MBFM noise?

[sebiiksbcs]

Hi,

sorry to ask again, but I always have some crackling when playing the MBFM. No unusual background noise when no note is playing though.

I am using a ebay-ed wallwart with +/- 12V (250 mA each) and 5V (1A) outputs. Too much?

Or is it normal due to OPL3 limitations?

[stryd_one]

No that's not normal.

Have you tested voltages and noise, of the PSU output, and at the amps?

[sebiiksbcs]

Thanks for your answer,

Voltages of the PSU are exactly +12V / -12V / +5V.

I read somewhere that the transformer for the DIY-PSU should have a few Volts more than 12V output, should the the wallwart be the same? I will check voltages of the amps as soon as I am outta work.

[sebiiksbcs]

Hmm, that's not normal.

The two amps after the YAC are at ca. +9V and -15V. The third amp next to the outputs is even at ca. +4V and -20V!

The error has to be between the +/-12V/ground power pins and the amps i guess. Maybe I soldered some cap wrong? I will check the voltages later.

[QBAS]

have you connected grounds (I mean from +5 with +/- 12V)?

[sebiiksbcs]

Ya I did. Or... actually I connected the +5V and ground from the PSU directly to the +5V input and ground on the OPL3. From there +5v and ground to the core, and to ground of the +/-12V on the OPL3, and to ... umm maybe the story is too hard to follow.

Whatever, maybe I just check all connections tomorrow[move]move[/move]

[sebiiksbcs]

I got the voltages of the amps straight to +13V/-11V. Is it acceptable or could there still be an error somewhere?

[TK.]

It's normal that there is some crackling noise in background, especially when slow envelopes are used.

Best Regards, Thorsten.

[sebiiksbcs]

I dont' think that my case is normal. Everything sounds distorted. But anyway, the YAC and the amps get hot and now I hear nothing! Gonna buy another soundcard.

[TK.]

For my own interest: could you please measure the DC voltage at following outputs:

IC3, O4

IC3, O3

IC5, O4

IC5, O3

Best Regards, Thorsten.

[sebiiksbcs]

Alright, I will check the voltages again tonight!

[sebiiksbcs]

sorry, i didn't check the voltages because i removed the yac to just solder it again. now the opl3 module doesn't make a sound, except that the yac and the amps get hot. so i guess i still have a short on the pcb.

[QBAS]

from my side: with bad switching PSU I get -13V and +11V on FM module and this give me distorted sound.

another PSU  (based on big traffo): without connecting to FM module I measure -13 and +11, but after connecting to FM module the voltages I get OK. (+12/-12V) and of course sound was good.

[sebiiksbcs]

i see, that has to be the PSU.

thanks for your comment!

[sebiiksbcs]

If I use a PSU that supplies clean +5V/+12V/-12V, should I remove the 7805 from the core module? Seen that in a file about a switching PSU for the MBLC, just wondering if that could have been the reason for the YAC and the amps got "incomfortable".

[Wilba]

You can't supply a 7805 with +5V, regulators need inputs of at least 2 volts higher than what it outputs... and especially can't supply Core:J1 with only +5V, as it goes through a bridge rectifier as well... even worse if you supply ground to J1 as well as supplying ground elsewhere to ground pins on other modules, because of the bridge rectifier...

You can supply +5V/ground directly to J2 on the Core.

[sebiiksbcs]

That's what i meant to do. I thought when giving +5V to J2, do I have to remove the 7805 and rectifier? Guess not.