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Old 5th September 2008, 12:03 AM   #1
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Default Survey: Experience with microphony ?

Hi there,

i have recently been pointed to an effect well known from
tube amplifiers.

Microphony also seems to be present in almost every
solid state ampilfier, cables and passive crossovers
(especially in capacitors and coils).

I am recently trying to keep my electronic boards, amplifier
cases and cables from ringing ...

The guy who pointed me to that effect has some experience
in doing that. One week ago i would have called him mad ...

Since i am experimenting myself i feel, hat microphony
should not be ignored in high end components or components
that would like to be called high end ...

Too esoteric ?

Opinions or experiences someone ?


Kind regards
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Old 5th September 2008, 02:58 AM   #2
Pano is offline Pano  United States
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I know for sure that tubes are microphonic, just tap one and hear! But the other stuff, I dunno. To some extent, perhaps.

We all know the infamous $400 wooden volume knob. They claim that it doesn't pick up nasty vibrations like big metal knobs (or something idea like that.)

Well I decieded to test the theory. Ran DC thru a pot - a Nobel and a cheap Panasonic and then AC coupled the wiper to a mic input. Figured that any movement in the pot should create enough signal to be picked up by the mic preamp.

Could not find a thing, nothing, nada. With knob, without, wood, brass, whatever. Even banged it with a hammer. Nothing.

That's been my experience. FWIW.
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Old 5th September 2008, 03:08 AM   #3
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early wireless guitar packs had microphonic cable. Something to do with the cable impedance affecting the radio oscillator frequency, but just the cable banging on your axe would cause a thumping sound.

My first tube guitar amp was microphonic, tapping the input tube produced sound output, but that was a loong time ago

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Old 5th September 2008, 03:13 AM   #4
Pano is offline Pano  United States
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Quote:
Originally posted by Iain McNeill
early wireless guitar packs had microphonic cable.
Do you remember what brands - what time period?

BTW, nice sig!
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Old 5th September 2008, 03:27 AM   #5
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I remember the Nady VHF models of the late '80s did this (was it the 101, 201?) By the time they went UHF they had it fixed and so, therefore, did all the ensuing knock-offs.
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Old 5th September 2008, 03:36 AM   #6
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I have got a solid state stereo amplifier, which causes
a "thump" if you clap on the cabinet when "phono" is
switched and volume is max ... i think there was no
pickup connected so the phono input was "open".

But i do not know how (where) the noise is coupled
into the amp .
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Old 5th September 2008, 04:16 AM   #7
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I think in many cases it's due to a change in physical/parasitic capacitance due to mechanical deformation. The ensuing charge flow causes all the problems.
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Old 5th September 2008, 11:07 AM   #8
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Something I've mentioned before but will again: piezo or triboelectric effects, especially in some Teflon-insulated cables terminated with high resistance.
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Old 6th September 2008, 04:40 AM   #9
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Ah - so maybe that's why some folks like cotton insulation - yeah? It has almost zero triboelectic (static) effect. Teflon would be very high on the static electric list. Never thought of that before.

BTW - how high a termination impedance?


Quote:
Originally posted by Iain McNeill
I remember the Nady VHF models of the late '80s
Yes, yes. No surprise there. I used a fleet of Nady wireless gear on tour in '91. Really rotten stuff, but cheap. When we switched over to Sennheiser it was a world of difference. The bass player said " Wow! It sounds like my rig again." A Classic case of You get what you pay for.
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Old 6th September 2008, 12:42 PM   #10
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Hi,

seems like microphony is a well known artefact in
PA and stage technology.

It has to be accounted for in pickups, amplifiers and cables
since cables are often very long in those applications.

There are strong sound fields to which some of the
components are exposed.

I am not experienced in PA, but i feel since the effect is
present under stage conditions it should not be ignored
entirely in high quality home components.

Even though some of you may say this is to aloof, i am trying
to supress microphony with cheap provisions like

- putting the amplifiers on thick rubber mats
- damp high Q case resonances of components with damping pads
- use soft and well damped cable insulation
- use low capacity cables

I am experimenting since one week. Resolution, spatial imaging
and reality has improved, for small money.

I can listen at lower levels and i am not tempted to go
louder to hear detail i can hear now.

Subjectively the negative effects of the listening room's
acoustic do not seem to be disturbing to he same extent
as before, when listening at louder levels.

The usable dynamic range has increased.

I tend to the opinion, that all components of the chain should
stand on a damped base and should be protected from
excitation by the sound field or footfall sound.
The components cases, boards and cables should be kept
from ringing or vibrating as far as possible.

Kind regards
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