Ken Byron
4 posts
Jan 08, 2015
9:54 PM
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Hi Guys.
I have a problem, not sure if it is coming from my amp or Green Bullet microphone. What happens while playing certain notes particularly draw on hole 4 on C harp or Bflat is I get a singular "doorbell" sound coming back at me. It is quite off putting while trying to concentrate. The amp is fully tubed and is of high quality.I have just had all the tubes replaced recently. Can anyone diagnose this problem?
Thanks so much.
OZ Ken
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5F6H
1847 posts
Jan 09, 2015
1:36 AM
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It might be process of elimination...
First check it isn't something common, but less obvious like reed rattle, not always easy to hear from behind the harp, maybe play into a recorder?
Do you have another mic to compare? How long have you had the mic, have you noticed this before?
Try some C & D notes on other harps (2 draw F, 6 blow G) is it related to frequency (from what you're saying maybe it is).
Keep any gain/boost down on the amp, maybe try to use middle control to get the note to cut through & reduce treble? Gain & high frequency can contribute to parasitic oscillations in amps, these often sound like metallic & mechanical rattles, but are artefacts created by gain structure, wiring routing, component layout...certain amps are well known to be prone.
If you are using the stock higher gain 12AX7 preamp tubes that come in just about all new guitar amps, try some lower gain preamp tubes, I'd start by replacing the tube farthest from the power tubes (knowing which amp we are talking about may help, others may have similar experience, some amps benefit from a gain drop at the tube nearest the power tubes, but this can also burn up resistors in some others, depends on what the typical voltages in the amp are designed to be).
Check that when the amp was retubed that exactly the same designation of tube was used to replace the old ones, if you had no issues with the old ones, preamp tubes are very unlikely to damage the amp if they fail, so if you still have the old ones and they are not noisy/faulty maybe try replacing the new ones methodically to eliminate the issue.
Again, unless we know what the amp is, I don't recommend changing the power tubes if they have been biased up in the amp.
Unplug the amp from the wall & allow to cool fully (10-15mins) before trying to handle any parts, observe the keyway in any tube pins when subbing.
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www.myspace.com/markburness
Last Edited by 5F6H on Jan 09, 2015 1:38 AM
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Ken Byron
5 posts
Jan 09, 2015
5:08 AM
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Thanks for info Mark. Most appreciated.
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rbeetsme
1610 posts
Jan 09, 2015
5:35 AM
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Might be a tube. There is actually a product, basically a small rubber band, you can put around the tube to keep it form doing this. Or you can replace the tube. There is a technical term for this, can't remember what it is. One of my big amps will do it. Haven't gotten around to isolating it yet.
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jimr
76 posts
Jan 09, 2015
6:51 PM
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Another possibility is frequency related speaker distortion, sometimes called "cone cry". Could develop after the signal is altered by new tubes or electronic mods. Might happen with one speaker and not others.
Jim
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Harpaholic
580 posts
Jan 09, 2015
7:12 PM
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Rick, microphonic tube. Swap preamps first as Mark suggests. Things can rattle in the chassis at certain frequencies. Hopefully its a simple fix.
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Thievin' Heathen
463 posts
Jan 10, 2015
1:53 PM
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"while playing certain notes particularly draw on hole 4 on C harp or Bflat is I get a singular "doorbell" sound coming back at me"
Perhaps.., It's someone at the door?
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