Microphonics

[booangler]

Good tidings,

I am enjoying this pre-amp as often as I possibly can. My kids still look at me funny, just as most teenagers would, when they see me sitting and listening intently to the beautiful music coming from my system. The one issue I am having is that the tubes are noticeably microphonic! When there is no source input, I can always hear a very bell like tone that lasts a good long time. Simple adjustments to the volume control can induce this into my system, and I won't even discribe what happens when you change the selector switch. Based on this I am concluding that this same tone is coming through while the music plays. I just have not picked it up yet. I still have "happy ear and brain disease" as I call it. Where, no matter what, I am so excited about the change in my system that the ringing has not presented it self to me. In an attempt to rectify this I changed the feet on the case which has had absolutely no impact.

So, now I am looking at other possible fixes, and of course your help. Could it be my tubes? I just realized that I have not yet checked to see if there is any difference between the right and left output. I'll check that when I get home this afternoon. Should I try and dampen the top plate or the tubes? I also noticed that the Tube Data Sheet Locator at Duncan's Amp Pages list three other tubes as possible replacements the: CV2370, CV484, DL92. Would any of these be better suited to the Quickie? Is there something else I might be overlooking?

Thanks,

Alan

[Grainger49]

I sold a tube preamp to a buddy and the line stage tube went out almost immediately.  He got the most microphonic tube I have ever heard to replace the bad one.  When the micro relay came out of mute the tube rang like a bell!  No exaggeration!  But he loved the extra echo it seemed to add to voices.

So, if you like the tubes in it you can install a DPDT toggle switch after the coupling cap that grounds the output temporarily when you adjust the volume.  If you fear you might leave it in mute, make it a spring return to one position DPDT toggle switch.

[Wanderer]

Just checking in to say another Quickie has arrived in the world.

Testing it in a very simple audio chain - Personal CD player to Quickie to Total Airhead to Sennheiser 497 phones.

Sounds good and worked right after assembly.

BUT.....

I also hear the microphonics. A light tap on the face plate gets a nice clear "ding" in the output. The "bell like tone" doesn't seem to last very long but it is certainly there. Kinda fun to lightly tap the tube directly and hear it move from channel to channel. 

Just the nature of tubes with low voltage heaters? I got the NOS GE 3S4. Are the Sylvania any different? Perhaps tuned to a different pitch?

Mine will end up as a headphone amp (not for the low Z Senns) when the parts get here, so microphonic is not a big deal. Interesting what the various approaches to a "fix" will be.           

[Paul Joppa]

...I also hear the microphonics. ... Just the nature of tubes with low voltage heaters?       

Probably. The Type 31 (for example) also has a reputation for microphonics.

Might be an interesting substitution - I think you can find sealed lead-acid D-cells ...  :^)

[Paul Birkeland]

The microphonic aspect to the Quickie is the one minor drawback.  When using the Quickie as a headphone amp, the step down tends to minimize this considerably. 

Part of the fun of DIY is playing around with solutions to this.  I would imagine some kind of suspended base, tube dampers, etc. etc. would be a fun way to play around with the Quickie and test anti microphonic devices and strategies.  Luckily, the 3S4 runs very cool, so you aren't very restricted in terms of material choices.

-Paul

[Dr. Toobz]

I can verify that with headphones, the ringing/microphonic issue is only slight. I can hear taps on the plate or tubes themselves (which have a nice "bell-like" tone) if I hit the amp when no music is playing, but it is quiet enough not to seem to have an effect on the actual music when it IS playing. I'm using Specos to step down the impedance to 500ohms (well, the tap is 500, but the actual impedance should be half that, i.e., 250ohms).

Ringing or no ringing, I love my Quickie!

[Koda]

The RCA 3S4 tubes that were included with my Quickie rang like a gong with even the lightest touch on the volume knob.
I bought some NOS (1969) Amprex tubes and the chimes have all but gone silent! The new tubes also have a "fuller" sound throughout the range, more solid bass as well as highs that are not as "shrill" as the RCA's.
I was worried that the ringing would just have to be accepted with this tube, fortunately tube rolling paid off in more than one way.
Of course, not everyone can expect these same results... but at least the 3S4 (or DL92) tubes are not expensive to try
YET.

[booangler]

The RCA 3S4 tubes that were included with my Quickie rang like a gong with even the lightest touch on the volume knob...

That is what I am talking about. I am going to have to get a second set of tubes.

Alan

[Dr. Toobz]

My tubes were GE - maybe they're a bit less microphonic? Good to know.

[induna]

My kit came with GEs that seemed very microphonic to me. They rang with the slightest touch, but I never heard anything during music playback.

I just received a pair of NOS RCA's from Antique Electronics, and they are much less microphonic than the GEs. I have to thump the chassis plate pretty hard with my index finger to get them to ring at all. I haven't had time yet to really listen to them though. I also have a pair of Amperex tubes on the way (these 3S4 tubes are so cheap they beg to be rolled).

And the plate chokes go in this weekend, with new output caps waiting in the wings. What a blast.

[russtafarian]

These tubes run so cool, would rubber bands around the tubes work?

[Grainger49]

Maybe an O-Ring?  Viton takes high temperatures well.  But you say you don't need that.

[booangler]

Hello my fellow quickers,

Here is a really quick tube update.

Ok I have gone a little over the top with tubes for the Quickie, 3 pair of 3S4's from a local supplier, a set of mullard and a set of Brimar on there way. In the mean time I ordered some DL92's from a seller in England off of flea bay. Of course when I got them they were not DL92 but CV 820. At first I was pissed, but then I relaxed and took a closer look at the tubes. What I found inside the boxes were tubes labeled 3S4 and CV 820. So, I tried them, first thing I noticed was very little micro-phonics, and I mean very little. They sounded good, but I didn't get a good listen to them as my wife Jean came home, and we started dinner.

Cheers,
Alan

PS I am going to head to the hardware store and try to find some grommets or washers that will work as dampers.

[JC]

If you're going to the hardware store, ask if they sell automotive heater hose by the foot.  It generally comes in a couple of sizes, and a foot of it is cheap.

Get the size that fits snugly over your small-signal tube; take one with you for sizing.

A 1/2" - 3/4" slice of the hose makes a good envelope damper for your tube.  It is designed to withstand 212+ degree engine coolant and life under your hood, so heat from small tubes won't have much of an effect on it.  It also generally has a layer of re-enforcing fabric molded into it, which adds to its damping ability.

What it won't do, of course, is have any effect on the innards of the tube, but what does?  

My favorite Ace sells it per foot, and a foot of it makes a lot of cheap dampers.

[Grainger49]

JC,

Don't you lose the glow if you put a heater hose condom on your tube?