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What is the "sound" of microphonic tubes?

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Posted on October 26, 2014 at 13:20:04
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 All,

I always wondered what the influence is of using microphonic tubes in ones system.

Yes, when I tap on my 6C45P, WE437A and Ba tubes I hear it back in the speakers clearly. But I'm not sure how this translates to the performance of my system when I'm playing music.

I use dampers where possible which add a very small bit of focus, but it for me the microphonic tubes do not seem to pose a problem at all.

Am I missing something? Is it worthwhile to undertake large efforts reducing microphonics?

NC

 

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When I have gotten rid of my very microphonic tubes I hear an ease to the music, posted on October 26, 2014 at 13:53:10
richardl
Audiophile

Posts: 3555
Joined: September 5, 2002
 And somehow more info. The ringing is often high pitched and masked by the music somewhat. For classical music, getting rid of microphonic tubes can really make violins easier to listen to. Great for some of us that really have trouble with "bright" systems.

 

RE: What is the "sound" of microphonic tubes?, posted on October 26, 2014 at 14:00:19
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 If your amp or preamp is located where sonic vibrations are prevalent you should hear the tube pick up the sounds from playback. I found that this can be noticed as an artifact on the original sound like cymbals that seem to shimmer too long. Best noticed on very familiar program material. Try and compare with a different tube to hear any differences. regards, Dak

 

if it's bad enough, they can actually cause feedback NT, posted on October 26, 2014 at 15:34:21
Alpha Al
Industry Professional

Posts: 2958
Location: N. Carolina
Joined: February 16, 2004
Contributor
  Since: December 3, 2015
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RE: What is the "sound" of microphonic tubes?, posted on October 26, 2014 at 16:07:06
Awe-d-o-file
Dealer

Posts: 21037
Location: 50 miles west of DC
Joined: January 10, 2004
 As you may know now there are levels of microphonic tubes. Like Al said depending on the type of tube and where it is in the circuit they can cause feedback (like from a PA system -squeal) you have tubes now that when you tap on them they make audible noise in the speaker; both are types of microphonic behavior.

When you change a tube it almost always sounds different obviously the same brand/type/run of tube will sound most similar. I would remove ANY tube with any type of microphonic behavior. The sound you get with the replacement will have many variables as you probably know.

In the end you'll decide the cost/benefit factor yourself and weigh all the data. I would replace any microphonic tube and the louder you play your system the more important it is IMO. I'd be less likely to replace a microphonic tube in a headphone only setup. The sound won't get back to the microphonc tube in a headphone system.

Like a turntable susceptible to feedback there are other [potential] ways than just the sound from the speakers feeding back to affect a microphonic tube and its system. Good luck.

ET
ET

"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936

 

RE: What is the "sound" of microphonic tubes?, posted on October 26, 2014 at 16:26:02
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 "I use dampers where possible which add a very small bit of focus"

I think you nailed it.

To me a microphonic tube adds a bit of false "reverb".

Removing the added "reverb" reveals the true focus.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What is the "sound" of microphonic tubes?, posted on October 26, 2014 at 16:36:02
Ray Moth
Audiophile

Posts: 2784
Location: Jakarta, Indonesia
Joined: November 10, 2003
 Here is an alternative view (which I do not endorse!)

 

Awesome (nt), posted on October 26, 2014 at 17:29:36
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012

 

RE: What is the "sound" of microphonic tubes?, posted on October 26, 2014 at 18:09:00
deathtube 667
 I recall DLM saying that DF finds only 1 in 15 samples of 7B4 acceptable for his SE DC 2A3 mono amps in term of microphonics.

Apparently this is needed for correct "jump factor" in a low current driver stage.

A microphonic tube would normally be dismissed by the average builder of typical mid-fi tube amps.

 

RE: What is the "sound" of microphonic tubes?, posted on October 26, 2014 at 18:55:36
Tre'
Industry Professional

Posts: 17294
Location: So. Cal.
Joined: February 9, 2002
 "A microphonic tube would normally be dismissed by the average builder of typical mid-fi tube amps."

If it takes a microphonic tube to make a design perform, there's something terribly wrong with the design.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: What is the "sound" of microphonic tubes?, posted on October 26, 2014 at 20:25:01
deathtube 667
 "If it takes a microphonic tube to make a design perform, there's something terribly wrong with the design."

I would agree with you, but the thought process involved in designing "alternative" low power SE tube amps is not conventional or grounded in known theory and measurement sciences.




 

Depends what makes them microphonic, posted on October 27, 2014 at 01:56:26
andy evans
Audiophile

Posts: 4378
Joined: October 20, 2000
 There are tubes where microphony is a malfunction. But there are a whole family of DHT small radio tubes that used to run off batteries and had very low consumption filaments - like 60mA, 120mA and stuff. Those were horribly microphonic, but a lot of them sounded great. Stuff like 1G4 - wonderful sounding little tube. You can tame the microphonics with starved filaments and massive engineering, but these kind of tubes really need about 2v input. Same with the 4P1L which is naturally microphonic but stonkingly good sounding.

 

The problem of course is..., posted on October 27, 2014 at 04:30:52
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 That ALL my WE437A and Ba tubes are microphonic...

I'm not in the position to test tens of these tube to find samples which are not microphonic. Moreover I suspect ALL of these tubes will be microphonic to a degree.

If I want to be anal about this, the only solution is to put my gear in a separate, isolated room.

Since I conclude from this thread that microphonics is relatively 'small' issue, I think I'm going to live with it.

NC

 

Basically vibration inside a hollow vacumn. The tail wags the dog!, posted on October 27, 2014 at 07:58:41
mobiasloop
Audiophile

Posts: 100
Location: SW Missouri
Joined: August 14, 2014
 The rigidity of the internal construction of the tube, the posts and the mica washers/wafers. For instance compare a 12ax7a/7025 with a 12bz7. The 12bz7 was designed as a TV oscillator and sync seperator but it has the same gain as a 12ax7a, twice the transconductance and half the plate resistance BUT notice the stack of mica wafers (many more in the 12ax7) and the size of the posts supporting the structures of the tube. The 12ax7 is better damped. Also though we can't see them the heater maybe wound differently inside the cathode. All of this is a tail wagging the dog and it's a matter of DAMPING those tail wags. Acoustic feedback from the speakers, semi tractor trailers and trains near your home, heavy stampers (I have a daughter this is Miss congeniality but can't walk without shaking the house) all contribute. Moe
"...the fool doth think he is wise but the wise man knows himself to be nothing but a fool." Will Shakespeare

 

RE: What is the "sound" of microphonic tubes?, posted on October 27, 2014 at 10:48:44
Jim McShane
Dealer

Posts: 5910
Location: Chicago
Joined: January 13, 2003
 "Am I missing something?"

Yes. ALL tubes are microphonic to some degree. As long as it isn't causing problems then it isn't an issue.

Nearly ALL tubes make noise when tapped. It's only when the noise is excessive or continues for a while after the tap that it could be considered excessive.

Don't tap on tubes unnecessarily, you can cause damage to the tube.

Finally, the amount of apparent microphonics varies greatly with the circuit the tube is used in. Sometimes a tube that is excessively microphonic in one position is just fine in another.

 

RE: The problem of course is..., posted on October 28, 2014 at 02:30:29
Thomas Mayer
Manufacturer

Posts: 602
Joined: May 8, 2001
 Hi!

>>> That ALL my WE437A and Ba tubes are microphonic... <<<

I have worked with the WE437A in phono stages and did not find them very microphonic. Even in the first stage of the phono. The WE437A can oscillate if not used in a careful layout that can appear like being microphonic. Of course when you tap a tube in the amp you will hear something, but I would not consider that as being microphonic. Just don't tap the tubes ;-)

Thomas

 

RE: When I have gotten rid of my very microphonic tubes I hear an ease to the music, posted on October 29, 2014 at 14:22:56
Sherwood Forest
Audiophile

Posts: 240
Joined: October 7, 2014
 It really all boils down to how microphonic a tube is when excited by musical vibrations in the air and the surface on which the tube sits.

Tapping the tube tells you that it is sensitive to a very large mechanical vibration, but not necessarily to sound.

I'd be curious to try an experiment - one where you take a speaker on a different amp, run a sweep through it while pointing it at the tube in a circuit, then measuring the output of the amp that tube is in, to see what actual sound gets picked up and amplified. I think that without doing that, what constitutes a microphonic tube is somewhat in doubt.

 

When they ring on and on, it is pretty bad, posted on October 29, 2014 at 15:08:20
richardl
Audiophile

Posts: 3555
Joined: September 5, 2002
 a light tap with the fingernail should not produce a 60 second ring but, with very microphonic tubes it can. Subs can certainly set them off by shaking the glass and the box of the amp/preamp.

 

In addition...., posted on November 3, 2014 at 11:07:51
wheezer
Audiophile

Posts: 4309
Joined: January 24, 2001
 To what Jim said, tubes get a bad rap for microphonics. Many times the sockets are the culprit.
An improperly secured coupling cap can not only mimic a microphonic tube but cause one heck of a feedback loop, even at low volume levels.
If one feels compelled to tap the tube, tap the chassis. Don't tap the tubes.

 

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