--- In email@example.com
, Ignacio Cembreros <eb4apl@...>
> Guido wrote:
> > On 7/30/07, *Ignacio Cembreros* <eb4apl@...
> > <mailto:eb4apl@...>> wrote:
> > Terry, Guido et all.
> > I bought the same kit mentioned in Nuts and Volts, more than
> > ago. Finally I found the kit documentation in digital format
so I can
> > describe the problems I had.
> > The picture has an error, a swapped resistor pair, which
> > balance. If you have followed the picture for placing the
> > like me, you swapped R11 and R13. R11 should be 6k8 and R13
> > 3k9 and they must be located as per the silkscreen, not per
> > picture.
> > Another error is in the PCB itself which doesn't agree with
> > schematic and is related to the supply method. This affects
> > performance, according to TI.
> > My solution is to cut the trace which goes from C2 to a via
> > finally
> > to U3 pins 8,9 and 27; do it just after C2 and solder a wire
> > jumper from
> > C2 (or C1) to R9 (VBUS in the schematic). All this rework is
> > in the
> > bottom side of the card.
> > As you can see, both problems can be easily fixed, and after
> > I use
> > this mini card for demos with an SR40 with reasonable results.
> > 73 de Ignacio, EB4APL
> > Hello Ignacio,
> > Thanks for reporting about your experience with the PCM2900
> > have no access to the Nuts and Volts schematic, but presume the
> > circuit is not different than the typical circuits as published
> > datasheet  ? Could you indicate which of the components
> > the performance?
> I was referring to a PCB layout error in the Nuts and Volts kit
> not in the schematic which is close to the TI evaluation boards,
> minor variations.. If you are interested in the schematics and the
> description, let me know it and I will send it directly to you.
> According to TI, the circuit can be powered from the internal
> or an external one. The use of the internal regulator affects
> negatively to the harmonic distortion and maybe the noise, I don't
> the application notes here but are on the TI site. So TI
> use a cheap external regulator, except for very cost sensitive low
> 73 de Ignacio, EB4APL
Thank you for the above information. I checked my ADDA board, and it
has both the problems you mentioned above. I purchased the assembled
units, not the kits, but the resistors were wrong anyway.
I ahve made both the changes you outlined above, and will test the
board for improvements. It certainly cannot be worse that the board
It will likely be a week before I can test it, as I have some travel
Thank you again for highlighting the two problems above. I do not
have the original Nuts & Volts article. I have only the schematic
that came with the board, and the TI datasheet.