Hello,
I just want to notice that when you increase QA403 generator from 7dBV to 8dBV there is a huge spike on output signal.
Best regards.
Sorin
Hello,
I just want to notice that when you increase QA403 generator from 7dBV to 8dBV there is a huge spike on output signal.
Hi @bmsorin, thanks very much for reporting this. This is when generating only in idle mode, is that right?
I think what is happening is this: Anyplace you have relay boundary in the output (8 dBV, -2 dBV, -12 dBV) the sine amplitude sent to the DAC needs to be in sync with the DAC attenuator setting. So, you are at 7 dBV and you are sending to the DAC an (almost) 0 dBFS sine. That is, the sine is at ~0 dBFS and the attenuator is at 10 dB.
And then you switch to 8 dBV output, and the relay attenuator goes to 0 dB attenuation, and the sine level goes to roughly -10 dBFS. What happens in the code is the relays always switch immediately (to maximize the settling time). And so, at 7 dBV you have a 0 dBFS sine in the various DAC buffers (USB PC side, USB firmware side, I2S buffers). And then the relay switches to 0 dB, and suddenly that 0 dBFS sine is playing with a 0 dB attenuation, getting you very close to the full scale output of the DAC.
There are probably a few different approaches to take here:
I think #2 might be the best. What do you think?
Looking at this more, I think the next release will do #3. This will give seamless amplitude transitions across the full range by locking the DAC output attenuator at 0 dB.
Hi Matt, yes, idle mode. I test an auto ranging device, and at 7-8dBV step the device switching relay to more that it should, testing with scope reveal what i post.
I think #3 will be best option. One think i have in mind right now, testing RIAA premp will be at limit.
Regards!