Hi all,
I have just built this and am facing an issue with loud pops and clicks on the output. I have a scope (which I fully admit I don't know how to properly use yet as evidenced by a phone picture when I'm sure it can capture!) which is showing random-ish but very regular - every couple of seconds - bursts of high frequency noise. I'm not sure if I should post the schematics as it's his work, but the attached pictures show the burst at the inverting input of a NE5534 RIAA / gain stage (yellow trace), and in the other picture the up closer and also showing the non inverting input, which is basically straight from the RCA.
I have tried turning off wifi / smart devices etc and that doesn't appear to change anything. Is this some kind of RF interference, or sporadic oscillation, if that is a thing that can happen? Any suggestions on where I should look next and things to try would be much appreciated!
Cheers
I have just built this and am facing an issue with loud pops and clicks on the output. I have a scope (which I fully admit I don't know how to properly use yet as evidenced by a phone picture when I'm sure it can capture!) which is showing random-ish but very regular - every couple of seconds - bursts of high frequency noise. I'm not sure if I should post the schematics as it's his work, but the attached pictures show the burst at the inverting input of a NE5534 RIAA / gain stage (yellow trace), and in the other picture the up closer and also showing the non inverting input, which is basically straight from the RCA.
I have tried turning off wifi / smart devices etc and that doesn't appear to change anything. Is this some kind of RF interference, or sporadic oscillation, if that is a thing that can happen? Any suggestions on where I should look next and things to try would be much appreciated!
Cheers
Attachments
Could be RF interference certainly, or perhaps squegging... (Yes, its definitely a thing that can happen - burst of oscillation, chip heats up and gain reduces, oscillation quenches, chip cools, gain increases, rinse and repeat).
Certainly an RIAA amp will be sensitive enough to pick up RF if not carefully filtered at the connector. Can you test this in a different location?
The frequency seems to be 2.2MHz though, which isn't typically used in mobile devices. That more suggests squegging due to some instability.
Perhaps check all the decoupling is present and correct, and that the semiconductors weren't counterfeit (like eBay parts or similar) - during the chip shortage there's a lot of crap swilling about if you don't pick reputable vendors. Perhaps you can swap sockets parts around to see if the problem moves with the part?
Certainly an RIAA amp will be sensitive enough to pick up RF if not carefully filtered at the connector. Can you test this in a different location?
The frequency seems to be 2.2MHz though, which isn't typically used in mobile devices. That more suggests squegging due to some instability.
Perhaps check all the decoupling is present and correct, and that the semiconductors weren't counterfeit (like eBay parts or similar) - during the chip shortage there's a lot of crap swilling about if you don't pick reputable vendors. Perhaps you can swap sockets parts around to see if the problem moves with the part?
Hi Mark
Thank you for your informative reply!
For anyone who might happen to run in the same problem, I managed to figure it out with much poking around. I removed an NE5532 which is part of the subsonic filter that comes straight after the RIAA / gain stage and the problem disappeared. On the PCB around these opamps there are two components R35 and R135. They are actually not on the schematic, but the BOM provided lists them as wire links. I followed the traces and it seems that these wire links were directly connecting the output pin of the RIAA opamp to the output pin of the subsonic filter opamp! I assume this is to make it easy to exclude the subsonic filter if it's not needed / wanted.
The MM input / output looks fine now, but I seem to have a problem with the MC input and the gain stage there oscillating when music is playing. I'm testing it out using my phone at the moment which is probably less than ideal, so maybe it's just something to do with that. It also oscillates for a few seconds when I unlock the phone even though no sound plays when that happens which is fun to see. I will try with a turntable in the next few days and see what happens.
Cheers
Thank you for your informative reply!
For anyone who might happen to run in the same problem, I managed to figure it out with much poking around. I removed an NE5532 which is part of the subsonic filter that comes straight after the RIAA / gain stage and the problem disappeared. On the PCB around these opamps there are two components R35 and R135. They are actually not on the schematic, but the BOM provided lists them as wire links. I followed the traces and it seems that these wire links were directly connecting the output pin of the RIAA opamp to the output pin of the subsonic filter opamp! I assume this is to make it easy to exclude the subsonic filter if it's not needed / wanted.
The MM input / output looks fine now, but I seem to have a problem with the MC input and the gain stage there oscillating when music is playing. I'm testing it out using my phone at the moment which is probably less than ideal, so maybe it's just something to do with that. It also oscillates for a few seconds when I unlock the phone even though no sound plays when that happens which is fun to see. I will try with a turntable in the next few days and see what happens.
Cheers
I suggest removing that link and put back the subsonic filter opamp so you don't get big output excursions in the sub 20Hz area.
Sorry, I am terrible at explaining things. I did reinstate the subsonic filter opamps after removing the links 🙂
The inputs are shorted to ground via a switch on the RCA when there's no input. No noise in that case. I have plugged the turntable in to it today and it seems good as far as I can tell. Must just be something weird about the phones I was using to test with I guess 🤔