Hey guys,

Need help.  I have a 26 preamp now.  It's very microphonic.  Some tube dampers have helped, but not enough.  So, I am looking at using some cones underneath, to help with reducing vibration.  I used to see wood (ebony?) cones, but I can't seem to find them.  Anyone know of any place that has them, for "cheaper" perhaps?

I used Vibrapods, and they sucked.  So, I'll experiment with wood next.

Thanks.

Shek

With so many options, I'm curious as to why you would get a pre-amp that cannot stand on its own 4 feet?
What does it say about the build quality and control?

Try loosening all the screws holding everything down. Including chassis
and transformer. Whats happening is all the energy is getting bottled up. Whatever those screws are holding down is not allowed to dissipate vibration. The energy looks for the easiest (loosest) outlet and its probably your tube sockets.

Remember those transport screws in 80s cd players? Well that was ahead of its time. Everything gets shipped too tight. Should be released at destination.

I used Vibrapods, and they sucked.  So, I'll experiment with wood next.

Some thoughts...

Did you load the vibrapods correctly? Like any elastic damper they need to have enough weight applied to work. They need to be squished firmly, otherwise they bounce like rubber and will hurt the sound quality. When loaded, the material turns very viscous and eats vibration, not bouncing around. There are several durometers available, each requires a different weight per pod. See the manual:
http://www.vibrapod.com/PDF/manual.pdf

Listen to the microphonic sound, try to hear a frequency, check it on a piano, or online keyboard. Target your damping to that specific freq.
http://en.wikipedia.org/wiki/Piano_key_frequencies

Metal chassis surfaces will ring, and could be the direct source of the microphonic vibrations, especially if they are in the midrange or higher frequency range where only metal will ring. There could be some parts inside the tube that are resonating also, but it will still be evident in the tone of the ring.  Apply damping materials to the interior surfaces of the metal to make the box quiet. Dynamat.

Experiment with Sorbothane.  This is what Vibrapods are made of, it is the best damping material available. Buy sheets of it on Amazon.
http://www.amazon.com/s/ref=bl_sr_industrial?ie=UTF8&field-brandtextbin=Isolate+It%21&node=16310091
there are different thicknesses and durometer. You can cut your own pieces to suit your application. This allows using very small pieces, which ensures adequate loading. You can add more small pieces if the loading per piece is too high.

Read sorbothane design guide to determine the size and durometer of the pieces needed for your preamp.
http://www.sorbothane.com/Sorbothane-Design-Guide101409.pdf

To increase loading, use a combination of smaller pieces, fewer pieces, and lower durometer. Too much loading will reduce damping but not damage SQ. Too little damping will dull the sound. This is the most common complaint of people who try damping without applying enough load and quickly go back to "draining" techniques.

You can only damp the glass of a tube, not the internal elements directly. You have to damp everything around the tube to quiet the internal tube parts.

Here is another trick. The 26 tube is very microphonic and sensitive in a line stage circuit. There is really not much you can do about it. The design itself is critical as with any DHT in a linestage.

Are you getting a lot of noise at idle with no music playing? Does it get worse when playing music at higher volume and are the tubes exposed. With no music playing, tap on the tube, if it rings through the speaker, the cover outlined below will help with that.

Exposed tubes are sensitive to airborne vibrations. Especially DHTs. One trick is to get some acrylic tube big enough to fit over the tube or build a box to fit over them. Use 1/4" minimum. It HAS to have a top on it as well or vibration can still get in. You can drill some vent holes in the BACK side of it depending on how hot the tubes get. I mention acrylic so you can still see the tubes and it has excelllent vibration control properties.

This cover will stop airborne vibrations from getting into the envelope of the tube.

The only other method for this type of tube is to design a hammock mounting system. The trick is to release any and all tension of the tube socket as possible. Not easy but can be done.

Oh....and you want to use heavy "soft damping" on the chassis with decoupling rather than coupling. Herbies Tenderfeet are an excellent option. Dont use wood.

Thanks Bill.  At idle, it's really stable, only some slight hiss out of the box, and only when I'm like 2 ft. in front of the speaker.  Only when I "touch" the chassis, etc. that the microphonics really act up.  The 26 tube by itself is microphonic, that I've learned.  Right now, I have tube dampers on the 26, GZ34, and another.... The sound seems fine. 

I had been told about a box over it.  I'm not an extreme nut case yet, so that's not being considered.  I just thought I'd put some "footers" underneath to fine-tune the sound, which is excellent now.  I had vibrapods directly put underneath (only the flat rounds ones, but not the cones).  The sound isn't really impressing on my ears.  So, I just thought of "experimenting" with wood.....  I was "warned" that vibrapod not being good, and it didn't please for sure.

Hey Shek
                  Come on over with the preamp. I have loads of stuff to fool with. Ebony, brass, Vibrapods, Sand boxes, tube dampers, chassis vibration, Pon-Tunes, Magnetic footers, etc.
    We will get it right and have some fun doing it.


charles

With so many options, I'm curious as to why you would get a pre-amp that cannot stand on its own 4 feet?
What does it say about the build quality and control?

Well, I'm not sure if you've heard a 26 preamp perform; you'd have to experience a 26 tube preamp.  The 26 tube is generally said to be more microphonic than other tubes.  IF I had been content with other preamps (if I never heard of the 26 tube), then you're absolutely justified in critiquing the situation.  But, I took the plunge.  .  Thanks.

Quote

, I'm curious as to why you would get a pre-amp that cannot stand on its own 4 feet?

Because that's what an audio neurotic does

Ditto  

Not tooooooo neurotic tho!  A little fanatical may be.

Incidentally, over last night and this morning, I experimented a little.  Picked up a sponge type foam packing piece, 4/5" thick (not the particle type), and put it underneath the 26 pre.  Similar to using the Vibrapods, slightly less sucky.  This morning, took the foam out.  Much more musical.  Harmonically richer the way I'm used to.

A friend suggested putting granite squares underneath.  I actually have a couple, but need couple more, I picked up at Home Depot, 3" square type.  May be I'll put them directly underneath the 26, see how it goes.  Right now, I have those squares underneath each of the rack legs, on top of the carpet.

Continue with my little game.