VS1000 and external amplifier

[BCluster]

Hi. I need to use VS1000B with external amplifier. But when I try - strong white noise in pauses. With headphones i can't observe it. Where I can find problem?

[Panu]

Hmmh, what kind of connection do you have at the outputs? The outputs are designed for driving headphones, and the headphone coil is a necessary part of the circuit. If you want to drive an external amplifier, you need to consider things such as DC level and Sigma-Delta noise.

For info on how to connect the VS10xx output to external amplifier see post:
viewtopic.php?f=9&t=69

-Panu

P.S. Hmmmh... With VS1000B... there may be something happening with the Low Power Pause... what kind of software are you running on the VS1000B?

[pasi]

Hi. I need to use VS1000B with external amplifier. But when I try - strong white noise in pauses. With headphones i can't observe it. Where I can find problem?

Note that you should NEVER connect headphone common (CBUF) to external amp ground. If you also connect USB or other ground connection, you are connecting 1.2V to ground, creating current flow through the VS1XXX chip, possibly breaking it.

In low-power pause mode (after about 3 seconds in pause without button activity) the analog drivers are turned off, which allows CBUF, LEFT and RIGHT levels be forced by the external amp. I have noticed this with our vs10xx laboratory measurement board when my "multimedia speakers" has its transformer replaced. Whenever vs10xx drivers are off, the speakers give out 50Hz noise signal.

However, if you hear white noise, it is more probable you pick up interference from nearby systems when vs1000 is not driving the output lines. Check the external connections application note from VLSI's web site, using the line out connection with the resistors to ground will probably help.

[BCluster]

Note that you should NEVER connect headphone common (CBUF) to external amp ground. If you also connect USB or other ground connection, you are connecting 1.2V to ground, creating current flow through the VS1XXX chip, possibly breaking it.

No, my amplifier is with differential inputs. In attach you can see fragment of my schematics.

I'm using custom software, if it is needed I can give you my listing. But i don't use any keyboard hook if it is important and player loop is overrided.

[Panu]

Thanks for the schematic. I think you need to add the sigma-delta reconstruction filter from the picture at viewtopic.php?f=9&t=69. But why do you use DC blocking caps if you have a differential amplifier? Isn't the 1.25V biased output from LEFT/RIGHT/CBUF in the amplifier's operational range? I think you should remove C14,15,16,18. BUT I would add a 100K resistor across each input so that they would be weakly together, limiting noise if VS1000 drivers are cut off.

Your schematic doesn't have the RC's that are marked "High frequency grounding path" in viewtopic.php?f=9&t=69 for LEFT and RIGHT (they are mandatory with all VS10xx chips).

Also, you could actively control the SHUTDOWN pin of the amp, to remove any power on-off clicks altogether.

So, in summa summarum I'd say: add 20R in series with 10nF from LEFT, RIGHT to AGND; change C14,15 to 470R; change C16,18 to 220R (or even to 0R); add 3.3nF from LINP, RINP to AGND and add 100KR across LINN,LINP and RINN,RINP.

If after that you still get noise at pause, check if the amp inputs drift to some strange voltage at pause (when VS1000 drivers are turned off). I guess it wouldn't hurt to have a 100K resistor from CBUF to AGND to stabilize the pins in that condition.

P.S. if you get it working, could you post the revised schematic here. I think people would be extremely happy

P.P.S. Seems you have SI floating... that can lead to extra power consumption. I suggest that all unused pins in the VS1000 are pulled low with 100K resistors... Except RX, which always needs to have a resistor to IOVDD so that the unconnected RX pin doesn't receive noise, which WILL halt VS1000 eventually (detect a "go to monitor" character from noise)... Of course, if the RX pin is always connected to some pin in your design, it's not a problem for you, but this is advise to other people too....

-Panu

[BCluster]

Hi, thanks for your reply. I put blocking caps because it was recommended by amp manufacturer, but I can see operating voltage is from 0 to 5V. Now I will put all you said in my schematics, thx

[shahira_du]

Thanks for that post... it's really help me...

[AmpKitteh]

Thanks for that post... it's really help me...

Hi. I need to use VS1000B with external amplifier. But when I try - strong white noise in pauses. With headphones i can't observe it. Where I can find problem?

I have to concur with shahira_du! I was actually having the same white noise problems as BCluster. Hopefully, with the advice everyone has provided, I'll be able to alleviate some of these amp issues. I'm hoping that by fixing this external amp issue, I can get my floor standing speakers working again.

Thanks a bunch guys! If I manage to fix the issue, I'll come back and let you guys know. =)

[Panu]

Thanks for the comments.

You could also take a look at the USB Recorder's schematics at http://www.vlsi.fi/fileadmin/software/V ... der_03.pdf . It's an old schematic, but the D class amp connection is ok. (I'm not sure if it's the best, but the sound is good)

(The VS1000 USB recorder is a semi-abandoned project that records sound from USB audio and microphone to an SD card; it works but with some SD cards the buffering memory of VS1000 is not enough to get a gapless 44100 Hz stereo recording in real time; so it doesn't work cleanly with all SD cards so we haven't looked at it for a long time... we have evaluation boards for it lying on the shelf somewhere, if anyone wants to take a look at it. http://www.vlsi.fi/en/support/software/ ... tions.html)

-Panu

[Milek]

Hi

Yes, that is. We have also had problems with audio output. The problem occurred when we used VS10xx with external amplifier and a common voltage or battery. Some on/off pops,noice..etc.When the voltage is separated works great. Several options or solutions can be made as using sigma-delta filter, or simply use CBUF output for mute or sleep function ,it saves energy from the batteries also,as long we use TA2021B.

regards