It was a Raspberry Pi running Volumio. Firstly using the on board audio jack through a 3.5mm to RCA cable. I've also tried it through a USB DAC (HRT Microstreamer) into the 3.5mm RCA cable.
Also despite what I said earlier there is hiss when no signal is applied, although I do need to be right up against the speaker to hear it.
There were also a couple of suspect solder joints on the 1uF caps next to the input caps which I re-soldered, but that doesn't appear to have helped.
I'm starting to suspect that either the laptop supply I'm using for the TPA3116 or the power supply for the Pi are injecting noise into the audio signal.
Note: The board/sockets etc. are all sitting free at the moment as I haven't sorted an enclosure.
Last edited:
There is typically hiss that is only audible with your ears right next to driver but inaudible at normal listening distances. This is normal. Try the output from a good old fashioned RCA outs from a CD player and see if you still have problem. Raspberry PI is digital computer source and I suspect the DAC is not the quietest. Also, are you using short as possible shielded cables from RCA jack to the board?
I recalled you mentioned:
"When the RCA inputs are hooked up to the board and it's powered on but without a signal of any sort there is no noticeable hum/hiss, it may be there but I can't hear it. However when I start to play any music or have the music playing and the volume set to zero in the playback software, there is a very noticeable hiss."
Based on that observation, it seems that the noise is related to your source.
My brother has one of the green board from "audiobah" and he reported similar observation - he put a volume pot at the input of the amp and then hooked up to his computer' sound card => quite a bit of hiss/noise. I then asked him to connect the amp board to the output of the DAC of his main rig ( substituting his tube preamp and amp) and try again, hardly any noise at all. He powered the board with a 19V laptop brick too. So sounds like the source could be the origin of the hiss/noise. I have no explanation. This is just an observation. I vaguely recalled that someone reported similar problem when using a computer sound card as the source quiet a number of posts back
Do you have a portable CD player that you can connect to the amp board and try?
Regards,
Thanks for the replies/suggestions.
The cables from the RCA inputs to the board are about 10-15cm and are shielded, with the shields grounded at both ends.
Having done some reading around this afternoon, I suspect that the Pi's audio output may well be the source of some of the hiss. Some suggestions were to use a better power supply for the Pi; make sure the USB cables used in the power supply had ferrite chokes etc.
I haven't got a portable CD player, but I have got an old full size unit In the attic that I could test with.
I need to do some more tests with the Microstreamer as well, since it's an external USB DAC it should avoid the hiss injected by internal audio circuitry of the Pi. Although it may still suffer from any noise injected into the USB path.
The cables from the RCA inputs to the board are about 10-15cm and are shielded, with the shields grounded at both ends.
Having done some reading around this afternoon, I suspect that the Pi's audio output may well be the source of some of the hiss. Some suggestions were to use a better power supply for the Pi; make sure the USB cables used in the power supply had ferrite chokes etc.
I haven't got a portable CD player, but I have got an old full size unit In the attic that I could test with.
I need to do some more tests with the Microstreamer as well, since it's an external USB DAC it should avoid the hiss injected by internal audio circuitry of the Pi. Although it may still suffer from any noise injected into the USB path.
Maybe I don't understand exactly what you wrote but shields of cable with 1 signal conductor and a shield should only be connected to ground (as in "case connected to GND and PE" ) at one spot. That is if you mean that you connected the shields to case/PE. Or do you simply mean that the audio-GND was connected at both sides. It should otherwise you wouldn't have sound
Last edited:
Maybe I don't understand exactly what you wrote but shields of cable with 1 signal conductor and a shield should only be connected to ground (as in "case connected to GND and PE" ) at one spot. That is if you mean that you connected the shields to case/PE. Or do you simply mean that the audio-GND was connected at both sides. It should otherwise you wouldn't have sound
Sorry, didn't make myself clear. What I meant was the shield was connected to the RCA socket shell and then to the GND point at the amp input for both input cables.
"Standard" is a broad definition
Is PE connected ?
I can't see the symbol for protected earth on the power supply.
Eh ? Three contacts on the power plug ? So one for protective earth (PE) ? It is good to know that earth is protected at your place
Yep, three pin plug
.
Ok, so I need to measure from the audio input ground on the amp board to the earth pin on the power supply plug. Or have I got it wrong?
Yeah, I could write in dutch or german if that is more clear
Just me being thick tonight
.Measured from the input GND to the power connector GND on the board and got 0 ohms.
Also just switched sources to my android phone using all the same cables/power supply and got no issues with hiss etc. So the source of the hiss is looking more likely to be the Pi and not the amp.
Yes, the Pi is plugged into an iPad USB power adapter in the same extension block.
Looks like I need to read up on ground loops and work out if that is the issue here.
Cheers for your help.
Received my second blue YJ board 2 days ago, after just 5 days from HK to Germany.
This one is running as it should, just a little bit warm with 26 volt. It has a little QC sticker on the pcb, maybe this is the special edition.
Anyway, I also found the reason for the heat issue of the first one: the gain network should be 100k/20K, as printed on the pcb. It was 100k/100k; I replaced the wrong 1k with a 20k, and all is back to normal. Just in case someone faces the same issue...
besides from that I am still very pleased with the performance, together with a good preamp this is really good.
I would be interested if someone compared such a TPA amp with some "real" amps like a Pass F5 or the like. Is it really worth the effort and $$$? I'm seriously doubting....
This one is running as it should, just a little bit warm with 26 volt. It has a little QC sticker on the pcb, maybe this is the special edition
.Anyway, I also found the reason for the heat issue of the first one: the gain network should be 100k/20K, as printed on the pcb. It was 100k/100k; I replaced the wrong 1k with a 20k, and all is back to normal. Just in case someone faces the same issue...
besides from that I am still very pleased with the performance, together with a good preamp this is really good.
I would be interested if someone compared such a TPA amp with some "real" amps like a Pass F5 or the like. Is it really worth the effort and $$$? I'm seriously doubting....