Microphonic behaviour - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st February 2006, 10:47 AM   #1
diyAudio Member
 
Onvinyl's Avatar
 
Join Date: Aug 2002
Location: Germany
Default Microphonic behaviour

Hello,
I would like to start a discussion about microphonic affections and effects in low-level high-gain solid-state circuits such as phonopres or mic-amps having cl-gain of 10.000 or even more. This might include discreet as well as opamp circuits.
Maybe I choose the wrong clue-words, but I only found one closely related thread here , and no solution or even explanation has been offered.
Every now and then I used to knock an certain components in previous designs, then thinking ‘strange to hear that knock in the speakers, what might that mean to accurate music reproduction?’ but then forgetting about it immediately.
My actual ‘project’ shows some (in my view) excessive microphonic behaviour. At maximum volume, cautios tapping on the top of decoupling caps makes quiet a boomy bassdrum, one cap in the voltage regulator serves just too well as a microphone at that same volume. It’s a mc-phonostage, but instead of asking for a fix I’d like to take a broader perspective:
  • How much microphonic behaviour is acceptable (read ‘unavoidable’)?
  • Which flaws and flakes provoke an overly microphonic behaviour? (maybe aside from loose ground nodes)
  • How do you cope with it?
  • When all is done what could be done circuitwise, what mechanical additions can you think of? In old radios you sometimes see some sort of wax poored over certain areas. Some people seem to embody the whole circuit in epoxy, a technique which I would not feel too well with, and it’s no option in the making. Speaker wool comes to my mind, but it certainly affects to many parameters of the circuit, e.g. temperature.
Should this all had been on the task too often, don’t blame but point me to it…
Rüdiger
  Reply With Quote
Old 21st February 2006, 09:33 PM   #2
diyAudio Member
 
Onvinyl's Avatar
 
Join Date: Aug 2002
Location: Germany
OK,
in this case, it was a degraded op-amp (or two) that were accidentially fed with one rail side (on of them serving as servo),
and the issue is gone for now with new ones. Do I presume right then, that microphony is always a failure in solid state?
Rüdiger
  Reply With Quote
Old 21st February 2006, 11:16 PM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
That's a new one for me! I've encountered two sources of microphony in new SS gear I've built- capacitors (especially the premium audiophile-grade ones) and Teflon shielded cable. In any of these cases, yes, it's a defect. A properly operating piece of solid state amplification should emit no noise when tapped.

In older gear, the most common cause is connections- cables, plugs, switch contacts, dodgy solder joints.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 21st February 2006, 11:29 PM   #4
diyAudio Member
 
Onvinyl's Avatar
 
Join Date: Aug 2002
Location: Germany
Hi SY,
probably, I was a bit unclear. Surely it were mostly the caps. But it was so severe, that all you tapped made a noise, and all those noises sounded a bit different. All this was due to those faulty opa's.
But one might get into thinking: what is with this special cap that served as a microphone that you could hear your voice through the speakers? Now that is gone, but maybe it would pay if you apply some damping on that device? Many audiochains tend to sound worse when played very loud, it would not surprise me if that is partially through acoustic coupling.,
Rüdiger
  Reply With Quote
Old 21st February 2006, 11:32 PM   #5
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
If a cap is microphonic, out it goes! Why band-aid it when there are plenty of good, non-microphonic caps widely available?
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 22nd February 2006, 03:53 AM   #6
diyAudio Member
 
Join Date: Feb 2006
Location: New England
Quote:
Originally posted by Onvinyl
OK,
in this case, it was a degraded op-amp (or two) that were accidentially fed with one rail side (on of them serving as servo),
and the issue is gone for now with new ones. Do I presume right then, that microphony is always a failure in solid state?
Rüdiger

Hi Rudiger,
Microphony is often a problem with high impedance, high gain circuits. Particularly bad are ceramic capacitors which exhibit a piezo electric effect. These should not be used in the signal path!Coaxial cables can also be microphonic, since they are essentially a long capacitor when feeding a high impedance. Some high end manufacturers go to great lengths to provide acoustic isolation for their PCB assemblies, with rubber mountings, and acoustic dampening panels inside the equipment box, and external isolation feet etc.

Paul J
  Reply With Quote
Old 22nd February 2006, 09:15 AM   #7
diyAudio Member
 
Join Date: Dec 2005
Location: Kuala Lumpur
Just about anything with voltage across it or current through it is potentially microphonic, I have used pcb track as a strain guage in the past.

It is important to mount a pcb rigidly, just supporting the corners of a large board is asking for it to be flexed. Once that happens you are straing the leads of components and will have some effect on the value.

Capacitors with a dc bias on them are very microphonic and the effect is proportional to value, so this is one reason why large ecaps in mc and mm preamps have a bad reputation.
  Reply With Quote
Old 22nd February 2006, 09:27 AM   #8
diyAudio Member
 
Onvinyl's Avatar
 
Join Date: Aug 2002
Location: Germany
Quote:
Originally posted by davidsrsb

Capacitors with a dc bias on them are very microphonic and the effect is proportional to value, so this is one reason why large ecaps in mc and mm preamps have a bad reputation.
Hi David, that is interesting, I will investigate that further!
Rüdiger
  Reply With Quote
Old 22nd February 2006, 09:35 AM   #9
diyAudio Member
 
darkfenriz's Avatar
 
Join Date: Jun 2004
Location: Warsaw
Quote:
mc and mm preamps
what mean these abbreviations?
  Reply With Quote
Old 22nd February 2006, 09:38 AM   #10
diyAudio Member
 
Onvinyl's Avatar
 
Join Date: Aug 2002
Location: Germany
Quote:
Originally posted by darkfenriz

what mean these abbreviations?

Moving Coil and Moving Magnet pickups for vinyl playback.
Rüdiger
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Microphonic s2kov Tubes / Valves 24 7th June 2010 04:20 PM
microphonic sub-miniature tubes? space-cake Tubes / Valves 11 10th October 2008 02:02 PM
Why do valves go microphonic? barretter Tubes / Valves 7 24th September 2008 06:35 PM
Microphonic phono preamplifier Jaime Tubes / Valves 3 5th June 2007 02:52 PM
12BH7 is microphonic Original Burnedfingers Tubes / Valves 7 1st May 2003 10:35 PM


New To Site? Need Help?

All times are GMT. The time now is 06:57 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2