power loss or distortion. It's a form of short circuit. For a similar reason, you have to be careful when plugging two power supplies in parallel to boost available current (see ballast resistors).

Jepael wrote:

Actually, if the output would be garbage, it would be garbage even if only one of them is outputing anything, because the other one is actively outputing steady state level.

For whatever reason, I would think that 'steady state level' would be about 0, so it would not affect anything if summed, but perhaps I'm completely wrong about this. The other things you mentioned are also obvious concerns.

Actually I am not sure I've ever used such a muxer myself (I did use it the other direction - as a splitter), so perhaps it's bad advice after all. 😀 Whenever I used a multi-card setup, I was using the line-out to line-in method, with one card passing through the other.

I used to daisy chain soundcards but I found it more trouble than to use separate input on receiver. Always muting unused card, making sure the second one is initiated and volume and input level don't overdrive... Maybe you could use an stereo sliding potentiometer and short the ground ? Just a thought as a I cannot see a good reason in mixing an AWE64 and SBlive.

I use a short extension cables from the back of my PC's and just plug the speaker into which ever PC I want sound from.

a mixer. I have a Rolls RM203, 10 stereo inputs and a couple of outputs. You can run the two cards into the inputs, add in any midi modules you want, have a single output to a little amp like a lepai2020 to bookshelf speakers.

+1 fr a simple little mixer - I tried all sorts of things but eventually ended up with a passive 4 input mixer from Rolls, and it's just perfect. You lose some gain but not much, and it's so nice to be able to forget about software mixer levels and looping cards via line-in.

chinny22 wrote:

I use a short extension cables from the back of my PC's and just plug the speaker into which ever PC I want sound from.

Of all myriad solutions in this post, your one is the best. Keep it simple! 😎

I was surprised to read that on the amiga1200 manual

amiga 1200 user manual page 1-11 wrote:

Audio connection to a Monaural Monitor
A monitor with monaural sound capability can still accept both Amiga audio channels. Either use a "Y" adapter cable plugged into both Amiga audio jacks, or plug a single audio cable into either one of the jacks. Insert the other end of the cable into the monitor's audio input jack. Both audio channels will be routed to the monitor speaker.

... who would do that on a 1000$ ebay amiga nowaday ? 😁