RE: isolation devices / coupling devices etc

Posted by rick_m (A) on July 4, 2012 at 08:09:34

In Reply to: isolation devices / coupling devices etc posted by gonzo on July 4, 2012 at 04:11:28:

"Any idea why they should affect things like amps or preamps, especially solid state components ?"

Sure, the parts can be sensitive to vibration. There are several mechanisms that account for the behavior.

Semiconductor chips are sensitive to flexure so if anything twists or bends the PCB they are attached to some of that motion will couple to the chip and usually show up as an offset term in the output. In other words it will be AM at the signal frequency but with a strange timing and have oddball distortion components. The same mechanism in the portion of a gate that determines the threshold will modulate the slicing point causing IFM (incidental frequency modulation) which is better known in these parts as jitter.

The sensitivity of a device to flexure depends upon the die layout, the package and the orientation on the PCB. I had an instance once where the problem was gravity. The product would respond to what angle it was held at, unfortunately it wasn't a builder's level... Turned out to be case flexure coupled to the PCB through the mounts which twisted the board changing the DC offset and producing a change in the indication. Moved the IC a little and flipped it 90 degrees and all was well.

Tubes are of course a lot worse in general and suffer from the grids and stuff rattling around imside and the pins wiggling in the socket. Loctals were better for the latter and frame-grids much better for the former.

Passives aren't innocent either, chip resistors are sensitive to bending, capacitors to triboelectric effects and capacitive variations from motion and flexure and crystals can just really be a problem. HC-18 styles have the crystal suspended by two leads internally which and will flop back and forth under Vib causing sidebands which get really bad at it's mechanical resonance.

And THEN there can be problems with stuff changing their relative locations. For instance if you have two film capacitors mounted vertically beside each other, they will flop a little with Vib changing their relative spacing and the capacitance between them.

Enough. I guess the bottom is almost anything is a little microphonic. On the bright side I've not had much problem that I'm aware of with home audio, but then again I haven't investigated it nearly as much as many other folks on this site have. My experience is from decades of work on stuff in iffier environments like missiles, airplanes and logging trucks. However the principles are all the same, it's just a matter of levels.

If you want to investigate it further you will need to invest in some special tooling and the thing to start with is a wooden pencil. But don't sharpen it. The approach is forced excitation: You poke it with your stick and see what happens. I know, it doesn't sound like "rocket science", but in this case it truly is! Tap around on things with the volume up and see what you hear. The idea is to find the areas of susceptibility and try and improve them, use the wooden end of your shock stimuluator to generate HF impulses, the eraser end for LF ones. If you spring for a second NASA approved shock stimulator you can sharpen the wooden end and take notes. Don't cheap out and try to use one for both, the pointed graphite will crumble onto your board causing a new layer of problems!

What to do next depends on what you find. Obviously for shock sensitive components you need to replace them with one's that are less so or try to isolate them.

Hmmm, I just realized that I'm going far far beyond what you asked. Sorry, got on a roll. Suffice to say there are approaches to make things better. But there is no way to make things perfect...

Regards, Rick

This post is made possible by the generous support of people like you and our sponsors:

Follow Ups Full Thread

Topic - isolation devices / coupling devices etc - gonzo 04:11:28 07/04/12 (31)

RE: isolation devices / coupling devices etc - stanwal 22:06:06 07/18/12 (0)

RE: isolation devices / coupling devices etc - hahax@verizon.net 20:49:37 07/04/12 (0)

RE: isolation devices / coupling devices etc - tmsorosk 18:47:03 07/04/12 (0)

A tool you might have fun with - Craiger56 10:50:13 07/04/12 (1)

RE: A tool you might have fun with - rick_m 12:18:28 07/04/12 (0)

RE: isolation devices / coupling devices etc - jayarr 10:41:55 07/04/12 (0)

RE: isolation devices / coupling devices etc - middleground 08:47:56 07/04/12 (6)

There you have it! Problem (or perceived problem) solved... - musetap 09:39:52 07/04/12 (5)

RE: There you have it! Problem (or perceived problem) solved... - middleground 12:48:54 07/04/12 (4)

"every tiny vibration of an electronic device causes audible effects" - musetap 18:18:27 07/04/12 (3)

AVM is a pain but it clearly works. - Norm 10:08:53 07/05/12 (0)

RE: "every tiny vibration of an electronic device causes audible effects" - middleground 04:30:16 07/05/12 (1)

"I never expected much from you and, at least, can say that I am not disappointed." - musetap 08:30:39 07/05/12 (0)

RE: isolation devices / coupling devices etc - rick_m 08:09:34 07/04/12 (3)

I don't really think tube circuits are more influenced by vibrations. - Norm 10:12:28 07/05/12 (0)

RE: isolation devices / coupling devices etc - gonzo 08:18:08 07/04/12 (1)

RE: isolation devices / coupling devices etc - rick_m 10:18:10 07/04/12 (0)

A wire moved in a magnetic field has an induced current. - Norm 07:29:56 07/04/12 (2)

RE: A wire moved in a magnetic field has an induced current. - middleground 08:51:12 07/04/12 (1)

No, I have no idea of their magnitude. - Norm 15:29:01 07/04/12 (0)

Mechanical vibration could certainly affect capacitors. And I have to say they work: stuff change the sound - Elizabeth 06:51:56 07/04/12 (1)

RE: Mechanical vibration could certainly affect capacitors. And I have to say they work: stuff change the sound - pictureguy 13:35:29 07/04/12 (0)

RE: isolation devices / coupling devices etc - soulfood 04:27:19 07/04/12 (8)

RE: The worth of your post . . . - Hi-Fi Nut 06:31:46 07/07/12 (0)

Agree with your comments. Either try them, or just say no, seems to be the way to go - Elizabeth 06:57:46 07/04/12 (6)

As I recall, the original TipToes were 50 cents apiece. - Norm 08:48:39 07/04/12 (1)

no. I bought them way back when they came out. short were like $4 tall $7.50 - Elizabeth 11:20:28 07/04/12 (0)

RE: Agree with your comments. Either try them, or just say no, seems to be the way to go - gonzo 07:58:48 07/04/12 (3)

Yeah, I hear you. half of my response is just laying the ground for the griping to follow. - Elizabeth 11:22:47 07/04/12 (0)

RE: Agree with your comments. Either try them, or just say no, seems to be the way to go - musetap 10:06:49 07/04/12 (1)

RE: Agree with your comments. Either try them, or just say no, seems to be the way to go - MylesJ 18:28:38 07/04/12 (0)

Follow Ups

RE: isolation devices / coupling devices etc - rick_m 08:09:34 07/04/12 (3)

I don't really think tube circuits are more influenced by vibrations. - Norm 10:12:28 07/05/12 (0)

RE: isolation devices / coupling devices etc - gonzo 08:18:08 07/04/12 (1)

RE: isolation devices / coupling devices etc - rick_m 10:18:10 07/04/12 (0)

RE: isolation devices / coupling devices etc

Post a Message!