Whistling Sound after modding Philips Player

[diyman]

I'm trying to mod my old Philips player running the TDA1541 Chip and did the following:-

a) Added 47n decoupling caps directly to legs 7-13 and 18-24 of the TDA1541
b) Cut off the analog ground track at pin 5 to separate it from the digital ground a run a connection from pin 5 directly to the chassis
c) Also separated digital ground at pin 14 from the rest of the audio circuitry and run a connection directly from the digital ground to to the Chasis.
4) Extensively decouple the audio ICs by soldering 47 caps directly to all the power supply pins.
5) Wrapping the filter chips and TDA1541 with copper foil tape and grounding foil to chassis.

Switched on and sound is very much more detailed but there is a steady soft whistling sound. Could it be oscillation of some sort and what could be the cause.??

Regards,

ckt

[mastertech]

well sounds like it, have you checked it on a scope?

[ash_dac]

Switched on and sound is very much more detailed but there is a steady soft whistling sound

Whistling sound sounds like my tinnitus

I would pay £ for a cure for that!

Anyway, Gudio Tent knows about this decoupling stuff!

Start here first.
http://www.tentlabs.com/Info/Article...decoupling.pdf

Kind regards,


Ashley.

[Francis_Vaughan]

Originally posted by diyman
b) Cut off the analog ground track at pin 5 to separate it from the digital ground a run a connection from pin 5 directly to the chassis
c) Also separated digital ground at pin 14 from the rest of the audio circuitry and run a connection directly from the digital ground to to the Chasis.

Bad. Real bad idea. Put them back right now. The idea of separating these grounds like this is simply wrong. This isn't an audio circuit - it is an RF speed one. The grounds do not work like audio. You have cut the ground return lines for very high speed signals and made them return via bits of wire and the chassis. This is going to introduce all sorts of evil problems.

[diyman]

Thanks Francis. Just reversed the grounding stunt and well, everything's fine but I must say soldering additional decoupling caps directly to the TDA chip does make it sound better. As for digital power supply decoupling, OSCONS are god sent. So much more details and more musical.

If it ain't broken, fix it!