English Amiga Board - View Single Post - Line level of the Amiga 600 (and possibly other models)

pandy71 · 05 December 2021, 18:57

Increase value of R325/335 - they form voltage divider with R324/334.
Sadly to say but Paula has no separate pin for Audio Vref so or they use some internal Vref source or using Vcc as Vref so expected Vpp for Audio signal will be =<5V for sure.
Hope you already replaced R309 with proper ferrite bead, normally i would also separate Paula GND and corresponding Audio GND trough ferrite beads (also add ferrite beads on Audio line outs from Paula to separate relatively slow SR OPAMP from HF).

Technically whole audio subsystem and PCB layout should be changed accordingly to nowadays rules for HiFi Audio.

05 December 2021, 18:57	#8
pandy71 Registered User Join Date: Jun 2010 Location: PL? Posts: 2,746	Increase value of R325/335 - they form voltage divider with R324/334. Sadly to say but Paula has no separate pin for Audio Vref so or they use some internal Vref source or using Vcc as Vref so expected Vpp for Audio signal will be =<5V for sure. Hope you already replaced R309 with proper ferrite bead, normally i would also separate Paula GND and corresponding Audio GND trough ferrite beads (also add ferrite beads on Audio line outs from Paula to separate relatively slow SR OPAMP from HF). Technically whole audio subsystem and PCB layout should be changed accordingly to nowadays rules for HiFi Audio.