Mobile phone mast breakthough on audio stages - Page 1
Forum section: electronics / projects

author: andybarrett1
author_rank: Regular Contributor
timestamp: November 23, 2020, 12:08:56 pm
content: HiThank you for reading ..... I have recently got hold of a decent turntable a "Rega P1 + plus"However I find I am getting Cell Breakthrough I think on the Op-amps for the RIAA circuit ... Opening the unit up I can see a couple of TL072s so I am blaming them :-)As well as not much grounding in the area ..... I cant see any filtering for EMC. I fitted ferrites but no differenceSo I am looking for suggestions / Ideas / HelpThank you for readingAndy

author: tggzzz
author_rank: Super Contributor
timestamp: November 23, 2020, 12:15:24 pm
content: Quote from: andybarrett1 on November 23, 2020, 12:08:56 pmMore details needed, e.g.the characteristics of the breakthroughhow far away the masts arehow far away your cellphone iswhat you have done with your ferritewhy you think the opamps are importantother features of your setup

author: andybarrett1
author_rank: Regular Contributor
timestamp: November 23, 2020, 12:39:30 pm
content: HISound file enclosed for characteristics.Mast is about 10Meters away horizontally level with flat.My Cellphone off. Broadband off. Microwave off. No Ethernet over mains in flat.Ferrites in mains lead and RCA CablesOpAmps in the RIAA circuit board (Pre-Amp from Turntable to PAAdditionally noise breaks through over other musical gear but not as bad ... Guitar amp etcAndy

author: tggzzz
author_rank: Super Contributor
timestamp: November 23, 2020, 04:24:41 pm
content: The audio is unhelpful: very low level and any buzzing is much quieter than the rustling.The 10m is close.Not sure what you mean by "ferrites in leads". "In" usually means in series.Presuming it is a TDMA signal such as GSM/DCS1800, you need to understand how interference occurs if you are to have a chance of removing it.The basic mechanism is that a piece of wire acts as an antenna, so that EM radiation causes RF voltage/current to flow in the wire.Any non-linearity (e.g. a semiconductor junction or imperfect switch or poor connection) will then rectify the RF voltage, and any capacitance will act to smooth the RF to produce a DC voltage that depends on the RF envelope.If the TDMA signal has a 4.6ms repetition interval, then there will be a 217Hz voltage fluctuation, and that will be amplified by an audio amplifier.So, you need toshield all cables that might act as antennas. That might be problematic with unshielded wires next to the pickup.shunt RF to signal common as near to the antenna as possible, using a low-value RF capacitor and good RF layout practices (1mm wire=0.8nH)be aware that at RF there is no such thing as "ground"ensure all components have a solid metal shield without holes that might "let the RF in"You will probably find useful practical information in any EMI/EMC textbook, or a radio ham book such as any of the ARRL handbooks. No need to buy the latest since this subject doesn't change.

author: Benta
author_rank: Super Contributor
timestamp: November 23, 2020, 06:35:48 pm
content: I would probably have opted for the Planar 1 without "plus" (which is the one without RIAA amp), selecting a good external amp instead.TL072 doesn't seem very "High end" to me.That being said, the interference can also come in through the RIAA amp outputs.

author: SilverSolder
author_rank: Super Contributor
timestamp: November 23, 2020, 10:00:34 pm
content: Is there a picture of the offending circuitry? and the wiring going in/out of it?

author: andybarrett1
author_rank: Regular Contributor
timestamp: November 24, 2020, 08:13:30 am
content: I did wonder given the cost of thing they are using TL072sI see them in the cheap guitar amp front ends :-)But to RF Noise an OpAmp is an OpAmpAndy

author: andybarrett1
author_rank: Regular Contributor
timestamp: November 24, 2020, 08:16:09 am
content: I suspect it is very similar to this :-"DISC AMP"The nearest Schematic I can findAndy

author: andybarrett1
author_rank: Regular Contributor
timestamp: November 24, 2020, 08:18:13 am
content: The Ferrites are just generic clamp on couple of turns typeOn RCA leads and MainsAndy

author: tggzzz
author_rank: Super Contributor
timestamp: November 24, 2020, 08:45:23 am
content: It can be difficult to diagnose EMI causes and solutions, doubly so at a distance since all the details matter.I suggest you insert some decent RF lowpass filtersin(not around) the signal lines. The location should be as near to the semiconductor junctions as possible, so as to reduce the antenna size.If the case is metal and without large slots, then it would probably be sufficient to mount them externally on the RCA socket inputs.

author: andybarrett1
author_rank: Regular Contributor
timestamp: November 24, 2020, 01:51:12 pm
content: OK thank youHave got a bit to be getting on with now so ....Lets see how I get on :-)Andy

author: LaserSteve
author_rank: Super Contributor
timestamp: November 25, 2020, 03:37:07 pm
content: "Tinfoil Hat" the unit with some aluminum foil, see if the noise goes down.Basic Faraday shield.Steve

author: andybarrett1
author_rank: Regular Contributor
timestamp: November 25, 2020, 03:46:11 pm
content: Tried thatGetting in holes

author: LaserSteve
author_rank: Super Contributor
timestamp: November 25, 2020, 04:26:59 pm
content: Sounds like you have a 500 Watt ERP cell site right next to you. Place stereo in metal filing cabinet, on an isolation transformer.Your version of the FCC is called OFCOM, they used to be quite interested in preventing interference. I'd be asking them to look up the tech details of what you are living next to, if I were you.Good luck..Steve

author: andybarrett1
author_rank: Regular Contributor
timestamp: November 26, 2020, 09:53:35 am
content: Not thought of Isolation TXI am assuming airborne RF