Ideas For Minimizing Microphonics

audioluvr · January 2020

So I've read microphonics are bad for tubes in a pre-amp. What are you all doing to prevent this? OR is it even necessary? Could this be one of those discussions like cables don't make any audible difference? Could some microphonics be a good thing?

I'll be installing my pre inside an open faced and backed oak cabinet between my speakers and it will have a low noise cooling fan below in the back behind the amps like this:
https://www.acinfinity.com/component-cooling/cabinet-fan-systems/airplate-s9-home-theater-and-av-cabinet-quiet-cooling-fan-system-18-inch/

pitdogg2 · January 2020

Personally microphonics of any sort is not something I want.

You get a new tube.

Ymmv

treitz3 · January 2020

Here is a good start for you...BTW, taming microphonics is not like the normal cable debates you see on some forums. It can make a small, almost negligable difference in the sound to a huge difference to the end result as to what hits your ears (and speakers).

https://herbiesaudiolab.com/pages/herbies-tube-damper-comparison

Here is another way to avoid them - https://www.stillpoints.us/index.php/product (just one company out of MANY that do this)

Tom

audioluvr · January 2020

Thanks. That's what I thought. I'll see if I can get an exhange on it. What about isolating the pre? what do you use? I've read you can put closed cell foam under the feet.

treitz3 · January 2020

I don't even know what I use. I picked it up from an audio buddy of mine a very long time ago. Some kind of military isolation dohicky thingamabobber blah, blah, blah.

I'd be lying to you if I tried to remember what all it is made of and the science behind it.

Other ones I use for different application are Sorbothane risers with a felt padding underneath as to not damage what it sits on (Sorbothane will stain wood and some metals).

Tom

marvda1 · January 2020

i use isoacoustics pucks $60 for two. they have mini pucks now so depending on the weight of your preamp you might be able to use them.

audioluvr · January 2020

Thanks Marvin! Those are $48 ea. for the ones I need at Amazon and I need 4

treitz3 · January 2020

Here is another way to do it. Many forum members have done this over the years, myself included.

https://www.morrowaudio.com/blogs/news/project-vibration-control

Tom

marvda1 · January 2020

audioluvr wrote: »

Thanks Marvin! Those are $48 ea. for the ones I need at Amazon and I need 4

these are the ones i am talking about not the more expensive ones.
https://www.guitarcenter.com/IsoAcoustics/Iso-Puck-Isolators-1500000138323.gc?source=4WWRWXMP&msclkid=d675aee3a9fd12af65dff0f0542bb32a&utm_source=bing&utm_medium=cpc&utm_campaign=[ADL] [GC] [PLA] [Shopping] - (Accessories - Studio Furniture) - {MQ} - [LV]&utm_term=4578091567465029&utm_content={MQ} Accessories - Studio Furniture (GC) (Bing)&adlclid=ADL-8257138a-8973-455a-bca3-a165a9a188e7

Nightfall · January 2020

If a tube is audibly microphonic probably I just replace it.

ZLTFUL · January 2020

Nightfall wrote: »

If a tube is audibly microphonic probably I just replace it.

So much this.

But I will also play devil's advocate and throw out there that sometimes bad iron (transformers) can cause them too. A delaminating core on a traditional style transformer has been known to cause a buzz between those separated plates which can make its way into the signal path. Stupid big azz magnets.

audioluvr · January 2020

Nightfall wrote: »

If a tube is audibly microphonic probably I just replace it.

You mean by tapping on it? Or just in general because I'm not sure how to test one other than tapping on it. I don't hear anything out of the ordinary other than the time I put in the 12ax7's the PO gave me by mistake. Those had a noticeable hum.

gmcman · January 2020

I was experiencing some noise once with my tube preamp and realized it was my cell phone too close to the pre. Switched to airplane mode and all was good...phone was about 5' away at the time.

I don't have an explanation except for removing the phone or shutting it down was the solution.

pitdogg2 · January 2020

You can tell by other means than tapping on it. If it is bad enough it like a microphone it can pick up the sound in the room and feeds it back through the speakers. Some ring like churchbells very annoying.

treitz3 · January 2020

From another thread....

audioluvr wrote: »

Tube rolling! Got a matched set of Sylvania tall black plate halo 12au7's with the Baldwin Logo on them today to match my Hallicrafters. I liked the sound of the Hallicrafters so much I bought these as a back up just in case something happened to these. I'm surprised there is even a difference in sound with identical tubes! These baldwins are a little more forward (?) and edgy or raspy or something. Haven't decided it I like that or not yet. Sounds great when listening to techno though. With the volume all the way down and tapping on the Hallicrafters they were virtually dead silent. One of the Baldwins gave out a good amount of tapping sound through the speaker so I may mark that one as noisy and see if I can find a quiet one.

Sounds like you may have a bad tube with the Baldwins.

Tom

Gardenstater · January 2020

Whatever system you use for vibration isolation, it should have a resonant frequency that is about 1/3 or lower than the minimum vibrational frequency you expect to isolate the equipment from. I doubt that many viscoelastomeric products on the market achieve this for typical seismic vibrations encountered in people's houses. Springs, of sufficient length and proper spring constant are the way to go and that's the method used by Townsend Audio, although I'm entirely in the DIY camp due to my budget.

Gardenstater · January 2020

Another way to go is with a minimally inflated bicycle tube, between two acoustically dead marble tiles or such, with a hole drilled in one of the tiles (mandatory). If you add some roller bearings to this also, you have a pretty cheap and pretty damn functional isolation system. FWIW and I realize this gets you out of the eye candy and wife friendly realm lol

Nightfall · January 2020

audioluvr wrote: »

Nightfall wrote: »

If a tube is audibly microphonic probably I just replace it.

You mean by tapping on it? Or just in general because I'm not sure how to test one other than tapping on it. I don't hear anything out of the ordinary other than the time I put in the 12ax7's the PO gave me by mistake. Those had a noticeable hum.

Sometimes you don't even have to tap the tube itself. I had one that if you tapped the shelf that the preamp was on you could hear the tap out the speakers. It would also give off a constant shhhh noise that you could hear from the listening position, not just with your ear right up to the tweeter.

dromunds · January 2020

Some tube families are known for more microphonics and some for less microphonics. As far as 12AU7's equivalents, those 7316's that were discussed previously are an example, made for aircraft equipment and medical grade, they were made for low noise with rigid micas and tight specs. I have several brands of 5814's that I adore, also known for low microphonics. In the 6DJ8 family, I like the 7308's for this reason, among others. If a single tube goes microphonic on you, I would replace the pair if you can't find a closely matched single to replace the microphonic one.

verb · January 2020

What every tube junkie should not be without! A tube tapper!

mhardy6647 · January 2020

In all seriousness: my father's weapon of choice was always a long-ish, straight, uncolored (natural finish) Tinkertoy.

I am pretty sure he borrowed it away from me when I was very young...

He used that sucka for decades -- come to think of it, I might have it downstairs with some of the stuff I do still have from his shop.

verb · January 2020

mhardy6647 wrote: »

In all seriousness: my father's weapon of choice was always a long-ish, straight, uncolored (natural finish) Tinkertoy.

I am pretty sure he borrowed it away from me when I was very young...
He used that sucka for decades -- come to think of it, I might have it downstairs with some of the stuff I do still have from his shop.

I’m sure it’s still at the @mhardy6647 household.

audioluvr · January 2020

verb wrote: »

What every tube junkie should not be without! A tube tapper!

Dude! That looks like a rubber mallet! I took @Nightfall ' s advice and just tapped a knuckle on the faceplate while putting an ear near each speaker. This, of course, works for me because I only have one tube per channel. I'm thinking as long as the microphonic tube doesn't add any audible noise it should be fine?🤔

mhardy6647 · January 2020

. . . . .

verb · January 2020

audioluvr wrote: »

verb wrote: »

What every tube junkie should not be without! A tube tapper!

Dude! That looks like a rubber mallet! I took @Nightfall ' s advice and just tapped a knuckle on the faceplate while putting an ear near each speaker. This, of course, works for me because I only have one tube per channel. I'm thinking as long as the microphonic tube doesn't add any audible noise it should be fine?🤔

Yep! A tiny one! The mallet ends look to be about 1/2" or less in diameter.

Ideas For Minimizing Microphonics

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