Quickie microphonics

[cpaul]

Repost of an earlier thread that doesn't show up at all in my browser despite refreshes.  Hope this isn't double posting...


A lot has been said about microphonics of the quickie and its 3S4 tubes.  Mine came with Sylvania 3S4s and they have proven to be fairly microphonic (OK, very much so, though much less annoyingly than some 12AU7s in another preamp).  They ring like a bell for 3-5 seconds when I touch the amp in any way (or fuss with the far end of some rigid interconnects).  Even moving my hand toward the switches or knob starts the ringing.  Once it dies down, it seemed to play quite well.

So today I did a little experiment that others may be interested in (though most here probably have much more knowledge than I do).  I wrapped some fat rubber bands around the tubes (after noticing that the tubes remain cool even after several hours of use) to mimic some higher quality tube dampers I have for larger tubes.  See the photos here:

http://picasaweb.google.com/103078014592468973736/Bottlehead#5537771006395854690

In short, even with this low-tech approach the microphonics have been cut at least in half.  If I do a L/R comparison, the side with the rubber bands is highly improved.  And...there is definitely a noticeable improvement in the playback quality with the bands on.  I assume there was some residual ringing during playback due to the fact that my speakers aren't too far from the quickie (about 3ft away, and using a 100wpc Marsh A200 amp and Vandersteen 1C speakers).  I suspect this ringing muddied certain frequencies when they played back, as now I get quite clear and highly separated playback.  To me it is very noticeable.

I will play around with playback using different dampening materials with the tubes and report back as I do.  I hope others will report their experiences too.

[JC]

I have dampened many a small tube with slices of automotive heater hose.  It's designed to carry automotive coolant at at least 212 degrees F, probably higher.  And, since it is re-enforced with a fabric layer, it dampens the glass envelope well.

On top of that, many hardware stores sell it for a buck or two per foot, and that foot can be sliced into a large number of 1/2" - 3/4" "dampers".

IIRC, it comes in 5/8" and 3/4" diameters, so you can usually fit most 7 pin and 9 pin miniatures.

[Grainger49]

And JC beat me to it.  Although your picture of the rubber band wrapped tube made me smile, I like ingenuity, the heater hose sounds like a more elegant solution.

Thanks for the description of the microphonics.  Since I don't have a Quickie I haven't experienced.  I had a friend with a highly microphonic tube in a preamp.  When the preamp came out of mute, the relay picked, the line stage tube rang like a triangle.  It distinctly said "Ping ! ! "  Your description of the problems makes the complaints I have read here easier to understand.

P.S. I see a listing of your other post in the new posts.  It doesn't load for me but I do get the URL in my browser.  This is it:

http://www.bottlehead.com/smf/index.php/topic,1245.msg0/topicseen.html#new

If it loads for you, then you can delete it by using the "Remove" option.

[bainjs]

I replaced mine with Amperex Bugle Boys from Tube World.  No more microphonics and better sound!

[JC]

bainjs:  Well, of course, that's another way to go!  Good deal!

Grainger:  I'm not sure how elegant the heater hose is, but I've always found it to be effective in damping the envelope.

Another approach I have seen quite a bit of in old guitar amps involved mounting the tube sockets themselves on little rubber-ish grommets.  I've never undertaken this myself, but it seems to me the trick would be to find grommets of the correct dimensions to fit in the screw holes, but not spill over into the socket hole.  The result is a socket mounting which "floats" on the two grommets instead of riding directly on the chassis.

[Grainger49]

I guess that the rubber band and heater hose cancels out one of the reasons for having tubes, their looks.  Notice that I didn't say the glow.  Most of the tubes used don't glow much.  But they have a positive visual impact that appeals to me.

To the OP, you have a PM.

[EKwisnek]

Hello all. I recently registered on the forum, but have been lurking about for some time. I just finished my first Bottlehead project, and I must say I'm hooked!

I'm having a very similar problem to the OP, but it seems to a much more severe degree.

A little about my setup:

Sony BDP-S350
Bottlehead Quickie
Rotel RB-1050
Tekton OB 4.5 Loudspeakers

With the system powered on, and the Rotel cranked all the way (normal operation), simply clapping loudly near (3ft.) the Quickie produces a tuning-fork-like harmonic that is incredibly disturbing. As posted above, touching the PreAmp in any way increases such microphonics. If I play music at moderate volumes and hit the pause button, the distinct ringing follows into the silence. I have tried to physically decouple everything as best I can, but it seems the preamp is so sensitive to the slightest vibrations that I can't control it. I've tried wrapping weather stripping and Teflon tape around the tubes, but I can't seem to quell the madness!

As I've read, I'm assuming the only way to fix this is to purchase some new 3S4 or DL92 tubes? Are all tubes of this type NOS? Anyone know a good tube to roll?

I'm a little frustrated, but not defeated...the sound on this thing is amazing after a couple nights of continuous play! For 99 bucks, one can't bee too upset about spending a few more dollars on some new tubes. I'm just not certain that will solve the problem.

Thanks All!
Evan

[Grainger49]

Bottlehead is keeping the price as low as possible.  Therefore they buy tubes in bulk and, as you can imagine, can't test them before sending out a batch of 20+ kits.

There are a couple of threads here on other tubes for the Quickie.  Sorry not to be help on which tubes are NOS and current production.

A quick search:

NOS unknown brand at $5.95   http://thetubestore.com/nos-3s4.html

NOS unknown brand at $4.95    http://www.tubedepot.com/nos-3s4.html

Unknown at $2.80    http://www.tubesandmore.com/

No association with any of the above vendors.

[EKwisnek]

Thanks Grainger... I'll just take the leap and buy 20 tubes or so...see what kind of mixed bag I can get!

Evan

[Grainger49]

There are recommendations in the Quickie folder.  You might want to check those first.

[Paul Joppa]

The Rotel is a 70 watt amp with fairly high sensitivity, and the Tekton speakers are pretty efficient - you have much more gain in the system than you need. Try this:

Crank the Quickie volume to maximum, then turn down the Rotel until music is about the loudest you want to listen at. This way, the Rotel will not amplify the microphonics nearly as much. The Quickie will amplify the input signal more, so the total net signal gain will remain the same, it just gets redistributed.

Then listen to be sure the Quickie is not being overloaded on signal peaks. You may have to back off a little to get to the sweet spot, but there should be plenty of improvement available this way. Once you have taken the edge off, you can shop for different tubes more carefully and with less stress.  :^)

[Doc B.]

Yes, "Rotel cranked all the way", that is a lot of the problem.

[EKwisnek]

Thank you Paul and Doc, great recommendation. I hadn't thought about the operation of the Quickie enough to realize what the volume control actually "controlled".

Paul, I read your piece on managing gain in a system; it's very interesting and informative!

I'm always a little afraid to adjust the Rotel's levels because they can only be adjusted individually with a flat-blade screwdriver. I can get it close by eye-balling the position of the slots, but I'm afraid of amplifying one channel greater than the other.

I'm excited to get home tonight and give it a try. I just ordered four new tubes to start with, as I'm finding 3S4s only available "as is" or "what's in stock".

Thanks again, and cheers on a great kit!

Evan

[Doc B.]

I'm always a little afraid to adjust the Rotel's levels because they can only be adjusted individually with a flat-blade screwdriver. I can get it close by eye-balling the position of the slots, but I'm afraid of amplifying one channel greater than the other.

Even with both controls up all the way there could be gain difference between channels. You would probably need test gear to get levels exact, so just adjust the balance by ear.

[EKwisnek]

As a brief follow up:

I pretty much followed Paul's instructions to the letter and I'm happy to report that it quelled the microphonics by quite a bit. They aren't completely gone, but during normal playback levels I can't hear any coloration or ringing. I'm still going to play with new tubes, but the system is definitely adequate as is!

Thanks again, and happy Thanksgiving!

Evan