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Old 01 January 2022, 10:33   #1
Heywood
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Question Amiga Stereo Crossfading

Does anyone have a preferred way that mixes left and right audio in a way that you can still have separate left and right audio with a bit of the other side included?

I am assuming something might need to be active rather than a purely passive solution and doing this at near line level would be fine as I would be using powered speakers.

If it’s something to build yourself- I would be interested in seeing that as well.
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Old 01 January 2022, 10:53   #2
Krashan
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My solution was KA71 amplifier however it is discontinued now. On the other hand schematic diagrams may be helpful for building similar device.
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Old 01 January 2022, 16:08   #3
Higgy
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The MiST FPGA board has a setup that has some mixing. Unfortunately it makes the Amiga and Sam Coupe Cores sound inaccurate due to not having hard sound separation.

Just to the right of the middle of the following picture is the audio circuit. R21 mixes the sound, if you remove R21 there is no mixing.
https://raw.githubusercontent.com/wi..._schematic.png

I assume the Amiga sound generated in the FPGA is effectively the phono output, so you might just need to build the circuit shown on the MiST schematic and feed in the Amiga's audio signal.
I removed R21 on my MiST.
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Old 01 January 2022, 21:13   #4
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I use a mini Rolls mixer to merge Paula, an AD516, and a One Stop Music Shop. My particular model is no longer available but this is the current iteration (functionally identical to what I have). You could plug Left audio into one input and Right audio into another and balance as needed. They also have a passive mixer that might work since you're using powered speakers.

Their DB14b seems to do exactly what you want and will be cheaper, but less versatile for other uses.

The caveats are that Rolls stuff is kind of expensive and I don't know if they have any distributors in Australia. But it's high-quality gear.
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Old 02 January 2022, 03:57   #5
Lineof7s
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I too have been searching for such a thing, and one of the most likely candidates is this little project from Ms Mad Lemon, which includes Youtube videos of its assembly.

https://www.vintageisthenewold.com/a...ation-solution

Unfortunately I currently solder about as well as I levitate so I haven't leapt into it yet, but it's there and it's calling to me.

The other alternative I've been looking at is a cheap multichannel mixer *with pan controls per channel* (important and surprisingly uncommon), connecting the left to one channel, right to another and panning them left/right as much or as little as I'd like. It'd work, but it seems like overkill.

I was about to say "like this one" and provide a link, but the cheap Chinese models that were apparently dumped on the market for about $50 last I looked seem to have gone away. The best I can find it something like this (you'd stick the Amiga left channel in the Left (mono) input of channel 2/3, and the Amiga right channel in the Left (mono) input of channel 4/5, then pan them independently as much as you want them separated in the stereo field): https://tinyurl.com/2p8aja2v

[edit] HA! After much searching, I found it. Like this (see how each channel has a Pan pot? Like that): https://tinyurl.com/2p8unntd

If you find something, feel free to come back and tell us.

[edit] Here's a slightly more complex homebrew solution: https://awesomeopensource.com/projec...igaStereoMixer

Last edited by Lineof7s; 02 January 2022 at 04:23. Reason: More info
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Old 20 January 2022, 23:14   #6
pandy71
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Quote:
Originally Posted by Heywood View Post
If it’s something to build yourself- I would be interested in seeing that as well.
Had no access to FV-1 SPN1001 but it looks very tempting from Amiga perspective as it can firstly mix both channels to reduce separation but additionally it may add small amount of reverb (even adding small 20ms delay before mixing channels) so audio can be substantially improved (not mentioning dynamic low pass filter and other processing so it could work better with Paula limitations).
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Old 21 January 2022, 00:09   #7
no9
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I do not know hardware solution to that problem but I think there is better idea to treat Amiga hard stereo problem. Listen to those
[ Show youtube player ]
[ Show youtube player ]

There is created subwoofer-like central channel, tuned to much higher frequency than usual subs. Lowpassed signal goes to the center so you are not annoyed with sub burts located only in one speaker. Highpassed signals stay on the sides so you still have some perception of stereo.

Maybe there is already a circuitry that does just that?


Btw, I recorded video to show the idea with use of a freeware VST plugin:

[ Show youtube player ]

Last edited by no9; 21 January 2022 at 14:42.
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Old 26 January 2022, 06:58   #8
Heywood
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Hi Everyone,

Thanks for the responses - it's a bit of a rainy public holiday here, so I decided to bang together project similar to what Ms Mad Lemon solution implemented with her single input version the only difference is instead of using two electrolytic caps back to back, I ended up using single unipolar electros.

With my very quick testing, it seems to work alright and was a fairly fun/simple build. I documented my build on github for those that are interested.

Thanks in particular to Lineof7s, a low cost option is certainly worth trying first and seems like it is good enough for me. However krashan - that KA71 does look like a nice thing, shame its no longer available!
no9, thanks for going the extra mile to explain what you were proposing hopefully someone else can take inspiration from that.
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Old 26 January 2022, 15:55   #9
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Heya Heywood. First of all, Brisbane represent!

Secondly, I'm glad you found yourself a working solution. With all due respect, that looks dodgy AF, but if it works it works! Any attempt of mine would look similar but would *not* work, so kudos to you. It gives me hope. Thank you for documenting things; I'll be bookmarking that for when I'm feeling bolder.
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Old 26 January 2022, 23:23   #10
Heywood
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Hey, I'm not sponsored by JLCPCB or anything! I guess you could consider my ham-fisted approach somewhat environmentally friendly As you are in Brisbane if you went to Jaycar (which is neither the cheapest nor the best for electronic components) it's only $14.10 for the parts (without the box) so it's a fairly low cost to muck around and a small amount of time to slap it together.

My dodgey box is probably going to get equal opportunity treatment with my Atari STE to bleed DMA audio across as well.

I reached out to the rasport guy, and he mentioned that he still has a couple of PCBs but no components or boxes to house the unit, I haven't investigated as to whether the components he uses are available but if others are considering something perhaps that's an option (and if you go that direction - if you make an extra one I'll be up for it!)
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Old 27 January 2022, 18:40   #11
Krashan
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Quote:
Originally Posted by Heywood View Post
I reached out to the rasport guy, and he mentioned that he still has a couple of PCBs but no components or boxes to house the unit
As I'm the RastPort guy, I can confirm I have 8 PCBs of KA71 left. Can give them away at cost of shipping. Blank boxes are available on AliExpress (SZOMK AK-C-C13). Most important components are LMR62014 (DC/DC converter, Texas Instruments) and two MC33178 (audio op-amp, OnSemi). Fitting audio minijack sockets are Cliff FC68133 for input and FC68131 for output. I have no stock of them.
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