John Curl's Blowtorch preamplifier part II

[Joshua_G]

Pavel,
I know very well you don't only theorize.
Please point to the thread, once it will be up.

John,
I, for one, never criticized you. I believer neither did Pavel. That RFI immunity can be improved doesn't mean that it would be cost-effective in case of the BT. You explained clearly how each and every shielding solution of yours is being criticized and I understand your considerations in each case.

[anatech]

Hi Bob,
Thank you.

If the amount of RFI ingress is sufficient to upset circuits and cause intermodulation with an audio signal, wouldn't most forms of RFI ingress also result in an audible disturbance in the absence of the audio signal?

I guess that would depend on whether anyone was around to hear it. If the volume is turned down in a preamp, then most of the gain is gone except for the 30 ish dB in the amplifier. The only sound you are likely to hear are difference frequencies and something that sounds like a hum with a "buzz" quality.

Once you are processing a signal, the effects will probably become far more pronounced. Now you have an audio signal for the RFI to interact with. By definition (of an audio signal), you can hear the effects for sure. You can also measure these effects. Note that most electronics benches are electrically quiet with a local ground node common to the test equipment. We do that so our readings will not be disturbed as much by the RFI surrounding us all. There have been many times when these problems do not show up on my bench, but they do once the equipment has been returned to it's normal environment. At least I expect this.

Its interesting to note that the old reliable cell phone test produces very audible artefacts.

It sure does, but that test has too many variables to be accepted. Now, can you imagine how much they can charge for a calibrated RF noise source with standard test formats and frequencies? They do use this when testing WiFi and radio link industrial devices.

I think that the goal is to restrict audio equipment to operate only in the audio range. That should improve the performance quite a lot. Also, expect the worst RFI environment for any new designs. I have no doubt this will become a common situation as time goes on.

-Chris

[Wavebourn]

Originally posted by john curl
Oh, going to criticize and run? Sounds like what they accuse me of.

You have different avatars guys so we can tell for sure who is writing.

But I want to support both of you referring Joshua to his cellphone he has in his personal possession now. It has powerful transmitter inside and a tiny microphone with it's amp and compressor. Opening it he can learn from the real example how can be done what he is asking about.

[simon7000]

I have now looked at most of both Blowtorch knots. At first I though having an avatar create a web thread, brilliant advertising. Then by page 200 or so the no more blowtorches to be, limited that thought.

A few errata; Donald L. Feucht & Aubrey G. Milnes wrote the semiconductor book. Dennis L. Feucht has the web site.

Crown Amplifiers have traditionally been the largest selling professional amplifiers used for applications where almost no one is within a hundred feet or so of the loudspeakers. In the past they have provided lots of power with little fuss.

John asked about resistor types, I have been using the tantalum nitride surface mounts.

Relays and audio switches should have bifurcated gold plated cross bar contacts. Western Electric used their own alloy, otherwise that is how they did it.

There is a base level of vibration in most places of 5 mG. This shows up as signal in all capacitors that have a DC bias.

But the real kicker is Ohms law is an observation, all conductors deviate from it.

Using an Audio Precision System 2 and an instrumentation amp with a 60 db gain using the LME49740 opamp allows me to measure audio interconnect distortion. If I attached it right, (Only seems to take a thumbnail, so this note may show up multiples) shown is a short silver cable vs a cheap gold plated 2 m piece. Test tones were 21 and 22 kHz at a level of 300 millivolts.

[scott wurcer]

Originally posted by simon7000
. If I attached it right,

Missed something

[john curl]

Joshua, you are having language translation problems. You are completely innocent of ALL doing, except for being 'pesty' once in a while.

[nicoch58]

there is a study on building materials cement-based EMI shielding and wave absorbing

[bear]

A friend of mine who works for Vicor turned me on to this link:

http://uk.geocities.com/cyrilb2@btin...m/cable_3.html

The dowload page has a .pdf that is worthy of a read. The comments on the D. Self "blameless" are worth the price of admission, imho.

I think this article explains the RFI & speaker cable issue satisfactorily... and shows how to make the proper network for your specific system.

<Blowtorch content>Wondering if the same effect occurs on "ordinary" RCA interconnects or not? </Blowtorch content>

Simon7000, not sure if you are suggesting that Mr. Curl is trying to sell any Blowtorches?, fyi. The product is in the "legacy" category at present. The discussion is for educational and edificational purposes only.

_-_-bear

[anatech]

Hi Bear,
Excellent site. I have already downloaded most of that stuff. The site is currently not responding because the bandwidth has been exceeded. It might come back on line in an hour or so.

Thank you for reminding me. Is that "Cables_at_AF.pdf" file a new one? It's the only one I want right now, looks interesting.

-Chris

[Joshua_G]

Originally posted by Wavebourn

But I want to support both of you referring Joshua to his cellphone he has in his personal possession now. It has powerful transmitter inside and a tiny microphone with it's amp and compressor. Opening it he can learn from the real example how can be done what he is asking about.

I used to service cell phones, so I know very well how they are constructed inside.
It doesn't answer my question.