Capacitor identification, RFI squelch circuit for audio

[captainate]

Hey all, I have an RFI eliminator from a company that is no longer in business, and I need to make four new ones based on the design. There are three tiny yellow capacitors that bridge each input. I need help identifying them. Their markings are as follows:

103 --- V16
ESM -- RCU

side 1 - side 2


Thanks for your help.

 

[ronv]

Maybe a picture would help.

 

[MikeMl]

103 sounds like 10nF

 

[captainate]

Thanks for your help. May I ask what your basis is for this conclusion and if it seems consistent for this type of circuit? I can't find any information on RFI squelch circuits online.

 

[MikeMl]

I know nothing about your RFI circuit; however, capacitor marking follows this scheme"
106=10uF
105=1uF
104=100nF
333=33nF
103=10nF
102=1nF=0.001uF, etc

 

[captainate]

Great. Thanks!

 

[KeepItSimpleStupid]

Those caps are probably of the ceramic type. Usually round flat discs with two leads out one end.

 

[captainate]

Actually they are PVC coated.

 

[KeepItSimpleStupid]

OK, I'll bite. This might be better for a type designation: https://www.electro-tech-online.com/custompdfs/2011/01/FC-C-AEC-ESM.pdf

Ceramics should be a better choice for a simple filter, but it depends on the circuit.

 

[crutschow]

If you look up EMI Suppression, you will get may hits.

A squelch circuit normally refers to a circuit the cuts off the audio noise in a receiver when the is no signal. It has nothing to do with RFI.

 

[KeepItSimpleStupid]

I hate when that happens. The title and the body of the message don't make sense. "RFI squelch" doesn't make sense.
"RFI filter" makes sense
"squelch" makes sense
and combining them makes sense i.e. (RFI filter) and squelch

 

[captainate]

Oops, sorry, I've been saying squelch!

I meant "snubber circuit." I don't know much about this stuff but I heard this term from a very respected source. EMI seems to be more accurate, although on the unit I'm trying to reverse engineer, it has a label that says "RFI filter"

 

[KeepItSimpleStupid]

EMI - Electromagnetic Interference
Usual supression technique is twisting wires in pairs and differential transmission of signals

RFI - Radio Frequency Interfierence
Usually suppression technique is shielding
With audio devices, it's possible for strong radio stations to be picked up by say speaker wires or an inut to an amplifier.

A snubber limits dv/dt usually.

You can combine both methods: e.g. twisted pair shielded cables where the shield is connected at one end only which is usually the sourcing end.

 

[captainate]

OK. I obviously don't know much about electronics, hence why I'm on here asking a simple question. But I DO have a ton of experience in audio, and most of the audio engineers I know throw around the term "RFI" to describe the phenomenon I'm trying to prevent. It is a permanent installation where we have experienced radio interference, and with this simple circuit it goes away. Once I'm able to build a new one, I will test if there is any degradation of audio signal. But now I'm on a tangent.

Your typical balanced audio cable has 3 wires: Hot, Neutral, and Ground (common). In all high-quality balanced audio cable, you will find the wires are already twisted in pairs, a braided shielding wire, and still this is not always effective enough.

In the fixture I am trying to recreate, the hot and neutral wires are twisted in a tight pair, spun around a toroid, and reconnected at the other end. The ground wire passes through the cylinder. There are three capacitors (the ones Mike identified as 10 nF) bridging each output. I would simply like to know why this works as well as it does, given it's simplicity.

 

[crutschow]

In the fixture I am trying to recreate, the hot and neutral wires are twisted in a tight pair, spun around a toroid, and reconnected at the other end. The ground wire passes through the cylinder. There are three capacitors (the ones Mike identified as 10 nF) bridging each output. I would simply like to know why this works as well as it does, given it's simplicity.

EMI is the modern generic term that covers the full spectrum of frequencies and basically includes RFI.

The toroid is a common-mode choke. It allows differential (normal signals) to readily pass but provides a high inductance to any high frequency signals common to both lines, such as radio interference. The caps help filter any normal mode radio interference signal between the two lines and also any common-mode signal between the lines and ground (they work in conjunction with the choke inductance to provide an LC low-pass filter).

 

[KeepItSimpleStupid]

Here is a simple "How to" article: https://www.electro-tech-online.com/custompdfs/2011/01/whitepaper_RFI.pdf

The Balanced form of transmission of audio signals, consists of an inphase, out of phase and a common signal and a screen. These would usually cancel if both the transmission and reception are differential. The coverage of the shield also plays a role. Foil can give 100% coverage. A braid, somewhat less.