A popular choice that would suit your needs as well seems to be the Behringer RX1602 line mixer. It has 16 input channels (so that's 8 stereo channels). Here in Germany they can be had for as low as 40€ used and about 90€ new (Edit: although prices for used gear seem to increase and new ones are often out of stock.)

Once I have enough space to set up multiple retro PCs at once (currently only room for two or max. three under my desk), I will get one of those.

Edit:
If the line mixer solution is something that would work for you, here are a few alternatives in case the Behringer is not available in your area, but they are all much more expensive:

• ART MX822
• Rolls RM219
• Samson SM10
• Tascam LM-8ST

I use an "audio switch". Kinda like a KVM but for audio. Mine is an 8 port to match my usual KVM. The output of the audio switch goes to the line in on my main daily desktop workstation (I run a Linux system as my daily driver). On my desktop I can simply switch audio inputs. It's cheap stuff but it works...

pan069 wrote on 2021-02-03, 10:45:

I use an "audio switch". Kinda like a KVM but for audio. Mine is an 8 port to match my usual KVM. The output of the audio switch goes to the line in on my main daily desktop workstation (I run a Linux system as my daily driver). On my desktop I can simply switch audio inputs. It's cheap stuff but it works...

IMG_20200518_154548.jpg

this is great! I'm still crawling behind PCs to manually move the things from one to the other! but then i tend to use one PC for some time before trying another, so it works out ok

This thread from last year has a lot of ideas and discussion: 6 or 8 channel audio mixer

I really want a nice big mixer but I lack the space at the moment. So I stuck with my quaint little Behringer Xenyx 502 (2x stereo channels) and went with a couple of AV switchboxes.

The switches: https://www.jaycar.com.au/4-way-a-v-selector/p/AC1652

Aux into line in on the one that stays on all the time

I've gone a bit mad recently, but here's my old setup:

Audio is on the right-hand side. Behringer RX1602 (already mentioned) taking inputs from the vintage PCs and MIDI devices. The RX1602 outputs to one of the inputs of the active speakers (the other input comes from the 'modern' PC on the right I use to download software and search for info while bashing around with the old stuff. The other devices in right-hand rack are an Edirol UM-550 MIDI patchbay and an Aten PS/2 KVM switch.

But... I ran out of ports on the RX1602 soon after this and you might also with 7 PCs if you also have multiple sound cards in any of those PCs or any MIDI modules or other external devices.

So I moved the Sun Sparcstation elsewhere (also freeing up desk space so that dratted keyboard doesn't keep getting in the way), shifted the RX1602 to the left and added a second one 😉

I have used old digital multitrack recorders as mixers . AFAIK, there aren't many people who have taken that approach .

My reasoning :
Pros :
- they were built to a very high quality standard (build and audio quality)
- they are now quite inexpensive (relative to when new) due to them being mostly obsolete/out of fashion
- Other than the analogue inputs, they often have a S/PDIF (coax and/or optical) input and output (only one S/PDIF input is usually present, as having more would imply having the ability to sync to multiple digital clocks simultaneously, which would requiring some sort of resampling/syncing ability, AFAIU)
- some of these have a loving and dedicated fanbase, which can help a lot when dealing with issues

Cons:
- old, so may need new hard drives/CF conversion, internal batteries or other repairs/parts
- way more complex than necessary for use as a mixer

So far, I have used

Akai DPS12
Roland VS-880EX
and soon, hopefully a Yamaha AW4416 (in the mail and likely in need of repairs/TLC)

If you want to know more about my experiences with those, search for posts that I have made with either "DPS12" or "VS-880EX" as search terms .

Honestly all the Versa stuff I've been doing is to experiment with having ONE laptop plastform where I can swap out computers to suit different desires/needs. 5 Laptops take up less space than 5 desktops, especially when all of them can share the same docking station.

As it stands, this is what it will be when all is done.....
NEC Ultralite Versa = Internal Speaker
NEC Versa 40EC = Internal Speaker
NEC Versa V/50 = Internal Speaker
NEC Versa M/75 = WSS Audio through Crystal CS-4231
NEC Versa P/75 = ESS 688

All of them share the same pair of NEC Branded Speakers or Altec Lanscing speakers, 15" SVGA monitor, keyboard, and mouse, and the internal speakers are routed through the HEadphone jack along with the Sound Cards in the two that have them. I have been tempted to figure more about the wiring in the Dock so I could maybe throw one of my spare SoundBlasters in there for gameport/MIDI Support.

Depending on future living arrangements, I might put more machines out and set them up, but they'll have their own speakers. That's just how I prefer it, esp since I Already have enough music-crap wired up in there with my bands and music recording. I'm not really too bothered with hooking things up and disconnecting them - after all, I have a Words+ that came with one of the Versas that I have to use almost like an Electric Guitar with my Bandlab setup for the weird Autotuned AAC based vocals I'm starting to use for some tracks.

I have lots of stuff hooked up:

Edit: I've just realised that diagram is out of date - I now route all the VGA signals through the OSSC, so the only analogue VGA connection to the monitor is now just a test cable that I use for quickly rigging stuff up. The OSSC output is much better.

Mixing of analogue sources is handled by a Hill Audio 16-channel (8x stereo) rackmount mixer fixed to 1U mounting ears just under the front edge of my desk:

It's not quite as tidy right now, but it all still works, and has actually been expanded by another 1U Extron AV switcher to the left of the mixer for selecting the audio output from my stack of retro computers (Mac IICi, 286 PC, 486 PC, Sharp X68000, NEC PC-98), which is then in turn fed in to a spare channel on the mixer.

Everything that can't do HDMI+USB via the HDMI KVM is handled by a big-old Belkin Omniview 16 port VGA+PS2 KVM on a shelf to the left of my desk. That handles all of the needs of the those old computers as well as some 8 and 16bit micros which I've invested in either VGA output or PS2 keyboards for.

megatron-uk wrote on 2021-02-03, 21:00:

I have lots of stuff hooked up: […]
Show full quote

I have lots of stuff hooked up:

av_logical_connections.png

Mixing of analogue sources is handled by a Hill Audio 16-channel (8x stereo) rackmount mixer fixed to 1U mounting ears just under the front edge of my desk:

img_20190429_200616.jpg

img_20190512_160224.jpg

It's not quite as tidy right now, but it all still works, and has actually been expanded by another 1U Extron AV switcher to the left of the mixer for selecting the audio output from my stack of retro computers (Mac IICi, 286 PC, 486 PC, Sharp X68000, NEC PC-98), which is then in turn fed in to a spare channel on the mixer.

Everything that can't do HDMI+USB via the HDMI KVM is handled by a big-old Belkin Omniview 16 port VGA+PS2 KVM on a shelf to the left of my desk. That handles all of the needs of the those old computers as well as some 8 and 16bit micros which I've invested in either VGA output or PS2 keyboards for.

That is neat . I am, shamefully, still operating in "big mess-o-wires" mode .

Well, I was forced to, unfortunately. I had a much bigger room, but then two mini-people quite rudely turned up at our house one day, and they just insist on staying, so I had to hand over my den to be one of their bedrooms. Big-mess-o-wires just doesn't work when you are relocated to a box room that you can just about spin your chair around in...

The ungrateful little things.

😁

My solution was to run audio extension cables from back of the PC , saves me having to go round the back of the PC and wear and tear on the socket of repeatedly plugging/unplugging.
With 14 soundcards in 10 PC's a proper mixer setup is out of my budget.

Some nice ideas here, I'm eyeing that behringer 8x line mixer. Seems to be what I need. Thanks @gex85

@megatron-uk you're nuts! thats so insane 🤣. you should do a quick video, i'd love to see it in detail.

chinny22 wrote on 2021-02-04, 09:17:

My solution was to run audio extension cables from back of the PC , saves me having to go round the back of the PC and wear and tear on the socket of repeatedly plugging/unplugging.
With 14 soundcards in 10 PC's a proper mixer setup is out of my budget.

I do not know you budget, nor is it any of my business, but depending on your patience/luck in finding a deal, something like an older multitrack recorder/audio workstation could be an option . The Yamaha AW4416 (will eventually require DS12887 desolderingand replacement), for example, can expanded to a total 24 inputs (or 12 stereo pairs, for example). Granted, the analogue expansion cards to do that are not usually cheap, but that's just an example .

Another option is getting multiple lower input units and linking/synching them through S/PDIF and MIDI . Some models allow that .

Another option is using multiple analogue mixers and feeding them into a "master" mixer . I have no idea if this a good idea or not, but it might be worth researching .

Sorry if you have already considered any or all of this, or if it does not apply to your setup .

I use a FIFINE 4 channel (stereo) mixer, I love it, it's super tiny and does the job. The only con is that it doesn't have mute buttons but I don't really care, very clean sound (if your cables are in good health). And to mix up all the midi stuff I use a MOTU Micro Express (4 in, 6 out), love it!, they have rack mount units with more ins/outs, but I'm happy with mine, actually I have 3 Motus in different set ups, and 2 Fifines for the stereo lines. I love how nice and small these are. I have others regular size mixers, but I use them for other stuff.
Yeah, Fifine sounds like a Mickey Mouse brand but I'm really impressed, as I said, it works really good, it goes for around $28 on amazon. The Motu Micro Express may go on ebay for around $50 (if you are lucky) to a $100. With those two, I solved all my audio problems regarding my retro gaming stuff.

I'm just realizing you said 7 PCs you want to connect to your main one.... well, I would suggest a rack mount mixer with a whole bunch of stereo lines, not sure if that exists, it's usually mono lines when it comes to that. In my case, I was trying to avoid using a regular audio mixer from the beginning, don't get me wrong, I used to work with pro audio, I love mixers, but want to avoid a full mixer when trying to connect just a bunch of stereo lines, it may end up being a little of a pain in the @#$%, not to mention the space it will take.

Dusko wrote on 2021-02-07, 09:10:

I'm just realizing you said 7 PCs you want to connect to your main one.... well, I would suggest a rack mount mixer with a whole bunch of stereo lines, not sure if that exists, it's usually mono lines when it comes to that. In my case, I was trying to avoid using a regular audio mixer from the beginning, don't get me wrong, I used to work with pro audio, I love mixers, but want to avoid a full mixer when trying to connect just a bunch of stereo lines, it may end up being a little of a pain in the @#$%, not to mention the space it will take.

well a few have already been mentioned in the second post. 1u rack space for a 16ch mixer (8x stereo) really isn't that much imho ^^

now there's also this Mackie LM-3204 which is tad bit larger, but still small imho for what it is and also very convenient with 16x stereo channels x3
I use that in my MIDI rack which houses 12 modules so far.

granted 2x RX1602 mixers would take up less space, but the Mackie has some very convenient features like a "solo" button, alternative routes, and a basic EQ

I use an Extron SMX 500. It’s nice that you can control it over the network. I wouldn’t recommend it though unless you are okay with a rack mount switch. It’s also difficult trying to collect the right cards you need for the switch. Generally people won’t sell the cards individually and want you to buy the whole unit. It also requires you to use Phoenix connectors - but it’ll also do your video.

Dog wrote on 2021-02-08, 04:02:

I use an Extron SMX 500. It’s nice that you can control it over the network. I wouldn’t recommend it though unless you are okay with a rack mount switch. It’s also difficult trying to collect the right cards you need for the switch. Generally people won’t sell the cards individually and want you to buy the whole unit. It also requires you to use Phoenix connectors - but it’ll also do your video.

Thats pretty interesting, but probably overkill. I'll be leaning over to beside my desk to flick a switch so network control is not too high up on the list. Very handy tho! I assume expensive, too 😜
Cheers