Battery Drain

sounds like a power supply coming up slowly and the DC operating conditions establishing themselves.
If it's battery opperated, maybe it doesn't need so much 'C' in the power supply?

Or maybe there is a dodgy C in there.
Del

hmmm. I'll admit I don't understand what 'C' you mean. (Just for clarity, there's no AC power supply on either device, strictly the 9 volt battery. Both have that "plastic snap on a cable" interface with the battery.)

To be perfectly accurate, the 'loud noise' is sometimes immediately on turning on. At other times it has kicked in later - maybe after ten or twenty seconds - for device #1 at least. In all cases followed by dramatic loss of signal gain.

I mistook this for something in the signals environment, but I was just on a road trip for a couple days, and the same thing was observed in a remote location. Made me think, could be something in the machine itself. (Please excuse my abysmal ignorance, but that's why I'm asking, right? )

The loud noise on device #1 (a receiver) resembles the signal from a commercial video jammer (at least that's what I thought, maybe not consistently?). Very kxxxxchchxxx noisy.

The loud noise on device #2 (a small preamp) sounds like nothing so much as a barrage of video game gunfire. P-tew, tew. p-p-p-tew. Think cheesy synth. Sorry me noise transliteration is a little crude. Invariably followed by dramatic loss in signal gain. In the case of device #2, I found that a brand new battery seemed to solve the problem for a few days, before giving over to the p-tews again.

Yes 'C' is Capacitance...
_{If you don't know what C is, you have no business arseing about with power supplies}
(Kris made me say that)
Del

Thank you and GA. I understood the general concept of capacitance but not the application of it in these circuits. Found a good wiki to read on the 'arseing about' advice (my ignorance may be shocking ). I still don't know where to find dodgy capacitors in the receiver and the preamp, but when I am done with cautionary reading I will open em up and see if I can recognize the capacitor(s) in the circuit.

These comments from wiki seemed like they might be relevant:

"Sometimes charge buildup affects the mechanics of the capacitor, causing the capacitance to vary." Also read bits about dampness affecting a paper dielectric, or breakdown voltage and temperature constraints on other dielectric materials, which might be considered probable types of environmentally produced dodginess in the aging (and perhaps "cheap") capacitor.

This was an interesting bit: "Capacitors, especially older components, can absorb sound waves resulting in a microphonic effect. Vibration moves the plates, causing the capacitance to vary, in turn inducing AC current. Some dielectrics also generate piezoelectricity. The resulting interference is especially problematic in audio applications, potentially causing feedback or unintended recording. In the reverse microphonic effect, the varying electric field between the capacitor plates exerts a physical force, moving them as a speaker. This can generate audible sound, but drains energy and stresses the dielectric and the electrolyte, if any."

This sounds like what is happening.

Solving the problem would then boil down to identifying and replacing the faulty capacitor.

The only other possibility would be "parasitic capacitance", which "occurs in circuits wherever the simple conductor-insulator-conductor sequence is formed unintentionally". I put a question mark by this, because I've noticed that the audio input connection to my little edirol is also becoming flakey of late.

If some kind of ??? non-conducting deposit was forming at the input or output due to ??? environmental conditions, thereby interrupting the connection, would this qualify as a potential source of parasitic capacitance? Would parasitic capacitance of this type be sufficient to cause the battery drain, or can it be ruled out as spurious and insufficient?

Rest assured my entire electronics expertise has been accumulated by 'arseing about'.
And I maintain it's one of the best ways to learn....

Del

Could be carbon build up on the variable resistor.

Is this one of those radios that the knob for turning it on is also the same knob for turning up the volume?

If so, then some contact cleaner sprayed on the volume switch might help. A build up of carbon and dirt sometimes cause the contact between the wiper of the pot to 'bounce'. From your sound effects, it sounds like the problems that use to be encounter on old time radios...you know the ones that actually had moving parts.

Greenja

Thanks for the suggestion. I'll be looking for contact cleaner next time I am in town. The preamp is indeed one of those that volume and on/off are the same switch. The volume control has been iffy for awhile. So this sounds like a reasonable cause and a good way to try and fix it. GA.

The radio receiver which has a similar problem, has separate volume control. It actually has an on/off switch that goes from AC to DC. Since I only use it battery operated, it is in the AC position when it's off. Don't know if this makes a difference or provides another clue as to the source of the problem.

I had a similar experience with a computer many, many years ago. Turned out to be a DEW Radar system a few miles away that was so powerful, it upset the working of the computer when it was switched on.

If I was looking for this problem today, I would use a car Radar detector. (if they are available in your area....)

By the way, be careful, many radar detectors also "send" a strong signal.....