Spin Semiconductor

For what it is worth, I would do the following before changing anything else:

1) Re-solder every connection on the entire board. I always use tin-lead solder for prototypes to get good flow.

2) Clean the entire board with alcohol to remove all of the flux. Make sure you get under the chip and any other big components.

3) Download a simple program, like one that reads the adc's, multiplies each by a pot, and writes them to the dac's.

4) Start with inputs grounded, and see if you get noise on the outputs. This is the configuration that I would use for any further testing.

5) Your ear is probably as good a test tool as a scope for this kind of audio circuit. Plug the outputs into an amp and leave it turned on for testing.

6) Sometimes it can be more productive to try things that you think will INCREASE the noise first. Like probing around with a bare wire in your finger, or using a noisy "wall wart" power supply. This will help isolate the issue.

Good luck,
Don

6) It is often

Hello Don,

thanks for answere and your good ideas.
1) I do always
2) I take Flux-OFF to clean the board, but it`s the same
3) sorry, but I don`t understand this point
4) It`s an importand point:
If I ground the input signal by the jack plug, it`s the same noise like everytime. If I ground the input signal nearly the FV-1 input, the noise was terribly, and I can hear the LFO very loud. Is it a problem with the ground plane ??

greetings Saxosun

Do you plug your board between an electric guitar and a guitar amplifier ?
Don't forget that an el. guitar outputs signals as low as 100 mV PP and guitar amplifiers have a lot of gain.
Try your board feed with a line level signal (2V PP) and listen it with another amplifier (for example a Hi-Fi or PC monitors). You should see the CLIP led lit sometimes.
Maybe this is not your problem but it's good to check that anyway.

Saxosun wrote:Hello Don,

thanks for answere and your good ideas.
1) I do always
2) I take Flux-OFF to clean the board, but it`s the same
3) sorry, but I don`t understand this point
4) It`s an importand point:
If I ground the input signal by the jack plug, it`s the same noise like everytime. If I ground the input signal nearly the FV-1 input, the noise was terribly, and I can hear the LFO very loud. Is it a problem with the ground plane ??

greetings Saxosun

When you ground the input, you should ground it after the decoupling capacitor, as even grounded, the input pin must be biased at the midpoint between GND and V+. Are you doind this or just grounding the pin directly?