John Curl's Blowtorch preamplifier part II

[john curl]

DF96, I think you are ON to something important. Maybe, just maybe, you now understand why I would put 2 power resistors, one for each lead, in series with the LED.

[sgrossklass]

It would be interesting to know what kind of frequencies were wreaking havoc with performance here. Then one could try, say, a common-mode choke in the LED wiring... or separate inductors.

EDIT: Or resistors, of course. For a retrofit I'd prefer something from the L department though.

[chrissugar]

Originally Posted by SY

More likely connecting wires. Presumably the LEDs are forward biased?

Only one of them.

chrissugar

[chrissugar]

Originally Posted by DF96

Hole in Faraday shield (with conductor to support TEM mode) lets in RF; who would have thought it? Circuits inside box can't cope with RF; another surprise?

This is not new info for me. I read most of the things related to this subject by Jim Brown, Neil Muncy and others and also the NASA study about RF influence on equipment.
Problem is that the wire that connect the speakers to the amplifiers are as much exposed to RF like the wires that connect the LEDs, but the speaker wires do not produce the same problems. I didn't mention that the loudspeaker has two chambers, one for the speakers and one housing the electronics (amps, crossover, balanced receiver). I shielded only the chamber with the electronics. Even if I would want I could not shield the acoustic chamber (maybe with some RF paint). I do not dismiss what you say but considering that the same length of wire is exposed outside the Faraday cage at the speakers I can only think the LEDs are doing something.


One more thing. I have a mastering processor made in US (costs some grands) which is used in some of the best mastering studios and is considered a top device. It is very well designed and constructed (steel case, all XLR connectors with pin1 connected directly to chasis, filtered power, etc). I can create a unique situation where even that device demodulates RF (which is an indicator about how RF problematic is the space I was talking about). I never heard from some fellow engineer who use this device and have this problem. Of course I know what to avoid to create that situation.


chrissugar

[hitsware]

Originally Posted by chrissugar

This is not new info for me. I read most of the things related to this subject by Jim Brown, Neil Muncy and others and also the NASA study about RF influence on equipment.
Problem is that the wire that connect the speakers to the amplifiers are as much exposed to RF like the wires that connect the LEDs, but the speaker wires do not produce the same problems. I didn't mention that the loudspeaker has two chambers, one for the speakers and one housing the electronics (amps, crossover, balanced receiver). I shielded only the chamber with the electronics. Even if I would want I could not shield the acoustic chamber (maybe with some RF paint). I do not dismiss what you say but considering that the same length of wire is exposed outside the Faraday cage at the speakers I can only think the LEDs are doing something.


One more thing. I have a mastering processor made in US (costs some grands) which is used in some of the best mastering studios and is considered a top device. It is very well designed and constructed (steel case, all XLR connectors with pin1 connected directly to chasis, filtered power, etc). I can create a unique situation where even that device demodulates RF (which is an indicator about how RF problematic is the space I was talking about). I never heard from some fellow engineer who use this device and have this problem. Of course I know what to avoid to create that situation.


chrissugar

Do your monitors have 2 or 3 wire mains connection ?

[Chris Hornbeck]

Originally Posted by chrissugar

considering that the same length of wire is exposed outside the Faraday cage at the speakers I can only think the LEDs are doing something.

Re-connecting with a resistor or a conventional forward-biased diode in place of the LED would narrow the mystery, but probably not worth the effort after all the grief it's already put you through. My money's on injection into the ground, but you've doubtlessly figured something along those lines.

Thanks,
Chris

[Joshua_G]

Chris Sugar, thank you for sharing. Your experience is illuminating.

[SY]

Originally Posted by Joshua_G

Your experience is illuminating.

LOL!!!!

[jam]

Chris Sugar has made a valid observation not so much in the defense of John Curl so are some of you going to ridicule him because of it or is refuting everything John Curl says the main sport of the day.

Sometimes I feel that a bunch of you need to grow up................If you disagree say so, state your reasons and move on.

Jam

[jcx]

John could have articulated his reasoning - stated 2 resistors can give RF/EMI ingress protection