Topic: Best USB Soundcard for LaserBoy

[flecom]

Ok so back in the long ago I purchased a 6 channel offset board at SELEM 2008 (and soldered it up right there) unfortunately its been sitting on my desk for a year and a half or so its time to put it to work... so... simple question I couldn't find an answer to... whats the best USB sound card to use with this thing?

[James]

Hey Frank!

How have you been? !!! 

For that amp that you have any sound card that has a DC offset voltage of about 2.25 V or so. This would be almost any PCI card and the 6 channel USB device that is based on the C-Media 106L. Unfortunately, there are a few design revision of the internal electronics found in the eBay blue box devices. The older ones are the CM-106L but the newer ones are not. I'm not sure about the DC offset of the newer ones. The problem arises when a sound device is powered with only 3.3VDC. The mid point voltage is about 1.2V and the amp board you have can not be set for an offset that low. Replacing the 10K offset pots with 50K will solve this problem at a cost of some adjustment resolution.

James. 

[flecom]

I am great, quit my job @ Miami-Dade Public Schools and working for Reality Kings (google it,  just not @ work)

listening to music on my speakers powered by some amps I was working on



and of course, listening to my headphones, working on a new amplifier for my electrostatics

hrmm, so I should hunt for a 106L USB device?... dont know how easy thats going to be 

[James]

You might want to skip it and go for the easily hacked 8 channel version. I can tell you about replacing the resisters, pots and voltage regulator on that board you have to make it work tits. 

http://akrobiz.com/laserboy/forum/index.php/topic,335.msg4091.html#new

What are your speakers?

James. 

[flecom]

thats fine, can I just leave the last 2 channels alone and use them for analog audio?

[James]

That's exactly the plan!

http://akrobiz.com/laserboy/forum/index.php/topic,333.msg4038.html#new

James. 

[flecom]

so this basically

http://cgi.ebay.com/Sabrent-USB-SND8-8Chl-3D-USB-2-0-Ext-7-1-Surround-Sound_W0QQitemZ230419137409QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item35a60d0381

[James]

Don't get it there.

Get it here:

http://usbgear.com/computer_cable_details.cfm?sku=USBG-SOUND-71&cats=121&catid=121%2C637%2C136

Go for the $6 shipping too!

James. 

[James]

Hey flecom, about modifying your current correction amp board...

You should probably swap out the 20K fixed resistors with 15K 1%.

If you use a 500 ohm trimmer, you'll have from aproximately 15 to 15.5K to adjust the offsets. With 20K resisters, your 500 ohms is less of a percentage of the whole. You might not have enough adjustment room for nulling all the offsets with only one negative voltage reference.

The reason I went with 15K is because you have to offset a voltage that might be as low as +1.2V. The negative voltage regulator won't adjust much lower than -1.25VDC. The ratio between the negative reference and the positive offset is 15K/10K, so that means you set the negative voltage at about -1.5 times the DC offset at about -1.8VDC.

I even went so far as to measure all the fixed resisters to find groups of 6 that were as close as possible.

James.