Hello friends,
i used the search function, i sailed the whole web, i did my due diligence.
Well, this DAC
https://www.aliexpress.com/item/1005002810554110.html?gatewayAdapt=glo2deu
which seems to be 100% analog to the teradak here
https://home.teradak.com/products/107.html
seems to suffer with a low level hiss (how could i define that? HF intruding anywhere?), which with audio files with low DR (classical music mostly) is really a pain.
My config is an underclocked (though it did not help) rasp 3b+, isolator board OSA electronics (with and without board no difference), the tda1387 dac.
At first I tought it was a faulty item, so i bought it again, the deluxe version this time, to discover the problem is common.
I don't know whether any of you experienced this issue or it is a common problem, it's quite a pity since the sound coming out of this system is very pleasing...
Is there any known diy workaround?
Thank you as always,
Mike
i used the search function, i sailed the whole web, i did my due diligence.
Well, this DAC
https://www.aliexpress.com/item/1005002810554110.html?gatewayAdapt=glo2deu
which seems to be 100% analog to the teradak here
https://home.teradak.com/products/107.html
seems to suffer with a low level hiss (how could i define that? HF intruding anywhere?), which with audio files with low DR (classical music mostly) is really a pain.
My config is an underclocked (though it did not help) rasp 3b+, isolator board OSA electronics (with and without board no difference), the tda1387 dac.
At first I tought it was a faulty item, so i bought it again, the deluxe version this time, to discover the problem is common.
I don't know whether any of you experienced this issue or it is a common problem, it's quite a pity since the sound coming out of this system is very pleasing...
Is there any known diy workaround?
Thank you as always,
Mike
Is the DAC board being powered by the same PSU as the Rasp 3B+? If so then swapping to a linear PSU for the 3B might help. The isolator board has its own PSU input, a linear supply just for the DAC might bring improvement. I'm speculating here as there could be more than one reason for your hiss given the Raspberry is an EMI aggressor, could be just moving the DAC board far enough away from the mainboard (or introducing a shield between them) would help.
Hello Abraxalito, it looks like this:
a 5V 3A power supply (a normal one, like these of phones) powers the Rasp 3B+;
a similar 5V 3 or 2,5A (don't remember) powers the isolator board and the DAC.
do i need a linear psu?
i could make a test and try to move the dac away, are long cables or shieldings for sale ? Never heard of them...
was just thinking about the culprit being these 2 inductors...
a 5V 3A power supply (a normal one, like these of phones) powers the Rasp 3B+;
a similar 5V 3 or 2,5A (don't remember) powers the isolator board and the DAC.
do i need a linear psu?
i could make a test and try to move the dac away, are long cables or shieldings for sale ? Never heard of them...
was just thinking about the culprit being these 2 inductors...
To get value from your isolator you would need to use a non-switching PSU for powering the DAC. Running it on the same kind of PSU defeats the purpose of it.
That would be my first experiment. You're right, it could be the inductors are picking up HF hash, you can always short those out with a wire between their pins to check.
That would be my first experiment. You're right, it could be the inductors are picking up HF hash, you can always short those out with a wire between their pins to check.
You could try attaching the Hat with this (but I'm a DIY fraud - not hardware guy ;-):
https://shop.pimoroni.com/products/40-pin-gpio-extension-cable?variant=32246715580499
https://shop.pimoroni.com/products/40-pin-gpio-extension-cable?variant=32246715580499
ok, thank you, so, since i need 2 PSUs, would you be so kind to suggest me a power unit for the two devices ? Have to be both on linear, or can i put the RB on a normal switching psu? Please give me a hint without spending big money...
what about shorting the inductors with a low-ish resistor, say, 4 or 5 ohms?
what about shorting the inductors with a low-ish resistor, say, 4 or 5 ohms?
A low value resistor across each inductor would at least reveal if the inductors are the primary culprit.
As for the DAC PSU, something like this would be a start - https://www.amazon.com/JAMECO-RELIA...ansformer-Single-Out/dp/B00B88EP1I/ref=sr_1_6. With the isolator in place you only need a linear supply for the DAC, not for the RPi. A step up from this PSU would be a higher voltage one (say 9V like this : www.amazon.com/Jameco-Reliapro-GPU41090500WD00-Regulated-Adapter/dp/B00B886SFO/ref=sr_1_3) followed by a very low noise linear regulator board to get back down to 5V, say like this : www.aliexpress.com/item/1005005751265055.html
As for the DAC PSU, something like this would be a start - https://www.amazon.com/JAMECO-RELIA...ansformer-Single-Out/dp/B00B88EP1I/ref=sr_1_6. With the isolator in place you only need a linear supply for the DAC, not for the RPi. A step up from this PSU would be a higher voltage one (say 9V like this : www.amazon.com/Jameco-Reliapro-GPU41090500WD00-Regulated-Adapter/dp/B00B886SFO/ref=sr_1_3) followed by a very low noise linear regulator board to get back down to 5V, say like this : www.aliexpress.com/item/1005005751265055.html
What do you think the dynamic range of the DAC is? (I didn't see it spec'd anywhere).
How are you doing volume control? Digital or analog?
What is the gain of your amplifier?
How sensitive are your speakers?
Without knowing the answer to these questions difficult to say if this is a routine noise / gain structure problem or a more complicated issue.
Michael
How are you doing volume control? Digital or analog?
What is the gain of your amplifier?
How sensitive are your speakers?
Without knowing the answer to these questions difficult to say if this is a routine noise / gain structure problem or a more complicated issue.
Michael
mdsimon,
What do you think the dynamic range of the DAC is? (I didn't see it spec'd anywhere).
I have no idea
How are you doing volume control? Digital or analog?
digital. I use moode VC, no rotary encoder. good point, it is always at 100%
What is the gain of your amplifier?
around 24dB the pre, around 22dB the power
How sensitive are your speakers?
104dB. too much.
however, with other sources and same volume setting, the amp is dead silent.
What do you think the dynamic range of the DAC is? (I didn't see it spec'd anywhere).
I have no idea
How are you doing volume control? Digital or analog?
digital. I use moode VC, no rotary encoder. good point, it is always at 100%
What is the gain of your amplifier?
around 24dB the pre, around 22dB the power
How sensitive are your speakers?
104dB. too much.
however, with other sources and same volume setting, the amp is dead silent.
Had time to experiment a little.
With resistors in place of inductors, the hiss is really really better. Measured R of inductors, ca. 28 Ohm, so used 22R.
Some hiss remains, however is more than tolerable.
It is only on right channel, which output is right above the rasp power in.
It looks like in picture attached:
It's tremendous, I know, I need some shielding, but how to fit in this "chassis"?
