What does a microphonic tube sound like

0 Members and 1 Guest are viewing this topic. Read 2844 times.

Yomaha

What does a microphonic tube sound like
« on: 1 Aug 2019, 07:15 pm »
I have been noticing a sound that reminds me of the sound that train brakes make...that metal on metal high pitched sound.  It's not as loud as train brakes obv, but it is noticeable immediately after my gear turns on (45-second delay for tubes heating up).  It seems to go away after 15 or so seconds and I don't really notice it during playback.  I also have been feeling like the upper-mids/highs have been a touch on the harsh side lately.

Any feedback/opinions as to what I may be hearing greatly appreciated!

timind

Re: What does a microphonic tube sound like
« Reply #1 on: 1 Aug 2019, 07:49 pm »
My experience with microphonic tubes is they ring with vibrations, kind of a whistling sound through  the speakers. Touching the amp in any manner could cause it.

If you tap on the tube(s) once the amp is warmed up and it produces no sound, the tube isn't microphonic.

Yomaha

Re: What does a microphonic tube sound like
« Reply #2 on: 2 Aug 2019, 01:10 am »
I could see whistling sound fit the description of what I'm hearing. Does a microphoic tube have any other sound characteristics besides the whistling?  Could that be what is causing the harshness in the higher end that I'm hearing?

FullRangeMan

  • Volunteer
  • Posts: 12363
  • To whom more was given more will be required.
    • Never go to a psychiatrist, adopt a straycat or dog. On the street they live only two years average.
Re: What does a microphonic tube sound like
« Reply #3 on: 2 Aug 2019, 01:24 am »
Could that be what is causing the harshness in the higher end that I'm hearing?
Hardly imo, using a tube damper made any change?
https://www.youtube.com/watch?v=13n1VCR6UXw


FullRangeMan

  • Volunteer
  • Posts: 12363
  • To whom more was given more will be required.
    • Never go to a psychiatrist, adopt a straycat or dog. On the street they live only two years average.
Re: What does a microphonic tube sound like
« Reply #4 on: 2 Aug 2019, 03:14 am »
This first 6sn7 tube is whistling:
https://www.youtube.com/watch?v=205__gxWJc8

rollo

  • Industry Participant
  • Posts: 4520
  • Rollo Audio Where Home demo rules
Re: What does a microphonic tube sound like
« Reply #5 on: 2 Aug 2019, 03:18 pm »
  Sounds like to me a tube gone bad. Just try another that simple. Good luck.

charles

audioengr

Re: What does a microphonic tube sound like
« Reply #6 on: 2 Aug 2019, 03:25 pm »
Tubes sometimes get some bad gas in them and powering on dissolves it.  They can also have a mechanical defect that changes as they heat-up.  You can sometimes tap the tube and it will go away. This is not microphonics.  Microphonics will make noise when you tap the tube.

Yomaha

Re: What does a microphonic tube sound like
« Reply #7 on: 2 Aug 2019, 06:13 pm »
I have rolled the tubes several times in my BHK250, and that tells me that it must be in my Modwright 9.0AE pre.  It's a pretty big pain in the rear to get to those tubes the way I have my rack set up.  I'll try tapping those to see if I get any microphonics, then roll.

viggen

Re: What does a microphonic tube sound like
« Reply #8 on: 2 Aug 2019, 07:10 pm »
sounds like money leaving your wallet  :popcorn:

avahifi

  • Industry Contributor
  • Posts: 4296
    • http://www.avahifi.com
Re: What does a microphonic tube sound like
« Reply #9 on: 2 Aug 2019, 08:22 pm »
Typically, you will get a PING sound through the speakers when you lightly tap on a microphonic tube.

Frank

Rusty Jefferson

  • Full Member
  • Posts: 441
Re: What does a microphonic tube sound like
« Reply #10 on: 2 Aug 2019, 08:39 pm »
Noise and microphonics are different things. Microphonics is what it's name implies. The structure of the tube acts like a microphone and amplifies sounds from outside the tube. If gently tapping the case of a piece of equipment, or the tube itself with your fingernail causes a lot of noise through the speakers, you can say that tube(s) is microphonic. In some severe cases, you'll be able to hear people walking across a floor through the system as the vibrational energy of the footfalls are amplified.

Hissing, spitting, pinging sounds are noise issues unrelated to microphonics. They are simply issues with the tube construction.  A tube can be noisy, but not microphonic, and vice versa.  Sometimes, a tube damper will control minor tube noise, and some tubes will quiet down after 10-20 run time.

When buying tubes, always request tubes that are low in noise and microphonics.  Especially important for preamps that have high gain.

Yomaha

Re: What does a microphonic tube sound like
« Reply #11 on: 3 Aug 2019, 05:52 am »
sounds like money leaving your wallet  :popcorn:

wut

twitch54

Re: What does a microphonic tube sound like
« Reply #12 on: 3 Aug 2019, 04:38 pm »
I have been noticing a sound that reminds me of the sound that train brakes make...that metal on metal high pitched sound. 

for the record the brakes on a train are not making that sound rather it's the flange of the wheel and the inside of the railhead on a tight radius curve.

twitch54

Re: What does a microphonic tube sound like
« Reply #13 on: 3 Aug 2019, 04:40 pm »
Tubes sometimes get some bad gas in them and powering on dissolves it. 

I've had that problem as well, 'Beano' usually works !

hagtech

  • Industry Participant
  • Posts: 2272
    • http://www.hagtech.com
Re: What does a microphonic tube sound like
« Reply #14 on: 16 Aug 2019, 06:41 am »
Sounds more like a heater-to-cathode insulation breakdown.  Sort of a whistle / sizzle.  Cathode follower by any chance?

Yomaha

Re: What does a microphonic tube sound like
« Reply #15 on: 21 Aug 2019, 03:01 am »
I swapped the stock 5687's that came with my preamp and violá, all better. I guess I've had good luck bc that was the first time I've dealt with (or realized) I had a microphonic tube in all the years I've been fooling with tube gear (counting my guitar playing days🙂)

FullRangeMan

  • Volunteer
  • Posts: 12363
  • To whom more was given more will be required.
    • Never go to a psychiatrist, adopt a straycat or dog. On the street they live only two years average.
Re: What does a microphonic tube sound like
« Reply #16 on: 21 Aug 2019, 11:46 am »
Sounds more like a heater-to-cathode insulation breakdown.  Sort of a whistle / sizzle.  Cathode follower by any chance?
Especially if the filament is AC heating.

Rusty Jefferson

  • Full Member
  • Posts: 441
Re: What does a microphonic tube sound like
« Reply #17 on: 21 Aug 2019, 11:49 am »
Again, noise and microphonics are different problems. Your tubes have noise issues, not microphonics.

Perhaps Andy can explain it if you contact him about the 5687s.

FullRangeMan

  • Volunteer
  • Posts: 12363
  • To whom more was given more will be required.
    • Never go to a psychiatrist, adopt a straycat or dog. On the street they live only two years average.
Re: What does a microphonic tube sound like
« Reply #18 on: 21 Aug 2019, 01:18 pm »
Dust in the pins can create noise.

Yomaha

Re: What does a microphonic tube sound like
« Reply #19 on: 21 Aug 2019, 05:33 pm »
Thanks for the info and clarification!  I'll be checking with Andy at VTS.