Isolation tweaks

[Doc B.]

Hey, it's a DHT preamp. We knew that microphony was a potential issue when we came up with the design. So I am starting a thread in which we will offer some ideas for isolation and damping.

After a little experimentation this week I have an initial tweak - 1-1/4" 30D Sorbothane hemispheres under each of the four corners of the chassis. I got some off ebay for $17 for the set. Tried smaller and higher durometer ones. They were not as effective, this one seems the sweet spot for the weight of the preamp (~12.4 lbs) and the dimension of the wood base panels. They should help to keep the floor/rack/shelf borne vibration out of the preamp chassis and they look pretty good.

A second and really cheapass approach that is very effective is to put each corner of the wood base on a folded piece of the larger bubble size bubble wrap. We folded four 6" squares over twice to make four roughly 2x2, four layer pads. This looks very lotech/dumpster diver/trailer park if that is the look you are going for.

Based upon a little experimentation yesterday I am also looking into an interesting tube damper concept, that I will share more about once I have given it a try.

[Doc B.]

My tube damper test subject showed up today. Seems to help.

[Doc B.]

And here is a close up of the amount of compression of one of the 30D 1-1/4" Sorbothane hemispheres on the base. These really do work well to cut down vibration from the shelf.

[Grainger49]

Dan, your tube damper looks like the ring off of a giant condom.  What is it?

[dbishopbliss]

Dan, your tube damper looks like the ring off of a giant condom.  What is it?

That condom looks sort of small to me.  :-)

[Doc B.]

I need to do a little more research before I share the details.

[Grainger49]

David,

I guess it depends on which tube it is on.  On my 76 drivers it is small, on the 300B a good bit larger.  But I've never seen the roll/ring that thick.

[saildoctor]

I use round welded stainless and bronze rings all the time at work.  Maybe plasti-dipped they could work as dampers?  Or maybe as is?  Hmm.. i should try this out.

[ssssly]

I thought it looked like one of those rings you see at the carnival. Where you have to toss it over a bottle neck to win a stuffed animal.

Could start a new fad Doc. The bottlehead ring toss.

[Doc B.]

I thought it looked like one of those rings you see at the carnival. Where you have to toss it over a bottle neck to win a stuffed animal.

Could start a new fad Doc. The bottlehead ring toss.

Ah shoot, I've been figured out! The other part of the package is an equipment rack made of giant stuffed animals.

[4krow]

Those kind of Sorbothane work good for me too, but a word of caution, they tend to be sticky, and most surfaces will show marks where they have sat. If sitting on top of a painted surface, it can really be bad, to the point that paint will have permanent marks. Sometimes, I use Scotch tape on the feet to provide a barrier. In spite of this problem, I still use Sorbothane feet for a lot of my components.

[Doc B.]

Very good point. They are really sticky, to the point where some smaller ones would stay stuck to the shelf when I pulled the preamp up! Tape is a good idea. I was thinking maybe talcum powder or pledge furniture polish, but those probably wouldn't last very long.

[ssssly]

My trick for those sticky Sorbothane balls is a cutting board.

Whatever those super thin, white cutting boards are made out of is actually a pretty decent dampening material (at least the ones they sell at the Japanese dollar store). And if you have a hole saw around the size of the Sorbothane ball you can make a nice little coaster out of it to protect your stuff.

[RPMac]

What about the felt furniture pads on the bottom of the sorbothane pads?

[4krow]

Ya know, I actually did try that. Funny thing was, they wouldn't stay on. For some reason, the chemistry just wasn't there.