English Amiga Board


Go Back   English Amiga Board > Support > support.Hardware

 
 
Thread Tools
Old 27 December 2021, 12:33   #21
ugrnm
Registered User

ugrnm's Avatar
 
Join Date: Sep 2020
Location: some / where
Posts: 37
Quote:
Originally Posted by Stedy View Post
Hi,
To boost the output change R325 and R335 from 390R to either 470R or 510R. This will get you a peak voltage of 0.9408V for 470R resistor or 0.9702V for 510R.
I don't understand how you end up with these values. If I aim at something around 3.472Vpp, R325 and R335 should be much higher, no?

Is there something wrong with my reasoning? See attached.

Click image for larger version

Name:	R335.png
Views:	37
Size:	29.9 KB
ID:	74221
ugrnm is offline  
Old 18 January 2022, 17:44   #22
ugrnm
Registered User

ugrnm's Avatar
 
Join Date: Sep 2020
Location: some / where
Posts: 37
I'm not sure it was clear what I was trying to do...

But...

In the end I changed all the components in the audio circuit path (new op amp and 1% resistors, new caps, etc). If anything it was a good way to learn about SMD package size, as well as resolder/solder these. The result is that my slight unbalance between L and R is gone and the overall audio signal is a bit louder.

Still not loud enough for my original plan, so I put a 1.5K at R335, and I'm getting close to "Pro" line level, all good.

I've also replaced the big 1ohm resistors on the video and audio power circuit with equivalent ferrite beads. I am not sure if it's snake oil, or if it's my maintenance work on the audio circuit, but now even at max volume/gain on the mixer, it's super silent. Before I had a slight hum, and could hear the optical mouse activity when moving it.

Been playing mods non stop for the past 2 weeks, everything is fine, stable, loud and clear
ugrnm is offline  
Old 18 January 2022, 20:05   #23
pandy71
Registered User
 
Join Date: Jun 2010
Location: PL
Posts: 1,974
Quote:
Originally Posted by ugrnm View Post
I've also replaced the big 1ohm resistors on the video and audio power circuit with equivalent ferrite beads. I am not sure if it's snake oil, or if it's my maintenance work on the audio circuit, but now even at max volume/gain on the mixer, it's super silent. Before I had a slight hum, and could hear the optical mouse activity when moving it.
You could record (PC card or external audio interface) noise level (silence sample) with active system (floppy, mouse activity) before and after modifications - this would give final answer for all doubt's (modern PC cards usually provide more than 80dB SNR so they can be used as decent objective audio analyzer and any modification can be verified in objective way).

Anyway as overall congratulations!
pandy71 is offline  
Old 18 January 2022, 20:39   #24
ugrnm
Registered User

ugrnm's Avatar
 
Join Date: Sep 2020
Location: some / where
Posts: 37
Thanks!

I know I should have measured things more seriously, I did not think of just recording with a soundcard... I was having way too much fun working on all this.

I did notice though that before I made all these changes, with all the gain up on the mixer, the Amiga noise floor was appearing on the meters at -30dB, bleeding a bit on the -20dB. And now, *nothing*
ugrnm is offline  
Old 18 January 2022, 22:22   #25
pandy71
Registered User
 
Join Date: Jun 2010
Location: PL
Posts: 1,974
Quote:
Originally Posted by ugrnm View Post
Thanks!

I know I should have measured things more seriously, I did not think of just recording with a soundcard... I was having way too much fun working on all this.

I did notice though that before I made all these changes, with all the gain up on the mixer, the Amiga noise floor was appearing on the meters at -30dB, bleeding a bit on the -20dB. And now, *nothing*

this is really nice - my assumption is that in original design 1ohm resistors together with some decoupling capacitance created low pass filter but i have impression that audio quality was never main goal for Amiga designers - 8 bit was anyway spectacular in those times so quality was less relevant but today our knowledge substantially increased so this is default scheme, ferrite beads, proper PCB layout to keep signal integrity, proper ground planes (in case of audio frequently local ground plane connected to rest of system also by ferrite bead).
Well done, if you share details perhaps other will follow your path.
pandy71 is offline  
Old 18 January 2022, 22:32   #26
ugrnm
Registered User

ugrnm's Avatar
 
Join Date: Sep 2020
Location: some / where
Posts: 37
Yes, my plan is to gather my notes and document the changes I made! I will bump this thread when done.
ugrnm is offline  
Old 19 January 2022, 07:41   #27
amigasith
Registered User

amigasith's Avatar
 
Join Date: Jan 2013
Location: Wild South / Germany
Age: 46
Posts: 259
I'd be interested in the details, too. Better sound never hurts
amigasith 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
Amiga 600 PSU -12v line is reading ~-1v Zxspectrum16k support.Hardware 2 21 July 2019 06:47
Amiga 600 with Vampire II, and PSU (possibly) woes! Mikerochip support.Hardware 11 09 May 2018 23:59
Amiga 600 production line photos DaveMB Nostalgia & memories 12 27 August 2014 20:25
Amiga models tesla support.Hardware 16 07 March 2013 19:12
Amiga models BippyM Amiga scene 21 18 February 2003 00:48

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 02:58.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, vBulletin Solutions Inc.
Page generated in 0.07471 seconds with 14 queries