[LAU] 1/4 inch to USB audio interfaces

There are a lot of "guitar" to USB "cables" out there. I picked one up
just for practice purposes: plug it in to my laptop and run it through
Guitarix.

My findings:
The board inside is a standard phones and mic usb dongle. So pipewire
will try to make the phones jack (which doesn't exist on these things)
the default output. Lucky for me there is an input only "profile" I can 
set pipewire to.

Next thing I noticed was that my volume pot was scatchy... I just bought 
this guitar and it is not scratchy on the amp or through pedals. Yeah,
the volt meter says 3vdc going to the guitar. The chip inside says it is
a C-Media HS-100B. The board inside is like I mentioned, meant for a
"computer" mic and seems to have followed exactly the schematic snip
in the c-media application notes:

Input has a varister and .1uf cap to ground and then goes through two 8.2k 
resisters, one then goes through another .1uf to micin... so far ok. 
However, the other 8.2k is followed by 47uf cap to ground (effectively 
making the input 8.2k) and then through a 2.2k to vbias.

NOT a good input setup for a guitar at all. I could not find out what the 
inout impedance is of micin is but if I can get the case open (enter the 
dremmel) and remove the R12 to vbias, my input impedance will at least 
double. I'll let people know how that goes.

So, 1/4inch to USB cable are not Guitar to USB cables.... put a preamp in 
front.... a looper for practice in cludes an aways on buffer.

Len

--
Len Ovens
www.ovenwerks.net
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