English Amiga Board

Go Back   English Amiga Board > Support > support.Hardware > Hardware mods

Thread Tools
Old 13 May 2014, 22:34   #1
Registered User

8bitbubsy's Avatar
Join Date: Sep 2009
Location: Norway
Posts: 1,535
Modifying the lowpass filter of the Amiga 4000D

As you may or may not know, the Amiga 4000D has a lowpass RC filter tuned to 4515Hz (according to schematics, but actual cutoff vary from machine to machine because of degrading and specs/tolerance).
This does help a bit with hiding 8-bit quantization, but it makes the sound very muddy in the upper frequency floor!

The Amiga 1200 and the CD32 are the only Amiga machines to have a cutoff set higher than 5kHz. In fact, it's set to 27205Hz (!) on the A1200 rev 1D.1. According to nyquist, you shouldn't even hear a lowpass filter at all with such a cutoff value. Crystal clear sound. Not Hi-Fi sound but much better than it was for sure. One might want to change the op-amp too if you're hunting for better sound. And no, I'm not using my Amiga for Hi-Fi stuff, because I know that it has rather cheap components inside, and probably not sufficent noise decoupling and the like. Not to mention 14-bit max with Paula.

I modified my "already hacked" A4000D to use the RC components from a broken A1200 rev 1D.1 motherboard I had laying. Two SMD resistors and two SMD capacitors. While I care about having collectors items in an original state, this machine is in bad shape and was already hacked on. Why not?

Here's two audio captures from my A4000D - 14-bit 48kHz AHI:
Before hack: http://16-bits.org/etc/a4000d_27khz_...d__5kHz_lp.mp3 (my A4000D was 5kHz)
After hack: http://16-bits.org/etc/a4000d_27khz_...__27kHz_lp.mp3
(I normalized these in Audacity, and made them start at the same sample, but I can assure you that I did no Audacity lowpass filtering or any sorts on them!)

Here's a reference picture I made:

Last edited by 8bitbubsy; 14 December 2017 at 15:08.
8bitbubsy is offline  
Old 13 May 2014, 22:57   #2
Global Moderator

prowler's Avatar
Join Date: Aug 2008
Location: Sidcup, England
Posts: 10,300
Worthwhile job!
prowler is offline  

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools

Similar Threads
Thread Thread Starter Forum Replies Last Post
Modifying PC floppy drives for Amiga use Jope Hardware mods 447 19 March 2021 23:09
Amiga 4000d mal101 support.Hardware 10 21 May 2013 07:12
Slowdown Amiga 4000D amigatv New to Emulation or Amiga scene 19 10 February 2013 09:44
FS: Amiga 4000D (1 of 2) r.cade MarketPlace 2 21 August 2012 19:35
Amiga 4000d booting drusso66 support.Hardware 6 09 August 2010 12:58

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT +2. The time now is 13:24.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Page generated in 0.07256 seconds with 15 queries