Amiga sound filter: Crisp on NTSC rev 5, but muffled on PAL Rev 3

c0dehunter · 30 May 2021, 20:22

Dear all,
My NTSC Rev 5 A500 sounds really crisp and sharp (recently recapped by a dear friend), but my Rev 3 PAL A500 sounds a bit muffled (again recapped).

I notice this specially on demos that turn the light OFF, and install the high-pass filter: On Rev 3 it makes no difference at all, but Rev 5 sounds even crisper, and more sharp (already sharp on non high-pass demos)

According to my friend who recapped, the audio circuitry of Rev 3 and Rev 5 are very different, but I am sure there has to be way to make it crisp sounding. (by installing and soldering a different value Amp maybe?)

How can I make this Rev 3 sound crisp?

Many thanks in advance!

r.cade · 31 May 2021, 04:04

I don't think the Rev3 A500 board has a software-switchable low pass filter. Like the A1000, it's always on. You'd need to wire up a switch and turn it on and off manually.

c0dehunter · 31 May 2021, 19:43

It that so? It seems correct as when I use the AMIGA TEST KIT v1.6, and run an audio test, turning on or off the LPF does not do anything, except the light.

1) I am confused, if it is always ON, how come the sound is muffled? Isn't it supposed to be the other way around?

2) Can I modify the system to have the the LPF (crisper, sharper sound) ON (or OFF), *at all times*?

3) How come this feature is available on other models?

4) Is wiring up that switch is difficult to accomplish?

Thanks!

r.cade · 01 June 2021, 01:59

Quote:

Originally Posted by c0dehunter

It that so? It seems correct as when I use the AMIGA TEST KIT v1.6, and run an audio test, turning on or off the LPF does not do anything, except the light.

1) I am confused, if it is always ON, how come the sound is muffled? Isn't it supposed to be the other way around?

The filter is always on, unless disabled. This is default Amiga behavior. It starts a low-pass frequency roll off at 7KHz to filter out the distortion from low sampling rates.

Quote:

Originally Posted by c0dehunter

2) Can I modify the system to have the the LPF (crisper, sharper sound) ON (or OFF), *at all times*?

Yes, you just have to disable or bypass the circuit.

Quote:

Originally Posted by c0dehunter

3) How come this feature is available on other models?

It's just how it is - the feature to disable it was added later.

Quote:

Originally Posted by c0dehunter

4) Is wiring up that switch is difficult to accomplish?

It depends on your electronics skill level.

I don't know the procedure to disable it on the A500 Rev3. There are plans to do it on the A1000, but I don't know if the audio circuit is the same. You would have to research this, sorry.

AmigaHope · 01 June 2021, 07:24

There is no "high-pass filter". There are just two low pass filters -- one that you can turn off (the power LED one) that is very aggressive, another not so aggressive that is permanently on. When you turn off the power LED-connected filter, you will still get some filtering.

Note that the permanent low-pass filter on older Amigas is more aggressive than the ones on later Amigas. The one on AGA machines is permissive enough that you only need to mod it if you want to play very high sample rates (using higher horizontal refresh to allow Paula to do it), but on older machines a hardware mod to the filter will greatly improve sound.

Pretty sure A500 Rev 3 can still disable the harsh low pass filter, but the permanent one on it might still be overly aggressive compared to later A500s.

nikosidis · 01 June 2021, 08:51

Very true that the rev. 3 sound closed inn. I have one so I know what I'm talking about

Not my go to model. A1200 sound fantastic.

LIV2 · 01 June 2021, 13:56

Quote:

Originally Posted by AmigaHope

Pretty sure A500 Rev 3 can still disable the harsh low pass filter, but the permanent one on it might still be overly aggressive compared to later A500s.

Rev 3 definitely doesn't have the ability to toggle the filter. here's the Rev 3 audio vs Rev 6

c0dehunter · 01 June 2021, 15:57

Thank you all for your awesome commented. I wish there were a guide on how to mod this for Rev 3.

sviru · 01 November 2023, 01:36

Quote:

Originally Posted by LIV2

Rev 3 definitely doesn't have the ability to toggle the filter. here's the Rev 3 audio vs Rev 6

Hi! From where did you get rev3 schematic??

Nowhere to be found

30 May 2021, 20:22	#1
c0dehunter Registered User Join Date: Apr 2011 Location: USA Posts: 399	Amiga sound filter: Crisp on NTSC rev 5, but muffled on PAL Rev 3 Dear all, My NTSC Rev 5 A500 sounds really crisp and sharp (recently recapped by a dear friend), but my Rev 3 PAL A500 sounds a bit muffled (again recapped). I notice this specially on demos that turn the light OFF, and install the high-pass filter: On Rev 3 it makes no difference at all, but Rev 5 sounds even crisper, and more sharp (already sharp on non high-pass demos) According to my friend who recapped, the audio circuitry of Rev 3 and Rev 5 are very different, but I am sure there has to be way to make it crisp sounding. (by installing and soldering a different value Amp maybe?) How can I make this Rev 3 sound crisp? Many thanks in advance! Last edited by c0dehunter; 30 May 2021 at 20:35.

31 May 2021, 19:43	#3
c0dehunter Registered User Join Date: Apr 2011 Location: USA Posts: 399	It that so? It seems correct as when I use the AMIGA TEST KIT v1.6, and run an audio test, turning on or off the LPF does not do anything, except the light. 1) I am confused, if it is always ON, how come the sound is muffled? Isn't it supposed to be the other way around? 2) Can I modify the system to have the the LPF (crisper, sharper sound) ON (or OFF), at all times? 3) How come this feature is available on other models? 4) Is wiring up that switch is difficult to accomplish? Thanks! Last edited by c0dehunter; 31 May 2021 at 21:56.

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31 May 2021, 04:04	#2
r.cade Registered User Join Date: Aug 2006 Location: Augusta, Georgia, USA Posts: 550	I don't think the Rev3 A500 board has a software-switchable low pass filter. Like the A1000, it's always on. You'd need to wire up a switch and turn it on and off manually.

01 June 2021, 07:24	#5
AmigaHope Registered User Join Date: Sep 2006 Location: New Sandusky Posts: 942	There is no "high-pass filter". There are just two low pass filters -- one that you can turn off (the power LED one) that is very aggressive, another not so aggressive that is permanently on. When you turn off the power LED-connected filter, you will still get some filtering. Note that the permanent low-pass filter on older Amigas is more aggressive than the ones on later Amigas. The one on AGA machines is permissive enough that you only need to mod it if you want to play very high sample rates (using higher horizontal refresh to allow Paula to do it), but on older machines a hardware mod to the filter will greatly improve sound. Pretty sure A500 Rev 3 can still disable the harsh low pass filter, but the permanent one on it might still be overly aggressive compared to later A500s.

01 June 2021, 08:51	#6
nikosidis Registered User Join Date: Jan 2020 Location: oslo/norway Posts: 1,607	Very true that the rev. 3 sound closed inn. I have one so I know what I'm talking about Not my go to model. A1200 sound fantastic.

01 June 2021, 15:57	#8
c0dehunter Registered User Join Date: Apr 2011 Location: USA Posts: 399	Thank you all for your awesome commented. I wish there were a guide on how to mod this for Rev 3.

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