Hi
Startup From Cold by A=432Hz | Free Listening on SoundCloud
The above audio file (also attached) was recorded with a Lavry AD11 AD converter/microphone preamp (at MAX Gain +65dB). When purchased it made this noise in the right channel when powered up from cold. After warm up it becomes barely noticeable but can always be detected in measurements as slightly more noise/and intermodulation distortion than the left channel which operates perfectly.
It has done this since I purchased it second hand but I wasn't to bothered as I planned to recap and change the opamps anyway - thinking this would cure it. After doing the mods the problem is still there despite every electrolytic cap in signal path and every opamp having been replaced. I've also thoroughly checked for shorts and dry solder joints and also cleaned the board extensively. The unit measures and sounds significantly better with the changes so it is very frustrating this problem remains.
Any help would be greatly appreciated with identifying what type of component could make the noise that is present in the above audio file - please note that the noise was captured with the unit at maximum gain (+65dB) with no load/termination (so both channels have normal high background noise for such conditions) - this noise in question cannot be missed though at startup - intermittent fizzing/popping/spitting/scratching almost like a worn vinyl record - then it fades to almost nothing and the unit operates normally. The left channel is works perfectly and always has.
Startup From Cold by A=432Hz | Free Listening on SoundCloud
The above audio file (also attached) was recorded with a Lavry AD11 AD converter/microphone preamp (at MAX Gain +65dB). When purchased it made this noise in the right channel when powered up from cold. After warm up it becomes barely noticeable but can always be detected in measurements as slightly more noise/and intermodulation distortion than the left channel which operates perfectly.
It has done this since I purchased it second hand but I wasn't to bothered as I planned to recap and change the opamps anyway - thinking this would cure it. After doing the mods the problem is still there despite every electrolytic cap in signal path and every opamp having been replaced. I've also thoroughly checked for shorts and dry solder joints and also cleaned the board extensively. The unit measures and sounds significantly better with the changes so it is very frustrating this problem remains.
Any help would be greatly appreciated with identifying what type of component could make the noise that is present in the above audio file - please note that the noise was captured with the unit at maximum gain (+65dB) with no load/termination (so both channels have normal high background noise for such conditions) - this noise in question cannot be missed though at startup - intermittent fizzing/popping/spitting/scratching almost like a worn vinyl record - then it fades to almost nothing and the unit operates normally. The left channel is works perfectly and always has.
I analyzed your mp4 file. R channel has much noise as you say. It almost fades out after one minute. The remaining ones are like a click of vinyl. But I would say this can't be from an analog problem because this has a very sharp rise and fall time detailed in next pic. It's impulse rather than vinyl click.
A faulty digital circuit is a significant source of this noise. There is a chance of some problem with your digital circuit of R-ch(logic or ADC). This problem usually occurs at power up and gradually decrease its occurrence like your case. If it comes from the digital side, I'm afraid repairment is not so easy unless you have enough information like the schematic.
A faulty digital circuit is a significant source of this noise. There is a chance of some problem with your digital circuit of R-ch(logic or ADC). This problem usually occurs at power up and gradually decrease its occurrence like your case. If it comes from the digital side, I'm afraid repairment is not so easy unless you have enough information like the schematic.
Attachments
Thank you so much for your responses.
I got freezer spray and used that along with an SMD hot air gun to test all over the board. I traced it down (or so I thought) to a small SOT-23 transistor at input and was convinced that was the problem.
I contacted the manufacturer to identify the component - they do not provide any details of components or schematics for their products which is understandable... They were helpful however and explained that it could not be the component I thought as it is only acting as a switch but could likely be the input connector. As it is a complex 10 connection switched combi XLR/jack connector it can become dirty and unreliable - plus it is acting as a switch to add 10dB of gain for unbalanced connections. The connector is right next to the component I thought was faulty so I think it may be reacting to heating cooling in that area. They suggested to manipulate it a bit with a jack connector to "exercise" the switch contacts - this didn't fix it it but seems to alter the noise.
Waiting for new sockets to arrive - hopefully this will correct the issue as I truly hope it is not a digital problem...
I got freezer spray and used that along with an SMD hot air gun to test all over the board. I traced it down (or so I thought) to a small SOT-23 transistor at input and was convinced that was the problem.
I contacted the manufacturer to identify the component - they do not provide any details of components or schematics for their products which is understandable... They were helpful however and explained that it could not be the component I thought as it is only acting as a switch but could likely be the input connector. As it is a complex 10 connection switched combi XLR/jack connector it can become dirty and unreliable - plus it is acting as a switch to add 10dB of gain for unbalanced connections. The connector is right next to the component I thought was faulty so I think it may be reacting to heating cooling in that area. They suggested to manipulate it a bit with a jack connector to "exercise" the switch contacts - this didn't fix it it but seems to alter the noise.
Waiting for new sockets to arrive - hopefully this will correct the issue as I truly hope it is not a digital problem...
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