I made this circuit and it works extremely well. Its not exactly what i use (I use more filtering) but this is the basic principle. And it is powered by external linear transformer with LM 5v ultra low noise regulator.
Problem i have is whenever the inductive loads in home like fan, grinder etc turned off, khadas will disconnect from pc. I know it is very sensitive to voltage fluctuations but never thought it would be on this scale. With khadas connected directly to pc, this problem never occurred. Can Someone from khadas shed some light? Adding more caps is not solving the problem. Is there any other way around? Thanks
I finally got to the bottom of the problem (I think)
Problem was my external linear regulated PSU: When it’s “cold” and I switch it on, it takes it some time to stabilise at 5VDC. It’s probably less than 1 second, but it’s long enough to put the Tone board is some kind of wrong state in which the sound is heavily distorted.
Easy workaround for me to switch off and on the “warm” PSU quickly, just so the Tone board is reset and gets the stable 5VDC upon restart.
Is this an issue that could be addressed somehow on the Tone board?
Perhaps you could add a turn on delay to your power supply. Could be a simple R-C circuit with relay. Or search the Bay using term “turn on delay circuit”. Caution, some poorly designed circuits may add noise.
Hi. Are you sure on this? Because according to the schematic, there is a Schottky-diode to separate the two power supply-paths. So if the voltage from usb c is higher than from the external psu connected to pins 2 and 5, it will not cut off the USB-C-line-power.
I did some experiments and measurements today. The schottky blocks the DC input from USB Vbus completely as soon as it drops below about 4 V with 5.0 V at Pin 2. Otherwise the load is shared between Vbus and Pin 2.
As I need to leave Vbus connected for my PC to recognize the tone but want the load completely on the LPS via pin 2/5 I soldered a 10k metal film resistor into the Vbus-line. The voltage drop at the resistor is such that all load is on the LPS but still enough voltage and current for the host to „see“ the device (0.2 mA).
your computer doesn’t recognize the Tone2 Pro if there is no power contact ?
I tried with a USB-C cable on which I cut the +5V contact (or wire), and it works perfectly on computers, smartphones… All the power comes from the USB-C I2S port (checked it with measurements as I also found before that the power was shared between the two port, even with a higher voltage on the USB-C I2S port.
Hi Grooved.
I am using the Tone 1. May be there is a difference. I tried it on several computers and smart-devices. Always same result: without Vbus, does not recognize the tone.
The sulution I figuered out is as follows: I soldered a 10k resistor into the 5 V Vbus-line. The voltage drop is such, that all power will be taken from the GPIO-connectors (connected to an external LPS). But there still is a 0,2 mA current on the vbus and obvously this is enables the Host to recognize the Tone1.
Hi, could you help me with similar, or the same issue. Could you show me more exactly where have you solder the resistor?
I have 2 main problems or let’s call it issues:
My DAC very often is disconnecting. Without any repetetive or avoidable reason. And very often i need to plug out the usb cable and again plug in.
I would prefer to use external power supply, but when I am doing it, Tone1 is not recognized by system. basicly 3 situations:
a) Tone1 is connected via USB-C and external power supply via PIn 1&21. It works, but I am not sure if in this case Tone1 is powered by LPS or by USB. And switching on/off LPS do not restart Tone1. (i would like to achieve that because of very often disconnecting the Tone1),
b) Tone1 is connected via USB-C with cutted of power wiring and powered via PIN 1&21. Tone1 is powered by LPS, but Windows do not see the device,
c) Tone1 is connected via USB-C cable modified as was shown on this forum. USB cable is modified, Power is cutted-off and there is connected power from LPS, so the power is also connected via USB but from the LPS not from the PC. Result = WIndows do not see the device.
I use PC and Win10. Any tips?
Hi. I built an internal connection cable. The resistor is in the heatshrink at the USB jack.
Everything very small. I don’t have issues with the tone disconnecting. Only the problem that my host does not recognize the tone without Vbus connected.
Others don’t have this issue so I think it is hardware/driver/firmware-related.
Klaus
okey, But where do you connect this resistor? Do you cut DC+ and put it simply in the wire? Sorry I am nut 100% what’s ‘VBUS’. So it will be red wire DC+ → 10k resistor → red wire DC+
