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Review and Measurements of WesionTEK Khadas Tone Board DAC

milw50717

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KTBD normally is power hungry (specification 5V/500mA). But with laptop work OK, but when connect to eg. Raspberry Pi I have often hangs. And now I must connect to KTBD external power 5V and maybe 1A. I will test...
What hangs, the KTB or the Pi - when you experience these hangs are you able to SSH into the Pi - and are the hangs during playback ?

Do you see any under-voltage messages in the output when you type 'dmesg | grep voltage' ?

Wired or Wi-Fi connectivity ?

I have an ethernet connected Pi 3B with a hifiberry Digi+ Pro HAT that feeds the KTB power via the USB and the audio via coax. unplug the USB cable from the Pi when not in use, so the KTB is not powered up but the Pi is left on 7x24. I've not experienced any hangs in even extended listening sessions lasting 5 or 6 hours. For a short time I also ran using just the Pi 3B feeding the KTB audio and power via the USB cable and can't recall any hangs.
 
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What hangs, the KTB or the Pi - when you experience these hangs are you able to SSH into the Pi - and are the hangs during playback ?

Do you see any under-voltage messages in the output when you type 'dmesg | grep voltage' ?

Wired or Wi-Fi connectivity ?

I have an ethernet connected Pi 3B with a hifiberry Digi+ Pro HAT that feeds the KTB power via the USB and the audio via coax. unplug the USB cable from the Pi when not in use, so the KTB is not powered up but the Pi is left on 7x24. I've not experienced any hangs in even extended listening sessions lasting 5 or 6 hours. For a short time I also ran using just the Pi 3B feeding the KTB audio and power via the USB cable and can't recall any hangs.
@milw50717 do you experience a loud thump when powering on or of the KTB that is connected to the running amp?
 
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I tested RPi 3B+ with KTBD and it turned out that the problem was the original USB cable. After replacement, everything seems OK.

About filters. I tested them a little and it's hard to spot the differences. The changes are subtle, it's hard to tell the differences.

Interesting information about filters can be read in diyaudio and archimago .
 
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@milw50717 do you experience a loud thump when powering on or of the KTB that is connected to the running amp?
I have this issue too. Very loud thump 30% of the time when I turn on KTB. When there is a thump, it also means that my KTB's audio outputs would be outputting about 1v of DC, which is rather dangerous. These days, I have to make sure that my amp is turned off before turning on KTB. Then I use a multimeter to measure DC at the DAC's outputs before connecting the DAC to the amp. Note that the USB receiver and DAC itself seem to be working even after a loud thump -- my computer recognizes the device and Foobar can play via ASIO -- so I am guessing the thump and DC offset come from the analogue (i.e., op amps) section.

The sound quality is great when everything works, and when it does I have no dropouts/noise/whatever other issues. But the turn on problem is material.
 
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I have this issue too. Very loud thump 30% of the time when I turn on KTB. When there is a thump, it also means that my KTB's audio outputs would be outputting about 1v of DC, which is rather dangerous. These days, I have to make sure that my amp is turned off before turning on KTB. Then I use a multimeter to measure DC at the DAC's outputs before connecting the DAC to the amp. Note that the USB receiver and DAC itself seem to be working even after a loud thump -- my computer recognizes the device and Foobar can play via ASIO -- so I am guessing the thump and DC offset come from the analogue (i.e., op amps) section.

The sound quality is great when everything works, and when it does I have no dropouts/noise/whatever other issues. But the turn on problem is material.
I'll install DC protection circuit just because of this. And yes, I'm powering on my amp last and powering off first...
 
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I'll install DC protection circuit just because of this. And yes, I'm powering on my amp last and powering off first...
I really hate to have a capacitor in the signal path -- my amp, which I built myself, has no DC-blocking input caps. Without the thump (i.e., when the DAC is working properly), I measure ~2mv DC in both channels, which is OK. After my amp's 22x amplification, I am getting ~24mv at the speaker outputs, which is tolerable for speakers. I have decided to live dangerously by doing my DAC/amp turn-on routine everyday.

I thought about leaving the DAC on 100% of the time, but I am not sure about the quality of the electrolytic caps used in KTD -- given there is measurable heat at the DAC, I don't want to shorten the life of the caps by keeping the DAC on 24/7.

I am still trying to figure out what gives rise to the thump, presumably at the analogue section.
 
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I really hate to have a capacitor in the signal path -- my amp, which I built myself, has no DC-blocking input caps. Without the thump (i.e., when the DAC is working properly), I measure ~2mv DC in both channels, which is OK. After my amp's 22x amplification, I am getting ~24mv at the speaker outputs, which is tolerable for speakers. I have decided to live dangerously by doing my DAC/amp turn-on routine everyday.

I thought about leaving the DAC on 100% of the time, but I am not sure about the quality of the electrolytic caps used in KTD -- given there is measurable heat at the DAC, I don't want to shorten the life of the caps by keeping the DAC on 24/7.

I am still trying to figure out what gives rise to the thump, presumably at the analogue section.
I ordered this:
https://www.aliexpress.com/item/32954006976.html?spm=a2g0s.9042311.0.0.73484c4dLieKcB
No caps in the signal path, and comes also with start protection.
 

somebodyelse

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I am still trying to figure out what gives rise to the thump, presumably at the analogue section.
If you can find the datasheet for the output opamp check what it says about the operation of the enable pin. The Tone Board has a pullup to the positive rail, but some datasheets suggest a potential divider or RC network (depending on how the pin operates) that will delay enabling the output until after the supply rails have stabilised at startup, and turn it off before the rails sag too far at shutdown.
 

hyperknot

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I'm panning to stack a KTB + Atom. Does anyone know if the super short Ghent A01 cable will "lift" the KTB up because of its lightness? Here a photo on Ghent website.

 

zermak

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The Kadas Tone Board is indeed a bare board and I don't see how you can stack it on Atom Amp. You need an eclosure for it first. And well it depends on the weight of the enclosure if the cable will lift it or not.
 
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If you can find the datasheet for the output opamp check what it says about the operation of the enable pin. The Tone Board has a pullup to the positive rail, but some datasheets suggest a potential divider or RC network (depending on how the pin operates) that will delay enabling the output until after the supply rails have stabilised at startup, and turn it off before the rails sag too far at shutdown.
Yep, that's my next step. Though I do have to say that the SMD components are getting smaller and smaller -- I am not sure if my hand is steady enough to do any mods on this board other than to get rid of components.
 
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I'm panning to stack a KTB + Atom. Does anyone know if the super short Ghent A01 cable will "lift" the KTB up because of its lightness? Here a photo on Ghent website.

There is a semi rigid cable option from JDS that might work if you're ordering the Atom direct. It will pretty much depend on your Khadas enclosure I suppose. https://jdslabs.com/product/stack-rca-cables/
 

FrantzM

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Sorry for the stupid question, but if I use an RCA (L+R) adapter to 6.35mm jack female with the Tone Board, can I plug my 150ohm headphones directly to that and listen to music?
Or always better to have a dedicated headphones amplifier like a JDS Atom?
 

somebodyelse

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Sorry for the stupid question, but if I use an RCA (L+R) adapter to 6.35mm jack female with the Tone Board, can I plug my 150ohm headphones directly to that and listen to music?
Or always better to have a dedicated headphones amplifier like a JDS Atom?
It will work, but not well. The output isn't built for driving headphones. Output impedance is 100ohm so the frequency response of your headphones will be altered - you may or may not like this. Distortion will probably rise driving the headphone load, and the available power will be limited. If your headphones are sensitive and/or you only listen quietly it may be enough. The Atom will drive any conventional headphone more than loud enough with lower distortion, and without altering the frequency response.
 

Veri

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Sorry for the stupid question, but if I use an RCA (L+R) adapter to 6.35mm jack female with the Tone Board, can I plug my 150ohm headphones directly to that and listen to music?
Or always better to have a dedicated headphones amplifier like a JDS Atom?
Like @somebodyelse explains, it will work but the output impedance and load will not be ideal. It might sound okay but an actual amplifier will do a much better job. You can try it out of course.
 

hyperknot

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The Kadas Tone Board is indeed a bare board and I don't see how you can stack it on Atom Amp. You need an eclosure for it first. And well it depends on the weight of the enclosure if the cable will lift it or not.
In the audiophonics case of course, I thought everyone uses that.
 

zermak

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In the audiophonics case of course, I thought everyone uses that.
Okay and sorry, I can't help you with that then. I don't own that encolsure. I printed mine myself. And I guess most of the owners here are using a 3D printed case.
Anyway looking at that cable I think the Audiophonics case could handle it and will not flip. If it doesn't work just put some weights inside it I guess.
 
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