The generation gap and ensuing technology clash

[nineno]

I recently relocated to Milwaukee, WI and with the move came a host of other mandatory changes, like cell phone service. I went with Nextel because I was sick of Cingular's BS. All and all great service.

So one night i was talking on my cell phone and listening to my ST-35. Shortly after the conversation started i heard my amplifier making a weird ticking noise inthe other room. It sounded EXACTLY like a rotating sprinkler that goes "tick-tick-tick-tick-t-t-t-t-t-t-t-t-t-t-t" (i hope someone knows what i'm trying to describe there). So while i'm on the phone i walk into the room to see if it was the record player freaking out or the amplifier. Lo-and-behold as i got closer it flipped out even more, and it seemed related to which board in the wooden floor i was stepping on! So i shut it down and waited until i could really deal with it.

A day or to later i turn it on to try to replicate the sound, but it works fine. So, i bias the amp and assuming the problem will resurface later. It did a few days later....

Now i may be dense, but it took until the 3rd time this happened for me to realize that it was my CELL PHONE setting the amplifier off. And how i realized this was that i heard the same sounds from my cell phone one day while using it outside a coffee shop. The noise was faint in the background, but it was the same exact ticking sounds.

As for why it seemed dependant on which board in the floor i stepped on, i can only assume i was "tunning" the problem based on my linear distance from the amplifier...does that make any sense?

So, the hollow state and solid state devices have gone to war. But i think the simple solution is to just turn off the amp when my phone rings.

Shannon, et al, do you have any ideas one why this might be happening? I don't think it's much of a problem, just a curiosity.

Anyone else have this problem?

Thanks!
drew*

[Shannon Parks]

Shannon, et al, do you have any ideas one why this might be happening?

My best guess would be a malfunctioning 12AX7 (heats up then gets microphonic) or maybe some EMI through the AC mains. I would try swapping the 12AX7 if possible. Also double check what is sharing the AC circuit next time. Could also be a suspect solder joint that gets funky after warmed up - is it one channel or both?

That said, RF energy can do some strange stuff. I work in an RF lab and have high powered GSM transmitters and PCS transmitters at my disposal and could do some tests. Does the ticking end as soon as you end the conversation?

Shannon

[EWBrown]

I also have NexTel, and have heard the pulsing interference. They way the Nextel radios work is that they digitize the voice signals and then send them in short data bursts, which have a fairly high level but very short duration. I've heard this on AM and FM radios and on my tube gear, if I am close to the equipment. The 33 pF cap across the input of the DIY35 (and ST-35) should help reduce this, but it still gets into the 12AX7 through the glass.

It would take some serious filtering and shielding to eliminate this pulsing garbage, but it won't do any harm, except perhaps to one's musical senses.

The ever-increasing RF spectrum pollution of cell phones, wireless web, TV "extenders", etc creat all sorts of troubles not only to audio gear, but to Short Wave listeners, ham radio, and even emergency communications.

/ed brown

[nineno]

You guys are too smart...

Seriously though, thanks for the information both of you. Ed, what you described seemed to hit the nail on the head.

Shannon, i will fire the amp up tonight and see what cause the trouble (eg: live conversation, or just proximity to the amp).

On an entirely different note, i just picked up a copy of Morgan Jones' "Valve Amplifiers." I'm told this is good "light tube reading." Yikes. Informative, but it takes me a few re-reads to get any/all of it.

Thanks again gents!
drew*

[EWBrown]

The Nextel phone will generate these pulses while connecting, and at a slower rate while just turned on. THe process does make for very good security, and for longer range communications than most analog cellphones. I have the 700i which is a larger and heavier unit, I need the extra "reach" to get in from the boonies.

/ed brown