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Old 30 January 2011, 14:12   #1
8bitbubsy
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Changing A600 sound cutoff/butterworth

As you know, the Amiga 600 has got the very bad cutoff sound to it just like the older Amigas --this is because of the resistance and capacitance of the butterworth/filter section of the PCB.
Anyways I want to make my A600 have the clear A1200-esque sound, do you guys know what components I need to change and what value I need to change them into?
Please understand that I do not mean the LED filter that you can turn on and off, I mean the cutoff filter that is always activated.

I know this is possible, this is circuitry laying outside of Paula.
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Old 30 January 2011, 14:37   #2
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Why don't you simply do a side by side comparison of A1200 sound section and A600 sound section, that would give you all the values you need and a good learning experience to boot?
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Old 30 January 2011, 15:27   #3
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Because it takes a long time and it's very tidious. Even counting where pin 30 and 31 (Audio R, Audio L) are is making me cry.
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Old 01 February 2011, 21:54   #4
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Update: I found the audio circuit schematics for A600 and A1200:
http://16-bits.org/amiga/a600/a600_audio_circuit.png
http://16-bits.org/amiga/a1200/a1200_audio_circuit.png

(The A1200 schematics seems to be super old or something, because several of the audio components had different values on my A1200 1D4)

I found out that these components were different on the A1200 r1D4 vs. A600 r1:

R331, R321
C331, C321
R335, R325
R345

I took my broken A1200 1D4 motherboard and swapped those components.
Now it sounds like this (playing MOD.blowaway in HippoPlayer, no AHI):
http://dl.dropbox.com/u/4846123/modi...d_blowaway.mp3
http://dl.dropbox.com/u/4846123/a1200_mod_blowaway.mp3

(The click that you hear on higher octaves is common on the Amiga, it's something shitty with Paula when playing samples in very low periods.)

It sounds nearly identical to the A1200 sound now. There seems to be a tiny bit more aliasing on the A600 sound, maybe I forgot to check some other components. Over all, I am very happy with the result but unfortunately I took no capture of the sound before I did the job, stupid I am.

But I know that the non-modified A500/A600 sound is kind of more cut-off .. like fog all over the sound image (not talking about the LED filter).

Last edited by 8bitbubsy; 01 February 2011 at 22:06.
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Old 01 February 2011, 22:16   #5
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Nice work
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Old 01 February 2011, 23:22   #6
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C331, C321 10nF should be ok - other components seems to be not very critical
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Old 02 February 2011, 00:37   #7
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Nice work!

Fixed MP3 sounds a bit clearer IMHO, just a tiny amount.

Would be cool to be able to switch between filtered and non filtered sound to compare favorite modules!
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Old 02 February 2011, 10:19   #8
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Sound is filtered - only integration time (first OPAMP work as a integrator) is different.
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Old 24 July 2015, 01:55   #9
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I achieved the clearer, A1200-like sound just by removing two SMD filters from the bottom of the motherboard, C331 and C321. It works great, sound is less muddy and has higher response on the higher frequencies
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Old 06 November 2018, 18:58   #10
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Akira, thank you very much, I did the same thing to my 600 almost 1 year ago and I also change the amp op for a new tl084, the sound quality is completely different!
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