John Curl's Blowtorch preamplifier

[KSTR]

Does anybody still have/use AM (SW/MW/LW) radio?

I use my pocket world-reciever to quickly find major RF emitters... it's amzing how much dirt is in the the air and on cables today, compared to like 10 or 20yrs ago... also emitted from displays of CDP's etc. People have reported that their systems sound better when all displays are turned off, for good reasons...

 

[john curl]

KTSR, did you happen to notice that the BLOWTORCH does NOT have any displays, not EVEN an LED? That is on purpose. We have known about RFI generation for decades in solid state displays.

 

[jam]

Mr.Curl,

How bad a source of RF radiation is a led?

Regards,

Jam

 

[Joshua_G]

The problem with LED is the opening in the case …

 

[jam]

Good point. I never thought of that.......

JAM

 

[KSTR]

We could even determine the cutoff freq of that 3mm hole with the formula in the ETS-Lundgen datasheet I linked to a few days ago...

 

[scott wurcer]

The problem with LED is the opening in the case …

What opening in the case? Clear plastic and black plastic have about the same RF properties.

Jam - I did a double take today one of my guys put a big plastic copy of your avatar on top of his desk.

 

[Wavebourn]

Good point. I never thought of that.......

Yeah, 20 GHz is a very dangerous frequency.

Sorry, Couldn't resist.

 

[john curl]

I can't say.

 

[KSTR]

Scott, while I have your attention...

... you once mentioned spark gap calibration etc of microphone capsules (Earthworks does this, IIRC). Are there any accessible sources that one could exploit? I think I understand the basic principle (the "rectangular" nature of the pulse -- not a dirac) but would like to learn more about it.

- Klaus (and, sorry John, polluting "your" thread )

 

[scott wurcer]

Scott, while I have your attention...

... you once mentioned spark gap calibration etc of microphone capsules (Earthworks does this, IIRC). Are there any accessible sources that one could exploit? I think I understand the basic principle (the "rectangular" nature of the pulse -- not a dirac) but would like to learn more about it.

- Klaus (and, sorry John, polluting "your" thread )

Klaus PM me and I'll send you what I have. I have a reference that confirms that a spark discharge really generates a doublet pressure wave, which is obvious once you think about it. The calibration at the highest frequencies remains elusive but I have convinced myself that what I have is close enough for "government work".

 

[KSTR]

@Scott: PM sent

 

[john curl]

Then best way to test a microphone transient response is with Manger's special microphone test, shown at AES in 1986, at Montreaux. Beats spark gaps. Very sophisticated. Good enough for B&K 1/2 inch measurement microphones and just about everything else.

 

[jam]

This might be off topic but......

Scott,
Big Brother is watching..........................

 

[jam]

Wavebourn,

............after this you won't be able to sleep at night.

 

[john curl]

Polluting the thread, Jam?

 

[jam]

Mr.Curl,

With all due respect nothing much was going on so I thought some levity was in order..............consider me sinn binned.

Regards,

Jam

 

[john curl]

I hope so.

 

[scott wurcer]

Then best way to test a microphone transient response is with Manger's special microphone test, shown at AES in 1986, at Montreaux. Beats spark gaps. Very sophisticated. Good enough for B&K 1/2 inch measurement microphones and just about everything else.

I use a Home Depot grill starter, DIY at its finest. YMMV.

 

[john curl]

Scott, there are more sophisticated measurement techniques. It would seem to me that you are working essentially blind, and helping amateurs to be in the same position as yourself. Microphone measurement is not an easy thing, and even understanding microphone frequency response has not yet been put up here or anywhere else on this thread, so far as I know. Why THIS thread?