QuantAsylum QA400 and QA401

[JensH]

Regarding MiniDSP I am looking at the possibility of using an external clock for the MiniDSP USBStreamer. I think I have found a method to do so. I am close to finishing the layout of an isolated interface board. If it works as intended, I will be able to get 8 channels in and 8 channels out (10 each with an add-on board), with a clean master clock.
I have also prepared the design for the use of an externally applied master clock, so that the clock can be chosen freely (as long as they are 24.576/22.5792MHz) and placed close to the converters. The internal clocks from the USBStreamer have too much jitter in my opinion.

When this is done I plan to design an ADC/DAC board to connect to this interface board.

[davada]

Hi Bear,

I dug out my QA400 and took some screen shots.

This is an overlay. Green is the left ch and red is the right.
192k. I'll post another at 48k
This is using the left out gen.

The 4th pic is with the gen running but not connected to either input.
You can see the crosstalk into the right channel but the left channel doesn't seem to be effected.

[1audio]

Originally Posted by davada

Just little off topic or maybe not so off topic, has anyone checked out the products at MiniDSP.com? A lot of very interesting stuff there at reasonable prices. All by DIYers.

I spent some time with the Minidsp guy at AES last year. They are very together. Not DIY really but pro operation trying to eke out a living in Hong Kong. The boxes are good and they are among the best for XMOS design.

[1audio]

Originally Posted by RNMarsh

Your input got lowered --- near zero in first 2.... -3.5dB on last test. Run it again with higher - zero - level and then compare.

THX-RNMarsh

I tried that with the loopback, the distortion was still much higher. I need to rework the prototype to get unity gain through it.

[bear]

davada, ur results appear to suggest that the source of the "extra" harmonics is in the generator side? Also I think I see your THD number is ~0.003%? That seems higher than spec??

I hope to be able to check a few more things over the weekend, including taking the osc from the VP-7725 and seeing how that looks, also doing the shorted input test...

Time permitting I could try running the output of the two gen channels to the VP-7725 and see how they stack up as well...

Anyone besides Demian, Davada and me actually have the box??

_-_-

[davada]

Originally Posted by 1audio

I spent some time with the Minidsp guy at AES last year. They are very together. Not DIY really but pro operation trying to eke out a living in Hong Kong. The boxes are good and they are among the best for XMOS design.

I thought their product line was a bit too developed for DIY. No DIYer has that kind of time unless retired. The USB stick is just what I need to get going.

[31697B]

Originally Posted by bear

davada, ur results appear to suggest that the source of the "extra" harmonics is in the generator side? Also I think I see your THD number is ~0.003%? That seems higher than spec??

I hope to be able to check a few more things over the weekend, including taking the osc from the VP-7725 and seeing how that looks, also doing the shorted input test...

Time permitting I could try running the output of the two gen channels to the VP-7725 and see how they stack up as well...

Anyone besides Demian, Davada and me actually have the box??

_-_-

I probabaly do. Or similar-something like it.

-RM

[bear]

Sorry? probably do? lost you on the curve...

----------

Fwiw, I looked again at the QA site at their own images for each channel and noticed that they too are showing similar harmonic spurs. Now with 20-20 hindsight I realize the significance of what is being shown...

[31697B]

Bear ---

Make that a - yes I do.
Just following along at the moment.
sup?

-RNM

[31697B]

Originally Posted by JensH

Regarding MiniDSP I am looking at the possibility of using an external clock for the MiniDSP USBStreamer. I think I have found a method to do so. I am close to finishing the layout of an isolated interface board. If it works as intended, I will be able to get 8 channels in and 8 channels out (10 each with an add-on board), with a clean master clock.
I have also prepared the design for the use of an externally applied master clock, so that the clock can be chosen freely (as long as they are 24.576/22.5792MHz) and placed close to the converters. The internal clocks from the USBStreamer have too much jitter in my opinion.

When this is done I plan to design an ADC/DAC board to connect to this interface board.

Sounds very interesting. what is your current progress... what has been done to date? And, what still needs to be done..... ETA?

-RM