Hi. I am running a powerful class D amp from the KTB. I am using volume control via Volumio UI so the amp is running “open”. I get a very loud off pop through the speakers. It does not occur if I disconnect the DAC from amp. I have read others referring to on/off noises due to the DAC. Is there an easy fix to this?
New user here, so please be kind!
I received my tone board today, and even after only a few hours testing it’s quite clearly providing a much better overall audio experience that my previous set-up, which I actually thought was sounding pretty good anyway (Audioengine D2).
However, I too experienced the very loud and disturbing ‘pop’ when I turned the tone board off before turning off my amp … ironically, as it happens I normally do shut down the amp first so wouldn’t have experienced this effect otherwise. When shutting down PC + tone board before amp, no problem, no ‘pop’.
So, I would also be interested to find if there’s any fix or workaround to prevent this happening? I’ve had a quick search around the forum but can’t see any obvious reference to this - unless any of you more regular members are able to point me/us to any info.?
Other than that, I’m seriously impressed with this little board so far! Only minor annoyance was regards the enclosure I obtained from Audiophonics, which was supplied with 2 x ‘rear’ panels only (i.e., the 'front panel with holes for RCA + USB) was missing completely!
Correction to my last post, just noticed, sorry guys - I of course meant to say “When shutting down amp before PC + tone board, no problem, no ‘pop’”.
Thanks
Hello and welcome to the community, we mean no harm 
Happy to know the Toneboard is working out well for you, but regarding the pop, maybe our other long term users like @AKBAAR can tell you something
the case for the tone is sold by Audiophonics, not khadas
they are just a 3rd party manufacturer of the accessories, try contacting them to see if your can get free replacement
cheers
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Hi @Electr1, many thanks for your prompt response, yes I’ll await for any more experienced users to offer their suggestions and/or recommendations.
And yes, I know the enclosure is sold by Audiophonics not Khadas, I just mentioned it in passing … I’ve already asked them if they can send me the correct front panel or replacement!
Thanks again
hi @Electr1 any new youtube videos for you ? miss you
ya regarding that pop noise when you turn on/off your DAC. I also get that noise its just due the DAC itself … I dont have immediate solution for this unfortunately … i tried Balance and unbalance, with amp and without amp. linux and windows. it seems its a just there. I am assuming you are using USB 3.0 hub on your pc .
I have read around the planar headphones minimizes the pop sound at a point you dont hear it. I have a planar headphones but didnt test yet.
Regarding Volumio, there is a plugin that can set the starting Volume at boot at a level of your choice e.g. 10 … so when starting the DAC the app sets the volume at lowest. check other plugins maybe find helpful.
just for probably helpful resource or not… check this website out.
i will add more inputs to this thread if i stumble on anything cool
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The only thing that I can suggest is to power down the amp first. In my case I have two SMPS in the same enclosure. One is 5v for the DAC and rpi. The other is 48V for my amp. I realised that even though power is cut to both at the same time when switching off, the amp hangs up long enough to hear the pop (a good few seconds)
My idea is to add a separate relay to cut the V+ to the amp which will hopefully reduce the hang up time (the hang up from the caps in the SMPS) long enough for the amp to power down before the DAC. I’m waiting for the relay to arrive to test. As my Class D amp does hang up a little from its own on board caps it will be close.
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Hi, he promised new videos, but I think he is busy with his daily activities, so I think he will soon please us with something
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Hi All,
Many thanks for your useful comments and thoughts. By the sound of it, without getting too complicated it seems like it’s a symptom that just has to be lived with. Odd though, not come across this before. I’ll just need to remember to shut down my amp before PC + tone board - luckily tone board if fed 5v via USB and amp has its own separate PSU.
Look forward to seeing any further advice or tips worth trying, in the meantime many thanks to all that have responded.
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Seems it would not be too difficult to make a turn on/turn off sequencer. Or even use something like a pulse timer relay to disconnect speakers prior to turn on or turn off.
When I was going through my speaker system building hobby, I recall an add-on debounce/anti-pop circuit sold. Don’t recall if it was for speaker or line level signals.
That would be the next thing to look at. Better to avoid added complication though if possible. I personally would prefer to avoid putting switches in the signal path if there is an alternative solution.
Well, a bit more searching on a selection of hi-fi forums seems to reveal that this is a very common, and often expected, hi-fi phenomenon! Unless any preventative delay circuitry is included as part of the product’s design, there’s every chance it will occur and that’s the end of it.
General acceptance does indeed seem to be to simply live with it and ensure your ‘turn on’ sequence is: source, followed by DAC, then lastly amp. And then for turn off it’s the reverse procedure: amp, then DAC, then finally source. In my case, of course, DAC is powered by PC USB anyway …
Amazing that I’ve not witnessed this effect before, I must have just been pretty lucky! So there you go, you never stop learning something new every day!
I agree with @Gilera, I’d also prefer to avoid adding anything extra in the signal path - so I’ll just learn to live with it. At the end of the day, the tone board sounds great as it is, so I’ll leave well alone I think.
Once again, thanks to all that have offered their advice and thoughts.
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I can confirm that adding the relay for the V+ wire from the SMPS to the amp has successfully removed the off pop. Cutting power to the amp reduces the amount of time that the amp hangs up so that is if off by the time the pop comes from the DAC. I used a relay with 240V coil with switching side rated to 28V DC. I am using 48V DC but no problem so far. It seems hard to find a 240V relay with higher DC rated switching side.
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