6 replies to this topic

[Schrabikus]

Hello, friends!
Can you please listen to attached mp3 and tell, is it normal, or something wrong?
Noise remains when i disconnect LCD and CS from the core.
So far i can not exclude PSU (it's one from dvd player +12v/-12v/+5v) but noise lasts about half a second after switching PSU off.
Cable from core to OPL3 board is about 12cm, soldered directly to core.
Thanks in advance.

And the OPL3 +5v led lights with only J2 connected.

Attached Files

•  MBFM_noise.mp3   620.8K   30 downloads

Edited by Schrabikus, 03 March 2012 - 08:22.

[Shuriken]

Although not easy, i would try a different PSU. The PSU is probably a switcher, which can cause noise if the switching frequency is low.

Edited by Shuriken, 15 January 2012 - 12:44.

[TK.]

It sounds like the noise is coming from the LED switching matrix, this could be the result of a certain coupling between the 5V and +/-12V voltage domain.

Try the following:
- ensure that the ground of the audio jacks + the OPL3 board is directly connected to the ground of the PSU (and not to the core module)
- add 100 uF caps between ground an the -12V and +12V supply input of the MBHP_OPL3 module (take care for the polarity!)
- if this still doesn't help, add 10 Ohm resistors in serial between the +12V and -12V output of your PSU and the appr. MBHP_OPL3 inputs, this helps to decouple the noise as well!

Best Regards, Thorsten.

[Schrabikus]

Have no words to thank you, Thorsten!!!
With 100 uf caps at OPL3 board the noise decreased by half (MBFM_noise_capacitors.mp3)
Than i've changed 47 uf PSU caps with 200 uf and added 2x10 ohm resistor
Aaaand the noise disappeared completely!!!!! (MBFM_noise_capacitors_resistors.mp3)

conclusion: switching PSU from dvd player can be used in audio apps!

Attached Files

•  MBFM_noise_capacitors.mp3   474.55K   19 downloads
•  MBFM_noise_capacitors_resistors.mp3   290.33K   20 downloads

Edited by Schrabikus, 15 January 2012 - 15:32.

[Schrabikus]

I've removed additional caps from OPL3 board and voila!!! No noise at all!
So increasing capacity of PSU output caps + adding 10 ohm resistors totally eliminates the noise.

[TK.]

Very cool!
Great to know that this simple method works!

Best Regards, Thorsten.

[mrspring]

I just had this problem, an idle noise in the background, using a TRACO TXL 035-1212D - a quite high end PSU for this application in fairness.

 

Cured it totally by moving the sleeve of the audio outs to the - on the PSU rather then the one on the Core as i was doing previously..

 

No need for caps or whatnot, this is a total solution!

Edited by mrspring, 20 March 2013 - 14:33.