Since I didn’t use the capacitor in the first place and still didn’t experience any RF interference, there could be two possible reasons:
- There’s little or no RF in my area, so the capacitor simply wasn’t necessary. If the amp were placed near a strong RF source, like a radio tower, it might start picking up interference.
- There is RF present, but the designed circuits and PCB layout are good enough to make the amp immune to RF interference.😉
Could also be that this "RF issue" is something one person concluded based on insufficient evidence and reported as the truth from there on. Confirmation bias then led them to strengthen their belief, after all, all capacitors and inductors near an LM3886 must indicate trouble with RF, right?! I asked them to provide evidence for their claims and they responded with "prove me wrong". So there's that...
Between my customers and I I'm sure we're deep into the thousands of LM3886es used at this point. I know I've gone through a few thousand of them through the past 11 years. Yet, it is in this thread that I encounter this "RF issue" for the first time.
Of course it is possible that there is an issue that I missed and that my customers never noticed. After all, I do use EMI/RFI filters on all my amps. But I doubt it. There are countless LM3886 circuits out there and nobody is clamouring about RF issues that I can tell. If you come across a thread where people are having issues with RFI in an LM3886 that can't be attributed to poor PCB layout or poor wiring please let me know.
Tom
Between my customers and I I'm sure we're deep into the thousands of LM3886es used at this point. I know I've gone through a few thousand of them through the past 11 years. Yet, it is in this thread that I encounter this "RF issue" for the first time.
Of course it is possible that there is an issue that I missed and that my customers never noticed. After all, I do use EMI/RFI filters on all my amps. But I doubt it. There are countless LM3886 circuits out there and nobody is clamouring about RF issues that I can tell. If you come across a thread where people are having issues with RFI in an LM3886 that can't be attributed to poor PCB layout or poor wiring please let me know.
Tom
Don’t have anything to do with commercial LM3886 designs but as indicated I have experience with the “RF issue” in devices and SMPS and like to solve such issues.
It is not a one person “RF issue”. It depends on local factors and varies over the day. It became worse when 5G was introduced. Quite a few opamps are sensitive to it too. If it does not happen to you and your customers that is fine. It does not exclude the issue elsewhere on the globe and the local situations there. Don’t downplay anything you have not witnessed. It is not a complaint against you and your products.
It is not a one person “RF issue”. It depends on local factors and varies over the day. It became worse when 5G was introduced. Quite a few opamps are sensitive to it too. If it does not happen to you and your customers that is fine. It does not exclude the issue elsewhere on the globe and the local situations there. Don’t downplay anything you have not witnessed. It is not a complaint against you and your products.
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I'm not downplaying anything and I'm not perceiving what's posted here as an attack on me or my products. I made that clear in Post #33.
All I'm asking for is evidence of the issue before an issue is claimed to exist. So far no evidence has been provided.
Sure.
Tom
There is absolutely no need for the OP to show "evidence" to you of a phenomenon he experiences with his DIY design. The phenomenon is described, a schematic has been posted and details are given and he asks for help. That is way more information than usual. Michael Chua experienced similar stuff. It could be a PCB layout imperfection combined with local circumstances. It could even be the LM3886 depending on batch/date of production, who knows at this stage? Why doubt the OPs experiences? Are you and your stuff the measure of things?
Sure:
https://laas.hal.science/hal-02319469v1/document
https://www.st.com/resource/en/appl...etic-interferences-emi-stmicroelectronics.pdf
https://www.ti.com/lit/an/sboa128a/sboa128a.pdf?ts=1748376997969
https://www.renesas.com/en/document...tMCChVNiUrHVgKhUAJRWSq7FSXHAnxgmj1hyUqBC-tfqn
Sure:
https://laas.hal.science/hal-02319469v1/document
https://www.st.com/resource/en/appl...etic-interferences-emi-stmicroelectronics.pdf
https://www.ti.com/lit/an/sboa128a/sboa128a.pdf?ts=1748376997969
https://www.renesas.com/en/document...tMCChVNiUrHVgKhUAJRWSq7FSXHAnxgmj1hyUqBC-tfqn
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Jean-paul, I think it would behove you to read the entire thread and view my comments in their proper context. I've never suggested that OP should provide evidence for anything. I asked Michael Chua to provide evidence for his claims that the LM3886 is particularly susceptible to RFI and he provided nothing substantive to back his claims.
I asked because if the LM3886 is particularly susceptible to RFI I would like to know about it so I can deal with it. But without anything of substance I have nothing to go by.
I'm not suggesting that opamps cannot be susceptible to RFI. All I'm saying is that in my experience I haven't found the LM3886 any more susceptible to RFI than other power opamps. I, therefore, don't see any need to churn the rumour mill.
You can turn just about any opamp into an RF receiver (or oscillator) with a crappy PCB layout. Is doing so the fault of the opamp or the fault of the PCB layout engineer?
Tom
I asked because if the LM3886 is particularly susceptible to RFI I would like to know about it so I can deal with it. But without anything of substance I have nothing to go by.
I'm not suggesting that opamps cannot be susceptible to RFI. All I'm saying is that in my experience I haven't found the LM3886 any more susceptible to RFI than other power opamps. I, therefore, don't see any need to churn the rumour mill.
You can turn just about any opamp into an RF receiver (or oscillator) with a crappy PCB layout. Is doing so the fault of the opamp or the fault of the PCB layout engineer?
Tom
The RF signal can be sneaking into your circuit through any long trace that is a part of your audio input circuit. Wires or circuit board traces act as antennas for RF. If you place a resistor like 1Kohm in series with a wire then you can kill the antenna effect significantly. You could try adding a series resistor in the longest wire or circuit trace in the input section of your circuit to see if it has an effect. If your layout was perfectly symmetric with respect to pin 9 and pin 10 then the input circuit would be immune to RF because the RF would be common in amplitude to both inputs and therefore would not get amplified. This cancelling effect would likely be lost if the RF signal is larger than the common mode range of the amplifier inputs.