Output Noise

elmood · Post by **elmood** » Mon Sep 01, 2008 4:21 pm

Hi, I've been working towards an effects product based on the FV-1 but am having some problems with output noise. The datasheet talks about out of band noise, but I'm hearing quite a lot of in-band hiss with the development board. It's much lower when I power the circuit from my own PSU and not from the USB port, but still too much for my needs. Is it the microcontroller/USB circuit causing this problem?

When the tests were made on the output noise figure for the datasheet, was the development board used for these tests? Because at the -97dB figure I would expect to hear little or no noise at all under typical use. I don't own a noise analyzer so can't measure what I'm getting, but compared with other equipment I use regularly, it's definitely not low.

Any comments or suggestions would be greatly appreciated... I'm very close to finishing the rest of the design but it's not going to fly unless I can get better performance from the chip.

frank · Post by **frank** » Mon Sep 01, 2008 6:20 pm

I would expect more noise when connected to the USB port. Noise when powered from another supply could be the other supply, the USB chip, etc. Difficult to say, but if the noise is too much you may want to make tests on the product PCB instead since the development board so that any unnecessary circuitry is eliminated.

Chip measurements were made on a different board, not the development board.

elmood · Post by **elmood** » Tue Sep 02, 2008 11:34 am

Hi Frank,

Thanks for the response. I am expecting my PCB to come in this week for my application circuit so I will be making tests with it. I'm hoping that a tighter layout combined with a shielded enclosure will help.

Cheers!