Mixing Paula and CD audio

[MarkAshley]

Found this just now and was thinking of going to Maplin to get the resistors and RCAs to wire it up. Is it really this easy? And is there any way of wiring this in to Paula to mix the CD audio in to the Amiga's RCA output jacks, or would I have to take the output from the twin phonos on the motherboard and then feed in to the mixer circuit?

Thanks
Mark

[zipper]

 or would I have to take the output from the twin phonos on the motherboard and then feed in to the mixer circuit?

Thanks
Mark

That's the way Eyetech did produce them, I have one installed to my A500T. Two pots adjustable by a screwdriver.

[MarkAshley]

zipper wrote:

 or would I have to take the output from the twin phonos on the motherboard and then feed in to the mixer circuit?

That's the way Eyetech did produce them, I have one installed to my A500T. Two pots adjustable by a screwdriver.

Messy :-(

Think I will look in to cutting the tracks from Paula to the RCA jacks, then take the Amiga audio feed from Paula, feed in to a mixing circuit along with the CD audio, then feed the output of the mixer to the RCA jacks on the motherboard.

Does the circuit I posted look ok?

[Doobrey]

If you're feeling adventurous, Ian Stedman has a design for an active mixer with adjustable input and output levels, which could be handy if the Amiga audio is louder than the CD audio. linkety link.

Edit: Hmm, the schematic page seems to have a broken image link

[MarkAshley]

If adding resistors is all I need to do, then I can add a pot instead so I can turn down paula so the CD audio is about the same level. Will this work, or do I really need to build a mixing circuit?

[kas1e]

@Mark

Some time ago (3-4 years to back), i just try to mix CD-AUDIO output (digital, from back side of cd-drive, not from front side where is a headphones output). I just mix output from cd, and from paula and for me, it was works, but as said your first link i was have "increased distortion in the sound." In other words, cd-audio output was have very low valume level. But, it was works. After this tests, i just take off this, becouse volume level was suck, and just do not remember it.. But after your post, i read your link, and must say, that 'resistors' must help (im sure on 85%). I will try this today or tommorow. Maybe will need not 10k resistors, but with voltmeter it is no problem.

[MarkAshley]

@kas1e
Some people say that mixing the audio sources directly like that can damage Paula, but it probably depends on the volume of your CD-ROM. I have also read about Paula being MUCH louder than the CD audio, so I have decided to build this.

I'm also thinking of cutting the tracks from Paula to the RCA jacks on the motherboard, soldering wires before the cuts to one of the inputs of the mixer circuit, then from the output of the mixer to the RCA jacks on the motherboard. That way I get CD Audio and Paula coming from the normal output of the A1200  :-D

[CD32Freak]

Edit: Hmm, the schematic page seems to have a broken image link

Go back in time with the Internet Archive Wayback Machine: http://web.archive.org/web/20040106145824/http://www.ianstedman.co.uk/Amiga/designs/audio_mixer/mixer_schematic/mixer_schematic.html

or
http://img520.imageshack.us/img520/2338/audiomixer5oy.png

:-D

[kas1e]

@CD32Freak
It is very big pcb for this kind of mix i think ?

@Mark
I think , the best way, try to do all what is possible without motherboard soldering, becouse a1200 mb is old, and one more solder work on it, and it can be done

[MarkAshley]

kas1e wrote:

I think , the best way, try to do all what is possible without motherboard soldering, becouse a1200 mb is old, and one more solder work on it, and it can be done

I haven't decided 100% to do this yet. I would only be soldering on to tracks on the motherboard if I do it, not on to Paula directly. I know it's risky, but it's tempting to have CD audio and Paula coming out of the Amiga's standard outputs  :-D

[Stedy]

Hi,

I've fixed the schematic link on my website now, the image got corrupted!

The PCB is 85x65mm and I have one or two available if you are interested.

You can not tap the audio directly from Paula, best to connect from pins 1 & 7 of U15 (LF347/TL084) but if you tap off the audio here you will need 22uF capacitors to block the DC content of the amplifier.

Have fun.

Ian

[doctorq]

@Stedy

I'm in for one or two. PM me with details

[MarkAshley]

@Stedy
Would you mind elaborating on where the capacitors would go? I haven't looked at my A1200 motherboard for a while. How accessible are the location to which I need to solder?


This afternoon I built the mixer with the potentiometer for volume control. Maplin only had one dual 10k pot (typical) so only one of the inputs has a volume control. This is fine though, as I will connect the Amiga's output to this, the CD audio to the other, and then turn down the Amiga output until they are level.

I haven't got a CD audio cable at the moment. They were £5 in Maplin which I thought was quite a lot, so I'll "borrow" one from work tomorrow :-D

[Stedy]

@MarkAshley

You would need to remove the RF shielf if you have no done so already. U15 is near the phono connectors. Why not just plug the audio mixer into the phono sockets?

I hope you bought a logarithmic potentiometer (it should have 10KB on it for the value) otherwise the volume level will sound weird when adjusted!

@doctorq

I will have to check how many PCBs I have left, rough price is about 8 UKP each! Small batches of PCBs get expensive.

Ian

[MarkAshley]

@Stedy
My A1200 is in a tower, so I will have to remove my Voodoo and Mediator to do this. I don't want any cables or external mixers showing outside of the case, which is why I want to cut the tracks to the Amiga's phono output, take the Amiga audio directly from the motherboard, then pipe the mixer output to the Amiga's phono connectors. And yes, I used a 10k logarithmic potentiometer.