Hello guys,
I have a chinese DAC based on XMOS U8, AK4490 DAC and NE5532 OP-AMP ( now OPA2134). The board should be externally powered by a 9V DC and the power route is like this:
9V->L7805->AMS1117 3.3V -> XMOS, Atmel chip, cloks
9V->L7805->DAC 5V pins -> AMS1117 3.3V -> DAC 3.3V pins
9V-> some filters -> Op-Amp - this is a guess because the board is multilayer and I can't trace the whole circuit, but on the +Vcc pin I have something like 8.5 V
I want to transform the DAC to be USB powered ( I know, a heresy), but I don't know what route to chose without breaking the bank(if needed) but still preserve a nice sound.
My findings until now are:
-the 5V from the USB is only used to power a LED
-the total power consumtion of the board is 160mA
-bypassing the 7805 reg and feeding directly 5V from the USB is working but the sound is very distorsed at higher volume - I suspect because the voltage on the Op-Amp is only 4.4V
-by using a lab power source I powered the board and I didn't hear any difference between 7 V(minum drop for the L7805) and 9V(the maximum that I would use for the 7805 to drop)
-in my local electronic shop I have found DC/DC 5V to 5V 3W isolated converter, isolated DC/DC 5V to 9V at decent price with 222mA(2W) otput current and very very expensive with 666mAh(6W) - nothing in between power wise and all switching at 100kHz
My options are:
1) use the 9V 2W DC/DC converted and ADUM4160 to fully isolate the USB, then some pasive filters followed by a good LDO to suply ~7-8V to the 7805's and Op-Amp
2) use the 5V DC/DC converter and ADUM4160, some filters and change the power route for the Op-Amp to get the minimum 5V
3) build a boost converted to reach 9V but with a much higher switching freq ~1M and more current output, and then the same: pasive filters followed by a good LDO to suply ~7-8V to the 7805's and Op-Amp
My concerns are:
-for method 1 the power consumtion is near the max power for the DC/DC converter
-for method 2 the Op-Amp will not get any LDO
-the DC/DC converter are working at low freq
-the method 3 is not galvanic isolated from the USB, but I saw that other good spec DACs like Khadas Tone 1 are also not galvanic isolated
What do you guys think? I am also opened to other sugestions.
This is the board, it has some changes on it because I am testing different power configurations.
I have a chinese DAC based on XMOS U8, AK4490 DAC and NE5532 OP-AMP ( now OPA2134). The board should be externally powered by a 9V DC and the power route is like this:
9V->L7805->AMS1117 3.3V -> XMOS, Atmel chip, cloks
9V->L7805->DAC 5V pins -> AMS1117 3.3V -> DAC 3.3V pins
9V-> some filters -> Op-Amp - this is a guess because the board is multilayer and I can't trace the whole circuit, but on the +Vcc pin I have something like 8.5 V
I want to transform the DAC to be USB powered ( I know, a heresy), but I don't know what route to chose without breaking the bank(if needed) but still preserve a nice sound.
My findings until now are:
-the 5V from the USB is only used to power a LED
-the total power consumtion of the board is 160mA
-bypassing the 7805 reg and feeding directly 5V from the USB is working but the sound is very distorsed at higher volume - I suspect because the voltage on the Op-Amp is only 4.4V
-by using a lab power source I powered the board and I didn't hear any difference between 7 V(minum drop for the L7805) and 9V(the maximum that I would use for the 7805 to drop)
-in my local electronic shop I have found DC/DC 5V to 5V 3W isolated converter, isolated DC/DC 5V to 9V at decent price with 222mA(2W) otput current and very very expensive with 666mAh(6W) - nothing in between power wise and all switching at 100kHz
My options are:
1) use the 9V 2W DC/DC converted and ADUM4160 to fully isolate the USB, then some pasive filters followed by a good LDO to suply ~7-8V to the 7805's and Op-Amp
2) use the 5V DC/DC converter and ADUM4160, some filters and change the power route for the Op-Amp to get the minimum 5V
3) build a boost converted to reach 9V but with a much higher switching freq ~1M and more current output, and then the same: pasive filters followed by a good LDO to suply ~7-8V to the 7805's and Op-Amp
My concerns are:
-for method 1 the power consumtion is near the max power for the DC/DC converter
-for method 2 the Op-Amp will not get any LDO
-the DC/DC converter are working at low freq
-the method 3 is not galvanic isolated from the USB, but I saw that other good spec DACs like Khadas Tone 1 are also not galvanic isolated
What do you guys think? I am also opened to other sugestions.
This is the board, it has some changes on it because I am testing different power configurations.
Attachments
that could work, I will give it a try, but forget to mention that I am using the DAC with headphones, they are AK612Pro so they need some juice to be driven. Will these opams will do the job?
All have output load current similar to OPA2134's so very likely they would work. AD823 probably has higher distortion but it may still be good enough for the task.
As you're using the DAC with HPs, there's no advantage to be gained in isolating the USB with ADUM4160.
The 'ground noise' needs to be a current flow to have the potential of doing harm to your audio. Since the HPs have no parasitic capacitance to ground to speak of, there's no current that can flow.
ok, so you all are saying that I should drop the DC converter and use straith 5V from the USB with apropiate filtering + low supply voltage op-amps. This will work, but my only consern remains that the DAC will have a non regulated 5V to use it as VrefHL. How could I fix this?
If I were you, I'd go for your option 3. I've had unimpressive results from directly using the USB Vbus to power DACs. A boost converter with passively filtered output (LC) would be a better option to give headroom for linear regs to operate.
You could use slightly lower VDDL/R & VREFHL/R. E.g. LP5907 has 4.5V output version or TPS7A94 which has adjustable output with only 150mV dropout.
Of course option 3 is ok as well but more complicated unless you use some prefabricated device. No need for an LDO between boost converter and L7805.
One of these modules (or similar) should suit. Its using MT3608 which runs at 1.2MHz - go for the variant of the module that uses a shielded inductor : https://www.aliexpress.com/item/1005006035788311.html. I'd avoid the earlier generation boost converters running below 100kHz as their output is harder to filter.