Microphonic disk caps ?

[pedro]

Hi,
Ive been messing last night with different treble caps in my Non HRM tone stack.......330pf..
I tried -
* good spec Silver Mica,
* various miniature ceramic disks 1000v
* some poly films

I replaced the SMica after reading that the ceramics might get me closer to "the tone". I think there is a discernible "grainier" quality, but found that at full input and master volume tapping with the old chopstick gave bad microphonics.
I replaced with SM and still found some , but less m'phonics.
finally tried the poly thinking it would be better but actually quite a bit of microphonics.

Now, should I be bothered by this - or is there actually a sympathetic resonance going on when ceramics are vibrating at one of the resonant frequencies while youre playing ?

To be honest at full volume there was as much if not microphonics going on from the 1st tube.

Anyone got silent ceramic disk caps ? What do you guys find / like best ?

cheers
Pete C

[BobW]

Hi Pedro,
There are a few ceramic cap that have different tolerance/drift coefficients due to temperature changes. NPO, COG, X75, and Y5V type ceramics are the typical. But to answer your question I have not noticed any difference from the NPO/COG in a guitar amp application. I have over the years found microphonic caps, in ceramic, polypropylene, and the silver micas. If you didn't buy a large quantity of the ceramics, then all I can suggest is to try another ceramic. Is your amp a combo? if so, this would obviously increase the chance of microphonics due to the mechanical coupling of the enclosure/chassis. I personally don't like to do this, but You could also try isolating/dampening this particular cap with either hot glue or a non-corrosive RTV. hth Bob

[Pete]

Hi guys
I'm really interested in this concept of "positioning" components with some sort of material (dare I say goop).

Does anyone know of an absolutely safe RTV (so I would be sure of no corrosion)?
How do I determine that it will not corrode anything?

Where would I get some? (bought a $10 tube from Mouser a long time ago and when I received it, it said corrosive on it)

Thanks (sorry, if this is a highjack or OT)

[pedro]

not at all... I will try hot gluing a few diferent type and prizing them off again in the spirit of experimentation to see how the microphonics changes.

will update this...........

cheers
Pete

[pedro]

just a thought - is standard hot melt glue ( glue gun ) OK at high voltages - say 200-250v - to damp the cap oscillations ?

I have epoxy glue and fibre glass filler as well as alternatives ( but messy to work with )

Pete C

[dinamanu]

all is microphonic , my guitar cable is microphonic !! diy cable.....

in my hifi preamp the tube is isolating/dampening with elastic rubber ,in my future dumble I will try with complete preamp section

manu

[pedro]

FWIW,
I tried using hot melt glue to damp various caps and it worked very well.
At mo I have polystyrene treble cap damped with glue and it sounds great.

I might try the troublesome ceramics with hot glue at some stage to see if they are damped sufficiently.

For now too much fun playing the amp to bother........

Pedro.

[BobW]

Pedro,
FWIW, I forgot to mention earlier that Peavey uses hot glue to help minimize component microphonics on their pc boards, and is also used to keep large axial caps in their place. Sorry about mentioning any manufacturers from Meridian, MS on this forum.

[gearhead]

GE Silicon II (caulk) is good to 400 degrees (F).

[Darkbluemurder]

I replaced the SMica after reading that the ceramics might get me closer to "the tone". I think there is a discernible "grainier" quality, but found that at full input and master volume tapping with the old chopstick gave bad microphonics.
Now, should I be bothered by this - or is there actually a sympathetic resonance going on when ceramics are vibrating at one of the resonant frequencies while youre playing ?
cheers
Pete C

Wow - where can you play at these kind of volumes to become concerned about microphonic disc caps?