• Cut the end off a RPi PSU
  
• Solder the wall plug end onto the In side of the filter and
  
• Solder the USB end onto the Out side of the filter.
  

(01-30-2024, 05:26 PM)hifinet Wrote: For my current setup, it would go between the SMPS and the Kali. These DC filters attenuate noise, but they don't eliminate it. People have used multiple filters in series. But then you are affecting the transient response of the power supply. It would be best to filter, then go into a capacitor or ultracapacitor reservoir.

There is still noise generated by the Raspberry Pi CPU and also the switching regulators of the RPi. Only the original RPi 1 had linear regulators. Some people would actually do microsurgery on RPis with switching regulators, and replace with linear regulators.

That noise from the SMPS gets everywhere. Not only on the positive line, but in the grounds and radiates back onto the AC line. Some EMI as well, but much less significant. Electronics need to pass EMI standards set by the FCC and European regulators.

Until I heard the 5V ultracap supply of the PurePi, I didn't fully appreciate the haze of noise that the Allo basic 5V SMPS was casting, even with the built-in filter of the Kali. I knew there was some noise, but didn't realize it was that much. For some reason, the Allo SMPS creates a larger soundstage, so it has that benefit in its corner. The LifePO4 battery and/or ultracap supplies plus isolation (to deal with the noise from the RPi) seem to be the best solutions.

1. Isolator Pi which seems to handle the issues of noise on the Raspberry Pi GPIO etc - think that the FiFoPi Q7 has this built in??
   
2. Shield Pi Pro which seems to fulfil two functions:
   a) Act as an EMI shield (less interesting based on your observations of EMI not impacting performance as much) and
   b) Power Supply noise filter
   

(01-30-2024, 07:09 PM)hifinet Wrote: Issues of pops. Some issues with ProtoDAC reported to me by a kit customer.

A pop when switching the preamp/amp input to ProtoDAC, with ProtoDAC powered. This is due to the fact that ProtoDAC is missing a "polite part". This part is a resistor from the center RCA to ground. It can be anything from 100k to 1M. It is not included for simplicity and sound quality.

Since ProtoDAC output is not tied to ground with a resistor, a charge can develop when the input of the preamp/amp is switched to another component. Then when the input is switched to ProtoDAC, that charge is suddenly discharged to ground and is amplified. The simple solution is to turn the volume down before switching to the ProtoDAC input.

The signal not passing through a signal to ground resistor is your signal. No resistor is a perfect resistive device (metal foil get close). It also has inductive and capacitive properties. Signal to ground resistors will affect sound quality, especially before an amplification stage. Some advocate for metal foil resistors in all signal to ground positions. That can get expensive. My recommendation is to just turn the volume down before switching the input.

The same customer reports a pop when turning on ProtoDAC with the amp already on. It is best practice to turn the amp on last (ProtoDAC-->preamp-->amp), and turn it off in reverse order.

The third pop is at the start of the first playback track. I think this is module related. My TeraDak TDA1387*8 always made a sound of a record skipping grooves at the beginning of the first track.

I can rarely get a tick after the last track of the playlist.