- Support for 4x20 LCD Display and large number display
- Brightness and contrast adjustment with remote
- (OPUS/Wolfson WM8741) DAC volume control: remote and rotary encoder
- (OPUS/Wolfson WM8741) DAC random filter selection 1 to 5 with remote
- (OPUS/Wolfson WM8741) DAC upsampling selection (L, M, H -this is the OSR setting)
- I2C level shifting (5V to 3.3V)
- Optimized power-up sequence

Wednesday, December 30, 2009

Reducing sources for noise

Elsewhere it has been measured that the DC-DC converters are a potential source for noise. Because I am not using the headphone output, I decided to cut the traces to these DC-DC converters. It is only required to cut two traces which you can later jumper if you decide to reverse the changes.

Power to the second DC-DC converter goes through a trace on the underside of the board

If you are using a different Musiland model, the traces will be in different places. But the procedure is as follows:

1- Identify the DC-DC converters. These are the 8-pin chips marked "3063". You can find the datasheet for these DC-DC converters here. (There are two of them).

2- Identify the Vcc pin:

3- Find the trace that feeds this line and cut. This line also connects a local resistor and capacitors for the DC-DC converter. It may not matter whether you cut before the local cap or after the local cap, but in my mod I cut it before the local cap.

4- Make sure you don't cut the line in a place that feeds the other linear regulators (there are two other linear regulator that feeds off the same lines - there are several traces but they all connect to the 5V USB power). In the second picture you can see the line (next to the crystal) that feeds both the DC-DC regulator and the linear regulator. It branches off and feeds the DC-DC regulator through a bridge underneath the board.

5- If you plan well, you can actually use external wiring and a switch to reconnect the traces. This will re-enable the local analog output in case you feel like using the built-in headphone amp.


Anonymous said...

Dear GLT

Thanks!! Now I do not have any more excuses not to try this.

Any plans regarding clock upgrade or modification.??

Best Regards

The Lazy Engineer said...

Hi Greg,

After looking at the configuration, I don't believe a "clock upgrade" will result in an improvement of the clodk. The way it is implemented, the USB chip uses a quartz crystal to generate a clock, so the clock circuitry is inside the chip. Some people believe that replacing the crystal with a clock will result in an improved clock, but I'm not convinced. I think replacing the cryatal with a better crystal may improve things, but if you look at the commrecially available crystals, they are all pretty much the same (you will have to go custom ordering or military application to get better crystals)

Thus if you want to improve the clock I would replace the 3.3 regulator with a low noise approach and this will help the generation of the clock inside the
USB chip.

Anonymous said...

Musiland just released the "exact sample rate" driver. This will improve the accuracy of the sample rate

Anonymous said...

Dear GLT

Thanks for sharing Your opinion on the clock.
I will thing about clean power supply on the clock.
Anyway lots of plans and ideas....
Just to keep You updated
I'm planing to do "cleaning" of my Musiland thought weekend.
I will let You know how it went and this time will make few pictures.

All the best

askchan said...

Do you know what is the function of the small 6-pin IC located on the board?

Anonymous said...

Looks like a linear regulator, but I don't know what is its function

askchan said...

The 6 pin IC with PGVI marking is a ultra low noise, fast rf 200ma low dropout regulator ( TI part number: TPS79301DBVR )

The Lazy Engineer said...

askchan, thanks for the info. That's a pretty nice regulator with 32 uV rms. Almost as good as the lt1763.